From 21ab4cba963838805ec27753c14adf558d14cf96 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Mon, 8 Jun 2026 10:20:25 +0000
Subject: [PATCH 1/6] deps: update memfs 4.57.2->4.57.6, @types/node
 25.6.0->25.9.2

All other dependencies (aontu, chokidar, shape, typescript) already at
latest. Clean rebuild produces byte-identical artifacts; build, test,
and coverage all pass.
---
 package.json | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/package.json b/package.json
index a24bea7..93d8b5f 100644
--- a/package.json
+++ b/package.json
@@ -46,7 +46,7 @@
     "aontu": "0.44.0",
     "chokidar": "5.0.0",
     "shape": "10.1.0",
-    "memfs": "4.57.2"
+    "memfs": "4.57.6"
   },
   "peerDependencies": {
     "@voxgig/util": ">=0",
@@ -58,7 +58,7 @@
     }
   },
   "devDependencies": {
-    "@types/node": "25.6.0",
+    "@types/node": "25.9.2",
     "typescript": "6.0.3"
   }
 }

From 9410a6789fd319091c4bea67f46e0c27466d403b Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Mon, 8 Jun 2026 10:56:48 +0000
Subject: [PATCH 2/6] fix: build error handling, CLI build args, watch
 lifecycle

Fixes found during strict review, each with a test:

- bin: pass parsed buildargs to Model. It was sending the raw --build
  string under the wrong key, so CLI -b/--build args never reached
  build actions.
- build: reset per-run error state and collect aontu errors via the
  `err` option key (aontu's current API) rather than the dead `errs`
  key. A reused BuildImpl no longer sticks one failure to every later
  watch rebuild, and model errors are collected instead of thrown.
- model: assign a `() => Build` thunk (matching BuildResult.build) so
  the model producer can call it on a config-triggered rebuild; stop
  the config watcher in Model.stop() so start() leaves no open handle;
  redirect promise-based fs writers under dryrun; de-dup writers list.
- local: fail with a clear message when an order entry names an unknown
  action, or one missing a load path, instead of an opaque TypeError.
- watch: fall back to cwd when the require base is unset; correct the
  misleading start() doc comment.

Tests added: error recovery, unknown-action error, dryrun promise
writers, watch rebuild-on-change, and CLI build-arg passing. Overall
line coverage 82.8% -> 92.0% (watch.ts 50.6% -> 91.5%).

https://claude.ai/code/session_01HxXpZNrKj3qonocwAtEP8r
---
 .gitignore                  |   3 +
 bin/voxgig-model            |   2 +-
 dist-test/cli.test.js       |  40 +++++++++++++
 dist-test/cli.test.js.map   |   1 +
 dist-test/fix.test.js       |  86 ++++++++++++++++++++++++++++
 dist-test/fix.test.js.map   |   1 +
 dist-test/watch.test.js     |  57 +++++++++++++++++++
 dist-test/watch.test.js.map |   1 +
 dist/build.js               |  26 ++++++++-
 dist/build.js.map           |   2 +-
 dist/model.js               |  27 +++++++--
 dist/model.js.map           |   2 +-
 dist/producer/local.js      |   7 +++
 dist/producer/local.js.map  |   2 +-
 dist/watch.js               |   5 +-
 dist/watch.js.map           |   2 +-
 src/build.ts                |  28 +++++++++-
 src/model.ts                |  27 +++++++--
 src/producer/local.ts       |  12 ++++
 src/watch.ts                |   5 +-
 test/cli.test.ts            |  51 +++++++++++++++++
 test/fix.test.ts            | 108 ++++++++++++++++++++++++++++++++++++
 test/watch.test.ts          |  74 ++++++++++++++++++++++++
 23 files changed, 546 insertions(+), 23 deletions(-)
 create mode 100644 dist-test/cli.test.js
 create mode 100644 dist-test/cli.test.js.map
 create mode 100644 dist-test/fix.test.js
 create mode 100644 dist-test/fix.test.js.map
 create mode 100644 dist-test/watch.test.js
 create mode 100644 dist-test/watch.test.js.map
 create mode 100644 test/cli.test.ts
 create mode 100644 test/fix.test.ts
 create mode 100644 test/watch.test.ts

diff --git a/.gitignore b/.gitignore
index 5931ce2..8ee4c30 100644
--- a/.gitignore
+++ b/.gitignore
@@ -107,6 +107,9 @@ typings/
 coverage
 test/cov
 
+# Generated fixtures written by tests at runtime
+test/_gen
+
 package-lock.json
 yarn.lock
 
diff --git a/bin/voxgig-model b/bin/voxgig-model
index 165484f..b53af43 100755
--- a/bin/voxgig-model
+++ b/bin/voxgig-model
@@ -183,7 +183,7 @@ async function generate(options) {
     require: process.cwd(),
     debug: options.debug,
     dryrun: options.dryrun,
-    build: options.build,
+    buildargs: options.buildargs,
 
     // TODO: read more complex options from elsewhere?
     watch: {
diff --git a/dist-test/cli.test.js b/dist-test/cli.test.js
new file mode 100644
index 0000000..682ed35
--- /dev/null
+++ b/dist-test/cli.test.js
@@ -0,0 +1,40 @@
+"use strict";
+/* Copyright © 2021-2025 Voxgig Ltd, MIT License. */
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+const node_child_process_1 = require("node:child_process");
+const promises_1 = require("node:fs/promises");
+const node_test_1 = require("node:test");
+const node_assert_1 = __importDefault(require("node:assert"));
+const GEN = __dirname + '/../test/_gen';
+const BIN = __dirname + '/../bin/voxgig-model';
+(0, node_test_1.describe)('cli', () => {
+    // The -b/--build flag is parsed into buildargs; confirm those args actually
+    // reach a build action via the real CLI entry point.
+    (0, node_test_1.test)('passes-build-args', async () => {
+        const dir = GEN + '/cli01';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir + '/model/.model-config', { recursive: true });
+        await (0, promises_1.mkdir)(dir + '/build', { recursive: true });
+        await (0, promises_1.writeFile)(dir + '/model/model.jsonic', 'top: 1\n');
+        await (0, promises_1.writeFile)(dir + '/model/.model-config/model-config.jsonic', "sys: model: action: { recordargs: load: 'build/recordargs' }\n");
+        await (0, promises_1.writeFile)(dir + '/build/recordargs.js', "const Path = require('node:path')\n" +
+            'module.exports = async function recordargs(model, build) {\n' +
+            "  const root = Path.resolve(build.path, '..', '..')\n" +
+            "  build.fs.writeFileSync(Path.resolve(root, 'args-out.json'),\n" +
+            '    JSON.stringify(build.args ?? null))\n' +
+            '  return { ok: true }\n' +
+            '}\n');
+        const out = dir + '/args-out.json';
+        await (0, promises_1.rm)(out, { force: true });
+        // No shell: args array avoids cross-platform quoting issues. Barewords
+        // keep the jsonic free of embedded quotes.
+        const res = (0, node_child_process_1.spawnSync)(process.execPath, [BIN, dir + '/model/model.jsonic', '-b', '{outer:{inner:VAL}}'], { encoding: 'utf8' });
+        node_assert_1.default.strictEqual(res.status, 0, 'cli should exit 0\nstdout:' + res.stdout + '\nstderr:' + res.stderr);
+        const args = JSON.parse(await (0, promises_1.readFile)(out, 'utf8'));
+        node_assert_1.default.deepStrictEqual(args, { outer: { inner: 'VAL' } });
+    });
+});
+//# sourceMappingURL=cli.test.js.map
\ No newline at end of file
diff --git a/dist-test/cli.test.js.map b/dist-test/cli.test.js.map
new file mode 100644
index 0000000..f46b697
--- /dev/null
+++ b/dist-test/cli.test.js.map
@@ -0,0 +1 @@
+{"version":3,"file":"cli.test.js","sourceRoot":"","sources":["../test/cli.test.ts"],"names":[],"mappings":";AAAA,oDAAoD;;;;;AAEpD,2DAA8C;AAC9C,+CAAiE;AACjE,yCAA0C;AAC1C,8DAAgC;AAGhC,MAAM,GAAG,GAAG,SAAS,GAAG,eAAe,CAAA;AACvC,MAAM,GAAG,GAAG,SAAS,GAAG,sBAAsB,CAAA;AAG9C,IAAA,oBAAQ,EAAC,KAAK,EAAE,GAAG,EAAE;IAEnB,4EAA4E;IAC5E,qDAAqD;IACrD,IAAA,gBAAI,EAAC,mBAAmB,EAAE,KAAK,IAAI,EAAE;QACnC,MAAM,GAAG,GAAG,GAAG,GAAG,QAAQ,CAAA;QAC1B,MAAM,IAAA,aAAE,EAAC,GAAG,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,CAAA;QAC/C,MAAM,IAAA,gBAAK,EAAC,GAAG,GAAG,sBAAsB,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QAC9D,MAAM,IAAA,gBAAK,EAAC,GAAG,GAAG,QAAQ,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QAEhD,MAAM,IAAA,oBAAS,EAAC,GAAG,GAAG,qBAAqB,EAAE,UAAU,CAAC,CAAA;QACxD,MAAM,IAAA,oBAAS,EAAC,GAAG,GAAG,0CAA0C,EAC9D,gEAAgE,CAAC,CAAA;QACnE,MAAM,IAAA,oBAAS,EAAC,GAAG,GAAG,sBAAsB,EAC1C,qCAAqC;YACrC,8DAA8D;YAC9D,uDAAuD;YACvD,iEAAiE;YACjE,2CAA2C;YAC3C,yBAAyB;YACzB,KAAK,CAAC,CAAA;QAER,MAAM,GAAG,GAAG,GAAG,GAAG,gBAAgB,CAAA;QAClC,MAAM,IAAA,aAAE,EAAC,GAAG,EAAE,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,CAAA;QAE9B,uEAAuE;QACvE,2CAA2C;QAC3C,MAAM,GAAG,GAAG,IAAA,8BAAS,EAAC,OAAO,CAAC,QAAQ,EACpC,CAAC,GAAG,EAAE,GAAG,GAAG,qBAAqB,EAAE,IAAI,EAAE,qBAAqB,CAAC,EAC/D,EAAE,QAAQ,EAAE,MAAM,EAAE,CAAC,CAAA;QAEvB,qBAAM,CAAC,WAAW,CAAC,GAAG,CAAC,MAAM,EAAE,CAAC,EAC9B,4BAA4B,GAAG,GAAG,CAAC,MAAM,GAAG,WAAW,GAAG,GAAG,CAAC,MAAM,CAAC,CAAA;QAEvE,MAAM,IAAI,GAAG,IAAI,CAAC,KAAK,CAAC,MAAM,IAAA,mBAAQ,EAAC,GAAG,EAAE,MAAM,CAAC,CAAC,CAAA;QACpD,qBAAM,CAAC,eAAe,CAAC,IAAI,EAAE,EAAE,KAAK,EAAE,EAAE,KAAK,EAAE,KAAK,EAAE,EAAE,CAAC,CAAA;IAC3D,CAAC,CAAC,CAAA;AAEJ,CAAC,CAAC,CAAA"}
\ No newline at end of file
diff --git a/dist-test/fix.test.js b/dist-test/fix.test.js
new file mode 100644
index 0000000..0a785f0
--- /dev/null
+++ b/dist-test/fix.test.js
@@ -0,0 +1,86 @@
+"use strict";
+/* Copyright © 2021-2025 Voxgig Ltd, MIT License. */
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+const node_fs_1 = __importDefault(require("node:fs"));
+const promises_1 = require("node:fs/promises");
+const node_test_1 = require("node:test");
+const node_assert_1 = __importDefault(require("node:assert"));
+const util_1 = require("@voxgig/util");
+const build_1 = require("../dist/build");
+const model_1 = require("../dist/model");
+const GEN = __dirname + '/../test/_gen';
+(0, node_test_1.describe)('fix', () => {
+    // A model failure must not stick to later builds. The BuildImpl is reused
+    // across watch rebuilds, so its error state has to reset every run. This
+    // also exercises that aontu errors are collected (not thrown) into errs.
+    (0, node_test_1.test)('recovers-from-model-error', async () => {
+        const dir = GEN + '/err01';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir, { recursive: true });
+        const path = dir + '/model.jsonic';
+        const log = (0, util_1.prettyPino)('test', {});
+        // Conflicting scalar values do not unify -> a collected model error.
+        await (0, promises_1.writeFile)(path, 'x: 1\nx: 2\n');
+        const b = (0, build_1.makeBuild)({ fs: node_fs_1.default, base: dir, path, res: [] }, log);
+        const bad = await b.run({ watch: false });
+        node_assert_1.default.strictEqual(bad.ok, false, 'invalid model should fail');
+        node_assert_1.default.ok(0 < bad.errs.length, 'invalid model should report errors');
+        // Repair the model and rebuild on the SAME instance.
+        await (0, promises_1.writeFile)(path, 'x: 1\n');
+        const good = await b.run({ watch: false });
+        node_assert_1.default.strictEqual(good.ok, true, 'build should recover after repair');
+        node_assert_1.default.strictEqual(good.errs.length, 0, 'errors must not leak across runs');
+        node_assert_1.default.deepStrictEqual(b.model, { x: 1 });
+    });
+    // An order entry that names an undefined action should fail with a clear
+    // message rather than an opaque "cannot read properties of undefined".
+    (0, node_test_1.test)('clear-error-on-unknown-action', async () => {
+        const dir = GEN + '/act01';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir + '/model/.model-config', { recursive: true });
+        await (0, promises_1.mkdir)(dir + '/build', { recursive: true });
+        await (0, promises_1.writeFile)(dir + '/model/model.jsonic', 'top: 1\n');
+        await (0, promises_1.writeFile)(dir + '/model/.model-config/model-config.jsonic', "sys: model: action: { real: load: 'build/real' }\n" +
+            "sys: model: order: action: 'real,ghost'\n");
+        await (0, promises_1.writeFile)(dir + '/build/real.js', 'module.exports = async () => ({ ok: true })\n');
+        const model = new model_1.Model({
+            path: dir + '/model/model.jsonic',
+            base: dir + '/model',
+            // The build deliberately errors; silence the expected log noise.
+            debug: 'silent',
+        });
+        const br = await model.run();
+        node_assert_1.default.strictEqual(br.ok, false, 'unknown action should fail the build');
+        const msg = String(br.errs[0]?.message ?? br.errs[0] ?? '');
+        node_assert_1.default.match(msg, /Unknown model action "ghost"/);
+    });
+    // dryrun must not write to the real filesystem, including via the
+    // promise-based fs API.
+    (0, node_test_1.test)('dryrun-readonly-promises', async () => {
+        const dir = GEN + '/dry01';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir, { recursive: true });
+        const model = new model_1.Model({
+            path: dir + '/model.jsonic',
+            base: dir,
+            dryrun: true,
+        });
+        // Parent dir (cwd) exists in the dryrun in-memory volume.
+        const target = process.cwd() + '/.dryrun-probe-' + Date.now() + '.tmp';
+        try {
+            await model.fs.promises.writeFile(target, 'NOPE');
+        }
+        catch {
+            // A rejection is also acceptable: nothing reached the real disk.
+        }
+        const onDisk = node_fs_1.default.existsSync(target);
+        if (onDisk) {
+            node_fs_1.default.unlinkSync(target);
+        }
+        node_assert_1.default.strictEqual(onDisk, false, 'dryrun promises.writeFile must not touch the real filesystem');
+    });
+});
+//# sourceMappingURL=fix.test.js.map
\ No newline at end of file
diff --git a/dist-test/fix.test.js.map b/dist-test/fix.test.js.map
new file mode 100644
index 0000000..daaa6bd
--- /dev/null
+++ b/dist-test/fix.test.js.map
@@ -0,0 +1 @@
+{"version":3,"file":"fix.test.js","sourceRoot":"","sources":["../test/fix.test.ts"],"names":[],"mappings":";AAAA,oDAAoD;;;;;AAEpD,sDAAwB;AACxB,+CAAuD;AACvD,yCAA0C;AAC1C,8DAAgC;AAEhC,uCAAyC;AAEzC,yCAAyC;AACzC,yCAAqC;AAGrC,MAAM,GAAG,GAAG,SAAS,GAAG,eAAe,CAAA;AAGvC,IAAA,oBAAQ,EAAC,KAAK,EAAE,GAAG,EAAE;IAEnB,0EAA0E;IAC1E,yEAAyE;IACzE,yEAAyE;IACzE,IAAA,gBAAI,EAAC,2BAA2B,EAAE,KAAK,IAAI,EAAE;QAC3C,MAAM,GAAG,GAAG,GAAG,GAAG,QAAQ,CAAA;QAC1B,MAAM,IAAA,aAAE,EAAC,GAAG,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,CAAA;QAC/C,MAAM,IAAA,gBAAK,EAAC,GAAG,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QAErC,MAAM,IAAI,GAAG,GAAG,GAAG,eAAe,CAAA;QAClC,MAAM,GAAG,GAAG,IAAA,iBAAU,EAAC,MAAM,EAAE,EAAE,CAAC,CAAA;QAElC,qEAAqE;QACrE,MAAM,IAAA,oBAAS,EAAC,IAAI,EAAE,cAAc,CAAC,CAAA;QAErC,MAAM,CAAC,GAAG,IAAA,iBAAS,EAAC,EAAE,EAAE,EAAE,iBAAE,EAAE,IAAI,EAAE,GAAG,EAAE,IAAI,EAAE,GAAG,EAAE,EAAE,EAAE,EAAE,GAAG,CAAC,CAAA;QAE9D,MAAM,GAAG,GAAG,MAAM,CAAC,CAAC,GAAG,CAAC,EAAE,KAAK,EAAE,KAAK,EAAE,CAAC,CAAA;QACzC,qBAAM,CAAC,WAAW,CAAC,GAAG,CAAC,EAAE,EAAE,KAAK,EAAE,2BAA2B,CAAC,CAAA;QAC9D,qBAAM,CAAC,EAAE,CAAC,CAAC,GAAG,GAAG,CAAC,IAAI,CAAC,MAAM,EAAE,oCAAoC,CAAC,CAAA;QAEpE,qDAAqD;QACrD,MAAM,IAAA,oBAAS,EAAC,IAAI,EAAE,QAAQ,CAAC,CAAA;QAE/B,MAAM,IAAI,GAAG,MAAM,CAAC,CAAC,GAAG,CAAC,EAAE,KAAK,EAAE,KAAK,EAAE,CAAC,CAAA;QAC1C,qBAAM,CAAC,WAAW,CAAC,IAAI,CAAC,EAAE,EAAE,IAAI,EAAE,mCAAmC,CAAC,CAAA;QACtE,qBAAM,CAAC,WAAW,CAAC,IAAI,CAAC,IAAI,CAAC,MAAM,EAAE,CAAC,EAAE,kCAAkC,CAAC,CAAA;QAC3E,qBAAM,CAAC,eAAe,CAAE,CAAS,CAAC,KAAK,EAAE,EAAE,CAAC,EAAE,CAAC,EAAE,CAAC,CAAA;IACpD,CAAC,CAAC,CAAA;IAGF,yEAAyE;IACzE,uEAAuE;IACvE,IAAA,gBAAI,EAAC,+BAA+B,EAAE,KAAK,IAAI,EAAE;QAC/C,MAAM,GAAG,GAAG,GAAG,GAAG,QAAQ,CAAA;QAC1B,MAAM,IAAA,aAAE,EAAC,GAAG,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,CAAA;QAC/C,MAAM,IAAA,gBAAK,EAAC,GAAG,GAAG,sBAAsB,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QAC9D,MAAM,IAAA,gBAAK,EAAC,GAAG,GAAG,QAAQ,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QAEhD,MAAM,IAAA,oBAAS,EAAC,GAAG,GAAG,qBAAqB,EAAE,UAAU,CAAC,CAAA;QACxD,MAAM,IAAA,oBAAS,EAAC,GAAG,GAAG,0CAA0C,EAC9D,oDAAoD;YACpD,2CAA2C,CAAC,CAAA;QAC9C,MAAM,IAAA,oBAAS,EAAC,GAAG,GAAG,gBAAgB,EACpC,+CAA+C,CAAC,CAAA;QAElD,MAAM,KAAK,GAAG,IAAI,aAAK,CAAC;YACtB,IAAI,EAAE,GAAG,GAAG,qBAAqB;YACjC,IAAI,EAAE,GAAG,GAAG,QAAQ;YACpB,iEAAiE;YACjE,KAAK,EAAE,QAAQ;SAChB,CAAC,CAAA;QACF,MAAM,EAAE,GAAG,MAAM,KAAK,CAAC,GAAG,EAAE,CAAA;QAE5B,qBAAM,CAAC,WAAW,CAAC,EAAE,CAAC,EAAE,EAAE,KAAK,EAAE,sCAAsC,CAAC,CAAA;QACxE,MAAM,GAAG,GAAG,MAAM,CAAC,EAAE,CAAC,IAAI,CAAC,CAAC,CAAC,EAAE,OAAO,IAAI,EAAE,CAAC,IAAI,CAAC,CAAC,CAAC,IAAI,EAAE,CAAC,CAAA;QAC3D,qBAAM,CAAC,KAAK,CAAC,GAAG,EAAE,8BAA8B,CAAC,CAAA;IACnD,CAAC,CAAC,CAAA;IAGF,kEAAkE;IAClE,wBAAwB;IACxB,IAAA,gBAAI,EAAC,0BAA0B,EAAE,KAAK,IAAI,EAAE;QAC1C,MAAM,GAAG,GAAG,GAAG,GAAG,QAAQ,CAAA;QAC1B,MAAM,IAAA,aAAE,EAAC,GAAG,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,CAAA;QAC/C,MAAM,IAAA,gBAAK,EAAC,GAAG,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QAErC,MAAM,KAAK,GAAQ,IAAI,aAAK,CAAC;YAC3B,IAAI,EAAE,GAAG,GAAG,eAAe;YAC3B,IAAI,EAAE,GAAG;YACT,MAAM,EAAE,IAAI;SACb,CAAC,CAAA;QAEF,0DAA0D;QAC1D,MAAM,MAAM,GAAG,OAAO,CAAC,GAAG,EAAE,GAAG,iBAAiB,GAAG,IAAI,CAAC,GAAG,EAAE,GAAG,MAAM,CAAA;QACtE,IAAI,CAAC;YACH,MAAM,KAAK,CAAC,EAAE,CAAC,QAAQ,CAAC,SAAS,CAAC,MAAM,EAAE,MAAM,CAAC,CAAA;QACnD,CAAC;QACD,MAAM,CAAC;YACL,iEAAiE;QACnE,CAAC;QAED,MAAM,MAAM,GAAG,iBAAE,CAAC,UAAU,CAAC,MAAM,CAAC,CAAA;QACpC,IAAI,MAAM,EAAE,CAAC;YACX,iBAAE,CAAC,UAAU,CAAC,MAAM,CAAC,CAAA;QACvB,CAAC;QACD,qBAAM,CAAC,WAAW,CAAC,MAAM,EAAE,KAAK,EAC9B,8DAA8D,CAAC,CAAA;IACnE,CAAC,CAAC,CAAA;AAEJ,CAAC,CAAC,CAAA"}
\ No newline at end of file
diff --git a/dist-test/watch.test.js b/dist-test/watch.test.js
new file mode 100644
index 0000000..a16fe27
--- /dev/null
+++ b/dist-test/watch.test.js
@@ -0,0 +1,57 @@
+"use strict";
+/* Copyright © 2021-2025 Voxgig Ltd, MIT License. */
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+const promises_1 = require("node:fs/promises");
+const node_test_1 = require("node:test");
+const node_assert_1 = __importDefault(require("node:assert"));
+const model_1 = require("../dist/model");
+const GEN = __dirname + '/../test/_gen';
+async function waitFor(fn, ms = 6000) {
+    const start = Date.now();
+    while (Date.now() - start < ms) {
+        if (await fn()) {
+            return true;
+        }
+        await new Promise(r => setTimeout(r, 50));
+    }
+    return false;
+}
+async function readVal(file) {
+    try {
+        return JSON.parse(await (0, promises_1.readFile)(file, 'utf8')).val;
+    }
+    catch {
+        return undefined;
+    }
+}
+(0, node_test_1.describe)('watch', () => {
+    // Start watching, then change a dependency file and confirm the model is
+    // rebuilt. Exercises the watch interval, change handling, drain queue,
+    // dependency tracking, and clean shutdown of both watchers.
+    (0, node_test_1.test)('rebuilds-on-change', async () => {
+        const base = GEN + '/wat01/model';
+        await (0, promises_1.rm)(GEN + '/wat01', { recursive: true, force: true });
+        await (0, promises_1.mkdir)(base + '/.model-config', { recursive: true });
+        await (0, promises_1.writeFile)(base + '/model.jsonic', 'top: 1\nval: @"./zed.jsonic"\n');
+        await (0, promises_1.writeFile)(base + '/zed.jsonic', '2');
+        // Standalone config (no actions) so we don't depend on package resolution.
+        await (0, promises_1.writeFile)(base + '/.model-config/model-config.jsonic', 'sys: model: action: {}\n');
+        const out = base + '/model.json';
+        const model = new model_1.Model({ path: base + '/model.jsonic', base });
+        try {
+            await model.start();
+            node_assert_1.default.ok(await waitFor(async () => (await readVal(out)) === 2), 'initial build should produce val:2');
+            // Let the dependency watchers attach before mutating zed.jsonic.
+            await new Promise(r => setTimeout(r, 250));
+            await (0, promises_1.writeFile)(base + '/zed.jsonic', '7');
+            node_assert_1.default.ok(await waitFor(async () => (await readVal(out)) === 7), 'changing the dependency should rebuild to val:7');
+        }
+        finally {
+            await model.stop();
+        }
+    });
+});
+//# sourceMappingURL=watch.test.js.map
\ No newline at end of file
diff --git a/dist-test/watch.test.js.map b/dist-test/watch.test.js.map
new file mode 100644
index 0000000..ac89ff9
--- /dev/null
+++ b/dist-test/watch.test.js.map
@@ -0,0 +1 @@
+{"version":3,"file":"watch.test.js","sourceRoot":"","sources":["../test/watch.test.ts"],"names":[],"mappings":";AAAA,oDAAoD;;;;;AAEpD,+CAAiE;AACjE,yCAA0C;AAC1C,8DAAgC;AAEhC,yCAAqC;AAGrC,MAAM,GAAG,GAAG,SAAS,GAAG,eAAe,CAAA;AAGvC,KAAK,UAAU,OAAO,CAAC,EAA0B,EAAE,EAAE,GAAG,IAAI;IAC1D,MAAM,KAAK,GAAG,IAAI,CAAC,GAAG,EAAE,CAAA;IACxB,OAAO,IAAI,CAAC,GAAG,EAAE,GAAG,KAAK,GAAG,EAAE,EAAE,CAAC;QAC/B,IAAI,MAAM,EAAE,EAAE,EAAE,CAAC;YACf,OAAO,IAAI,CAAA;QACb,CAAC;QACD,MAAM,IAAI,OAAO,CAAC,CAAC,CAAC,EAAE,CAAC,UAAU,CAAC,CAAC,EAAE,EAAE,CAAC,CAAC,CAAA;IAC3C,CAAC;IACD,OAAO,KAAK,CAAA;AACd,CAAC;AAGD,KAAK,UAAU,OAAO,CAAC,IAAY;IACjC,IAAI,CAAC;QACH,OAAO,IAAI,CAAC,KAAK,CAAC,MAAM,IAAA,mBAAQ,EAAC,IAAI,EAAE,MAAM,CAAC,CAAC,CAAC,GAAG,CAAA;IACrD,CAAC;IACD,MAAM,CAAC;QACL,OAAO,SAAS,CAAA;IAClB,CAAC;AACH,CAAC;AAGD,IAAA,oBAAQ,EAAC,OAAO,EAAE,GAAG,EAAE;IAErB,yEAAyE;IACzE,uEAAuE;IACvE,4DAA4D;IAC5D,IAAA,gBAAI,EAAC,oBAAoB,EAAE,KAAK,IAAI,EAAE;QACpC,MAAM,IAAI,GAAG,GAAG,GAAG,cAAc,CAAA;QACjC,MAAM,IAAA,aAAE,EAAC,GAAG,GAAG,QAAQ,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,CAAA;QAC1D,MAAM,IAAA,gBAAK,EAAC,IAAI,GAAG,gBAAgB,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QAEzD,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,eAAe,EAAE,gCAAgC,CAAC,CAAA;QACzE,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,aAAa,EAAE,GAAG,CAAC,CAAA;QAC1C,2EAA2E;QAC3E,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,oCAAoC,EACzD,0BAA0B,CAAC,CAAA;QAE7B,MAAM,GAAG,GAAG,IAAI,GAAG,aAAa,CAAA;QAChC,MAAM,KAAK,GAAG,IAAI,aAAK,CAAC,EAAE,IAAI,EAAE,IAAI,GAAG,eAAe,EAAE,IAAI,EAAE,CAAC,CAAA;QAE/D,IAAI,CAAC;YACH,MAAM,KAAK,CAAC,KAAK,EAAE,CAAA;YAEnB,qBAAM,CAAC,EAAE,CACP,MAAM,OAAO,CAAC,KAAK,IAAI,EAAE,CAAC,CAAC,MAAM,OAAO,CAAC,GAAG,CAAC,CAAC,KAAK,CAAC,CAAC,EACrD,oCAAoC,CAAC,CAAA;YAEvC,iEAAiE;YACjE,MAAM,IAAI,OAAO,CAAC,CAAC,CAAC,EAAE,CAAC,UAAU,CAAC,CAAC,EAAE,GAAG,CAAC,CAAC,CAAA;YAC1C,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,aAAa,EAAE,GAAG,CAAC,CAAA;YAE1C,qBAAM,CAAC,EAAE,CACP,MAAM,OAAO,CAAC,KAAK,IAAI,EAAE,CAAC,CAAC,MAAM,OAAO,CAAC,GAAG,CAAC,CAAC,KAAK,CAAC,CAAC,EACrD,iDAAiD,CAAC,CAAA;QACtD,CAAC;gBACO,CAAC;YACP,MAAM,KAAK,CAAC,IAAI,EAAE,CAAA;QACpB,CAAC;IACH,CAAC,CAAC,CAAA;AAEJ,CAAC,CAAC,CAAA"}
\ No newline at end of file
diff --git a/dist/build.js b/dist/build.js
index 0705372..6382b60 100644
--- a/dist/build.js
+++ b/dist/build.js
@@ -35,6 +35,11 @@ class BuildImpl {
     async run(rspec) {
         let hasErr = false;
         let runlog = [];
+        // Reset per-run error state. The BuildImpl is reused across watch
+        // rebuilds, so without this a single failure would stick to every
+        // later build. Reassign (don't clear in place) so a previously
+        // returned BuildResult keeps its own errors.
+        this.errs = [];
         this.ctx = { step: 'pre', state: {}, watch: rspec.watch };
         const plog = [];
         if (!hasErr) {
@@ -113,11 +118,26 @@ class BuildImpl {
             }
         }
         if (!hasErr) {
-            this.opts.errs = this.errs;
+            // Collect this generation's errors into a fresh array. The option key
+            // is `err` (not `errs`) — that is what aontu reads, and providing it
+            // puts aontu in collect mode so model errors are gathered rather than
+            // thrown. A per-call array avoids leaking errors into later builds.
+            const modelErrs = [];
+            this.opts.err = modelErrs;
             this.opts.deps = this.deps;
             this.opts.fs = this.fs;
-            this.model = this.aontu.generate(src, this.opts);
-            hasErr = this.opts.errs && 0 < this.opts.errs.length;
+            try {
+                this.model = this.aontu.generate(src, this.opts);
+            }
+            catch (err) {
+                // collect mode normally prevents throws, but guard the rare cases
+                // (e.g. unresolved imports) so they surface as build errors.
+                modelErrs.push(err);
+            }
+            if (0 < modelErrs.length) {
+                hasErr = true;
+                this.errs.push(...modelErrs);
+            }
         }
         this.cacheSig = hasErr ? null : this.snapshotSig();
         return hasErr;
diff --git a/dist/build.js.map b/dist/build.js.map
index 82e87cb..3fd2170 100644
--- a/dist/build.js.map
+++ b/dist/build.js.map
@@ -1 +1 @@
-{"version":3,"file":"build.js","sourceRoot":"","sources":["../src/build.ts"],"names":[],"mappings":";AAAA,oDAAoD;;AA2NlD,8BAAS;AAxNX,iCAA6B;AAc7B,MAAM,SAAS;IAuBb,YAAY,IAAe,EAAE,GAAQ;QAfrC,QAAG,GAAG,EAAE,CAAA;QACR,SAAI,GAAU,EAAE,CAAA;QAShB,6EAA6E;QAC7E,2EAA2E;QAC3E,aAAQ,GAA+B,IAAI,CAAA;QAIzC,IAAI,CAAC,EAAE,GAAG,MAAM,CAAC,IAAI,CAAC,MAAM,EAAE,CAAC,CAAC,SAAS,CAAC,CAAC,EAAE,CAAC,CAAC,CAAA;QAC/C,IAAI,CAAC,GAAG,GAAG,GAAG,CAAA;QAEd,IAAI,CAAC,IAAI,GAAG,IAAI,CAAA;QAEhB,IAAI,CAAC,MAAM,GAAG,CAAC,CAAC,IAAI,CAAC,MAAM,CAAA;QAC3B,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,SAAS,CAAA;QAC1B,IAAI,CAAC,EAAE,GAAG,IAAI,CAAC,EAAE,CAAA;QACjB,IAAI,CAAC,IAAI,GAAG,IAAI,IAAI,IAAI,CAAC,IAAI,CAAC,CAAC,CAAC,EAAE,CAAC,CAAC,CAAC,IAAI,CAAC,IAAI,CAAA;QAC9C,IAAI,CAAC,IAAI,GAAG,IAAI,IAAI,IAAI,CAAC,IAAI,CAAC,CAAC,CAAC,EAAE,CAAC,CAAC,CAAC,IAAI,CAAC,IAAI,CAAA;QAC9C,IAAI,CAAC,IAAI,GAAG,EAAE,CAAA;QACd,IAAI,CAAC,GAAG,GAAG,EAAE,IAAI,EAAE,KAAK,EAAE,KAAK,EAAE,KAAK,EAAE,KAAK,EAAE,EAAE,EAAE,CAAA;QAEnD,IAAI,IAAI,IAAI,IAAI,CAAC,IAAI,EAAE,CAAC;YACtB,IAAI,CAAC,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,IAAI,CAAA;YAC1B,IAAI,CAAC,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,IAAI,CAAA;QAC5B,CAAC;QAED,IAAI,IAAI,IAAI,IAAI,CAAC,OAAO,EAAE,CAAC;YACzB,IAAI,CAAC,IAAI,CAAC,OAAO,GAAG,IAAI,CAAC,OAAO,CAAA;QAClC,CAAC;QAED,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,GAAG,IAAI,EAAE,CAAA;QAE1B,MAAM,CAAC,MAAM,CAAC,IAAI,CAAC,GAAG,EAAE,IAAI,CAAC,GAAG,IAAI,EAAE,CAAC,CAAA;QAEvC,IAAI,CAAC,IAAI,GAAG,EAAE,CAAA;QACd,IAAI,CAAC,KAAK,GAAG,IAAI,aAAK,EAAE,CAAA;IAC1B,CAAC;IAGD,KAAK,CAAC,GAAG,CAAC,KAAc;QACtB,IAAI,MAAM,GAAG,KAAK,CAAA;QAClB,IAAI,MAAM,GAAG,EAAE,CAAA;QAEf,IAAI,CAAC,GAAG,GAAG,EAAE,IAAI,EAAE,KAAK,EAAE,KAAK,EAAE,EAAE,EAAE,KAAK,EAAE,KAAK,CAAC,KAAK,EAAE,CAAA;QACzD,MAAM,IAAI,GAAU,EAAE,CAAA;QAEtB,IAAI,CAAC,MAAM,EAAE,CAAC;YACZ,MAAM,CAAC,IAAI,CAAC,eAAe,CAAC,CAAA;YAC5B,MAAM,GAAG,MAAM,IAAI,CAAC,YAAY,EAAE,CAAA;QACpC,CAAC;QAED,IAAI,WAAW,GAAG,KAAK,CAAA;QAEvB,IAAI,CAAC,MAAM,EAAE,CAAC;YACZ,KAAK,IAAI,QAAQ,IAAI,IAAI,CAAC,IAAI,EAAE,CAAC;gBAC/B,IAAI,CAAC;oBACH,MAAM,CAAC,IAAI,CAAC,eAAe,GAAG,QAAQ,CAAC,KAAK,CAAC,IAAI,CAAC,CAAA;oBAClD,IAAI,EAAE,GAAG,MAAM,QAAQ,CAAC,KAAK,CAAC,IAAI,EAAE,IAAI,CAAC,GAAG,CAAC,CAAA;oBAC7C,WAAW,GAAG,WAAW,IAAI,EAAE,CAAC,MAAM,CAAA;oBACtC,IAAI,CAAC,IAAI,CAAC,EAAE,CAAC,CAAA;oBACb,IAAI,CAAC,EAAE,CAAC,EAAE,EAAE,CAAC;wBACX,MAAM,GAAG,IAAI,CAAA;wBACb,MAAK;oBACP,CAAC;gBACH,CAAC;gBACD,OAAO,GAAQ,EAAE,CAAC;oBAChB,MAAM,GAAG,IAAI,CAAA;oBACb,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,GAAG,CAAC,CAAA;oBACnB,MAAK;gBACP,CAAC;YACH,CAAC;QACH,CAAC;QAED,kEAAkE;QAClE,oEAAoE;QACpE,MAAM,MAAM,GAAG,WAAW,IAAI,CAAC,MAAM,CAAA;QAErC,IAAI,MAAM,EAAE,CAAC;YACX,MAAM,CAAC,IAAI,CAAC,YAAY,CAAC,CAAA;YACzB,MAAM,GAAG,MAAM,IAAI,CAAC,YAAY,EAAE,CAAA;QACpC,CAAC;QAED,IAAI,CAAC,MAAM,EAAE,CAAC;YACZ,IAAI,CAAC,GAAG,CAAC,IAAI,GAAG,MAAM,CAAA;YAEtB,KAAK,IAAI,QAAQ,IAAI,IAAI,CAAC,IAAI,EAAE,CAAC;gBAC/B,IAAI,CAAC;oBACH,MAAM,CAAC,IAAI,CAAC,gBAAgB,GAAG,QAAQ,CAAC,KAAK,CAAC,IAAI,CAAC,CAAA;oBACnD,IAAI,EAAE,GAAG,MAAM,QAAQ,CAAC,KAAK,CAAC,IAAI,EAAE,IAAI,CAAC,GAAG,CAAC,CAAA;oBAC7C,IAAI,CAAC,IAAI,CAAC,EAAE,CAAC,CAAA;oBACb,IAAI,CAAC,EAAE,CAAC,EAAE,EAAE,CAAC;wBACX,MAAM,GAAG,IAAI,CAAA;wBACb,MAAK;oBACP,CAAC;gBACH,CAAC;gBACD,OAAO,GAAQ,EAAE,CAAC;oBAChB,MAAM,GAAG,IAAI,CAAA;oBACb,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,GAAG,CAAC,CAAA;oBACnB,MAAK;gBACP,CAAC;YACH,CAAC;QAEH,CAAC;QAED,MAAM,EAAE,GACR;YACE,6BAA6B;YAC7B,KAAK,EAAE,GAAG,EAAE,CAAC,IAAI;YAEjB,EAAE,EAAE,CAAC,MAAM;YACX,SAAS,EAAE,IAAI;YACf,IAAI,EAAE,IAAI,CAAC,IAAI;YACf,MAAM;SACP,CAAA;QAED,OAAO,EAAE,CAAA;IACX,CAAC;IAGD,KAAK,CAAC,YAAY;QAChB,IAAI,IAAI,CAAC,KAAK,IAAI,IAAI,CAAC,QAAQ,IAAI,IAAI,CAAC,QAAQ,EAAE,EAAE,CAAC;YACnD,OAAO,KAAK,CAAA;QACd,CAAC;QAED,IAAI,MAAM,GAAG,KAAK,CAAA;QAElB,IAAI,GAAG,GAAW,EAAE,CAAA;QACpB,IAAI,CAAC,MAAM,EAAE,CAAC;YACZ,IAAI,CAAC;gBACH,GAAG,GAAG,IAAI,CAAC,EAAE,CAAC,YAAY,CAAC,IAAI,CAAC,IAAI,EAAE,MAAM,CAAC,CAAA;YAC/C,CAAC;YACD,OAAO,GAAQ,EAAE,CAAC;gBAChB,MAAM,GAAG,IAAI,CAAA;gBACb,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,GAAG,CAAC,CAAA;YACrB,CAAC;QACH,CAAC;QAED,IAAI,CAAC,MAAM,EAAE,CAAC;YACZ,IAAI,CAAC,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,IAAI,CAAA;YAC1B,IAAI,CAAC,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,IAAI,CAAA;YAC1B,IAAI,CAAC,IAAI,CAAC,EAAE,GAAG,IAAI,CAAC,EAAE,CAAA;YACtB,IAAI,CAAC,KAAK,GAAG,IAAI,CAAC,KAAK,CAAC,QAAQ,CAAC,GAAG,EAAE,IAAI,CAAC,IAAI,CAAC,CAAA;YAEhD,MAAM,GAAG,IAAI,CAAC,IAAI,CAAC,IAAI,IAAI,CAAC,GAAG,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,MAAM,CAAA;QACtD,CAAC;QAED,IAAI,CAAC,QAAQ,GAAG,MAAM,CAAC,CAAC,CAAC,IAAI,CAAC,CAAC,CAAC,IAAI,CAAC,WAAW,EAAE,CAAA;QAElD,OAAO,MAAM,CAAA;IACf,CAAC;IAGD,4EAA4E;IAC5E,WAAW;QACT,MAAM,GAAG,GAAG,IAAI,GAAG,EAAkB,CAAA;QACrC,GAAG,CAAC,GAAG,CAAC,IAAI,CAAC,IAAI,EAAE,KAAK,CAAC,IAAI,CAAC,EAAE,EAAE,IAAI,CAAC,IAAI,CAAC,CAAC,CAAA;QAC7C,KAAK,MAAM,MAAM,IAAI,MAAM,CAAC,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,EAAE,CAAC;YAC5C,KAAK,MAAM,KAAK,IAAI,MAAM,CAAC,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,MAAM,CAAC,CAAC,EAAE,CAAC;gBACnD,IAAI,CAAC,GAAG,CAAC,GAAG,CAAC,KAAK,CAAC;oBAAE,GAAG,CAAC,GAAG,CAAC,KAAK,EAAE,KAAK,CAAC,IAAI,CAAC,EAAE,EAAE,KAAK,CAAC,CAAC,CAAA;YAC5D,CAAC;QACH,CAAC;QACD,OAAO,GAAG,CAAA;IACZ,CAAC;IAGD,QAAQ;QACN,IAAI,CAAC,IAAI,CAAC,QAAQ;YAAE,OAAO,KAAK,CAAA;QAChC,KAAK,MAAM,CAAC,IAAI,EAAE,IAAI,CAAC,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\ No newline at end of file
+{"version":3,"file":"build.js","sourceRoot":"","sources":["../src/build.ts"],"names":[],"mappings":";AAAA,oDAAoD;;AAiPlD,8BAAS;AA9OX,iCAA6B;AAc7B,MAAM,SAAS;IAuBb,YAAY,IAAe,EAAE,GAAQ;QAfrC,QAAG,GAAG,EAAE,CAAA;QACR,SAAI,GAAU,EAAE,CAAA;QAShB,6EAA6E;QAC7E,2EAA2E;QAC3E,aAAQ,GAA+B,IAAI,CAAA;QAIzC,IAAI,CAAC,EAAE,GAAG,MAAM,CAAC,IAAI,CAAC,MAAM,EAAE,CAAC,CAAC,SAAS,CAAC,CAAC,EAAE,CAAC,CAAC,CAAA;QAC/C,IAAI,CAAC,GAAG,GAAG,GAAG,CAAA;QAEd,IAAI,CAAC,IAAI,GAAG,IAAI,CAAA;QAEhB,IAAI,CAAC,MAAM,GAAG,CAAC,CAAC,IAAI,CAAC,MAAM,CAAA;QAC3B,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,SAAS,CAAA;QAC1B,IAAI,CAAC,EAAE,GAAG,IAAI,CAAC,EAAE,CAAA;QACjB,IAAI,CAAC,IAAI,GAAG,IAAI,IAAI,IAAI,CAAC,IAAI,CAAC,CAAC,CAAC,EAAE,CAAC,CAAC,CAAC,IAAI,CAAC,IAAI,CAAA;QAC9C,IAAI,CAAC,IAAI,GAAG,IAAI,IAAI,IAAI,CAAC,IAAI,CAAC,CAAC,CAAC,EAAE,CAAC,CAAC,CAAC,IAAI,CAAC,IAAI,CAAA;QAC9C,IAAI,CAAC,IAAI,GAAG,EAAE,CAAA;QACd,IAAI,CAAC,GAAG,GAAG,EAAE,IAAI,EAAE,KAAK,EAAE,KAAK,EAAE,KAAK,EAAE,KAAK,EAAE,EAAE,EAAE,CAAA;QAEnD,IAAI,IAAI,IAAI,IAAI,CAAC,IAAI,EAAE,CAAC;YACtB,IAAI,CAAC,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,IAAI,CAAA;YAC1B,IAAI,CAAC,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,IAAI,CAAA;QAC5B,CAAC;QAED,IAAI,IAAI,IAAI,IAAI,CAAC,OAAO,EAAE,CAAC;YACzB,IAAI,CAAC,IAAI,CAAC,OAAO,GAAG,IAAI,CAAC,OAAO,CAAA;QAClC,CAAC;QAED,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,GAAG,IAAI,EAAE,CAAA;QAE1B,MAAM,CAAC,MAAM,CAAC,IAAI,CAAC,GAAG,EAAE,IAAI,CAAC,GAAG,IAAI,EAAE,CAAC,CAAA;QAEvC,IAAI,CAAC,IAAI,GAAG,EAAE,CAAA;QACd,IAAI,CAAC,KAAK,GAAG,IAAI,aAAK,EAAE,CAAA;IAC1B,CAAC;IAGD,KAAK,CAAC,GAAG,CAAC,KAAc;QACtB,IAAI,MAAM,GAAG,KAAK,CAAA;QAClB,IAAI,MAAM,GAAG,EAAE,CAAA;QAEf,kEAAkE;QAClE,kEAAkE;QAClE,+DAA+D;QAC/D,6CAA6C;QAC7C,IAAI,CAAC,IAAI,GAAG,EAAE,CAAA;QAEd,IAAI,CAAC,GAAG,GAAG,EAAE,IAAI,EAAE,KAAK,EAAE,KAAK,EAAE,EAAE,EAAE,KAAK,EAAE,KAAK,CAAC,KAAK,EAAE,CAAA;QACzD,MAAM,IAAI,GAAU,EAAE,CAAA;QAEtB,IAAI,CAAC,MAAM,EAAE,CAAC;YACZ,MAAM,CAAC,IAAI,CAAC,eAAe,CAAC,CAAA;YAC5B,MAAM,GAAG,MAAM,IAAI,CAAC,YAAY,EAAE,CAAA;QACpC,CAAC;QAED,IAAI,WAAW,GAAG,KAAK,CAAA;QAEvB,IAAI,CAAC,MAAM,EAAE,CAAC;YACZ,KAAK,IAAI,QAAQ,IAAI,IAAI,CAAC,IAAI,EAAE,CAAC;gBAC/B,IAAI,CAAC;oBACH,MAAM,CAAC,IAAI,CAAC,eAAe,GAAG,QAAQ,CAAC,KAAK,CAAC,IAAI,CAAC,CAAA;oBAClD,IAAI,EAAE,GAAG,MAAM,QAAQ,CAAC,KAAK,CAAC,IAAI,EAAE,IAAI,CAAC,GAAG,CAAC,CAAA;oBAC7C,WAAW,GAAG,WAAW,IAAI,EAAE,CAAC,MAAM,CAAA;oBACtC,IAAI,CAAC,IAAI,CAAC,EAAE,CAAC,CAAA;oBACb,IAAI,CAAC,EAAE,CAAC,EAAE,EAAE,CAAC;wBACX,MAAM,GAAG,IAAI,CAAA;wBACb,MAAK;oBACP,CAAC;gBACH,CAAC;gBACD,OAAO,GAAQ,EAAE,CAAC;oBAChB,MAAM,GAAG,IAAI,CAAA;oBACb,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,GAAG,CAAC,CAAA;oBACnB,MAAK;gBACP,CAAC;YACH,CAAC;QACH,CAAC;QAED,kEAAkE;QAClE,oEAAoE;QACpE,MAAM,MAAM,GAAG,WAAW,IAAI,CAAC,MAAM,CAAA;QAErC,IAAI,MAAM,EAAE,CAAC;YACX,MAAM,CAAC,IAAI,CAAC,YAAY,CAAC,CAAA;YACzB,MAAM,GAAG,MAAM,IAAI,CAAC,YAAY,EAAE,CAAA;QACpC,CAAC;QAED,IAAI,CAAC,MAAM,EAAE,CAAC;YACZ,IAAI,CAAC,GAAG,CAAC,IAAI,GAAG,MAAM,CAAA;YAEtB,KAAK,IAAI,QAAQ,IAAI,IAAI,CAAC,IAAI,EAAE,CAAC;gBAC/B,IAAI,CAAC;oBACH,MAAM,CAAC,IAAI,CAAC,gBAAgB,GAAG,QAAQ,CAAC,KAAK,CAAC,IAAI,CAAC,CAAA;oBACnD,IAAI,EAAE,GAAG,MAAM,QAAQ,CAAC,KAAK,CAAC,IAAI,EAAE,IAAI,CAAC,GAAG,CAAC,CAAA;oBAC7C,IAAI,CAAC,IAAI,CAAC,EAAE,CAAC,CAAA;oBACb,IAAI,CAAC,EAAE,CAAC,EAAE,EAAE,CAAC;wBACX,MAAM,GAAG,IAAI,CAAA;wBACb,MAAK;oBACP,CAAC;gBACH,CAAC;gBACD,OAAO,GAAQ,EAAE,CAAC;oBAChB,MAAM,GAAG,IAAI,CAAA;oBACb,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,GAAG,CAAC,CAAA;oBACnB,MAAK;gBACP,CAAC;YACH,CAAC;QAEH,CAAC;QAED,MAAM,EAAE,GACR;YACE,6BAA6B;YAC7B,KAAK,EAAE,GAAG,EAAE,CAAC,IAAI;YAEjB,EAAE,EAAE,CAAC,MAAM;YACX,SAAS,EAAE,IAAI;YACf,IAAI,EAAE,IAAI,CAAC,IAAI;YACf,MAAM;SACP,CAAA;QAED,OAAO,EAAE,CAAA;IACX,CAAC;IAGD,KAAK,CAAC,YAAY;QAChB,IAAI,IAAI,CAAC,KAAK,IAAI,IAAI,CAAC,QAAQ,IAAI,IAAI,CAAC,QAAQ,EAAE,EAAE,CAAC;YACnD,OAAO,KAAK,CAAA;QACd,CAAC;QAED,IAAI,MAAM,GAAG,KAAK,CAAA;QAElB,IAAI,GAAG,GAAW,EAAE,CAAA;QACpB,IAAI,CAAC,MAAM,EAAE,CAAC;YACZ,IAAI,CAAC;gBACH,GAAG,GAAG,IAAI,CAAC,EAAE,CAAC,YAAY,CAAC,IAAI,CAAC,IAAI,EAAE,MAAM,CAAC,CAAA;YAC/C,CAAC;YACD,OAAO,GAAQ,EAAE,CAAC;gBAChB,MAAM,GAAG,IAAI,CAAA;gBACb,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,GAAG,CAAC,CAAA;YACrB,CAAC;QACH,CAAC;QAED,IAAI,CAAC,MAAM,EAAE,CAAC;YACZ,sEAAsE;YACtE,qEAAqE;YACrE,sEAAsE;YACtE,oEAAoE;YACpE,MAAM,SAAS,GAAU,EAAE,CAAA;YAC3B,IAAI,CAAC,IAAI,CAAC,GAAG,GAAG,SAAS,CAAA;YACzB,IAAI,CAAC,IAAI,CAAC,IAAI,GAAG,IAAI,CAAC,IAAI,CAAA;YAC1B,IAAI,CAAC,IAAI,CAAC,EAAE,GAAG,IAAI,CAAC,EAAE,CAAA;YAEtB,IAAI,CAAC;gBACH,IAAI,CAAC,KAAK,GAAG,IAAI,CAAC,KAAK,CAAC,QAAQ,CAAC,GAAG,EAAE,IAAI,CAAC,IAAI,CAAC,CAAA;YAClD,CAAC;YACD,OAAO,GAAQ,EAAE,CAAC;gBAChB,kEAAkE;gBAClE,6DAA6D;gBAC7D,SAAS,CAAC,IAAI,CAAC,GAAG,CAAC,CAAA;YACrB,CAAC;YAED,IAAI,CAAC,GAAG,SAAS,CAAC,MAAM,EAAE,CAAC;gBACzB,MAAM,GAAG,IAAI,CAAA;gBACb,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,GAAG,SAAS,CAAC,CAAA;YAC9B,CAAC;QACH,CAAC;QAED,IAAI,CAAC,QAAQ,GAAG,MAAM,CAAC,CAAC,CAAC,IAAI,CAAC,CAAC,CAAC,IAAI,CAAC,WAAW,EAAE,CAAA;QAElD,OAAO,MAAM,CAAA;IACf,CAAC;IAGD,4EAA4E;IAC5E,WAAW;QACT,MAAM,GAAG,GAAG,IAAI,GAAG,EAAkB,CAAA;QACrC,GAAG,CAAC,GAAG,CAAC,IAAI,CAAC,IAAI,EAAE,KAAK,CAAC,IAAI,CAAC,EAAE,EAAE,IAAI,CAAC,IAAI,CAAC,CAAC,CAAA;QAC7C,KAAK,MAAM,MAAM,IAAI,MAAM,CAAC,IAAI,CAAC,IAAI,CAAC,IAAI,CAAC,EAAE,CAAC;YAC5C,KAAK,MAAM,KAAK,IAAI,MAAM,CAAC,IAAI,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\ No newline at end of file
diff --git a/dist/model.js b/dist/model.js
index 03edd7c..be43b6c 100644
--- a/dist/model.js
+++ b/dist/model.js
@@ -74,8 +74,12 @@ class Model {
                 }
                 if (self.trigger_model) {
                     // TODO: better design
-                    if (self.build.use) {
-                        self.build.use.config.watch.last.build = build;
+                    // Point the config's last result at the current build so the model
+                    // producer reads fresh config state. It must be a thunk to satisfy
+                    // BuildResult.build's `() => Build` contract (consumers call it).
+                    const lastConfig = self.build.use?.config?.watch?.last;
+                    if (lastConfig) {
+                        lastConfig.build = () => build;
                     }
                     const br = await self.watch.run('model', true);
                     pres.ok = br.ok;
@@ -134,6 +138,9 @@ class Model {
         return br.ok ? this.watch.start() : br;
     }
     async stop() {
+        // start() also spins up a config-file watcher; stop both so no
+        // chokidar handle is left open keeping the process alive.
+        await this.config.stop();
         return this.watch.stop();
     }
 }
@@ -199,8 +206,6 @@ function makeReadOnly(fsm) {
         'unlink',
         'unlinkSync',
         'write',
-        'writeFile',
-        'writeFileSync',
         'writev',
     ];
     const { fs } = (0, memfs_1.memfs)({ [process.cwd()]: {} });
@@ -209,6 +214,20 @@ function makeReadOnly(fsm) {
             fsm[w] = fs[w].bind(fs);
         }
     }
+    // Also redirect the promise-based writers. fsm.promises is shared by
+    // reference with the real fs module, so replace it with a copy rather
+    // than mutating the caller's fs.
+    const memPromises = fs.promises;
+    if (fsm.promises && memPromises) {
+        const promises = { ...fsm.promises };
+        for (let w of writers) {
+            if ('function' === typeof memPromises[w]) {
+                promises[w] = memPromises[w].bind(memPromises);
+            }
+        }
+        ;
+        fsm.promises = promises;
+    }
     return fsm;
 }
 //# sourceMappingURL=model.js.map
\ No newline at end of file
diff --git a/dist/model.js.map b/dist/model.js.map
index 690edd0..35bd0c0 100644
--- a/dist/model.js.map
+++ b/dist/model.js.map
@@ -1 +1 @@
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+{"version":3,"file":"model.js","sourceRoot":"","sources":["../src/model.ts"],"names":[],"mappings":";AAAA,oDAAoD;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;AAGpD,gDAAiC;AAEjC,iCAAsC;AAEtC,uCAAyC;AAezC,qCAAiC;AACjC,mCAA+B;AAE/B,4CAAiD;AACjD,4CAAiD;AAGjD,MAAM,KAAK;IAUT,YAAY,KAAgB;QAL5B,kBAAa,GAAG,KAAK,CAAA;QAMnB,MAAM,IAAI,GAAG,IAAI,CAAA;QAEjB,IAAI,CAAC,EAAE,GAAG,EAAE,GAAG,CAAC,KAAK,CAAC,EAAE,IAAI,MAAM,CAAC,EAAE,CAAA;QAErC,IAAI,KAAK,CAAC,MAAM,EAAE,CAAC;YACjB,YAAY,CAAC,IAAI,CAAC,EAAE,CAAC,CAAA;QACvB,CAAC;QAED,MAAM,IAAI,GAAG,IAAA,iBAAU,EAAC,OAAO,EAAE,KAAY,CAAC,CAAA;QAE9C,IAAI,CAAC,GAAG,GAAG,IAAI,CAAC,KAAK,CAAC,EAAE,GAAG,EAAE,OAAO,EAAE,CAAC,CAAA;QAEvC,IAAI,CAAC,GAAG,CAAC,IAAI,CAAC,EAAE,KAAK,EAAE,YAAY,EAAE,CAAC,CAAA;QACtC,IAAI,IAAI,CAAC,GAAG,CAAC,cAAc,CAAC,OAAO,CAAC,EAAE,CAAC;YACrC,IAAI,CAAC,GAAG,CAAC,KAAK,CAAC;gBACb,KAAK,EAAE,YAAY,EAAE,KAAK,EAAE,IAAI,EAAE,IAAI;oBACpC,IAAI,CAAC,SAAS,CAAC,EAAE,GAAG,KAAK,EAAE,GAAG,EAAE,aAAa,EAAE,EAAE,IAAI,EAAE,CAAC,CAAC;yBACtD,OAAO,CAAC,IAAI,EAAE,EAAE,CAAC;yBACjB,UAAU,CAAC,OAAO,CAAC,GAAG,EAAE,EAAE,GAAG,CAAC;aACpC,CAAC,CAAA;QACJ,CAAC;QAED,oDAAoD;QACpD,IAAI,CAAC,MAAM,GAAG,UAAU,CAAC,KAAK,EAAE,IAAI,CAAC,GAAG,EAAE,IAAI,CAAC,EAAE,EAAE;YACjD,IAAI,EAAE,GAAG;YACT,KAAK,EAAE,KAAK,UAAU,aAAa,CAAC,KAAY,EAAE,GAAiB;gBACjE,IAAI,IAAI,GAAmB;oBACzB,EAAE,EAAE,KAAK,EAAE,IAAI,EAAE,QAAQ,EAAE,IAAI,EAAE,EAAE,EAAE,MAAM,EAAE,IAAI,EAAE,MAAM,EAAE,KAAK,EAAE,IAAI,EAAE,EAAE,EAAE,MAAM,EAAE,EAAE;iBACvF,CAAA;gBAED,IAAI,MAAM,KAAK,GAAG,CAAC,IAAI,EAAE,CAAC;oBACxB,IAAI,CAAC,EAAE,GAAG,IAAI,CAAA;oBACd,OAAO,IAAI,CAAA;gBACb,CAAC;gBAGD,IAAI,IAAI,CAAC,aAAa,EAAE,CAAC;oBAEvB,sBAAsB;oBACtB,mEAAmE;oBACnE,mEAAmE;oBACnE,kEAAkE;oBAClE,MAAM,UAAU,GAAG,IAAI,CAAC,KAAK,CAAC,GAAG,EAAE,MAAM,EAAE,KAAK,EAAE,IAAI,CAAA;oBACtD,IAAI,UAAU,EAAE,CAAC;wBACf,UAAU,CAAC,KAAK,GAAG,GAAG,EAAE,CAAC,KAAK,CAAA;oBAChC,CAAC;oBAED,MAAM,EAAE,GAAG,MAAM,IAAI,CAAC,KAAK,CAAC,GAAG,CAAC,OAAO,EAAE,IAAI,CAAC,CAAA;oBAC9C,IAAI,CAAC,EAAE,GAAG,EAAE,CAAC,EAAE,CAAA;oBACf,IAAI,CAAC,IAAI,GAAG,EAAE,CAAC,IAAI,CAAA;gBACrB,CAAC;qBACI,CAAC;oBACJ,IAAI,CAAC,aAAa,GAAG,IAAI,CAAA;oBACzB,IAAI,CAAC,EAAE,GAAG,IAAI,CAAA;gBAChB,CAAC;gBAED,IAAI,GAAG,CAAC,KAAK,EAAE,CAAC;oBACd,MAAM,QAAQ,GAAG,KAAK,CAAC,KAAK,EAAE,GAAG,EAAE,KAAK,EAAE,KAAK,CAAA;oBAE/C,IAAI,QAAQ,EAAE,CAAC;wBACb,MAAM,CAAC,IAAI,CAAC,QAAQ,CAAC,CAAC,OAAO,CAAC,CAAC,IAAY,EAAE,EAAE;4BAC7C,IAAI,CAAC,KAAK,CAAC,GAAG,CAAC,IAAI,CAAC,CAAA;wBACtB,CAAC,CAAC,CAAA;oBACJ,CAAC;gBACH,CAAC;gBAED,OAAO,IAAI,CAAA;YACb,CAAC;SACF,CAAC,CAAA;QAEF,oBAAoB;QACpB,IAAI,CAAC,KAAK,GAAG;YACX,IAAI,EAAE,KAAK,CAAC,IAAI;YAChB,IAAI,EAAE,KAAK,CAAC,IAAI;YAChB,KAAK,EAAE,KAAK,CAAC,KAAK;YAClB,MAAM,EAAE,KAAK,CAAC,MAAM;YACpB,SAAS,EAAE,KAAK,CAAC,SAAS;YAC1B,GAAG,EAAE,EAAE,MAAM,EAAE,IAAI,CAAC,MAAM,EAAE;YAC5B,GAAG,EAAE;gBACH;oBACE,IAAI,EAAE,GAAG;oBACT,KAAK,EAAE,sBAAc;iBACtB;gBACD;oBACE,IAAI,EAAE,GAAG;oBACT,KAAK,EAAE,sBAAc;iBACtB;aACF;YACD,OAAO,EAAE,KAAK,CAAC,OAAO;YACtB,GAAG,EAAE,IAAI,CAAC,GAAG;YACb,EAAE,EAAE,IAAI,CAAC,EAAE;YACX,KAAK,EAAE,KAAK,CAAC,KAAK;SACnB,CAAA;QAED,IAAI,CAAC,KAAK,GAAG,IAAI,aAAK,CAAC,IAAI,CAAC,KAAK,EAAE,IAAI,CAAC,GAAG,CAAC,CAAA;IAC9C,CAAC;IAGD,YAAY;IACZ,KAAK,CAAC,GAAG;QACP,IAAI,CAAC,aAAa,GAAG,KAAK,CAAA;QAC1B,MAAM,EAAE,GAAG,MAAM,IAAI,CAAC,MAAM,CAAC,GAAG,CAAC,KAAK,CAAC,CAAA;QACvC,OAAO,EAAE,CAAC,EAAE,CAAC,CAAC,CAAC,IAAI,CAAC,KAAK,CAAC,GAAG,CAAC,OAAO,EAAE,KAAK,EAAE,SAAS,CAAC,CAAC,CAAC,CAAC,EAAE,CAAA;IAC/D,CAAC;IAGD,uDAAuD;IACvD,KAAK,CAAC,KAAK;QACT,IAAI,CAAC,aAAa,GAAG,KAAK,CAAA;QAC1B,MAAM,EAAE,GAAG,MAAM,IAAI,CAAC,MAAM,CAAC,GAAG,CAAC,IAAI,CAAC,CAAA;QACtC,OAAO,EAAE,CAAC,EAAE,CAAC,CAAC,CAAC,IAAI,CAAC,KAAK,CAAC,KAAK,EAAE,CAAC,CAAC,CAAC,EAAE,CAAA;IACxC,CAAC;IAGD,KAAK,CAAC,IAAI;QACR,+DAA+D;QAC/D,0DAA0D;QAC1D,MAAM,IAAI,CAAC,MAAM,CAAC,IAAI,EAAE,CAAA;QACxB,OAAO,IAAI,CAAC,KAAK,CAAC,IAAI,EAAE,CAAA;IAC1B,CAAC;CACF;AAsGC,sBAAK;AAnGP,SAAS,UAAU,CAAC,KAAgB,EAAE,GAAQ,EAAE,EAAO,EAAE,mBAAgC;IACvF,IAAI,KAAK,GAAG,KAAK,CAAC,IAAI,GAAG,gBAAgB,CAAA;IACzC,IAAI,KAAK,GAAG,KAAK,GAAG,sBAAsB,CAAA;IAE1C,IAAI,CAAC,EAAE,CAAC,UAAU,CAAC,KAAK,CAAC,EAAE,CAAC;QAC1B,EAAE,CAAC,SAAS,CAAC,KAAK,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QACxC,EAAE,CAAC,aAAa,CAAC,KAAK,EAAE;;;;CAI3B,CAAC,CAAA;IACA,CAAC;IAED,IAAI,KAAK,GAAc;QACrB,IAAI,EAAE,QAAQ;QACd,IAAI,EAAE,KAAK;QACX,IAAI,EAAE,KAAK;QACX,KAAK,EAAE,KAAK,CAAC,KAAK;QAClB,GAAG,EAAE;YAEH,iDAAiD;YACjD;gBACE,IAAI,EAAE,GAAG;gBACT,KAAK,EAAE,sBAAc;aACtB;YAED,4BAA4B;YAC5B,mBAAmB;SACpB;QACD,OAAO,EAAE,KAAK,CAAC,OAAO;QACtB,GAAG;QACH,EAAE;KACH,CAAA;IAED,OAAO,IAAI,eAAM,CAAC,KAAK,EAAE,GAAG,CAAC,CAAA;AAC/B,CAAC;AAGD,SAAS,YAAY,CAAC,GAAQ;IAE5B,sBAAsB;IACtB,yBAAyB;IACzB,MAAM,OAAO,GAAG;QACd,WAAW;QACX,eAAe;QACf,YAAY;QACZ,gBAAgB;QAChB,OAAO;QACP,WAAW;QACX,OAAO;QACP,WAAW;QACX,IAAI;QACJ,QAAQ;QACR,mBAAmB;QACnB,OAAO;QACP,WAAW;QACX,QAAQ;QACR,YAAY;QACZ,IAAI;QACJ,QAAQ;QACR,OAAO;QACP,WAAW;QACX,SAAS;QACT,aAAa;QACb,UAAU;QACV,cAAc;QACd,QAAQ;QACR,YAAY;QACZ,OAAO;QACP,QAAQ;KACT,CAAA;IAED,MAAM,EAAE,EAAE,EAAE,GAAG,IAAA,aAAK,EAAC,EAAE,CAAC,OAAO,CAAC,GAAG,EAAE,CAAC,EAAE,EAAE,EAAE,CAAC,CAAA;IAE7C,KAAK,IAAI,CAAC,IAAI,OAAO,EAAE,CAAC;QACtB,IAAK,EAAU,CAAC,CAAC,CAAC,EAAE,CAAC;YAClB,GAAW,CAAC,CAAC,CAAC,GAAI,EAAU,CAAC,CAAC,CAAC,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\ No newline at end of file
diff --git a/dist/producer/local.js b/dist/producer/local.js
index 2062f4d..9418931 100644
--- a/dist/producer/local.js
+++ b/dist/producer/local.js
@@ -28,6 +28,13 @@ const local_producer = async (build, ctx) => {
         // load actions
         for (let name of ordering) {
             let actiondef = actions[name];
+            if (null == actiondef) {
+                throw new Error('Unknown model action "' + name +
+                    '" referenced in sys.model.order.action');
+            }
+            if (null == actiondef.load) {
+                throw new Error('Model action "' + name + '" is missing a "load" path');
+            }
             let actionpath = path_1.default.join(root, actiondef.load);
             let action = require(actionpath);
             if (action instanceof Promise) {
diff --git a/dist/producer/local.js.map b/dist/producer/local.js.map
index 27e4c92..6c75a61 100644
--- a/dist/producer/local.js.map
+++ b/dist/producer/local.js.map
@@ -1 +1 @@
-{"version":3,"file":"local.js","sourceRoot":"","sources":["../../src/producer/local.ts"],"names":[],"mappings":";;;;;;AACA,gDAAuB;AAIvB,MAAM,iBAAiB,GAAG,UAAU,CAAA;AAEpC,wCAAwC;AACxC,MAAM,cAAc,GAAa,KAAK,EAAE,KAAY,EAAE,GAAiB,EAAE,EAAE;IAEzE,GAAG,CAAC,KAAK,CAAC,KAAK,GAAG,CAAC,GAAG,CAAC,KAAK,CAAC,KAAK,IAAI,EAAE,CAAC,CAAA;IACzC,IAAI,UAAU,GAAG,GAAG,CAAC,KAAK,CAAC,KAAK,CAAC,UAAU,CAAA;IAE3C,IAAI,IAAI,IAAI,UAAU,EAAE,CAAC;QACvB,UAAU,GAAG,GAAG,CAAC,KAAK,CAAC,KAAK,CAAC,UAAU,GAAG,EAAE,CAAA;QAE5C,+CAA+C;QAC/C,IAAI,IAAI,GAAG,cAAI,CAAC,OAAO,CAAC,KAAK,CAAC,IAAI,EAAE,IAAI,EAAE,IAAI,CAAC,CAAA;QAE/C,6BAA6B;QAC7B,IAAI,iBAAiB,GAAG,KAAK,CAAC,GAAG,CAAC,MAAM,CAAC,KAAK,CAAC,IAAI,CAAA;QACnD,IAAI,WAAW,GAAG,iBAAiB,EAAE,KAAK,EAAE,CAAA;QAC5C,IAAI,MAAM,GAAG,WAAW,EAAE,KAAK,IAAI,EAAE,CAAA;QAErC,IAAI,OAAO,GAAG,MAAM,CAAC,GAAG,EAAE,KAAK,EAAE,MAAM;YACrC,yBAAyB;YACzB,MAAM,CAAC,GAAG,EAAE,KAAK,EAAE,QAAQ;YAC3B,EAAE,CAAA;QAEJ,IAAI,QAAQ,GAAG,MAAM,CAAC,GAAG,EAAE,KAAK,EAAE,KAAK,EAAE,MAAM,CAAA;QAC/C,QAAQ,GAAG,IAAI,IAAI,QAAQ,CAAC,CAAC,CAAC,MAAM,CAAC,IAAI,CAAC,OAAO,CAAC,CAAC,CAAC;YAClD,QAAQ,CAAC,KAAK,CAAC,iBAAiB,CAAC,CAAC,MAAM,CAAC,CAAC,CAAS,EAAE,EAAE,CAAC,IAAI,IAAI,CAAC,IAAI,EAAE,IAAI,CAAC,CAAC,CAAA;QAE/E,eAAe;QACf,KAAK,IAAI,IAAI,IAAI,QAAQ,EAAE,CAAC;YAC1B,IAAI,SAAS,GAAG,OAAO,CAAC,IAAI,CAAC,CAAA;YAC7B,IAAI,UAAU,GAAG,cAAI,CAAC,IAAI,CAAC,IAAI,EAAE,SAAS,CAAC,IAAI,CAAC,CAAA;YAEhD,IAAI,MAAM,GAAG,OAAO,CAAC,UAAU,CAAC,CAAA;YAEhC,IAAI,MAAM,YAAY,OAAO,EAAE,CAAC;gBAC9B,MAAM,GAAG,MAAM,MAAM,CAAA;YACvB,CAAC;YAED,MAAM,IAAI,GAAG,MAAM,CAAC,IAAI,IAAI,MAAM,CAAA;YAElC,UAAU,CAAC,IAAI,CAAC,EAAE,IAAI,EAAE,SAAS,EAAE,MAAM,EAAE,IAAI,EAAE,CAAC,CAAA;QACpD,CAAC;IACH,CAAC;IAED,MAAM,aAAa,GAAG,UAAU,CAAC,MAAM,CAAC,CAAC,EAAO,EAAE,EAAE,CAAC,GAAG,CAAC,IAAI,KAAK,EAAE,CAAC,IAAI,IAAI,KAAK,KAAK,EAAE,CAAC,IAAI,CAAC,CAAA;IAE/F,KAAK,CAAC,GAAG,CAAC,IAAI,CAAC;QACb,KAAK,EAAE,GAAG,CAAC,IAAI,GAAG,UAAU,EAAE,IAAI,EAAE,GAAG,CAAC,IAAI,EAAE,OAAO,EAAE,aAAa;QACpE,IAAI,EAAE,aAAa,CAAC,GAAG,CAAC,CAAC,EAAO,EAAE,EAAE,CAAC,EAAE,CAAC,IAAI,CAAC,CAAC,IAAI,CAAC,GAAG,CAAC;KACxD,CAAC,CAAA;IAEF,IAAI,EAAE,GAAG,IAAI,CAAA;IACb,IAAI,OAAO,GAAG,EAAE,CAAA;IAChB,IAAI,MAAM,GAAG,KAAK,CAAA;IAElB,KAAK,IAAI,SAAS,IAAI,aAAa,EAAE,CAAC;QACpC,IAAI,CAAC;YACH,oFAAoF;YACpF,IAAI,IAAI,GAAG,MAAM,SAAS,CAAC,MAAM,CAAC,KAAK,CAAC,KAAK,EAAE,KAAK,EAAE,GAAG,CAAC,CAAA;YAC1D,EAAE,GAAG,EAAE,IAAI,CAAC,IAAI,IAAI,IAAI,IAAI,CAAC,CAAC,IAAI,CAAC,EAAE,CAAC,CAAA;YACtC,MAAM,GAAG,MAAM,IAAI,IAAI,EAAE,MAAM,CAAA;YAE/B,OAAO,CAAC,IAAI,CAAC,IAAI,CAAC,CAAA;YAElB,IAAI,CAAC,EAAE,EAAE,CAAC;gBAAC,MAAK;YAAC,CAAC;QACpB,CAAC;QACD,OAAO,GAAQ,EAAE,CAAC;YAChB,IAAI,CAAC,GAAG,CAAC,UAAU,EAAE,CAAC;gBACpB,KAAK,CAAC,GAAG,CAAC,KAAK,CAAC;oBACd,KAAK,EAAE,GAAG,CAAC,IAAI,GAAG,SAAS,EAAE,IAAI,EAAE,GAAG,CAAC,IAAI,EAAE,MAAM,EAAE,SAAS;oBAC9D,IAAI,EAAE,SAAS,CAAC,IAAI;oBACpB,GAAG;iBACJ,CAAC,CAAA;gBACF,GAAG,CAAC,UAAU,GAAG,IAAI,CAAA;YACvB,CAAC;YACD,MAAM,GAAG,CAAA;QACX,CAAC;IACH,CAAC;IAED,IAAI,EAAE,GAAmB;QACvB,EAAE;QACF,MAAM;QACN,IAAI,EAAE,OAAO;QACb,IAAI,EAAE,GAAG,CAAC,IAAI;QACd,MAAM,EAAE,IAAI;QACZ,IAAI,EAAE,EAAE;QACR,MAAM,EAAE,EAAE;KACX,CAAA;IAED,OAAO,EAAE,CAAA;AACX,CAAC,CAAA;AAIC,wCAAc"}
\ No newline at end of file
+{"version":3,"file":"local.js","sourceRoot":"","sources":["../../src/producer/local.ts"],"names":[],"mappings":";;;;;;AACA,gDAAuB;AAIvB,MAAM,iBAAiB,GAAG,UAAU,CAAA;AAEpC,wCAAwC;AACxC,MAAM,cAAc,GAAa,KAAK,EAAE,KAAY,EAAE,GAAiB,EAAE,EAAE;IAEzE,GAAG,CAAC,KAAK,CAAC,KAAK,GAAG,CAAC,GAAG,CAAC,KAAK,CAAC,KAAK,IAAI,EAAE,CAAC,CAAA;IACzC,IAAI,UAAU,GAAG,GAAG,CAAC,KAAK,CAAC,KAAK,CAAC,UAAU,CAAA;IAE3C,IAAI,IAAI,IAAI,UAAU,EAAE,CAAC;QACvB,UAAU,GAAG,GAAG,CAAC,KAAK,CAAC,KAAK,CAAC,UAAU,GAAG,EAAE,CAAA;QAE5C,+CAA+C;QAC/C,IAAI,IAAI,GAAG,cAAI,CAAC,OAAO,CAAC,KAAK,CAAC,IAAI,EAAE,IAAI,EAAE,IAAI,CAAC,CAAA;QAE/C,6BAA6B;QAC7B,IAAI,iBAAiB,GAAG,KAAK,CAAC,GAAG,CAAC,MAAM,CAAC,KAAK,CAAC,IAAI,CAAA;QACnD,IAAI,WAAW,GAAG,iBAAiB,EAAE,KAAK,EAAE,CAAA;QAC5C,IAAI,MAAM,GAAG,WAAW,EAAE,KAAK,IAAI,EAAE,CAAA;QAErC,IAAI,OAAO,GAAG,MAAM,CAAC,GAAG,EAAE,KAAK,EAAE,MAAM;YACrC,yBAAyB;YACzB,MAAM,CAAC,GAAG,EAAE,KAAK,EAAE,QAAQ;YAC3B,EAAE,CAAA;QAEJ,IAAI,QAAQ,GAAG,MAAM,CAAC,GAAG,EAAE,KAAK,EAAE,KAAK,EAAE,MAAM,CAAA;QAC/C,QAAQ,GAAG,IAAI,IAAI,QAAQ,CAAC,CAAC,CAAC,MAAM,CAAC,IAAI,CAAC,OAAO,CAAC,CAAC,CAAC;YAClD,QAAQ,CAAC,KAAK,CAAC,iBAAiB,CAAC,CAAC,MAAM,CAAC,CAAC,CAAS,EAAE,EAAE,CAAC,IAAI,IAAI,CAAC,IAAI,EAAE,IAAI,CAAC,CAAC,CAAA;QAE/E,eAAe;QACf,KAAK,IAAI,IAAI,IAAI,QAAQ,EAAE,CAAC;YAC1B,IAAI,SAAS,GAAG,OAAO,CAAC,IAAI,CAAC,CAAA;YAE7B,IAAI,IAAI,IAAI,SAAS,EAAE,CAAC;gBACtB,MAAM,IAAI,KAAK,CACb,wBAAwB,GAAG,IAAI;oBAC/B,wCAAwC,CAAC,CAAA;YAC7C,CAAC;YAED,IAAI,IAAI,IAAI,SAAS,CAAC,IAAI,EAAE,CAAC;gBAC3B,MAAM,IAAI,KAAK,CACb,gBAAgB,GAAG,IAAI,GAAG,4BAA4B,CAAC,CAAA;YAC3D,CAAC;YAED,IAAI,UAAU,GAAG,cAAI,CAAC,IAAI,CAAC,IAAI,EAAE,SAAS,CAAC,IAAI,CAAC,CAAA;YAEhD,IAAI,MAAM,GAAG,OAAO,CAAC,UAAU,CAAC,CAAA;YAEhC,IAAI,MAAM,YAAY,OAAO,EAAE,CAAC;gBAC9B,MAAM,GAAG,MAAM,MAAM,CAAA;YACvB,CAAC;YAED,MAAM,IAAI,GAAG,MAAM,CAAC,IAAI,IAAI,MAAM,CAAA;YAElC,UAAU,CAAC,IAAI,CAAC,EAAE,IAAI,EAAE,SAAS,EAAE,MAAM,EAAE,IAAI,EAAE,CAAC,CAAA;QACpD,CAAC;IACH,CAAC;IAED,MAAM,aAAa,GAAG,UAAU,CAAC,MAAM,CAAC,CAAC,EAAO,EAAE,EAAE,CAAC,GAAG,CAAC,IAAI,KAAK,EAAE,CAAC,IAAI,IAAI,KAAK,KAAK,EAAE,CAAC,IAAI,CAAC,CAAA;IAE/F,KAAK,CAAC,GAAG,CAAC,IAAI,CAAC;QACb,KAAK,EAAE,GAAG,CAAC,IAAI,GAAG,UAAU,EAAE,IAAI,EAAE,GAAG,CAAC,IAAI,EAAE,OAAO,EAAE,aAAa;QACpE,IAAI,EAAE,aAAa,CAAC,GAAG,CAAC,CAAC,EAAO,EAAE,EAAE,CAAC,EAAE,CAAC,IAAI,CAAC,CAAC,IAAI,CAAC,GAAG,CAAC;KACxD,CAAC,CAAA;IAEF,IAAI,EAAE,GAAG,IAAI,CAAA;IACb,IAAI,OAAO,GAAG,EAAE,CAAA;IAChB,IAAI,MAAM,GAAG,KAAK,CAAA;IAElB,KAAK,IAAI,SAAS,IAAI,aAAa,EAAE,CAAC;QACpC,IAAI,CAAC;YACH,oFAAoF;YACpF,IAAI,IAAI,GAAG,MAAM,SAAS,CAAC,MAAM,CAAC,KAAK,CAAC,KAAK,EAAE,KAAK,EAAE,GAAG,CAAC,CAAA;YAC1D,EAAE,GAAG,EAAE,IAAI,CAAC,IAAI,IAAI,IAAI,IAAI,CAAC,CAAC,IAAI,CAAC,EAAE,CAAC,CAAA;YACtC,MAAM,GAAG,MAAM,IAAI,IAAI,EAAE,MAAM,CAAA;YAE/B,OAAO,CAAC,IAAI,CAAC,IAAI,CAAC,CAAA;YAElB,IAAI,CAAC,EAAE,EAAE,CAAC;gBAAC,MAAK;YAAC,CAAC;QACpB,CAAC;QACD,OAAO,GAAQ,EAAE,CAAC;YAChB,IAAI,CAAC,GAAG,CAAC,UAAU,EAAE,CAAC;gBACpB,KAAK,CAAC,GAAG,CAAC,KAAK,CAAC;oBACd,KAAK,EAAE,GAAG,CAAC,IAAI,GAAG,SAAS,EAAE,IAAI,EAAE,GAAG,CAAC,IAAI,EAAE,MAAM,EAAE,SAAS;oBAC9D,IAAI,EAAE,SAAS,CAAC,IAAI;oBACpB,GAAG;iBACJ,CAAC,CAAA;gBACF,GAAG,CAAC,UAAU,GAAG,IAAI,CAAA;YACvB,CAAC;YACD,MAAM,GAAG,CAAA;QACX,CAAC;IACH,CAAC;IAED,IAAI,EAAE,GAAmB;QACvB,EAAE;QACF,MAAM;QACN,IAAI,EAAE,OAAO;QACb,IAAI,EAAE,GAAG,CAAC,IAAI;QACd,MAAM,EAAE,IAAI;QACZ,IAAI,EAAE,EAAE;QACR,MAAM,EAAE,EAAE;KACX,CAAA;IAED,OAAO,EAAE,CAAA;AACX,CAAC,CAAA;AAIC,wCAAc"}
\ No newline at end of file
diff --git a/dist/watch.js b/dist/watch.js
index 3b34840..aa492a6 100644
--- a/dist/watch.js
+++ b/dist/watch.js
@@ -48,7 +48,8 @@ class Watch {
         }
         return this.fsw;
     }
-    // Returns first BuildResult
+    // Begin watching. The initial build, and every subsequent rebuild, is
+    // enqueued asynchronously once the watcher settles, so nothing is returned.
     start() {
         this.ensureFSW();
         this.startTime = Date.now();
@@ -116,7 +117,7 @@ class Watch {
     }
     async add(path) {
         if (!node_path_1.default.isAbsolute(path)) {
-            path = node_path_1.default.join(this.wspec.require, path);
+            path = node_path_1.default.join(this.wspec.require || process.cwd(), path);
         }
         // Ignore if already added
         if (this.canonPaths.has(path)) {
diff --git a/dist/watch.js.map b/dist/watch.js.map
index ca1ecd1..3c52c49 100644
--- a/dist/watch.js.map
+++ b/dist/watch.js.map
@@ -1 +1 @@
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\ No newline at end of file
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\ No newline at end of file
diff --git a/src/build.ts b/src/build.ts
index aeafa7b..4d2e0c7 100644
--- a/src/build.ts
+++ b/src/build.ts
@@ -74,6 +74,12 @@ class BuildImpl implements Build {
     let hasErr = false
     let runlog = []
 
+    // Reset per-run error state. The BuildImpl is reused across watch
+    // rebuilds, so without this a single failure would stick to every
+    // later build. Reassign (don't clear in place) so a previously
+    // returned BuildResult keeps its own errors.
+    this.errs = []
+
     this.ctx = { step: 'pre', state: {}, watch: rspec.watch }
     const plog: any[] = []
 
@@ -169,12 +175,28 @@ class BuildImpl implements Build {
     }
 
     if (!hasErr) {
-      this.opts.errs = this.errs
+      // Collect this generation's errors into a fresh array. The option key
+      // is `err` (not `errs`) — that is what aontu reads, and providing it
+      // puts aontu in collect mode so model errors are gathered rather than
+      // thrown. A per-call array avoids leaking errors into later builds.
+      const modelErrs: any[] = []
+      this.opts.err = modelErrs
       this.opts.deps = this.deps
       this.opts.fs = this.fs
-      this.model = this.aontu.generate(src, this.opts)
 
-      hasErr = this.opts.errs && 0 < this.opts.errs.length
+      try {
+        this.model = this.aontu.generate(src, this.opts)
+      }
+      catch (err: any) {
+        // collect mode normally prevents throws, but guard the rare cases
+        // (e.g. unresolved imports) so they surface as build errors.
+        modelErrs.push(err)
+      }
+
+      if (0 < modelErrs.length) {
+        hasErr = true
+        this.errs.push(...modelErrs)
+      }
     }
 
     this.cacheSig = hasErr ? null : this.snapshotSig()
diff --git a/src/model.ts b/src/model.ts
index 0d4809a..48a7414 100644
--- a/src/model.ts
+++ b/src/model.ts
@@ -77,8 +77,12 @@ class Model {
         if (self.trigger_model) {
 
           // TODO: better design
-          if (self.build.use) {
-            self.build.use.config.watch.last.build = build
+          // Point the config's last result at the current build so the model
+          // producer reads fresh config state. It must be a thunk to satisfy
+          // BuildResult.build's `() => Build` contract (consumers call it).
+          const lastConfig = self.build.use?.config?.watch?.last
+          if (lastConfig) {
+            lastConfig.build = () => build
           }
 
           const br = await self.watch.run('model', true)
@@ -149,6 +153,9 @@ class Model {
 
 
   async stop() {
+    // start() also spins up a config-file watcher; stop both so no
+    // chokidar handle is left open keeping the process alive.
+    await this.config.stop()
     return this.watch.stop()
   }
 }
@@ -223,8 +230,6 @@ function makeReadOnly(fsm: FST) {
     'unlink',
     'unlinkSync',
     'write',
-    'writeFile',
-    'writeFileSync',
     'writev',
   ]
 
@@ -236,6 +241,20 @@ function makeReadOnly(fsm: FST) {
     }
   }
 
+  // Also redirect the promise-based writers. fsm.promises is shared by
+  // reference with the real fs module, so replace it with a copy rather
+  // than mutating the caller's fs.
+  const memPromises = (fs as any).promises
+  if ((fsm as any).promises && memPromises) {
+    const promises: any = { ...(fsm as any).promises }
+    for (let w of writers) {
+      if ('function' === typeof memPromises[w]) {
+        promises[w] = memPromises[w].bind(memPromises)
+      }
+    }
+    ;(fsm as any).promises = promises
+  }
+
   return fsm
 }
 
diff --git a/src/producer/local.ts b/src/producer/local.ts
index 047c2d0..f2ecceb 100644
--- a/src/producer/local.ts
+++ b/src/producer/local.ts
@@ -34,6 +34,18 @@ const local_producer: Producer = async (build: Build, ctx: BuildContext) => {
     // load actions
     for (let name of ordering) {
       let actiondef = actions[name]
+
+      if (null == actiondef) {
+        throw new Error(
+          'Unknown model action "' + name +
+          '" referenced in sys.model.order.action')
+      }
+
+      if (null == actiondef.load) {
+        throw new Error(
+          'Model action "' + name + '" is missing a "load" path')
+      }
+
       let actionpath = Path.join(root, actiondef.load)
 
       let action = require(actionpath)
diff --git a/src/watch.ts b/src/watch.ts
index 0919a88..5a24e96 100644
--- a/src/watch.ts
+++ b/src/watch.ts
@@ -95,7 +95,8 @@ class Watch {
   }
 
 
-  // Returns first BuildResult
+  // Begin watching. The initial build, and every subsequent rebuild, is
+  // enqueued asynchronously once the watcher settles, so nothing is returned.
   start() {
     this.ensureFSW()
     this.startTime = Date.now()
@@ -180,7 +181,7 @@ class Watch {
 
   async add(path: string) {
     if (!Path.isAbsolute(path)) {
-      path = Path.join(this.wspec.require, path)
+      path = Path.join(this.wspec.require || process.cwd(), path)
     }
 
     // Ignore if already added
diff --git a/test/cli.test.ts b/test/cli.test.ts
new file mode 100644
index 0000000..81d4082
--- /dev/null
+++ b/test/cli.test.ts
@@ -0,0 +1,51 @@
+/* Copyright © 2021-2025 Voxgig Ltd, MIT License. */
+
+import { spawnSync } from 'node:child_process'
+import { mkdir, writeFile, readFile, rm } from 'node:fs/promises'
+import { test, describe } from 'node:test'
+import assert from 'node:assert'
+
+
+const GEN = __dirname + '/../test/_gen'
+const BIN = __dirname + '/../bin/voxgig-model'
+
+
+describe('cli', () => {
+
+  // The -b/--build flag is parsed into buildargs; confirm those args actually
+  // reach a build action via the real CLI entry point.
+  test('passes-build-args', async () => {
+    const dir = GEN + '/cli01'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir + '/model/.model-config', { recursive: true })
+    await mkdir(dir + '/build', { recursive: true })
+
+    await writeFile(dir + '/model/model.jsonic', 'top: 1\n')
+    await writeFile(dir + '/model/.model-config/model-config.jsonic',
+      "sys: model: action: { recordargs: load: 'build/recordargs' }\n")
+    await writeFile(dir + '/build/recordargs.js',
+      "const Path = require('node:path')\n" +
+      'module.exports = async function recordargs(model, build) {\n' +
+      "  const root = Path.resolve(build.path, '..', '..')\n" +
+      "  build.fs.writeFileSync(Path.resolve(root, 'args-out.json'),\n" +
+      '    JSON.stringify(build.args ?? null))\n' +
+      '  return { ok: true }\n' +
+      '}\n')
+
+    const out = dir + '/args-out.json'
+    await rm(out, { force: true })
+
+    // No shell: args array avoids cross-platform quoting issues. Barewords
+    // keep the jsonic free of embedded quotes.
+    const res = spawnSync(process.execPath,
+      [BIN, dir + '/model/model.jsonic', '-b', '{outer:{inner:VAL}}'],
+      { encoding: 'utf8' })
+
+    assert.strictEqual(res.status, 0,
+      'cli should exit 0\nstdout:' + res.stdout + '\nstderr:' + res.stderr)
+
+    const args = JSON.parse(await readFile(out, 'utf8'))
+    assert.deepStrictEqual(args, { outer: { inner: 'VAL' } })
+  })
+
+})
diff --git a/test/fix.test.ts b/test/fix.test.ts
new file mode 100644
index 0000000..353adc0
--- /dev/null
+++ b/test/fix.test.ts
@@ -0,0 +1,108 @@
+/* Copyright © 2021-2025 Voxgig Ltd, MIT License. */
+
+import Fs from 'node:fs'
+import { mkdir, writeFile, rm } from 'node:fs/promises'
+import { test, describe } from 'node:test'
+import assert from 'node:assert'
+
+import { prettyPino } from '@voxgig/util'
+
+import { makeBuild } from '../dist/build'
+import { Model } from '../dist/model'
+
+
+const GEN = __dirname + '/../test/_gen'
+
+
+describe('fix', () => {
+
+  // A model failure must not stick to later builds. The BuildImpl is reused
+  // across watch rebuilds, so its error state has to reset every run. This
+  // also exercises that aontu errors are collected (not thrown) into errs.
+  test('recovers-from-model-error', async () => {
+    const dir = GEN + '/err01'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir, { recursive: true })
+
+    const path = dir + '/model.jsonic'
+    const log = prettyPino('test', {})
+
+    // Conflicting scalar values do not unify -> a collected model error.
+    await writeFile(path, 'x: 1\nx: 2\n')
+
+    const b = makeBuild({ fs: Fs, base: dir, path, res: [] }, log)
+
+    const bad = await b.run({ watch: false })
+    assert.strictEqual(bad.ok, false, 'invalid model should fail')
+    assert.ok(0 < bad.errs.length, 'invalid model should report errors')
+
+    // Repair the model and rebuild on the SAME instance.
+    await writeFile(path, 'x: 1\n')
+
+    const good = await b.run({ watch: false })
+    assert.strictEqual(good.ok, true, 'build should recover after repair')
+    assert.strictEqual(good.errs.length, 0, 'errors must not leak across runs')
+    assert.deepStrictEqual((b as any).model, { x: 1 })
+  })
+
+
+  // An order entry that names an undefined action should fail with a clear
+  // message rather than an opaque "cannot read properties of undefined".
+  test('clear-error-on-unknown-action', async () => {
+    const dir = GEN + '/act01'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir + '/model/.model-config', { recursive: true })
+    await mkdir(dir + '/build', { recursive: true })
+
+    await writeFile(dir + '/model/model.jsonic', 'top: 1\n')
+    await writeFile(dir + '/model/.model-config/model-config.jsonic',
+      "sys: model: action: { real: load: 'build/real' }\n" +
+      "sys: model: order: action: 'real,ghost'\n")
+    await writeFile(dir + '/build/real.js',
+      'module.exports = async () => ({ ok: true })\n')
+
+    const model = new Model({
+      path: dir + '/model/model.jsonic',
+      base: dir + '/model',
+      // The build deliberately errors; silence the expected log noise.
+      debug: 'silent',
+    })
+    const br = await model.run()
+
+    assert.strictEqual(br.ok, false, 'unknown action should fail the build')
+    const msg = String(br.errs[0]?.message ?? br.errs[0] ?? '')
+    assert.match(msg, /Unknown model action "ghost"/)
+  })
+
+
+  // dryrun must not write to the real filesystem, including via the
+  // promise-based fs API.
+  test('dryrun-readonly-promises', async () => {
+    const dir = GEN + '/dry01'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir, { recursive: true })
+
+    const model: any = new Model({
+      path: dir + '/model.jsonic',
+      base: dir,
+      dryrun: true,
+    })
+
+    // Parent dir (cwd) exists in the dryrun in-memory volume.
+    const target = process.cwd() + '/.dryrun-probe-' + Date.now() + '.tmp'
+    try {
+      await model.fs.promises.writeFile(target, 'NOPE')
+    }
+    catch {
+      // A rejection is also acceptable: nothing reached the real disk.
+    }
+
+    const onDisk = Fs.existsSync(target)
+    if (onDisk) {
+      Fs.unlinkSync(target)
+    }
+    assert.strictEqual(onDisk, false,
+      'dryrun promises.writeFile must not touch the real filesystem')
+  })
+
+})
diff --git a/test/watch.test.ts b/test/watch.test.ts
new file mode 100644
index 0000000..f6b154e
--- /dev/null
+++ b/test/watch.test.ts
@@ -0,0 +1,74 @@
+/* Copyright © 2021-2025 Voxgig Ltd, MIT License. */
+
+import { mkdir, writeFile, readFile, rm } from 'node:fs/promises'
+import { test, describe } from 'node:test'
+import assert from 'node:assert'
+
+import { Model } from '../dist/model'
+
+
+const GEN = __dirname + '/../test/_gen'
+
+
+async function waitFor(fn: () => Promise<boolean>, ms = 6000): Promise<boolean> {
+  const start = Date.now()
+  while (Date.now() - start < ms) {
+    if (await fn()) {
+      return true
+    }
+    await new Promise(r => setTimeout(r, 50))
+  }
+  return false
+}
+
+
+async function readVal(file: string): Promise<number | undefined> {
+  try {
+    return JSON.parse(await readFile(file, 'utf8')).val
+  }
+  catch {
+    return undefined
+  }
+}
+
+
+describe('watch', () => {
+
+  // Start watching, then change a dependency file and confirm the model is
+  // rebuilt. Exercises the watch interval, change handling, drain queue,
+  // dependency tracking, and clean shutdown of both watchers.
+  test('rebuilds-on-change', async () => {
+    const base = GEN + '/wat01/model'
+    await rm(GEN + '/wat01', { recursive: true, force: true })
+    await mkdir(base + '/.model-config', { recursive: true })
+
+    await writeFile(base + '/model.jsonic', 'top: 1\nval: @"./zed.jsonic"\n')
+    await writeFile(base + '/zed.jsonic', '2')
+    // Standalone config (no actions) so we don't depend on package resolution.
+    await writeFile(base + '/.model-config/model-config.jsonic',
+      'sys: model: action: {}\n')
+
+    const out = base + '/model.json'
+    const model = new Model({ path: base + '/model.jsonic', base })
+
+    try {
+      await model.start()
+
+      assert.ok(
+        await waitFor(async () => (await readVal(out)) === 2),
+        'initial build should produce val:2')
+
+      // Let the dependency watchers attach before mutating zed.jsonic.
+      await new Promise(r => setTimeout(r, 250))
+      await writeFile(base + '/zed.jsonic', '7')
+
+      assert.ok(
+        await waitFor(async () => (await readVal(out)) === 7),
+        'changing the dependency should rebuild to val:7')
+    }
+    finally {
+      await model.stop()
+    }
+  })
+
+})

From a9cb988d1c77ca8d2605cef3855db8955e0ec201 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Mon, 8 Jun 2026 11:23:00 +0000
Subject: [PATCH 3/6] feat: watch config files for changes in Model.start()

start() previously ran the config build once but never started the
config watcher's interval, so config-file edits were detected yet never
acted on (and the watcher leaked until stop()). It now also watches the
config files: a config change rebuilds the config and re-triggers the
model build - the path the BuildResult.build thunk fix enables.

To keep the initial config build from racing the first model build,
Watch.start()/Config.start() take an `initial` flag; start() keeps the
synchronous initial config build and begins config watching with
initial=false.

Tests: config-change-triggers-rebuild (verified it fails without the
wiring), plus missing-load and throwing-action coverage for the local
producer. Line coverage now 93.3% (config.ts 100%, local.ts 96.5%).

Known limitation: a simultaneous config + model file change can still
drive two overlapping model builds, because the config trigger calls
watch.run() directly rather than via the main queue. The per-run error
reset makes this self-healing; unifying the queues is left as follow-up.

https://claude.ai/code/session_01HxXpZNrKj3qonocwAtEP8r
---
 dist-test/fix.test.js       | 38 ++++++++++++++++++++++
 dist-test/fix.test.js.map   |  2 +-
 dist-test/watch.test.js     | 45 ++++++++++++++++++++++++++
 dist-test/watch.test.js.map |  2 +-
 dist/config.d.ts            |  2 +-
 dist/config.js              |  4 +--
 dist/config.js.map          |  2 +-
 dist/model.js               | 12 +++++--
 dist/model.js.map           |  2 +-
 dist/watch.d.ts             |  2 +-
 dist/watch.js               |  8 +++--
 dist/watch.js.map           |  2 +-
 src/config.ts               |  4 +--
 src/model.ts                | 12 +++++--
 src/watch.ts                |  8 +++--
 test/fix.test.ts            | 51 +++++++++++++++++++++++++++++
 test/watch.test.ts          | 64 ++++++++++++++++++++++++++++++++++++-
 17 files changed, 240 insertions(+), 20 deletions(-)

diff --git a/dist-test/fix.test.js b/dist-test/fix.test.js
index 0a785f0..c6795c0 100644
--- a/dist-test/fix.test.js
+++ b/dist-test/fix.test.js
@@ -57,6 +57,44 @@ const GEN = __dirname + '/../test/_gen';
         const msg = String(br.errs[0]?.message ?? br.errs[0] ?? '');
         node_assert_1.default.match(msg, /Unknown model action "ghost"/);
     });
+    // An action definition with no load path should also fail clearly.
+    (0, node_test_1.test)('clear-error-on-missing-load', async () => {
+        const dir = GEN + '/act02';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir + '/model/.model-config', { recursive: true });
+        await (0, promises_1.writeFile)(dir + '/model/model.jsonic', 'top: 1\n');
+        await (0, promises_1.writeFile)(dir + '/model/.model-config/model-config.jsonic', 'sys: model: action: { noload: {} }\n' +
+            "sys: model: order: action: 'noload'\n");
+        const model = new model_1.Model({
+            path: dir + '/model/model.jsonic',
+            base: dir + '/model',
+            debug: 'silent',
+        });
+        const br = await model.run();
+        node_assert_1.default.strictEqual(br.ok, false, 'action without load should fail');
+        const msg = String(br.errs[0]?.message ?? br.errs[0] ?? '');
+        node_assert_1.default.match(msg, /Model action "noload" is missing a "load" path/);
+    });
+    // An action that throws at run time must fail the build and surface the
+    // error rather than silently passing.
+    (0, node_test_1.test)('action-error-fails-build', async () => {
+        const dir = GEN + '/throw01';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir + '/model/.model-config', { recursive: true });
+        await (0, promises_1.mkdir)(dir + '/build', { recursive: true });
+        await (0, promises_1.writeFile)(dir + '/model/model.jsonic', 'top: 1\n');
+        await (0, promises_1.writeFile)(dir + '/model/.model-config/model-config.jsonic', "sys: model: action: { boom: load: 'build/boom' }\n");
+        await (0, promises_1.writeFile)(dir + '/build/boom.js', "module.exports = async () => { throw new Error('boom-action') }\n");
+        const model = new model_1.Model({
+            path: dir + '/model/model.jsonic',
+            base: dir + '/model',
+            debug: 'silent',
+        });
+        const br = await model.run();
+        node_assert_1.default.strictEqual(br.ok, false, 'a throwing action should fail the build');
+        const msg = String(br.errs[0]?.message ?? br.errs[0] ?? '');
+        node_assert_1.default.match(msg, /boom-action/);
+    });
     // dryrun must not write to the real filesystem, including via the
     // promise-based fs API.
     (0, node_test_1.test)('dryrun-readonly-promises', async () => {
diff --git a/dist-test/fix.test.js.map b/dist-test/fix.test.js.map
index daaa6bd..804f06a 100644
--- a/dist-test/fix.test.js.map
+++ b/dist-test/fix.test.js.map
@@ -1 +1 @@
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\ No newline at end of file
diff --git a/dist-test/watch.test.js b/dist-test/watch.test.js
index a16fe27..2fd4946 100644
--- a/dist-test/watch.test.js
+++ b/dist-test/watch.test.js
@@ -27,6 +27,14 @@ async function readVal(file) {
         return undefined;
     }
 }
+async function read(file) {
+    try {
+        return await (0, promises_1.readFile)(file, 'utf8');
+    }
+    catch {
+        return undefined;
+    }
+}
 (0, node_test_1.describe)('watch', () => {
     // Start watching, then change a dependency file and confirm the model is
     // rebuilt. Exercises the watch interval, change handling, drain queue,
@@ -53,5 +61,42 @@ async function readVal(file) {
             await model.stop();
         }
     });
+    // A change to a config file should rebuild the config and re-trigger the
+    // model build. The `mark` action bumps a counter on every model build, so
+    // a change in its output proves the config change drove a rebuild.
+    (0, node_test_1.test)('config-change-triggers-rebuild', async () => {
+        const dir = GEN + '/wat02';
+        const base = dir + '/model';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(base + '/.model-config', { recursive: true });
+        await (0, promises_1.mkdir)(dir + '/build', { recursive: true });
+        await (0, promises_1.writeFile)(base + '/model.jsonic', 'top: 1\n');
+        await (0, promises_1.writeFile)(base + '/.model-config/model-config.jsonic', "sys: model: action: { mark: load: 'build/mark' }\n");
+        await (0, promises_1.writeFile)(dir + '/build/mark.js', "const Path = require('node:path')\n" +
+            'let n = 0\n' +
+            'module.exports = async function mark(model, build) {\n' +
+            "  n++\n" +
+            "  const root = Path.resolve(build.path, '..', '..')\n" +
+            "  build.fs.writeFileSync(Path.resolve(root, 'mark.txt'), String(n))\n" +
+            '  return { ok: true }\n' +
+            '}\n');
+        const mark = dir + '/mark.txt';
+        const model = new model_1.Model({ path: base + '/model.jsonic', base });
+        try {
+            await model.start();
+            node_assert_1.default.ok(await waitFor(async () => null != await read(mark)), 'initial build should run the mark action');
+            const first = await read(mark);
+            // Let the config watcher attach, then edit a config file.
+            await new Promise(r => setTimeout(r, 250));
+            await (0, promises_1.appendFile)(base + '/.model-config/model-config.jsonic', '\n# touch to trigger a config rebuild\n');
+            node_assert_1.default.ok(await waitFor(async () => {
+                const cur = await read(mark);
+                return null != cur && cur !== first;
+            }), 'config change should re-run the model build (mark should advance)');
+        }
+        finally {
+            await model.stop();
+        }
+    });
 });
 //# sourceMappingURL=watch.test.js.map
\ No newline at end of file
diff --git a/dist-test/watch.test.js.map b/dist-test/watch.test.js.map
index ac89ff9..324f4d3 100644
--- a/dist-test/watch.test.js.map
+++ b/dist-test/watch.test.js.map
@@ -1 +1 @@
-{"version":3,"file":"watch.test.js","sourceRoot":"","sources":["../test/watch.test.ts"],"names":[],"mappings":";AAAA,oDAAoD;;;;;AAEpD,+CAAiE;AACjE,yCAA0C;AAC1C,8DAAgC;AAEhC,yCAAqC;AAGrC,MAAM,GAAG,GAAG,SAAS,GAAG,eAAe,CAAA;AAGvC,KAAK,UAAU,OAAO,CAAC,EAA0B,EAAE,EAAE,GAAG,IAAI;IAC1D,MAAM,KAAK,GAAG,IAAI,CAAC,GAAG,EAAE,CAAA;IACxB,OAAO,IAAI,CAAC,GAAG,EAAE,GAAG,KAAK,GAAG,EAAE,EAAE,CAAC;QAC/B,IAAI,MAAM,EAAE,EAAE,EAAE,CAAC;YACf,OAAO,IAAI,CAAA;QACb,CAAC;QACD,MAAM,IAAI,OAAO,CAAC,CAAC,CAAC,EAAE,CAAC,UAAU,CAAC,CAAC,EAAE,EAAE,CAAC,CAAC,CAAA;IAC3C,CAAC;IACD,OAAO,KAAK,CAAA;AACd,CAAC;AAGD,KAAK,UAAU,OAAO,CAAC,IAAY;IACjC,IAAI,CAAC;QACH,OAAO,IAAI,CAAC,KAAK,CAAC,MAAM,IAAA,mBAAQ,EAAC,IAAI,EAAE,MAAM,CAAC,CAAC,CAAC,GAAG,CAAA;IACrD,CAAC;IACD,MAAM,CAAC;QACL,OAAO,SAAS,CAAA;IAClB,CAAC;AACH,CAAC;AAGD,IAAA,oBAAQ,EAAC,OAAO,EAAE,GAAG,EAAE;IAErB,yEAAyE;IACzE,uEAAuE;IACvE,4DAA4D;IAC5D,IAAA,gBAAI,EAAC,oBAAoB,EAAE,KAAK,IAAI,EAAE;QACpC,MAAM,IAAI,GAAG,GAAG,GAAG,cAAc,CAAA;QACjC,MAAM,IAAA,aAAE,EAAC,GAAG,GAAG,QAAQ,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,CAAA;QAC1D,MAAM,IAAA,gBAAK,EAAC,IAAI,GAAG,gBAAgB,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QAEzD,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,eAAe,EAAE,gCAAgC,CAAC,CAAA;QACzE,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,aAAa,EAAE,GAAG,CAAC,CAAA;QAC1C,2EAA2E;QAC3E,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,oCAAoC,EACzD,0BAA0B,CAAC,CAAA;QAE7B,MAAM,GAAG,GAAG,IAAI,GAAG,aAAa,CAAA;QAChC,MAAM,KAAK,GAAG,IAAI,aAAK,CAAC,EAAE,IAAI,EAAE,IAAI,GAAG,eAAe,EAAE,IAAI,EAAE,CAAC,CAAA;QAE/D,IAAI,CAAC;YACH,MAAM,KAAK,CAAC,KAAK,EAAE,CAAA;YAEnB,qBAAM,CAAC,EAAE,CACP,MAAM,OAAO,CAAC,KAAK,IAAI,EAAE,CAAC,CAAC,MAAM,OAAO,CAAC,GAAG,CAAC,CAAC,KAAK,CAAC,CAAC,EACrD,oCAAoC,CAAC,CAAA;YAEvC,iEAAiE;YACjE,MAAM,IAAI,OAAO,CAAC,CAAC,CAAC,EAAE,CAAC,UAAU,CAAC,CAAC,EAAE,GAAG,CAAC,CAAC,CAAA;YAC1C,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,aAAa,EAAE,GAAG,CAAC,CAAA;YAE1C,qBAAM,CAAC,EAAE,CACP,MAAM,OAAO,CAAC,KAAK,IAAI,EAAE,CAAC,CAAC,MAAM,OAAO,CAAC,GAAG,CAAC,CAAC,KAAK,CAAC,CAAC,EACrD,iDAAiD,CAAC,CAAA;QACtD,CAAC;gBACO,CAAC;YACP,MAAM,KAAK,CAAC,IAAI,EAAE,CAAA;QACpB,CAAC;IACH,CAAC,CAAC,CAAA;AAEJ,CAAC,CAAC,CAAA"}
\ No newline at end of file
+{"version":3,"file":"watch.test.js","sourceRoot":"","sources":["../test/watch.test.ts"],"names":[],"mappings":";AAAA,oDAAoD;;;;;AAEpD,+CAA6E;AAC7E,yCAA0C;AAC1C,8DAAgC;AAEhC,yCAAqC;AAGrC,MAAM,GAAG,GAAG,SAAS,GAAG,eAAe,CAAA;AAGvC,KAAK,UAAU,OAAO,CAAC,EAA0B,EAAE,EAAE,GAAG,IAAI;IAC1D,MAAM,KAAK,GAAG,IAAI,CAAC,GAAG,EAAE,CAAA;IACxB,OAAO,IAAI,CAAC,GAAG,EAAE,GAAG,KAAK,GAAG,EAAE,EAAE,CAAC;QAC/B,IAAI,MAAM,EAAE,EAAE,EAAE,CAAC;YACf,OAAO,IAAI,CAAA;QACb,CAAC;QACD,MAAM,IAAI,OAAO,CAAC,CAAC,CAAC,EAAE,CAAC,UAAU,CAAC,CAAC,EAAE,EAAE,CAAC,CAAC,CAAA;IAC3C,CAAC;IACD,OAAO,KAAK,CAAA;AACd,CAAC;AAGD,KAAK,UAAU,OAAO,CAAC,IAAY;IACjC,IAAI,CAAC;QACH,OAAO,IAAI,CAAC,KAAK,CAAC,MAAM,IAAA,mBAAQ,EAAC,IAAI,EAAE,MAAM,CAAC,CAAC,CAAC,GAAG,CAAA;IACrD,CAAC;IACD,MAAM,CAAC;QACL,OAAO,SAAS,CAAA;IAClB,CAAC;AACH,CAAC;AAGD,KAAK,UAAU,IAAI,CAAC,IAAY;IAC9B,IAAI,CAAC;QACH,OAAO,MAAM,IAAA,mBAAQ,EAAC,IAAI,EAAE,MAAM,CAAC,CAAA;IACrC,CAAC;IACD,MAAM,CAAC;QACL,OAAO,SAAS,CAAA;IAClB,CAAC;AACH,CAAC;AAGD,IAAA,oBAAQ,EAAC,OAAO,EAAE,GAAG,EAAE;IAErB,yEAAyE;IACzE,uEAAuE;IACvE,4DAA4D;IAC5D,IAAA,gBAAI,EAAC,oBAAoB,EAAE,KAAK,IAAI,EAAE;QACpC,MAAM,IAAI,GAAG,GAAG,GAAG,cAAc,CAAA;QACjC,MAAM,IAAA,aAAE,EAAC,GAAG,GAAG,QAAQ,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,CAAA;QAC1D,MAAM,IAAA,gBAAK,EAAC,IAAI,GAAG,gBAAgB,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QAEzD,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,eAAe,EAAE,gCAAgC,CAAC,CAAA;QACzE,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,aAAa,EAAE,GAAG,CAAC,CAAA;QAC1C,2EAA2E;QAC3E,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,oCAAoC,EACzD,0BAA0B,CAAC,CAAA;QAE7B,MAAM,GAAG,GAAG,IAAI,GAAG,aAAa,CAAA;QAChC,MAAM,KAAK,GAAG,IAAI,aAAK,CAAC,EAAE,IAAI,EAAE,IAAI,GAAG,eAAe,EAAE,IAAI,EAAE,CAAC,CAAA;QAE/D,IAAI,CAAC;YACH,MAAM,KAAK,CAAC,KAAK,EAAE,CAAA;YAEnB,qBAAM,CAAC,EAAE,CACP,MAAM,OAAO,CAAC,KAAK,IAAI,EAAE,CAAC,CAAC,MAAM,OAAO,CAAC,GAAG,CAAC,CAAC,KAAK,CAAC,CAAC,EACrD,oCAAoC,CAAC,CAAA;YAEvC,iEAAiE;YACjE,MAAM,IAAI,OAAO,CAAC,CAAC,CAAC,EAAE,CAAC,UAAU,CAAC,CAAC,EAAE,GAAG,CAAC,CAAC,CAAA;YAC1C,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,aAAa,EAAE,GAAG,CAAC,CAAA;YAE1C,qBAAM,CAAC,EAAE,CACP,MAAM,OAAO,CAAC,KAAK,IAAI,EAAE,CAAC,CAAC,MAAM,OAAO,CAAC,GAAG,CAAC,CAAC,KAAK,CAAC,CAAC,EACrD,iDAAiD,CAAC,CAAA;QACtD,CAAC;gBACO,CAAC;YACP,MAAM,KAAK,CAAC,IAAI,EAAE,CAAA;QACpB,CAAC;IACH,CAAC,CAAC,CAAA;IAGF,yEAAyE;IACzE,0EAA0E;IAC1E,mEAAmE;IACnE,IAAA,gBAAI,EAAC,gCAAgC,EAAE,KAAK,IAAI,EAAE;QAChD,MAAM,GAAG,GAAG,GAAG,GAAG,QAAQ,CAAA;QAC1B,MAAM,IAAI,GAAG,GAAG,GAAG,QAAQ,CAAA;QAC3B,MAAM,IAAA,aAAE,EAAC,GAAG,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,KAAK,EAAE,IAAI,EAAE,CAAC,CAAA;QAC/C,MAAM,IAAA,gBAAK,EAAC,IAAI,GAAG,gBAAgB,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QACzD,MAAM,IAAA,gBAAK,EAAC,GAAG,GAAG,QAAQ,EAAE,EAAE,SAAS,EAAE,IAAI,EAAE,CAAC,CAAA;QAEhD,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,eAAe,EAAE,UAAU,CAAC,CAAA;QACnD,MAAM,IAAA,oBAAS,EAAC,IAAI,GAAG,oCAAoC,EACzD,oDAAoD,CAAC,CAAA;QACvD,MAAM,IAAA,oBAAS,EAAC,GAAG,GAAG,gBAAgB,EACpC,qCAAqC;YACrC,aAAa;YACb,wDAAwD;YACxD,SAAS;YACT,uDAAuD;YACvD,uEAAuE;YACvE,yBAAyB;YACzB,KAAK,CAAC,CAAA;QAER,MAAM,IAAI,GAAG,GAAG,GAAG,WAAW,CAAA;QAC9B,MAAM,KAAK,GAAG,IAAI,aAAK,CAAC,EAAE,IAAI,EAAE,IAAI,GAAG,eAAe,EAAE,IAAI,EAAE,CAAC,CAAA;QAE/D,IAAI,CAAC;YACH,MAAM,KAAK,CAAC,KAAK,EAAE,CAAA;YAEnB,qBAAM,CAAC,EAAE,CACP,MAAM,OAAO,CAAC,KAAK,IAAI,EAAE,CAAC,IAAI,IAAI,MAAM,IAAI,CAAC,IAAI,CAAC,CAAC,EACnD,0CAA0C,CAAC,CAAA;YAC7C,MAAM,KAAK,GAAG,MAAM,IAAI,CAAC,IAAI,CAAC,CAAA;YAE9B,0DAA0D;YAC1D,MAAM,IAAI,OAAO,CAAC,CAAC,CAAC,EAAE,CAAC,UAAU,CAAC,CAAC,EAAE,GAAG,CAAC,CAAC,CAAA;YAC1C,MAAM,IAAA,qBAAU,EAAC,IAAI,GAAG,oCAAoC,EAC1D,yCAAyC,CAAC,CAAA;YAE5C,qBAAM,CAAC,EAAE,CACP,MAAM,OAAO,CAAC,KAAK,IAAI,EAAE;gBACvB,MAAM,GAAG,GAAG,MAAM,IAAI,CAAC,IAAI,CAAC,CAAA;gBAC5B,OAAO,IAAI,IAAI,GAAG,IAAI,GAAG,KAAK,KAAK,CAAA;YACrC,CAAC,CAAC,EACF,mEAAmE,CAAC,CAAA;QACxE,CAAC;gBACO,CAAC;YACP,MAAM,KAAK,CAAC,IAAI,EAAE,CAAA;QACpB,CAAC;IACH,CAAC,CAAC,CAAA;AAEJ,CAAC,CAAC,CAAA"}
\ No newline at end of file
diff --git a/dist/config.d.ts b/dist/config.d.ts
index 4f0919e..10c5309 100644
--- a/dist/config.d.ts
+++ b/dist/config.d.ts
@@ -6,7 +6,7 @@ declare class Config {
     log: Log;
     constructor(spec: BuildSpec, log: Log);
     run(watch: boolean): Promise<BuildResult>;
-    start(): Promise<void>;
+    start(initial?: boolean): Promise<void>;
     stop(): Promise<void>;
 }
 export { Config, BuildSpec };
diff --git a/dist/config.js b/dist/config.js
index 28ba4c7..1c97871 100644
--- a/dist/config.js
+++ b/dist/config.js
@@ -21,8 +21,8 @@ class Config {
     async run(watch) {
         return this.watch.run('config', watch, '<config>');
     }
-    async start() {
-        return this.watch.start();
+    async start(initial = true) {
+        return this.watch.start(initial);
     }
     async stop() {
         return this.watch.stop();
diff --git a/dist/config.js.map b/dist/config.js.map
index db47642..8930559 100644
--- a/dist/config.js.map
+++ b/dist/config.js.map
@@ -1 +1 @@
-{"version":3,"file":"config.js","sourceRoot":"","sources":["../src/config.ts"],"names":[],"mappings":";AAAA,oDAAoD;;;AAKpD,mCAA+B;AAI/B,MAAM,MAAM;IAKV,YAAY,IAAe,EAAE,GAAQ;QACnC,IAAI,CAAC,GAAG,GAAG,GAAG,CAAA;QAEd,IAAI,CAAC,KAAK,GAAG;YACX,IAAI,EAAE,IAAI,CAAC,IAAI;YACf,IAAI,EAAE,IAAI,CAAC,IAAI;YACf,GAAG,EAAE;gBACH,GAAG,CAAC,IAAI,CAAC,GAAG,IAAI,EAAE,CAAC;aACpB;YACD,OAAO,EAAE,IAAI,CAAC,OAAO;YACrB,GAAG,EAAE,IAAI,CAAC,GAAG;YACb,EAAE,EAAE,IAAI,CAAC,EAAE;SACZ,CAAA;QAED,IAAI,CAAC,KAAK,GAAG,IAAI,aAAK,CAAC,IAAI,CAAC,KAAK,EAAE,IAAI,CAAC,GAAG,CAAC,CAAA;IAC9C,CAAC;IAED,KAAK,CAAC,GAAG,CAAC,KAAc;QACtB,OAAO,IAAI,CAAC,KAAK,CAAC,GAAG,CAAC,QAAQ,EAAE,KAAK,EAAE,UAAU,CAAC,CAAA;IACpD,CAAC;IAED,KAAK,CAAC,KAAK;QACT,OAAO,IAAI,CAAC,KAAK,CAAC,KAAK,EAAE,CAAA;IAC3B,CAAC;IAED,KAAK,CAAC,IAAI;QACR,OAAO,IAAI,CAAC,KAAK,CAAC,IAAI,EAAE,CAAA;IAC1B,CAAC;CACF;AAGQ,wBAAM"}
\ No newline at end of file
+{"version":3,"file":"config.js","sourceRoot":"","sources":["../src/config.ts"],"names":[],"mappings":";AAAA,oDAAoD;;;AAKpD,mCAA+B;AAI/B,MAAM,MAAM;IAKV,YAAY,IAAe,EAAE,GAAQ;QACnC,IAAI,CAAC,GAAG,GAAG,GAAG,CAAA;QAEd,IAAI,CAAC,KAAK,GAAG;YACX,IAAI,EAAE,IAAI,CAAC,IAAI;YACf,IAAI,EAAE,IAAI,CAAC,IAAI;YACf,GAAG,EAAE;gBACH,GAAG,CAAC,IAAI,CAAC,GAAG,IAAI,EAAE,CAAC;aACpB;YACD,OAAO,EAAE,IAAI,CAAC,OAAO;YACrB,GAAG,EAAE,IAAI,CAAC,GAAG;YACb,EAAE,EAAE,IAAI,CAAC,EAAE;SACZ,CAAA;QAED,IAAI,CAAC,KAAK,GAAG,IAAI,aAAK,CAAC,IAAI,CAAC,KAAK,EAAE,IAAI,CAAC,GAAG,CAAC,CAAA;IAC9C,CAAC;IAED,KAAK,CAAC,GAAG,CAAC,KAAc;QACtB,OAAO,IAAI,CAAC,KAAK,CAAC,GAAG,CAAC,QAAQ,EAAE,KAAK,EAAE,UAAU,CAAC,CAAA;IACpD,CAAC;IAED,KAAK,CAAC,KAAK,CAAC,UAAmB,IAAI;QACjC,OAAO,IAAI,CAAC,KAAK,CAAC,KAAK,CAAC,OAAO,CAAC,CAAA;IAClC,CAAC;IAED,KAAK,CAAC,IAAI;QACR,OAAO,IAAI,CAAC,KAAK,CAAC,IAAI,EAAE,CAAA;IAC1B,CAAC;CACF;AAGQ,wBAAM"}
\ No newline at end of file
diff --git a/dist/model.js b/dist/model.js
index be43b6c..cae1e73 100644
--- a/dist/model.js
+++ b/dist/model.js
@@ -131,11 +131,19 @@ class Model {
         const br = await this.config.run(false);
         return br.ok ? this.watch.run('model', false, '<start>') : br;
     }
-    // Start watching for file changes. Run once initially.
+    // Start watching for file changes. Runs an initial build, then watches
+    // both the model files and the config files for ongoing changes.
     async start() {
         this.trigger_model = false;
         const br = await this.config.run(true);
-        return br.ok ? this.watch.start() : br;
+        if (!br.ok) {
+            return br;
+        }
+        // Watch config files too. The initial config build is already done
+        // above, so start without forcing another one; a later config change
+        // rebuilds the config and re-triggers the model build.
+        this.config.start(false);
+        return this.watch.start();
     }
     async stop() {
         // start() also spins up a config-file watcher; stop both so no
diff --git a/dist/model.js.map b/dist/model.js.map
index 35bd0c0..65ac2d8 100644
--- a/dist/model.js.map
+++ b/dist/model.js.map
@@ -1 +1 @@
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\ No newline at end of file
diff --git a/dist/watch.d.ts b/dist/watch.d.ts
index 732f6a9..5b01078 100644
--- a/dist/watch.d.ts
+++ b/dist/watch.d.ts
@@ -26,7 +26,7 @@ declare class Watch {
     };
     constructor(bspec: BuildSpec, log: Log);
     ensureFSW(): FSWatcher;
-    start(): void;
+    start(initial?: boolean): void;
     canon(path: string): string;
     handleChange(path: string): void;
     drain(): Promise<void>;
diff --git a/dist/watch.js b/dist/watch.js
index aa492a6..8eeeefc 100644
--- a/dist/watch.js
+++ b/dist/watch.js
@@ -50,10 +50,14 @@ class Watch {
     }
     // Begin watching. The initial build, and every subsequent rebuild, is
     // enqueued asynchronously once the watcher settles, so nothing is returned.
-    start() {
+    // Pass initial=false to start watching without forcing that first build
+    // (e.g. when the caller has already produced one).
+    start(initial = true) {
         this.ensureFSW();
         this.startTime = Date.now();
-        this.handleChange('<start>');
+        if (initial) {
+            this.handleChange('<start>');
+        }
         // Check if there have been no recent changes, if so, run build.
         this.intervalId = setInterval(() => {
             // const start = this.startTime
diff --git a/dist/watch.js.map b/dist/watch.js.map
index 3c52c49..a14c940 100644
--- a/dist/watch.js.map
+++ b/dist/watch.js.map
@@ -1 +1 @@
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\ No newline at end of file
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\ No newline at end of file
diff --git a/src/config.ts b/src/config.ts
index 210964a..871fcbb 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -33,8 +33,8 @@ class Config {
     return this.watch.run('config', watch, '<config>')
   }
 
-  async start() {
-    return this.watch.start()
+  async start(initial: boolean = true) {
+    return this.watch.start(initial)
   }
 
   async stop() {
diff --git a/src/model.ts b/src/model.ts
index 48a7414..12f7e7a 100644
--- a/src/model.ts
+++ b/src/model.ts
@@ -144,11 +144,19 @@ class Model {
   }
 
 
-  // Start watching for file changes. Run once initially.
+  // Start watching for file changes. Runs an initial build, then watches
+  // both the model files and the config files for ongoing changes.
   async start() {
     this.trigger_model = false
     const br = await this.config.run(true)
-    return br.ok ? this.watch.start() : br
+    if (!br.ok) {
+      return br
+    }
+    // Watch config files too. The initial config build is already done
+    // above, so start without forcing another one; a later config change
+    // rebuilds the config and re-triggers the model build.
+    this.config.start(false)
+    return this.watch.start()
   }
 
 
diff --git a/src/watch.ts b/src/watch.ts
index 5a24e96..6fadab3 100644
--- a/src/watch.ts
+++ b/src/watch.ts
@@ -97,10 +97,14 @@ class Watch {
 
   // Begin watching. The initial build, and every subsequent rebuild, is
   // enqueued asynchronously once the watcher settles, so nothing is returned.
-  start() {
+  // Pass initial=false to start watching without forcing that first build
+  // (e.g. when the caller has already produced one).
+  start(initial: boolean = true) {
     this.ensureFSW()
     this.startTime = Date.now()
-    this.handleChange('<start>')
+    if (initial) {
+      this.handleChange('<start>')
+    }
 
     // Check if there have been no recent changes, if so, run build.
     this.intervalId = setInterval(() => {
diff --git a/test/fix.test.ts b/test/fix.test.ts
index 353adc0..6babe5c 100644
--- a/test/fix.test.ts
+++ b/test/fix.test.ts
@@ -75,6 +75,57 @@ describe('fix', () => {
   })
 
 
+  // An action definition with no load path should also fail clearly.
+  test('clear-error-on-missing-load', async () => {
+    const dir = GEN + '/act02'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir + '/model/.model-config', { recursive: true })
+
+    await writeFile(dir + '/model/model.jsonic', 'top: 1\n')
+    await writeFile(dir + '/model/.model-config/model-config.jsonic',
+      'sys: model: action: { noload: {} }\n' +
+      "sys: model: order: action: 'noload'\n")
+
+    const model = new Model({
+      path: dir + '/model/model.jsonic',
+      base: dir + '/model',
+      debug: 'silent',
+    })
+    const br = await model.run()
+
+    assert.strictEqual(br.ok, false, 'action without load should fail')
+    const msg = String(br.errs[0]?.message ?? br.errs[0] ?? '')
+    assert.match(msg, /Model action "noload" is missing a "load" path/)
+  })
+
+
+  // An action that throws at run time must fail the build and surface the
+  // error rather than silently passing.
+  test('action-error-fails-build', async () => {
+    const dir = GEN + '/throw01'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir + '/model/.model-config', { recursive: true })
+    await mkdir(dir + '/build', { recursive: true })
+
+    await writeFile(dir + '/model/model.jsonic', 'top: 1\n')
+    await writeFile(dir + '/model/.model-config/model-config.jsonic',
+      "sys: model: action: { boom: load: 'build/boom' }\n")
+    await writeFile(dir + '/build/boom.js',
+      "module.exports = async () => { throw new Error('boom-action') }\n")
+
+    const model = new Model({
+      path: dir + '/model/model.jsonic',
+      base: dir + '/model',
+      debug: 'silent',
+    })
+    const br = await model.run()
+
+    assert.strictEqual(br.ok, false, 'a throwing action should fail the build')
+    const msg = String(br.errs[0]?.message ?? br.errs[0] ?? '')
+    assert.match(msg, /boom-action/)
+  })
+
+
   // dryrun must not write to the real filesystem, including via the
   // promise-based fs API.
   test('dryrun-readonly-promises', async () => {
diff --git a/test/watch.test.ts b/test/watch.test.ts
index f6b154e..d87261e 100644
--- a/test/watch.test.ts
+++ b/test/watch.test.ts
@@ -1,6 +1,6 @@
 /* Copyright © 2021-2025 Voxgig Ltd, MIT License. */
 
-import { mkdir, writeFile, readFile, rm } from 'node:fs/promises'
+import { mkdir, writeFile, readFile, appendFile, rm } from 'node:fs/promises'
 import { test, describe } from 'node:test'
 import assert from 'node:assert'
 
@@ -32,6 +32,16 @@ async function readVal(file: string): Promise<number | undefined> {
 }
 
 
+async function read(file: string): Promise<string | undefined> {
+  try {
+    return await readFile(file, 'utf8')
+  }
+  catch {
+    return undefined
+  }
+}
+
+
 describe('watch', () => {
 
   // Start watching, then change a dependency file and confirm the model is
@@ -71,4 +81,56 @@ describe('watch', () => {
     }
   })
 
+
+  // A change to a config file should rebuild the config and re-trigger the
+  // model build. The `mark` action bumps a counter on every model build, so
+  // a change in its output proves the config change drove a rebuild.
+  test('config-change-triggers-rebuild', async () => {
+    const dir = GEN + '/wat02'
+    const base = dir + '/model'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(base + '/.model-config', { recursive: true })
+    await mkdir(dir + '/build', { recursive: true })
+
+    await writeFile(base + '/model.jsonic', 'top: 1\n')
+    await writeFile(base + '/.model-config/model-config.jsonic',
+      "sys: model: action: { mark: load: 'build/mark' }\n")
+    await writeFile(dir + '/build/mark.js',
+      "const Path = require('node:path')\n" +
+      'let n = 0\n' +
+      'module.exports = async function mark(model, build) {\n' +
+      "  n++\n" +
+      "  const root = Path.resolve(build.path, '..', '..')\n" +
+      "  build.fs.writeFileSync(Path.resolve(root, 'mark.txt'), String(n))\n" +
+      '  return { ok: true }\n' +
+      '}\n')
+
+    const mark = dir + '/mark.txt'
+    const model = new Model({ path: base + '/model.jsonic', base })
+
+    try {
+      await model.start()
+
+      assert.ok(
+        await waitFor(async () => null != await read(mark)),
+        'initial build should run the mark action')
+      const first = await read(mark)
+
+      // Let the config watcher attach, then edit a config file.
+      await new Promise(r => setTimeout(r, 250))
+      await appendFile(base + '/.model-config/model-config.jsonic',
+        '\n# touch to trigger a config rebuild\n')
+
+      assert.ok(
+        await waitFor(async () => {
+          const cur = await read(mark)
+          return null != cur && cur !== first
+        }),
+        'config change should re-run the model build (mark should advance)')
+    }
+    finally {
+      await model.stop()
+    }
+  })
+
 })

From fd5e2fa1d5326622a62b66f79ea0e908537c2de0 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Mon, 8 Jun 2026 11:46:53 +0000
Subject: [PATCH 4/6] docs: comprehensive documentation set + AI-agent files

Add a four-part documentation set under docs/ and rework the README into
a navigable entry point:

- tutorial.md    learn the tool by building a model step by step
- how-to.md      task recipes (build args, actions, custom producers,
                 in-memory fs, dry run, watch tuning, ...)
- reference.md   CLI, project layout, config, actions, the full
                 programmatic API, build lifecycle, modeling-language
                 essentials, logging, scripts, and troubleshooting
- explanation.md the problem, why unification, architecture, the build
                 lifecycle, caching/watch design, and known limitations

Add agent guides for working on the codebase:

- AGENTS.md      environment, build/test, repo map, conventions, test
                 patterns, task playbooks, and the key gotchas
- CLAUDE.md      Claude Code entry point (imports AGENTS.md), essentials
                 up front

Every runnable example is verified against the built tool. Two
easy-to-hit modeling rules that surfaced while writing are now
documented: keys are jsonic identifiers (quote hyphens), and every
emitted field must resolve to a concrete value (give it a default or
mark it optional).

https://claude.ai/code/session_01HxXpZNrKj3qonocwAtEP8r
---
 AGENTS.md           | 216 +++++++++++++++
 CLAUDE.md           |  37 +++
 README.md           | 131 ++++++++-
 docs/explanation.md | 254 ++++++++++++++++++
 docs/how-to.md      | 378 ++++++++++++++++++++++++++
 docs/reference.md   | 630 ++++++++++++++++++++++++++++++++++++++++++++
 docs/tutorial.md    | 264 +++++++++++++++++++
 7 files changed, 1906 insertions(+), 4 deletions(-)
 create mode 100644 AGENTS.md
 create mode 100644 CLAUDE.md
 create mode 100644 docs/explanation.md
 create mode 100644 docs/how-to.md
 create mode 100644 docs/reference.md
 create mode 100644 docs/tutorial.md

diff --git a/AGENTS.md b/AGENTS.md
new file mode 100644
index 0000000..ca91a4b
--- /dev/null
+++ b/AGENTS.md
@@ -0,0 +1,216 @@
+# AGENTS.md
+
+Guidance for AI coding agents (and humans) working **on** the `@voxgig/model`
+codebase. For using the tool, start at the [README](./README.md) and
+[docs/](./docs/). This file is about developing the package itself.
+
+Keep this file accurate: if you change the build, test layout, or a convention
+below, update it in the same change.
+
+
+## What this project is
+
+`@voxgig/model` unifies `.jsonic` source into a single JSON model (via the
+[aontu](https://github.com/voxgig/aontu) CUE-style engine) and runs generator
+"actions" over it. It can build once or watch and rebuild. It ships a library
+(`Model`) and a CLI (`voxgig-model`).
+
+A 90-second tour of how it fits together is in
+[docs/explanation.md](./docs/explanation.md#architecture-at-a-glance). Read that
+before making structural changes.
+
+
+## Environment
+
+- **Node.js 24** is the target (CI matrix). Node 20.19+ works; the `shape`
+  dependency declares `engines.node >= 24`, so older Node prints an
+  `EBADENGINE` warning — harmless here.
+- TypeScript, CommonJS output (`"type": "commonjs"`).
+- Install with `npm install`. No lockfile is committed (it is gitignored).
+
+
+## Build, test, run
+
+```bash
+npm install            # once
+npm run build          # tsc --build src test  -> dist/ and dist-test/
+npm test               # node --test dist-test/**/*.test.js
+```
+
+```bash
+# a single suite / pattern
+TEST_PATTERN='watch' npm run test-some
+
+# coverage (writes coverage/lcov.info)
+npm run test-cov
+
+# recompile on save
+npm run watch
+
+# exercise the CLI against the bundled sample model
+npm run test-model     # build once on test/sys01/model/model.jsonic
+npm run model          # watch model/sys.jsonic
+```
+
+**You must `npm run build` before `npm test`.** Tests are TypeScript compiled to
+`dist-test/`, and they import the compiled library from `dist/`. Source edits do
+not take effect in tests until rebuilt. For a fully clean rebuild use
+`npx tsc --build src test --force`.
+
+
+## Critical gotchas
+
+1. **Run commands from the repository root.** `tsc --build src test` resolves
+   `src` and `test` as project paths relative to the current directory. Running
+   it from a subdirectory fails with `TS5083: Cannot read file '.../src/
+   tsconfig.json'` and silently leaves `dist/` stale — so tests then run against
+   old code. If a build looks like it "passed" but tests don't reflect your
+   change, check your working directory.
+
+2. **`dist/` and `dist-test/` are committed.** They are tracked in git (in the
+   `files` allowlist for publishing). After any source change, rebuild and
+   commit the regenerated `dist/`/`dist-test/` alongside the `.ts`. CI rebuilds
+   them, but the repo convention is to commit them.
+
+3. **The CLI (`bin/voxgig-model`) is plain JavaScript**, not compiled. Edits to
+   it take effect immediately (no build needed for the bin itself), but it
+   `require`s `dist/model.js`, so the library must be built.
+
+4. **`aontu` reads `opts.err`, not `opts.errs`.** When invoking
+   `aontu.generate(src, opts)`, set `opts.err = <array>` to enable collect mode
+   (errors gathered into the array instead of thrown). This is easy to get
+   wrong — see `src/build.ts: resolveModel`.
+
+5. **Generated test fixtures go in `test/_gen/`** (gitignored). Tests write their
+   own fixtures there at runtime; do not commit them. See "Writing tests".
+
+
+## Repository map
+
+```
+src/
+  model.ts            Model: public entry; wires config build + model build
+  config.ts           Config: specialized build for .model-config
+  watch.ts            Watch: chokidar, debounce, rebuild queue, dep tracking
+  build.ts            BuildImpl/makeBuild: resolve model (aontu) + run producers
+  types.ts            shared interfaces (Build, BuildSpec, Producer, ...)
+  producer/
+    model.ts          model_producer: write the unified model as JSON
+    local.ts          local_producer: load & run actions declared in config
+  tsconfig.json       project config for src
+
+bin/voxgig-model      CLI entry (plain JS): arg parsing -> new Model().run/start
+
+test/
+  *.test.ts           node:test suites (compiled to dist-test/)
+  tsconfig.json       project config for tests
+  sys01/, p01/, e01/, w01/   committed fixtures
+  _gen/               GITIGNORED scratch fixtures written by tests at runtime
+
+model/                the package's own sample model (sys.jsonic + config)
+dist/, dist-test/     COMMITTED build output
+docs/                 tutorial / how-to / reference / explanation
+```
+
+Data flow: `CLI/Model` → `Config` (resolves actions) + `Watch` → `BuildImpl`
+(`aontu` unify → producers). The model build runs `model_producer` then
+`local_producer`. Full detail:
+[docs/explanation.md](./docs/explanation.md).
+
+
+## Code conventions
+
+Match the surrounding style; in this codebase that means:
+
+- **2-space indent, no semicolons, single quotes.**
+- Prefer `let`; use `const` where the existing file does.
+- Null checks as `null == x` / `null != x`. Comparisons are often "yoda"
+  (`'post' === ctx.step`). Follow the local file.
+- CommonJS modules. Keep imports grouped: node builtins, then deps, then local.
+- Keep the public type surface in `src/types.ts`. Many internal fields are typed
+  `any` by design; do not tighten them speculatively.
+- Logging goes through the pino logger (`build.log` / `this.log`) with a `point`
+  (short event name) and a human `note`. Do not `console.log` in library code.
+- Copyright header comment at the top of each source file (see existing files).
+
+
+## Writing tests
+
+- Use `node:test` (`describe`/`test`) and `node:assert`. Import the library from
+  `../dist/...` (compiled output), mirroring existing suites.
+- **Put runtime fixtures under `test/_gen/<name>/`** and create them in the test
+  (write `.jsonic`, config, and any action `.js`). This keeps fixtures
+  self-contained and out of git. Clean the dir at the start of the test
+  (`rm -rf` then `mkdir -p`).
+- **Watch-mode tests must call `model.stop()` in a `finally`.** `start()` opens
+  chokidar watchers (for both the model and the config); leaving them open hangs
+  the test process. Poll for the expected result with a timeout helper rather
+  than fixed sleeps (see `test/watch.test.ts`).
+- **CLI tests** spawn the built bin without a shell, for cross-platform
+  safety:
+  ```js
+  const { spawnSync } = require('node:child_process')
+  const res = spawnSync(process.execPath, [BIN, modelPath, '-b', '{a:1}'],
+                        { encoding: 'utf8' })
+  ```
+  Use jsonic barewords (`{a:b}`) to avoid embedded-quote escaping.
+- Make tests **meaningful guards**: when adding a test for a fix, confirm it
+  fails without the fix (temporarily revert, run, restore).
+
+Existing suites to model new ones on:
+
+| Suite | Covers |
+|-------|--------|
+| `test/build.test.ts` | end-to-end builds (`makeBuild`, `Model.run`) with the `p01`/`sys01` fixtures |
+| `test/fix.test.ts` | error recovery, unknown/misconfigured actions, dry-run filesystem |
+| `test/watch.test.ts` | watch rebuilds on model and config changes |
+| `test/cli.test.ts` | the CLI passes build args through to actions |
+
+
+## Common tasks (playbooks)
+
+### Add a build action (product-level generator)
+Actions are user-space, not framework code — declare in a model's
+`.model-config/model-config.jsonic` and implement under `build/`. See
+[docs/how-to.md](./docs/how-to.md#write-a-build-action). No library change.
+
+### Add a built-in producer (framework-level)
+1. Create `src/producer/<name>.ts` exporting a `Producer`
+   `(build, ctx) => Promise<ProducerResult>` (see `src/producer/model.ts`).
+2. Add it to the pipeline in `src/model.ts` (`this.build.res`), or document it
+   for `makeBuild` users.
+3. Rebuild, add a test, commit `dist/` too.
+
+### Add or change a CLI flag
+Edit `bin/voxgig-model`: add to `resolveOptions` (`parseArgs` `options`) and
+`validateOptions` (the `Shape`), then include it in the `spec` passed to
+`new Model(spec)`. Thread the field through `ModelSpec` in `src/types.ts` and
+read it in the `Model` constructor. (The CLI maps `--build` → `buildargs`; keep
+spec keys aligned with `ModelSpec`.)
+
+### Change the model/build types
+Edit `src/types.ts`. Rebuild so `dist/*.d.ts` regenerates; commit them.
+
+### Touch the build/error/cache logic
+`src/build.ts`. Remember the `opts.err` collect-mode rule (gotcha #4) and that
+`this.errs` is reset per run so a reused build instance doesn't accumulate stale
+errors. Add a regression test in `test/fix.test.ts`.
+
+
+## Before you commit
+
+- `npm run build` is clean (`tsc rc 0`) **from the repo root**.
+- `npm test` is green; add/adjust tests for behavior changes.
+- Regenerated `dist/` and `dist-test/` are staged with the source.
+- No `test/_gen/` artifacts are staged (they are gitignored — verify with
+  `git status`).
+- Keep this file and `docs/` in sync with any behavior or convention change.
+
+
+## More documentation
+
+- [docs/tutorial.md](./docs/tutorial.md) — learn the tool by building a model.
+- [docs/how-to.md](./docs/how-to.md) — task recipes.
+- [docs/reference.md](./docs/reference.md) — CLI, API, config, language.
+- [docs/explanation.md](./docs/explanation.md) — architecture and design
+  rationale (read before structural changes).
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..5d4f840
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,37 @@
+# CLAUDE.md
+
+Guidance for Claude Code (and other AI agents) working in this repository.
+
+The full contributor/agent guide — environment, repository map, conventions,
+test patterns, and task playbooks — is in **@AGENTS.md**. Read it before making
+changes. The essentials:
+
+## Build & test
+- Run everything **from the repository root**.
+- `npm run build` (`tsc --build src test`) **before** `npm test`; tests run
+  against compiled output in `dist-test/` and import the library from `dist/`.
+- `dist/` and `dist-test/` are **committed** — rebuild and stage them with any
+  source change.
+- Single suite: `TEST_PATTERN='<name>' npm run test-some`. Coverage:
+  `npm run test-cov`.
+
+## Watch out for
+- Stale `dist/` from a build that failed because it ran in a subdirectory
+  (`TS5083`) — tests then pass against old code. Verify cwd is the repo root.
+- Watch-mode tests must `await model.stop()` in a `finally`, or the process
+  hangs on open file watchers.
+- Runtime test fixtures belong in `test/_gen/` (gitignored); don't commit them.
+- `aontu.generate` collects errors only when given `opts.err` (not `opts.errs`).
+
+## Where things are
+- Library: `src/` (`model.ts`, `config.ts`, `watch.ts`, `build.ts`, `types.ts`,
+  `producer/`). CLI: `bin/voxgig-model` (plain JS). Docs: `docs/`.
+- Architecture overview: `docs/explanation.md`.
+
+## Style
+- 2-space indent, no semicolons, single quotes, CommonJS. Match the local file.
+- Log via the pino logger (`build.log`/`this.log`), never `console.log` in
+  library code.
+
+When you change behavior or a convention, update `@AGENTS.md` and the relevant
+file in `docs/` in the same change.
diff --git a/README.md b/README.md
index 9ce1c78..8d0e013 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,130 @@
-# Model
+# @voxgig/model
 
-A framework for universal application modeling.
+A framework for **universal application modeling**: describe a system once as a
+single declarative model, then generate every downstream artifact — code,
+configuration, documentation, infrastructure — from that one source of truth.
 
-PROTOTYPE.
+The core tool unifies `.jsonic` source (using [CUE](https://cuelang.org)-style
+unification, via [aontu](https://github.com/voxgig/aontu)) into one canonical
+JSON model, then hands that model to your generators ("actions"). It can build
+once or watch and rebuild on change.
 
-INSPIRED BY: http://cuelang.org
+> **Status: prototype.** The concepts are stable; specific APIs and conventions
+> may still change. Inspired by [CUE](https://cuelang.org).
+
+
+## Install
+
+```bash
+npm install @voxgig/model pino
+```
+
+`pino` is a peer dependency (logging). Requires Node.js — CI runs Node 24;
+Node 20.19+ generally works.
+
+
+## Quick start
+
+```bash
+# 1. a model
+mkdir -p model && cat > model/model.jsonic <<'EOF'
+service: name: 'orders'
+service: port: *8080 | integer
+EOF
+
+# 2. build it -> writes model/model.json
+npx voxgig-model model/model.jsonic
+
+# 3. or watch and rebuild on change
+npx voxgig-model --watch model/model.jsonic
+```
+
+`model/model.json`:
+
+```json
+{ "service": { "name": "orders", "port": 8080 } }
+```
+
+Use it from code instead of the CLI:
+
+```js
+const { Model } = require('@voxgig/model')
+
+const model = new Model({ path: 'model/model.jsonic', base: 'model' })
+const result = await model.run()
+if (!result.ok) throw new Error(result.errs.join('; '))
+```
+
+
+## What it does
+
+- **Unifies** `.jsonic` source — with types, defaults, references, wildcards,
+  and imports — into a single validated JSON model.
+- **Generates** artifacts from that model through **actions**: small JS modules
+  you declare in config and that receive the unified model.
+- **Watches** source and config files and rebuilds incrementally, tracking
+  imports as dependencies.
+- **Previews** safely with `--dryrun` (writes redirected to an in-memory
+  filesystem), and can build against any `fs` implementation.
+
+
+## Documentation
+
+| If you want to… | Read |
+|------------------|------|
+| Learn by building a model step by step | [Tutorial](./docs/tutorial.md) |
+| Accomplish a specific task | [How-to guides](./docs/how-to.md) |
+| Look up a flag, type, config key, or language construct | [Reference](./docs/reference.md) |
+| Understand how and why it works | [Explanation](./docs/explanation.md) |
+
+Working **on** this repository (including with an AI coding agent)?
+See [AGENTS.md](./AGENTS.md).
+
+
+## A fuller example
+
+A model that generates an environment file from its services:
+
+```
+my-project/
+├─ model/
+│  ├─ model.jsonic
+│  └─ .model-config/model-config.jsonic
+└─ build/envFile.js
+```
+
+```jsonic
+# model/model.jsonic
+shape: service: { name?: string, port: *8080 | integer }
+service: orders: $.shape.service & { name: 'orders' }
+service: web:    $.shape.service & { name: 'web', port: 443 }
+```
+
+```jsonic
+# model/.model-config/model-config.jsonic
+sys: model: action: { envFile: load: 'build/envFile' }
+```
+
+```js
+// build/envFile.js
+const Path = require('node:path')
+module.exports = async function envFile(model, build) {
+  const root = Path.resolve(build.path, '..', '..')
+  const lines = Object.entries(model.service)
+    .map(([n, s]) => `PORT_${n.toUpperCase()}=${s.port}`)
+  build.fs.writeFileSync(Path.resolve(root, 'services.env'), lines.join('\n') + '\n')
+  return { ok: true }
+}
+```
+
+```bash
+npx voxgig-model model/model.jsonic   # writes model/model.json and services.env
+```
+
+See the [tutorial](./docs/tutorial.md) for the same example built up from
+scratch.
+
+
+## License
+
+MIT © Voxgig Ltd. See [LICENSE](./LICENSE).
diff --git a/docs/explanation.md b/docs/explanation.md
new file mode 100644
index 0000000..79c6695
--- /dev/null
+++ b/docs/explanation.md
@@ -0,0 +1,254 @@
+# Explanation: concepts and design
+
+This document explains *why* `@voxgig/model` works the way it does. It is
+background reading, not a task list — for steps see the
+[tutorial](./tutorial.md) and [how-to guides](./how-to.md), and for exhaustive
+detail the [reference](./reference.md).
+
+- [The problem: one model, many artifacts](#the-problem-one-model-many-artifacts)
+- [Why unification](#why-unification)
+- [Architecture at a glance](#architecture-at-a-glance)
+- [The build lifecycle](#the-build-lifecycle)
+- [Producers and actions](#producers-and-actions)
+- [Why there are two builds](#why-there-are-two-builds)
+- [Watching and incremental rebuilds](#watching-and-incremental-rebuilds)
+- [Caching](#caching)
+- [Dry run and the filesystem boundary](#dry-run-and-the-filesystem-boundary)
+- [Error handling philosophy](#error-handling-philosophy)
+- [Known limitations](#known-limitations)
+- [Status](#status)
+
+
+## The problem: one model, many artifacts
+
+Most non-trivial systems describe the *same* concepts in many places: an API is
+defined in route code, in an OpenAPI file, in client SDKs, in infrastructure
+config, in documentation, in test fixtures. Each copy drifts from the others.
+The cost of a change is multiplied by the number of representations, and the
+bugs live in the gaps between them.
+
+`@voxgig/model` is a framework for **universal application modeling**: describe
+the system once, as a single declarative model, then *generate* every
+downstream artifact from that one source. The model is the truth; the code,
+config, and docs are projections of it.
+
+This is a generative approach. The tool itself is deliberately small: its job is
+to turn source into a trustworthy unified model and hand that model to
+generators (here called **actions**). The domain knowledge lives in your model
+and your actions, not in the framework.
+
+
+## Why unification
+
+A model needs to express more than values — it needs rules: defaults,
+constraints, types, and composition. Plain JSON or YAML cannot; they only carry
+data, so the rules end up in code that interprets the data.
+
+`@voxgig/model` borrows from [CUE](https://cuelang.org) (via the
+[aontu](https://github.com/voxgig/aontu) engine) and uses **unification** as its
+core operation. Unification merges two descriptions into the single most
+specific description consistent with both — or fails if they conflict. A few
+consequences make this powerful for modeling:
+
+- **Types and values are the same kind of thing.** `port: integer` and
+  `port: 8080` unify to `8080`; `port: 1` and `port: 2` *conflict* and fail.
+  Validation is not a separate pass — it is what unification does.
+- **Order does not matter.** `a & b` is the same as `b & a`. You can layer a
+  base shape, environment overrides, and per-instance tweaks in any arrangement
+  and get the same result.
+- **Defaults are first-class.** `*true | boolean` says "default to `true`, but
+  any boolean is allowed." Composition naturally fills in defaults only where
+  nothing more specific was said.
+- **Composition is explicit and safe.** Reusing a shape with `&` cannot quietly
+  produce something that violates the shape — a conflict is an error, not a
+  silent overwrite.
+
+The result of resolving a model is a single canonical data structure (written as
+`model.json`) with every default applied and every constraint satisfied. That
+structure is what actions consume.
+
+
+## Architecture at a glance
+
+The pieces, from outside in:
+
+```
+CLI (bin/voxgig-model)
+  └─ Model                         orchestrates the whole thing
+       ├─ Config   ── Watch        resolves .model-config, declares actions
+       └─ Watch                    resolves the main model, runs actions
+            └─ Build (BuildImpl)   resolve + run the producer pipeline
+                 ├─ aontu          unify source into a model
+                 └─ producers
+                      ├─ model_producer   write model.json
+                      └─ local_producer   load & run your actions
+```
+
+| Component | File | Responsibility |
+|-----------|------|----------------|
+| `Model` | `src/model.ts` | Public entry. Wires a config build and a model build together; exposes `run`/`start`/`stop`. |
+| `Config` | `src/config.ts` | A specialized build for `.model-config/model-config.jsonic`. |
+| `Watch` | `src/watch.ts` | File watching, debouncing, the rebuild queue, dependency tracking. |
+| `Build` / `BuildImpl` | `src/build.ts` | One build: resolve the model via aontu, run the producer pipeline, cache by mtime. |
+| `model_producer` | `src/producer/model.ts` | Serialize the unified model to JSON. |
+| `local_producer` | `src/producer/local.ts` | Load action modules from config and run them. |
+| types | `src/types.ts` | The shared interfaces (`Build`, `BuildSpec`, `Producer`, …). |
+
+`aontu` (unification), `chokidar` (file watching), `memfs` (the dry-run
+filesystem), and `pino`/`@voxgig/util` (logging) are the external moving parts.
+
+
+## The build lifecycle
+
+A single build is a small state machine (`BuildImpl.run`):
+
+1. **Reset error state.** A build instance is reused across watch rebuilds, so
+   each run starts with a clean slate.
+2. **Resolve the model.** Read the root file and unify it (and its imports) with
+   aontu into `build.model`. If nothing relevant changed since last time, the
+   cached model is reused (see [Caching](#caching)).
+3. **Pre phase.** Run every producer with `step = 'pre'`. Producers may signal
+   `reload` if they changed model source.
+4. **Reload if asked.** If a pre-producer requested a reload and there were no
+   errors, resolve the model again so the post phase sees the new source.
+5. **Post phase.** Run every producer with `step = 'post'`.
+6. **Return a result.** `ok`, the per-producer results, collected `errs`, and a
+   `runlog` of the phases.
+
+The `pre` → `reload` → `post` shape exists for a specific need: actions that
+*generate model source*. A code generator might emit a `.jsonic` fragment that
+the model itself imports; running it in `pre` and reloading lets that generated
+source participate in the final model that `post` actions consume.
+
+
+## Producers and actions
+
+There are two extension layers, and the distinction matters.
+
+A **producer** is the low-level unit: a function `(build, ctx) => ProducerResult`
+that the build runs in both phases. Producers are how the pipeline is assembled.
+The framework ships two — one to write the model JSON, one to run actions.
+
+An **action** is the high-level, user-facing unit: a JS module declared in the
+config file. Actions exist because most users do not want to think about the
+producer protocol — they want "given the model, write these files." The
+`local_producer` is the bridge: it reads the action declarations from the config
+model, loads the modules, and runs them at the right phase.
+
+So: *producers are the framework's plug-in mechanism; actions are the product's
+plug-in mechanism.* Use actions for normal generation. Drop to a custom producer
+pipeline (via `makeBuild`) when you need control over the whole build.
+
+
+## Why there are two builds
+
+A model build needs to know which actions to run *before* it can run them — and
+that list is itself modeled, in `.model-config/model-config.jsonic`. So a `Model`
+resolves **two** models:
+
+1. The **config build** unifies the config file into a config model and writes
+   `model-config.json`. Its declarations (`sys.model.action`, `sys.model.order`)
+   tell the main build what to do.
+2. The **model build** unifies your root model, writes `model.json`, and runs
+   the actions the config declared.
+
+Treating config as just another model is deliberate: the config benefits from
+the same unification, defaults, and imports as everything else. A shared base
+config can be imported by package path, and projects layer their own actions on
+top.
+
+An internal trigger producer on the config build kicks off the model build, so
+the two stay in step. In watch mode both the model's sources and the config's
+sources are watched, and a change to either rebuilds the model.
+
+
+## Watching and incremental rebuilds
+
+Watch mode is built around three ideas:
+
+- **Dependency tracking.** aontu records every file a model imports. After each
+  successful build the watcher adds those files (plus the root) to the set it
+  watches, so editing an imported fragment rebuilds the whole model.
+- **Debouncing.** External tools often write many files in a burst (a compiler
+  emitting output, a formatter rewriting a tree). The watcher waits for an
+  `idle` quiet period (default 111 ms) after the last change before queuing a
+  build, coalescing the burst into one rebuild.
+- **A serial queue.** Changes enqueue build requests that drain one at a time,
+  so rebuilds never overlap within a watcher.
+
+Because the model build and config build are separate watchers, the model's
+sources and the config's sources are tracked independently; a config edit
+rebuilds the config, which re-triggers the model build.
+
+
+## Caching
+
+Re-unifying a large model on every keystroke is wasteful, so a build caches its
+last result by a **signature** of file modification times. After a successful
+resolve, the build snapshots the mtime of the root file and every recorded
+dependency. On the next resolve, if every tracked file still has the same mtime,
+the cached model is reused and unification is skipped entirely.
+
+This is why `model_producer` skips writing when the output is byte-identical:
+rewriting an unchanged file would bump its mtime, invalidate caches downstream,
+and re-trigger watchers in a loop. Avoiding needless writes keeps incremental
+rebuilds cheap and prevents feedback loops between cooperating tools.
+
+
+## Dry run and the filesystem boundary
+
+Every build carries an `fs` object, and producers/actions are expected to write
+through `build.fs` rather than importing `fs` directly. That indirection is the
+seam that makes `--dryrun` work: in dry-run mode the build swaps the write
+methods (both synchronous and promise-based) for ones backed by an in-memory
+[`memfs`](https://github.com/streamich/memfs) volume. Reads still hit the real
+disk; writes go nowhere. The same seam lets you supply any `fs` implementation
+to build entirely in memory.
+
+This is a pragmatic, internal-use safeguard — it covers the standard write
+methods, not every conceivable path to disk. An action that bypasses `build.fs`
+escapes it.
+
+
+## Error handling philosophy
+
+Builds aim to **fail loudly and recover cleanly**:
+
+- A build collects errors rather than throwing on the first one where it can, so
+  a `BuildResult` reports what went wrong.
+- Error state is reset at the start of each build. A build instance is reused
+  across watch rebuilds, so without this a single transient failure would stick
+  to every later build. Resetting means a watcher self-heals: fix the source and
+  the next rebuild succeeds.
+- Model (unification) errors, missing files, unknown or misconfigured actions,
+  and actions that throw all converge on the same outcome — `ok: false` with the
+  cause in `errs` — so callers have one thing to check.
+
+
+## Known limitations
+
+This is an early framework; some sharp edges are known and documented rather
+than hidden:
+
+- **Concurrent model builds.** A change to a config file triggers a model
+  rebuild directly, outside the model watcher's serial queue. If a config file
+  and a model file change at the very same moment, two model builds can overlap.
+  The per-build error reset makes this self-healing, but unifying the two
+  watchers' queues is future work.
+- **Dry-run coverage.** The read-only filesystem shim covers the common write
+  methods; it is explicitly "not complete." Treat `--dryrun` as a strong
+  convenience, not a security boundary.
+- **Project layout assumption.** Action `load` paths resolve against the
+  directory two levels above the root model file, which bakes in the
+  `project/model/model.jsonic` convention.
+- **Error capture in the language layer.** Capturing *all* syntax and model
+  errors as structured data (rather than some surfacing as thrown exceptions)
+  depends on continued work in aontu.
+
+
+## Status
+
+`@voxgig/model` is a **prototype**. The concepts — model-once, generate-many,
+unification as the core operation — are stable and intended; the specific APIs,
+file conventions, and internals may still change. It is inspired by, and tracks
+the ideas of, [CUE](https://cuelang.org).
diff --git a/docs/how-to.md b/docs/how-to.md
new file mode 100644
index 0000000..02f4252
--- /dev/null
+++ b/docs/how-to.md
@@ -0,0 +1,378 @@
+# How-to guides
+
+Focused recipes for specific tasks. Each is self-contained. If you are new to
+the tool, do the [tutorial](./tutorial.md) first; for exhaustive detail see the
+[reference](./reference.md).
+
+- [Build once vs. watch](#build-once-vs-watch)
+- [Pass build arguments to actions](#pass-build-arguments-to-actions)
+- [Write a build action](#write-a-build-action)
+- [Order and select actions](#order-and-select-actions)
+- [Regenerate model source, then rebuild (pre + reload)](#regenerate-model-source-then-rebuild-pre--reload)
+- [Split a model across files and packages](#split-a-model-across-files-and-packages)
+- [Define and reuse a shape](#define-and-reuse-a-shape)
+- [Embed the model in your own program](#embed-the-model-in-your-own-program)
+- [Run a custom producer pipeline](#run-a-custom-producer-pipeline)
+- [Preview without writing files (dry run)](#preview-without-writing-files-dry-run)
+- [Build against an in-memory filesystem](#build-against-an-in-memory-filesystem)
+- [Control logging](#control-logging)
+- [Handle and surface build errors](#handle-and-surface-build-errors)
+- [Tune watch behavior](#tune-watch-behavior)
+
+
+## Build once vs. watch
+
+Once, then exit:
+
+```bash
+voxgig-model model/model.jsonic
+```
+
+```js
+const { Model } = require('@voxgig/model')
+const model = new Model({ path: 'model/model.jsonic', base: 'model' })
+const result = await model.run()
+if (!result.ok) process.exitCode = 1
+```
+
+Watch and rebuild until stopped:
+
+```bash
+voxgig-model --watch model/model.jsonic
+```
+
+```js
+const model = new Model({ path: 'model/model.jsonic', base: 'model' })
+await model.start()
+// ... later, to release the watchers:
+await model.stop()
+```
+
+> `start()` returns once watching has begun; the first build is enqueued
+> asynchronously. Always `stop()` when done — otherwise the file watchers keep
+> the process alive.
+
+
+## Pass build arguments to actions
+
+Build arguments are arbitrary data exposed to every action as `build.args`.
+
+```bash
+voxgig-model -b '{env:prod, region:eu-west-1}' model/model.jsonic
+```
+
+```js
+new Model({ path: 'model/model.jsonic', base: 'model',
+            buildargs: { env: 'prod', region: 'eu-west-1' } })
+```
+
+```js
+// build/deploy.js
+module.exports = async function deploy(model, build) {
+  const env = build.args?.env ?? 'dev'
+  build.log.info({ point: 'deploy', note: 'env=' + env })
+  return { ok: true }
+}
+```
+
+
+## Write a build action
+
+1. Declare it in `model/.model-config/model-config.jsonic`:
+
+   ```jsonic
+   sys: model: action: {
+     genDocs: load: 'build/genDocs'
+   }
+   ```
+
+   `load` is relative to the **project root** (the directory above `model/`),
+   without a file extension. Action names are plain identifiers — use `genDocs`,
+   not `gen-docs` (a hyphenated name would need quoting: `'gen-docs'`).
+
+2. Implement `build/genDocs.js`:
+
+   ```js
+   const Path = require('node:path')
+
+   module.exports = async function genDocs(model, build, ctx) {
+     const root = Path.resolve(build.path, '..', '..')
+     build.fs.mkdirSync(Path.resolve(root, 'out'), { recursive: true })
+     build.fs.writeFileSync(
+       Path.resolve(root, 'out', 'model.html'),
+       '<pre>' + JSON.stringify(model, null, 2) + '</pre>'
+     )
+     return { ok: true }
+   }
+   ```
+
+Use `build.fs` (not `require('fs')`) so the action honors `--dryrun`. Use
+`build.log` for logging so output is consistent and respects the log level.
+
+
+## Order and select actions
+
+Declare several actions and set an explicit order:
+
+```jsonic
+sys: model: action: {
+  genTypes: load: 'build/genTypes'
+  genDocs:  load: 'build/genDocs'
+  lint:     load: 'build/lint'
+}
+
+# comma-separated; runs in this order
+sys: model: order: action: 'genTypes,genDocs,lint'
+```
+
+Omit `order.action` to run every declared action in declaration order. Naming an
+action in `order.action` that has no definition fails the build with a clear
+error.
+
+Control **when** an action runs with its `step` export:
+
+```js
+module.exports = async function genTypes(model, build) { /* ... */ }
+module.exports.step = 'post'   // 'pre' | 'post' | 'all'; default 'post'
+```
+
+
+## Regenerate model source, then rebuild (pre + reload)
+
+Sometimes an action must generate `.jsonic` that the model itself consumes. Run
+it in the `pre` phase and request a reload:
+
+```js
+// build/genSource.js  (declared as `genSource: load: 'build/genSource'`)
+const Path = require('node:path')
+
+module.exports = async function genSource(model, build) {
+  const root = Path.resolve(build.path, '..', '..')
+  // write a .jsonic file the root model imports
+  build.fs.writeFileSync(
+    Path.resolve(root, 'model', 'generated.jsonic'),
+    'generated: ok: true\n'
+  )
+  return { ok: true, reload: true }   // re-resolve before the post phase
+}
+
+module.exports.step = 'pre'
+```
+
+With `reload: true`, the model is re-resolved after the `pre` phase, so `post`
+actions and `model_producer` see the regenerated source.
+
+
+## Split a model across files and packages
+
+Import another file relative to the current one:
+
+```jsonic
+@"./shapes.jsonic"
+color: @"./palette.jsonic"
+```
+
+Import from an installed package by its module path:
+
+```jsonic
+@"@voxgig/model/model/.model-config/model-config.jsonic"
+```
+
+All imports are tracked as dependencies — editing an imported file rebuilds the
+model in watch mode.
+
+
+## Define and reuse a shape
+
+A "shape" is a reusable structure of defaults and constraints. Define it once,
+then unify it into each instance:
+
+```jsonic
+shape: endpoint: {
+  method: *'GET' | string
+  auth:   *true  | boolean
+  path?:  string              # optional in the shape; each endpoint sets it
+}
+
+api: list:   $.shape.endpoint & { path: '/items' }
+api: create: $.shape.endpoint & { path: '/items', method: 'POST' }
+```
+
+Apply a shape to **every** entry of a map with the `&:` wildcard:
+
+```jsonic
+api: &: $.shape.endpoint     # every child of `api` must satisfy endpoint
+api: list:   { path: '/items' }
+api: create: { path: '/items', method: 'POST' }
+```
+
+
+## Embed the model in your own program
+
+`Model` is a normal class — drive it from your own tooling:
+
+```js
+const { Model } = require('@voxgig/model')
+
+async function buildModel() {
+  const model = new Model({
+    path: __dirname + '/model/model.jsonic',
+    base: __dirname + '/model',
+    require: __dirname,            // project root for action resolution
+    buildargs: { env: process.env.NODE_ENV ?? 'dev' },
+    debug: 'warn',                 // quieter logging
+  })
+
+  const result = await model.run()
+  if (!result.ok) {
+    throw new Error('model build failed: ' +
+      result.errs.map(e => e.message ?? e).join('; '))
+  }
+  // the unified model:
+  return result.build?.().model
+}
+```
+
+
+## Run a custom producer pipeline
+
+Skip the config/action layer entirely and assemble producers yourself with
+`makeBuild`. A **producer** runs in both the `pre` and `post` phases and returns
+a `ProducerResult`.
+
+```js
+const Fs = require('node:fs')
+const { makeBuild } = require('@voxgig/model/dist/build')
+const { model_producer } = require('@voxgig/model/dist/producer/model')
+const { prettyPino } = require('@voxgig/util')
+
+const build = makeBuild({
+  fs: Fs,
+  base: __dirname + '/model',
+  path: __dirname + '/model/model.jsonic',
+  res: [
+    { path: '/', build: model_producer },          // write model.json
+    { path: '/', build: async function summary(build, ctx) {
+        if (ctx.step === 'post') {
+          const n = Object.keys(build.model).length
+          build.log.info({ point: 'summary', note: n + ' top-level keys' })
+        }
+        return { ok: true, name: 'summary', step: ctx.step,
+                 active: true, reload: false, errs: [], runlog: [] }
+      }
+    },
+  ],
+}, prettyPino('custom', {}))
+
+const result = await build.run({ watch: false })
+```
+
+
+## Preview without writing files (dry run)
+
+```bash
+voxgig-model --dryrun model/model.jsonic
+```
+
+```js
+new Model({ path: 'model/model.jsonic', base: 'model', dryrun: true })
+```
+
+The build runs fully — the model resolves and actions execute — but every write
+(sync or promise-based) is redirected to an in-memory filesystem. Nothing on
+disk changes. This is the safe way to test a model or a new action.
+
+
+## Build against an in-memory filesystem
+
+Provide your own `fs` implementation (for example
+[`memfs`](https://github.com/streamich/memfs)) to build entirely in memory —
+useful for tests or sandboxed generation:
+
+```js
+const { memfs } = require('memfs')
+const { Model } = require('@voxgig/model')
+
+// Seed the in-memory volume. Include a config file: a pure in-memory build
+// cannot resolve the package import that an auto-created config would use.
+const { fs, vol } = memfs({
+  '/proj/model/model.jsonic': 'service: name: orders\n',
+  '/proj/model/.model-config/model-config.jsonic': 'sys: model: action: {}\n',
+})
+
+const model = new Model({
+  path: '/proj/model/model.jsonic',
+  base: '/proj/model',
+  fs,
+})
+await model.run()
+
+console.log(vol.toJSON())   // includes the generated /proj/model/model.json
+```
+
+The provided `fs` must support the synchronous methods the build uses
+(`readFileSync`, `writeFileSync`, `mkdirSync`, `statSync`, `existsSync`).
+
+
+## Control logging
+
+Set the level with `--debug`/`debug`:
+
+```bash
+voxgig-model -g debug model/model.jsonic     # verbose
+voxgig-model -g warn  model/model.jsonic     # quieter
+voxgig-model -g silent model/model.jsonic    # no logs
+```
+
+```js
+new Model({ path, base, debug: 'silent' })   // string level
+new Model({ path, base, debug: true })       // shorthand for 'debug'
+```
+
+Levels: `trace`, `debug`, `info` (default), `warn`, `error`, `fatal`, `silent`.
+In your actions and producers, log through `build.log` so output stays
+consistent:
+
+```js
+build.log.info({ point: 'my-action', note: 'did the thing' })
+```
+
+
+## Handle and surface build errors
+
+`run()` resolves with a `BuildResult`; check `ok` and inspect `errs`:
+
+```js
+const result = await model.run()
+if (!result.ok) {
+  for (const err of result.errs) {
+    console.error(err.message ?? err)
+  }
+  process.exitCode = 1
+}
+```
+
+Errors are reset at the start of each build, so a result reflects only that
+build. Model (unification) errors, missing files, unknown actions, and actions
+that throw all surface through `result.errs` with `result.ok === false`.
+
+
+## Tune watch behavior
+
+Choose which filesystem events trigger a rebuild and adjust the debounce:
+
+```js
+new Model({
+  path, base,
+  idle: 250,            // debounce window in ms (default 111)
+  watch: {
+    mod: true,          // rebuild on file modification (default true)
+    add: true,          // rebuild on file addition    (default false)
+    rem: true,          // rebuild on file deletion     (default false)
+  },
+})
+```
+
+The CLI enables `mod`, `add`, and `rem` by default in watch mode. A larger
+`idle` coalesces bursts of changes (e.g. an external tool writing many files)
+into a single rebuild.
diff --git a/docs/reference.md b/docs/reference.md
new file mode 100644
index 0000000..87f1904
--- /dev/null
+++ b/docs/reference.md
@@ -0,0 +1,630 @@
+# Reference
+
+Complete technical reference for `@voxgig/model`. For a guided introduction
+start with the [tutorial](./tutorial.md); for goal-oriented recipes see the
+[how-to guides](./how-to.md); for the ideas behind the design read the
+[explanation](./explanation.md).
+
+- [Command line interface](#command-line-interface)
+- [Project layout](#project-layout)
+- [The config file](#the-config-file)
+- [Actions](#actions)
+- [Build arguments](#build-arguments)
+- [Programmatic API](#programmatic-api)
+- [Producers](#producers)
+- [The build lifecycle](#the-build-lifecycle)
+- [Modeling language essentials](#modeling-language-essentials)
+- [Logging](#logging)
+- [npm scripts](#npm-scripts)
+- [Troubleshooting](#troubleshooting)
+- [Requirements](#requirements)
+
+
+## Command line interface
+
+```
+voxgig-model <root-file> [options]
+```
+
+`<root-file>` is the root `.jsonic` file of the model. It is also accepted as
+`--model <file>`. The directory containing the root file is the model **base**;
+generated model JSON is written next to the root file.
+
+| Flag | Short | Type | Default | Description |
+|------|-------|------|---------|-------------|
+| `--model <file>` | `-m` | string | first positional | Root model file path. |
+| `--watch` | `-w` | boolean | `false` | Watch source and config files; rebuild on change. Runs until interrupted. |
+| `--debug <level>` | `-g` | string | `info` | Log level: `trace`, `debug`, `info`, `warn`, `error`, `fatal`, `silent`. |
+| `--dryrun` | `-y` | boolean | `false` | Resolve and run the build, but redirect all file writes to an in-memory filesystem (nothing touches disk). |
+| `--build <jsonic>` | `-b` | string | `''` | A [jsonic](https://github.com/jsonic-lang/jsonic) document of build arguments, exposed to actions as `build.args`. |
+| `--help` | `-h` | boolean | | Print usage and exit. |
+| `--version` | `-v` | boolean | | Print version and exit. |
+
+The model path is resolved relative to the current working directory. The
+current working directory is also recorded as the project `require` base used
+to resolve action modules.
+
+**Exit codes:** `0` on success or after `--help`/`--version`; `1` on a usage
+error, a missing model file, or an uncaught build error.
+
+```bash
+# Build once, writing model/model.json
+voxgig-model model/model.jsonic
+
+# Watch and rebuild, with debug logging
+voxgig-model -w -g debug model/model.jsonic
+
+# Dry run (no files written)
+voxgig-model --dryrun model/model.jsonic
+
+# Pass build arguments to actions
+voxgig-model -b '{env:prod, region:eu-west-1}' model/model.jsonic
+```
+
+
+## Project layout
+
+A model is a directory tree. The conventional shape:
+
+```
+my-project/
+├─ model/
+│  ├─ model.jsonic                  # root model file (your entry point)
+│  ├─ ...more .jsonic files         # imported by the root
+│  ├─ model.json                    # GENERATED: the unified model
+│  └─ .model-config/
+│     ├─ model-config.jsonic        # config: declares actions
+│     └─ model-config.json          # GENERATED: the unified config
+└─ build/
+   ├─ foo.js                        # an action module
+   └─ bar.js
+```
+
+Two paths are derived from the root file `model/model.jsonic`:
+
+- **base** = `model/` — the directory of the root file. Generated model JSON
+  (`model.json`) and the `.model-config/` directory live here.
+- **project root** = `my-project/` — the directory **two levels above** the
+  root file (`resolve(rootFile, '..', '..')`). Action `load` paths are
+  resolved against the project root, so `build/foo` means
+  `my-project/build/foo.js`.
+
+This two-levels-up rule means the root model file is expected to sit one
+directory below the project root (e.g. `model/model.jsonic`).
+
+
+## The config file
+
+`<base>/.model-config/model-config.jsonic` declares the **actions** that run
+during a build. If it does not exist, the `Model` constructor creates a minimal
+one that imports the package's base config.
+
+The config is itself a model, unified the same way as your main model. The
+keys the tool reads:
+
+```jsonic
+# Each action has a load path (relative to the project root, no extension).
+# Action names are jsonic identifiers (no hyphens unless quoted).
+sys: model: action: {
+  genDocs:  load: 'build/genDocs'
+  genTypes: load: 'build/genTypes'
+}
+
+# Optional explicit run order (comma-separated action names).
+# When omitted, every declared action runs in declaration order.
+sys: model: order: action: 'genTypes,genDocs'
+```
+
+| Config key | Type | Meaning |
+|------------|------|---------|
+| `sys.model.action.<name>.load` | string | Module path for the action, relative to the project root, without file extension. **Required** for each action. |
+| `sys.model.order.action` | string | Comma-separated action names defining run order. Names are split on commas and surrounding whitespace; empty entries are ignored. If absent, the order is the key order of `sys.model.action`. |
+
+> Backwards compatibility: if `sys.model.action` is absent, `sys.model.builders`
+> is read instead.
+
+An `order.action` entry that names an action with no matching `action.<name>`
+fails the build with `Unknown model action "<name>"`. An action whose
+definition has no `load` fails with `Model action "<name>" is missing a "load"
+path`.
+
+The generated `model-config.json` is written next to `model-config.jsonic`.
+
+
+## Actions
+
+An action is a CommonJS module that receives the unified model and produces
+side effects — typically generating source files, documentation, infrastructure
+config, or other artifacts.
+
+### Module signature
+
+```js
+// build/genDocs.js
+module.exports = async function genDocs(model, build, ctx) {
+  // model — the unified model object (plain data)
+  // build — the Build instance (see API reference)
+  // ctx   — the BuildContext: { step, watch, state }
+
+  build.fs.writeFileSync('out/docs.html', render(model))
+
+  return { ok: true, reload: false }
+}
+
+// Optional: when does this action run? 'pre' | 'post' | 'all'. Default 'post'.
+module.exports.step = 'post'
+```
+
+The module's default export may also be a `Promise` that resolves to the
+function (it is awaited once at load time).
+
+### Arguments
+
+| Argument | Description |
+|----------|-------------|
+| `model` | The unified model as plain JSON-compatible data. Same value as `build.model`. |
+| `build` | The [`Build`](#build) instance. Useful members: `build.fs` (honors `--dryrun`), `build.args` (build arguments), `build.path`, `build.opts.base`, `build.log`, `build.dryrun`. |
+| `ctx` | The [`BuildContext`](#buildcontext). `ctx.step` is `'pre'` or `'post'`; `ctx.state` is a per-build scratch object shared across producers. |
+
+### Return value
+
+Return `{ ok, reload }`, or nothing:
+
+| Field | Type | Meaning |
+|-------|------|---------|
+| `ok` | boolean | `false` fails the build and stops remaining actions. A missing/`null` return is treated as success. |
+| `reload` | boolean | When `true` (typically from a `pre` action that rewrote model source files), the model is re-resolved before `post` actions run. |
+
+A thrown error fails the build; the error is logged once and surfaced in
+`BuildResult.errs`.
+
+### Steps
+
+| Step | Runs | Use for |
+|------|------|---------|
+| `pre` | before the model is finalized | Generating or rewriting `.jsonic` source that the model itself depends on; pair with `reload: true`. |
+| `post` (default) | after the model is finalized | Emitting artifacts from the finished model. |
+| `all` | both phases | Actions that must observe both phases. |
+
+### Example: a `pre` action that feeds back into the model
+
+```js
+// build/pre.js — writes a source file the model imports, then asks for a reload
+const Path = require('node:path')
+const Fs = require('node:fs')
+
+module.exports = async function pre(model, build) {
+  const root = Path.resolve(build.path, '..', '..')
+  if (!build.dryrun) {
+    Fs.writeFileSync(Path.resolve(root, 'model', 'pre.jsonic'), 'OK')
+  }
+  return { ok: true, reload: true }
+}
+
+module.exports.step = 'pre'
+```
+
+
+## Build arguments
+
+Build arguments are arbitrary data passed into a build and exposed to actions as
+`build.args`.
+
+- **CLI:** `-b '<jsonic>'` — parsed with jsonic. e.g. `-b '{env:prod}'`.
+- **API:** `new Model({ ..., buildargs: { env: 'prod' } })`.
+
+```js
+module.exports = async function deploy(model, build) {
+  const env = build.args?.env ?? 'dev'
+  // ...
+}
+```
+
+
+## Programmatic API
+
+The package main export provides `Model` and the `BuildSpec` type:
+
+```js
+const { Model } = require('@voxgig/model')
+// or: import { Model } from '@voxgig/model'
+```
+
+Lower-level building blocks are available from subpaths (no `exports` map is
+defined, so deep imports resolve directly to files):
+
+```js
+const { makeBuild } = require('@voxgig/model/dist/build')
+const { model_producer } = require('@voxgig/model/dist/producer/model')
+const { local_producer } = require('@voxgig/model/dist/producer/local')
+```
+
+### Model
+
+```ts
+class Model {
+  constructor(mspec: ModelSpec)
+  run(): Promise<BuildResult>            // build once
+  start(): Promise<void | BuildResult>   // build once, then watch and rebuild
+  stop(): Promise<void>                  // stop all watchers
+  fs: any                                // the (possibly dryrun) fs in use
+  log: Log                               // the pino logger
+}
+```
+
+- `run()` performs a single build (config then model) and resolves with the
+  model `BuildResult`. If the config build fails, its result is returned
+  instead.
+- `start()` performs the initial build, then watches both the model files and
+  the config files, rebuilding on change. It resolves once watching has begun
+  (the initial build is enqueued asynchronously). On a failed initial config
+  build it resolves with that result. **Always call `stop()`** to release
+  watchers, or the process stays alive.
+- `stop()` clears the watch interval and closes the file watchers for both the
+  model and config.
+
+### ModelSpec
+
+```ts
+interface ModelSpec {
+  path?: string        // root model file path
+  base?: string        // model base directory (defaults from path)
+  require?: any        // project root used to resolve action modules
+  buildargs?: any      // build arguments, exposed as build.args
+  debug?: boolean | string  // log level (string) or true => 'debug'
+  dryrun?: boolean     // redirect writes to an in-memory fs
+  idle?: number        // watch debounce in ms (default 111)
+  fs?: any             // a custom fs implementation (e.g. memfs)
+  log?: Log            // a pre-built pino logger
+  watch?: {            // which filesystem events trigger rebuilds
+    mod?: boolean      //   modifications (default true)
+    add?: boolean      //   additions     (default false)
+    rem?: boolean      //   deletions     (default false)
+  }
+}
+```
+
+### BuildResult
+
+```ts
+interface BuildResult {
+  ok: boolean                  // did the build succeed?
+  errs: any[]                  // errors collected this build
+  runlog: string[]             // ordered log of build phases
+  producers?: ProducerResult[] // per-producer results
+  build?: () => Build          // accessor for the underlying Build
+  builder?: string
+  path?: string
+  step?: string
+}
+```
+
+`errs` is reset at the start of every build, so a `BuildResult` reflects only
+that build (a `Build` reused across watch rebuilds does not accumulate stale
+errors).
+
+### makeBuild and BuildSpec
+
+`makeBuild(spec, log)` constructs a single `Build` you can drive directly,
+bypassing `Model`'s config/watch machinery. Useful for embedding a custom
+producer pipeline.
+
+```ts
+function makeBuild(spec: BuildSpec, log: Log): Build
+
+interface BuildSpec {
+  path?: string                 // root model file
+  base?: string                 // base dir (enables model JSON output)
+  res?: ProducerDef[]           // the producer pipeline
+  fs: FST                       // filesystem (required)
+  use?: { [name: string]: any } // shared services made available on build.use
+  require?: any                 // project root for action resolution
+  buildargs?: any               // build.args
+  debug?: boolean | string
+  dryrun?: boolean
+  idle?: number                 // watch debounce (ms)
+  name?: string                 // build name (default 'model')
+  watch?: { mod?: boolean; add?: boolean; rem?: boolean }
+  log?: Log
+}
+```
+
+```js
+const Fs = require('node:fs')
+const { makeBuild } = require('@voxgig/model/dist/build')
+const { model_producer } = require('@voxgig/model/dist/producer/model')
+const { prettyPino } = require('@voxgig/util')
+
+const build = makeBuild({
+  fs: Fs,
+  base: __dirname + '/model',
+  path: __dirname + '/model/model.jsonic',
+  res: [
+    { path: '/', build: model_producer },
+    { path: '/', build: async (build, ctx) => {
+        if (ctx.step === 'post') console.log('model:', build.model)
+        return { ok: true, name: 'inspect', step: ctx.step,
+                 active: true, reload: false, errs: [], runlog: [] }
+      }
+    },
+  ],
+}, prettyPino('demo', {}))
+
+const result = await build.run({ watch: false })
+```
+
+### Build
+
+The `Build` instance passed to producers and actions.
+
+```ts
+interface Build {
+  id: string                 // random build id
+  path: string               // root model file
+  base: string               // base directory
+  model: any                 // the unified model (after resolveModel)
+  opts: { [key: string]: any }  // aontu options; opts.base is the output base
+  fs: FST                    // filesystem (honors dryrun)
+  args: any                  // build arguments
+  dryrun: boolean
+  log: Log
+  use: { [name: string]: any }  // shared services (e.g. use.config)
+  deps: any                  // import dependency graph recorded by aontu
+  errs: any[]
+  ctx: BuildContext
+  aontu: Aontu               // the unification engine instance
+  run: (rspec: RunSpec) => Promise<BuildResult>
+  spec: BuildSpec
+  pdef: ProducerDef[]
+}
+```
+
+### BuildContext
+
+```ts
+interface BuildContext {
+  step: 'pre' | 'post'        // current build phase
+  watch: boolean              // is this a watch-mode build?
+  state: Record<string, any>  // scratch shared across producers in one build
+}
+```
+
+### Producer and ProducerResult
+
+```ts
+type Producer = (build: Build, ctx: BuildContext) => Promise<ProducerResult>
+
+interface ProducerDef { path: string; build: Producer }
+
+interface ProducerResult {
+  ok: boolean
+  name: string
+  step: string
+  active: boolean
+  reload: boolean    // request a model re-resolve before the post phase
+  errs: any[]
+  runlog: string[]
+}
+```
+
+
+## Producers
+
+A **producer** is a function run by a build during both the `pre` and `post`
+phases. Producers are the extension point; **actions** are a convenience layer
+built on top of the `local_producer`.
+
+The default `Model` pipeline is, in order:
+
+1. `model_producer` — serializes and writes the unified model.
+2. `local_producer` — loads and runs project actions.
+
+### model_producer
+
+- **Runs:** `post` phase only.
+- **Effect:** writes `build.model` as pretty JSON to
+  `<opts.base>/<root-file-name>.json` (the root file's basename with its
+  extension replaced by `.json`).
+- **Idempotent:** if the target file already contains identical JSON, the write
+  is skipped to avoid mtime churn that would invalidate caches and re-trigger
+  watchers.
+
+### local_producer
+
+- **Runs:** both phases. On first call it loads the action modules declared in
+  the config (resolving each `load` against the project root) and caches them in
+  `ctx.state.local`.
+- **Effect:** runs the actions whose `step` matches the current phase (`pre`
+  actions in `pre`, `post` actions in `post`, `all` actions in both), in the
+  configured order. Propagates each action's `ok` and `reload`.
+
+### Custom producers
+
+Provide your own pipeline via `makeBuild({ res: [...] })`, or compose with the
+built-ins. A producer should return a `ProducerResult`; set `reload: true` to
+request the model be re-resolved before the post phase.
+
+
+## The build lifecycle
+
+A single build (`Build.run`) proceeds as:
+
+1. **Reset** — clear per-build error state.
+2. **resolveModel** — read the root file and unify it (and its imports) with
+   `aontu`, producing `build.model`. Results are cached by file modification
+   time; an unchanged model is reused.
+3. **pre phase** — run every producer with `ctx.step = 'pre'`. Collect `reload`
+   flags. Stop on the first failure.
+4. **reload** — if any `pre` producer requested a reload (and there were no
+   errors), run `resolveModel` again to pick up regenerated source.
+5. **post phase** — run every producer with `ctx.step = 'post'`.
+6. **result** — return a `BuildResult` with `ok`, `producers`, `errs`, `runlog`.
+
+A `Model` orchestrates **two** builds:
+
+- The **config build** resolves `.model-config/model-config.jsonic` (writing
+  `model-config.json`) and, via an internal trigger producer, drives the main
+  model build.
+- The **model build** resolves your root model (writing `model.json`) and runs
+  your actions.
+
+In watch mode both the model's source files and the config's source files are
+watched; a change to either rebuilds the model.
+
+See [explanation](./explanation.md) for the reasoning and the caching and watch
+designs in depth.
+
+
+## Modeling language essentials
+
+Models are written in **[jsonic](https://github.com/jsonic-lang/jsonic)**
+(a relaxed JSON superset) and unified with **[aontu](https://github.com/voxgig/aontu)**,
+which implements [CUE](https://cuelang.org)-style unification. This is a
+practical summary; consult the CUE and aontu docs for the full language.
+
+### jsonic basics
+
+```jsonic
+# Comments start with #
+foo: 1                  # quotes are optional for keys and simple strings
+bar: 'a string'
+list: [1, 2, 3]
+a: b: c: 1              # dotted/nested keys: same as a:{b:{c:1}}
+obj: {
+  x: 10
+  y: 20                 # commas between entries are optional
+}
+```
+
+The top level is an implicit object; you do not wrap the file in `{ }`.
+
+> **Key syntax.** Bareword keys are identifiers — letters, digits, and
+> underscores (`envFile`, `gen_docs`, `srv2`). Quote any key containing a
+> hyphen, dot, space, or other punctuation: `'env-file': …`. An unquoted
+> `env-file:` is a syntax error.
+
+### Unification and types
+
+| Construct | Meaning |
+|-----------|---------|
+| `string` `number` `integer` `boolean` | Type constraints (a value must be of that type). |
+| `x: number` then `x: 2` | Unify the constraint with the value → `2`. Conflicting concrete values (`x: 1` and `x: 2`) fail to unify. |
+| `A & B` | Unify two structures/values into one. |
+| `*V \| T` | A **default**: value `V` if nothing more specific is provided, otherwise constrained to type `T`. e.g. `active: *true \| boolean`. |
+| `field?: T` | An **optional** field (no error if absent). |
+| `type({})` | Declare a struct type. |
+
+> **Every emitted field must be concrete.** The generated model is plain data,
+> so each field that survives into it must resolve to a value: a literal, a
+> default (`*v | T`), or an optional field (`f?: T`) that is simply absent. A
+> bare type constraint such as `name: string`, left with nothing to satisfy it,
+> fails to generate. Give reusable shapes defaults or optional fields and let
+> concrete instances supply the rest. (Constraints applied through a `&:`
+> wildcard are fine — they are not emitted directly; the children that satisfy
+> them are.)
+
+### References
+
+| Reference | Meaning |
+|-----------|---------|
+| `$.a.b.c` | **Absolute** reference from the model root. |
+| `.a.b` | **Relative** reference. |
+
+```jsonic
+sys: shape: srv: std: { api: web: active: *true | boolean }
+
+# Reuse a shape by unifying with an absolute reference:
+main: srv: foo: $.sys.shape.srv.std & { api: web: method: 'GET' }
+```
+
+### Wildcards and `key()`
+
+`&:` defines a constraint applied to **every** child of a map. `key()` resolves
+to the current map key.
+
+```jsonic
+color: &: {
+  name: key()        # each entry's name becomes its key
+  value: string
+}
+color: red:  { value: 'f00' }
+color: blue: { value: '00f' }
+# => color.red.name == 'red', color.blue.name == 'blue'
+```
+
+### Imports
+
+Pull in another file with `@"..."`:
+
+```jsonic
+# relative to the importing file
+color: @"./color.jsonic"
+
+# a path inside an installed package
+@"@voxgig/model/model/.model-config/model-config.jsonic"
+```
+
+Imported files are tracked as dependencies, so changing one triggers a rebuild
+in watch mode.
+
+
+## Logging
+
+Logging uses [pino](https://github.com/pinojs/pino) via
+`@voxgig/util`'s `prettyPino`. The level comes from `debug`
+(`ModelSpec.debug` / `--debug`):
+
+- absent → `info`
+- `true` → `debug`
+- a string → used as the level verbatim (`trace`…`fatal`, or `silent`)
+
+Each log line carries a `point` (a short event name such as `build-start`,
+`write-model`, `pre-actions`, `build-end`) and a human-readable `note`. Paths in
+notes are shown relative to the current working directory.
+
+
+## npm scripts
+
+For working **on** this repository (see [AGENTS.md](../AGENTS.md) for the full
+contributor/agent guide):
+
+| Script | What it does |
+|--------|--------------|
+| `npm run build` | Compile `src` → `dist` and `test` → `dist-test` (`tsc --build src test`). |
+| `npm test` | Run the compiled tests (`node --test dist-test/**/*.test.js`). |
+| `npm run test-some` | Run tests matching `TEST_PATTERN` (env var). |
+| `npm run test-cov` | Run tests with coverage, writing `coverage/lcov.info`. |
+| `npm run watch` | Recompile on change (`tsc --build -w`). |
+| `npm run model` | Run the CLI in watch mode on the package's own `model/sys.jsonic`. |
+| `npm run test-model` | Run the CLI once on `test/sys01/model/model.jsonic`. |
+| `npm run clean` | Remove `node_modules`, `dist`, `dist-test`, lockfiles. |
+| `npm run reset` | `clean` + install + build + test. |
+
+> Always `build` before `test`: tests run against compiled output in
+> `dist-test/`, importing the compiled library from `dist/`. Run these scripts
+> from the repository root.
+
+
+## Troubleshooting
+
+| Symptom | Likely cause and fix |
+|---------|----------------------|
+| Build fails with a `syntax` / parse error | An unquoted key contains a hyphen or other punctuation (`env-file:`). Use an identifier (`envFile`) or quote it (`'env-file':`). |
+| Model "fails to generate", or a field is reported as nil/incomplete | A bare type constraint (`name: string`) survived into the output with nothing to satisfy it. Give it a default (`name: *'' \| string`) or make it optional (`name?: string`), or provide a concrete value. |
+| `Unknown model action "X"` | `sys.model.order.action` names an action that has no `sys.model.action.X` definition. Add the action or fix the order list. |
+| `Model action "X" is missing a "load" path` | An action definition has no `load`. Add `load: 'build/X'`. |
+| A required action does not run | Check its `step` (`pre`/`post`/`all`) and that it appears in `order.action` (or that `order.action` is absent so all run). |
+| In-memory (`fs`) build fails to resolve `@voxgig/model/...` | The auto-created config imports a package path that is not in your volume. Seed a self-contained `.model-config/model-config.jsonic` (e.g. `sys: model: action: {}`). |
+| Watch process never exits | This is expected for `--watch` (runs until interrupted). For the API, call `model.stop()`. |
+| A change does not trigger a rebuild | Only tracked files rebuild: the root model, its imports, and the config files. Editing an unrelated file does nothing. Also note `add`/`rem` events are off by default in the API (`watch: { add, rem }`). |
+| Edits seem ignored after a failed build | Errors reset each build; fix the source and the next rebuild should succeed. If running the repo's own tooling, ensure you rebuilt (`dist/` can go stale — see [AGENTS.md](../AGENTS.md)). |
+
+
+## Requirements
+
+- **Node.js.** CI tests on Node 24 (recommended). Node 20.19+ generally works;
+  the `shape` dependency declares `engines.node >= 24`, so older versions emit
+  an `EBADENGINE` warning.
+- **Peer dependencies:** `pino` (`>=10`) and `@voxgig/util`. Install them in the
+  host project.
+- **Module system:** CommonJS (`"type": "commonjs"`).
diff --git a/docs/tutorial.md b/docs/tutorial.md
new file mode 100644
index 0000000..285e13f
--- /dev/null
+++ b/docs/tutorial.md
@@ -0,0 +1,264 @@
+# Tutorial: your first model
+
+This walkthrough takes you from an empty folder to a working model that
+generates a file, with live rebuilds. It assumes only that you can run `node`
+and `npm`. Follow it top to bottom — each step builds on the last.
+
+By the end you will have:
+
+- written a model in `.jsonic`,
+- unified it into a single JSON document,
+- generated an artifact from it with an action,
+- and watched it all rebuild on save.
+
+> New to the ideas here? You can do the tutorial first and read the
+> [explanation](./explanation.md) afterwards — the concepts will land better
+> once you have seen them work.
+
+
+## 1. Set up a project
+
+```bash
+mkdir hello-model && cd hello-model
+npm init -y
+npm install @voxgig/model pino
+```
+
+`pino` is a peer dependency used for logging. Installing it now avoids a warning
+later.
+
+Create the conventional layout:
+
+```bash
+mkdir -p model build
+```
+
+
+## 2. Write a model
+
+Create `model/model.jsonic`:
+
+```jsonic
+# model/model.jsonic
+service: name: 'orders'
+service: port: 8080
+```
+
+Build it once:
+
+```bash
+npx voxgig-model model/model.jsonic
+```
+
+You will see a few log lines, and a new file `model/model.json`:
+
+```json
+{
+  "service": {
+    "name": "orders",
+    "port": 8080
+  }
+}
+```
+
+That is the whole job of the core tool: take your `.jsonic` source, **unify** it,
+and write the result as a single canonical JSON model. Everything else builds on
+that model.
+
+
+## 3. Add structure with types and defaults
+
+The point of a modeling language is to capture rules, not just values. Replace
+`model/model.jsonic` with:
+
+```jsonic
+# model/model.jsonic
+
+# A reusable "shape" for a service: defaults plus type constraints.
+shape: service: {
+  name?: string              # optional in the shape; each service supplies it
+  port: *8080 | integer      # default 8080, but must be an integer
+  public: *false | boolean   # default false
+}
+
+# Two services, each built from the shape.
+service: orders:  $.shape.service & { name: 'orders' }
+service: web:     $.shape.service & { name: 'web', public: true, port: 443 }
+```
+
+Rebuild:
+
+```bash
+npx voxgig-model model/model.jsonic
+```
+
+`model/model.json` now contains:
+
+```json
+{
+  "shape": { "service": { "port": 8080, "public": false } },
+  "service": {
+    "orders": { "name": "orders", "port": 8080, "public": false },
+    "web":    { "name": "web",    "port": 443,  "public": true }
+  }
+}
+```
+
+Notice what happened:
+
+- `orders` inherited the default `port: 8080` and `public: false`.
+- `web` overrode both. The override **unifies** with the shape — if you tried
+  `port: 'https'` it would fail, because `port` must be an `integer`.
+
+`$.shape.service` is an **absolute reference** (from the model root) and `&`
+**unifies** it with the per-service overrides. This is how you keep one source
+of truth for structure and reuse it everywhere.
+
+> Why is `name` optional (`name?`)? The shape itself appears in the output, and
+> every field in the generated model must resolve to a concrete value. A bare
+> `name: string` with nothing to satisfy it would fail to generate — so the
+> shape leaves `name` optional (it may be absent) and each concrete service
+> supplies its own.
+
+
+## 4. Split the model across files
+
+Real models grow. Move the shape into its own file.
+
+`model/shapes.jsonic`:
+
+```jsonic
+# model/shapes.jsonic
+shape: service: {
+  name?: string
+  port: *8080 | integer
+  public: *false | boolean
+}
+```
+
+`model/model.jsonic`:
+
+```jsonic
+# model/model.jsonic
+@"./shapes.jsonic"
+
+service: orders: $.shape.service & { name: 'orders' }
+service: web:    $.shape.service & { name: 'web', public: true, port: 443 }
+```
+
+Rebuild — the output is identical. `@"./shapes.jsonic"` **imports** the file and
+unifies it into the model. Imports are tracked as dependencies, which matters in
+step 6.
+
+
+## 5. Generate something with an action
+
+A model is only useful if it drives output. An **action** is a small JS module
+that receives the unified model and produces an artifact.
+
+First, declare the action in the config file
+`model/.model-config/model-config.jsonic`:
+
+```jsonic
+# model/.model-config/model-config.jsonic
+sys: model: action: {
+  envFile: load: 'build/envFile'
+}
+```
+
+The `load` path is relative to the **project root** (the folder above `model/`)
+and has no extension, so this points at `build/envFile.js`. (Action names are
+plain identifiers — use `envFile`, not `env-file`; a hyphen would need quoting.)
+
+Now write the action, `build/envFile.js`:
+
+```js
+// build/envFile.js
+const Path = require('node:path')
+
+module.exports = async function envFile(model, build) {
+  // project root is two levels up from the model root file
+  const root = Path.resolve(build.path, '..', '..')
+
+  const lines = Object.entries(model.service).map(
+    ([name, svc]) => `# ${name}\nPORT_${name.toUpperCase()}=${svc.port}`
+  )
+
+  build.fs.writeFileSync(
+    Path.resolve(root, 'services.env'),
+    lines.join('\n') + '\n'
+  )
+
+  return { ok: true }
+}
+```
+
+Build again:
+
+```bash
+npx voxgig-model model/model.jsonic
+```
+
+You now have a generated `services.env`:
+
+```
+# orders
+PORT_ORDERS=8080
+# web
+PORT_WEB=443
+```
+
+Using `build.fs` (rather than `require('fs')` directly) means your action
+automatically respects `--dryrun`.
+
+
+## 6. Watch and iterate
+
+Generating on demand is fine; generating as you type is better. Start watch
+mode:
+
+```bash
+npx voxgig-model --watch model/model.jsonic
+```
+
+Leave it running. In another terminal (or your editor), change a value — set
+`orders` to `port: 9090` in `model/model.jsonic`, or edit `model/shapes.jsonic`.
+Within a moment the tool rebuilds and `services.env` updates. Editing the
+imported `shapes.jsonic` works too, because imports are tracked dependencies.
+
+Press `Ctrl-C` to stop.
+
+
+## 7. Try a dry run
+
+Before wiring a model into anything destructive, preview it without writing
+files:
+
+```bash
+npx voxgig-model --dryrun model/model.jsonic
+```
+
+The build runs exactly as normal — actions execute, the model resolves — but
+every write is redirected to an in-memory filesystem. Nothing on disk changes.
+
+
+## What you learned
+
+- A model is `.jsonic` source unified into one JSON document.
+- **Types** (`integer`, `string`, …) and **defaults** (`*value | type`) let the
+  model enforce its own rules.
+- **References** (`$.path`) and **unification** (`&`) reuse structure.
+- **Imports** (`@"./file"`) split a model across files.
+- **Actions** turn the model into artifacts, and respect `--dryrun` via
+  `build.fs`.
+- **Watch mode** rebuilds on every change, including changes to imports.
+
+
+## Where to next
+
+- [How-to guides](./how-to.md) — focused recipes (build args, custom producers,
+  embedding the API, in-memory filesystems, and more).
+- [Reference](./reference.md) — every CLI flag, config key, API type, and
+  language construct.
+- [Explanation](./explanation.md) — why unification, how the build lifecycle and
+  watcher actually work, and the current limitations.

From fb215d1ec9f046be5ebda0af66edecb3d161ef57 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Mon, 8 Jun 2026 18:15:45 +0000
Subject: [PATCH 5/6] restructure: split into ts/ and go/, add Go port, bump
 aontu

Mirror the voxgig/util layout: the TypeScript package now lives in ts/
(canonical) and a new Go port lives in go/ (kept in parity). A root
Makefile builds and tests both.

- Move the TypeScript project (src, test, dist, dist-test, bin, model,
  package.json) into ts/. Relative paths inside are unchanged, so the npm
  scripts work as before when run from ts/.
- Bump aontu 0.44.0 -> 0.45.1 (ts). Build clean; 11/11 tests pass; the
  compiled dist is byte-identical (runtime-only change).
- Add go/ - module github.com/voxgig/model/go, package model. Ports the
  build lifecycle (pre/reload/post), producers, dryrun and watch
  semantics, using the real Go aontu engine
  (github.com/rjrodger/aontu/go) for unification. Go adaptations: actions
  are a programmatic registry (no runtime require), watching polls mtimes
  (no chokidar), and imports resolve via a base chdir (Go aontu Generate
  takes no base param). gofmt/vet clean; go test passes.
- Add root Makefile (build/test/clean/publish-go) and go/README.md.
- Update README, AGENTS.md, CLAUDE.md and docs/ for the dual-language
  layout and the canonical-TS / parity-Go workflow.

Note: .github/workflows/build.yml still needs updating for the new
layout; it could not be pushed from this session (token lacks GitHub
'workflow' scope).

https://claude.ai/code/session_01HxXpZNrKj3qonocwAtEP8r
---
 .gitignore                                    |   6 +-
 AGENTS.md                                     | 265 ++++++++----------
 CLAUDE.md                                     |  47 ++--
 Makefile                                      |  51 ++++
 README.md                                     |  12 +
 docs/explanation.md                           |  14 +-
 docs/reference.md                             |   7 +-
 go/README.md                                  |  72 +++++
 go/build.go                                   | 251 +++++++++++++++++
 go/build_test.go                              |  87 ++++++
 go/cmd/voxgig-model/main.go                   |  78 ++++++
 go/fs.go                                      |  68 +++++
 go/go.mod                                     |  13 +
 go/go.sum                                     |  12 +
 go/log.go                                     |  79 ++++++
 go/model.go                                   |  87 ++++++
 go/model_test.go                              | 108 +++++++
 go/producer.go                                | 107 +++++++
 go/producer_test.go                           | 102 +++++++
 go/types.go                                   | 119 ++++++++
 go/watch.go                                   | 166 +++++++++++
 {bin => ts/bin}/voxgig-model                  |   0
 {dist-test => ts/dist-test}/build.test.js     |   0
 {dist-test => ts/dist-test}/build.test.js.map |   0
 {dist-test => ts/dist-test}/cli.test.js       |   0
 {dist-test => ts/dist-test}/cli.test.js.map   |   0
 {dist-test => ts/dist-test}/fix.test.js       |   0
 {dist-test => ts/dist-test}/fix.test.js.map   |   0
 {dist-test => ts/dist-test}/model.test.js     |   0
 {dist-test => ts/dist-test}/model.test.js.map |   0
 {dist-test => ts/dist-test}/watch.test.js     |   0
 {dist-test => ts/dist-test}/watch.test.js.map |   0
 {dist => ts/dist}/build.d.ts                  |   0
 {dist => ts/dist}/build.js                    |   0
 {dist => ts/dist}/build.js.map                |   0
 {dist => ts/dist}/config.d.ts                 |   0
 {dist => ts/dist}/config.js                   |   0
 {dist => ts/dist}/config.js.map               |   0
 {dist => ts/dist}/model.d.ts                  |   0
 {dist => ts/dist}/model.js                    |   0
 {dist => ts/dist}/model.js.map                |   0
 {dist => ts/dist}/producer/local.d.ts         |   0
 {dist => ts/dist}/producer/local.js           |   0
 {dist => ts/dist}/producer/local.js.map       |   0
 {dist => ts/dist}/producer/model.d.ts         |   0
 {dist => ts/dist}/producer/model.js           |   0
 {dist => ts/dist}/producer/model.js.map       |   0
 {dist => ts/dist}/types.d.ts                  |   0
 {dist => ts/dist}/types.js                    |   0
 {dist => ts/dist}/types.js.map                |   0
 {dist => ts/dist}/watch.d.ts                  |   0
 {dist => ts/dist}/watch.js                    |   0
 {dist => ts/dist}/watch.js.map                |   0
 .../model}/.model-config/model-config.json    |   0
 .../model}/.model-config/model-config.jsonic  |   0
 {model => ts/model}/sys.json                  |   0
 {model => ts/model}/sys.jsonic                |   0
 package.json => ts/package.json               |   2 +-
 {src => ts/src}/build.ts                      |   0
 {src => ts/src}/config.ts                     |   0
 {src => ts/src}/model.ts                      |   0
 {src => ts/src}/producer/local.ts             |   0
 {src => ts/src}/producer/model.ts             |   0
 {src => ts/src}/tsconfig.json                 |   0
 {src => ts/src}/types.ts                      |   0
 {src => ts/src}/watch.ts                      |   0
 {test => ts/test}/build.test.ts               |   0
 {test => ts/test}/cli.test.ts                 |   0
 {test => ts/test}/e01/doc.html                |   0
 .../test}/e01/model/config/config.jsonic      |   0
 {test => ts/test}/e01/model/config/model.json |   0
 {test => ts/test}/e01/model/model.json        |   0
 {test => ts/test}/e01/model/model.jsonic      |   0
 {test => ts/test}/fix.test.ts                 |   0
 {test => ts/test}/model.test.ts               |   0
 {test => ts/test}/p01/doc.html                |   0
 {test => ts/test}/p01/model/model.json        |   0
 {test => ts/test}/p01/model/model.jsonic      |   0
 {test => ts/test}/p01/model/zed.jsonic        |   0
 {test => ts/test}/perf-bench.js               |   0
 {test => ts/test}/quick.js                    |   0
 {test => ts/test}/sys01/build/foo.js          |   0
 {test => ts/test}/sys01/build/pre.js          |   0
 {test => ts/test}/sys01/foo.txt               |   0
 .../model/.model-config/model-config.json     |   0
 .../model/.model-config/model-config.jsonic   |   0
 {test => ts/test}/sys01/model/color.jsonic    |   0
 {test => ts/test}/sys01/model/model.json      |  54 ++--
 {test => ts/test}/sys01/model/model.jsonic    |   0
 {test => ts/test}/sys01/model/pre.jsonic      |   0
 {test => ts/test}/sys01/pre.txt               |   0
 {test => ts/test}/t01.jsonic                  |   0
 {test => ts/test}/t02.jsonic                  |   0
 {test => ts/test}/t03.jsonic                  |   0
 {test => ts/test}/tsconfig.json               |   0
 {test => ts/test}/util.js                     |   0
 {test => ts/test}/w01/doc.html                |   0
 {test => ts/test}/w01/model/model.json        |   0
 {test => ts/test}/w01/model/model.jsonic      |   0
 {test => ts/test}/w01/model/zed.jsonic        |   0
 {test => ts/test}/watch-w01.js                |   0
 {test => ts/test}/watch.test.ts               |   0
 102 files changed, 1593 insertions(+), 214 deletions(-)
 create mode 100644 Makefile
 create mode 100644 go/README.md
 create mode 100644 go/build.go
 create mode 100644 go/build_test.go
 create mode 100644 go/cmd/voxgig-model/main.go
 create mode 100644 go/fs.go
 create mode 100644 go/go.mod
 create mode 100644 go/go.sum
 create mode 100644 go/log.go
 create mode 100644 go/model.go
 create mode 100644 go/model_test.go
 create mode 100644 go/producer.go
 create mode 100644 go/producer_test.go
 create mode 100644 go/types.go
 create mode 100644 go/watch.go
 rename {bin => ts/bin}/voxgig-model (100%)
 rename {dist-test => ts/dist-test}/build.test.js (100%)
 rename {dist-test => ts/dist-test}/build.test.js.map (100%)
 rename {dist-test => ts/dist-test}/cli.test.js (100%)
 rename {dist-test => ts/dist-test}/cli.test.js.map (100%)
 rename {dist-test => ts/dist-test}/fix.test.js (100%)
 rename {dist-test => ts/dist-test}/fix.test.js.map (100%)
 rename {dist-test => ts/dist-test}/model.test.js (100%)
 rename {dist-test => ts/dist-test}/model.test.js.map (100%)
 rename {dist-test => ts/dist-test}/watch.test.js (100%)
 rename {dist-test => ts/dist-test}/watch.test.js.map (100%)
 rename {dist => ts/dist}/build.d.ts (100%)
 rename {dist => ts/dist}/build.js (100%)
 rename {dist => ts/dist}/build.js.map (100%)
 rename {dist => ts/dist}/config.d.ts (100%)
 rename {dist => ts/dist}/config.js (100%)
 rename {dist => ts/dist}/config.js.map (100%)
 rename {dist => ts/dist}/model.d.ts (100%)
 rename {dist => ts/dist}/model.js (100%)
 rename {dist => ts/dist}/model.js.map (100%)
 rename {dist => ts/dist}/producer/local.d.ts (100%)
 rename {dist => ts/dist}/producer/local.js (100%)
 rename {dist => ts/dist}/producer/local.js.map (100%)
 rename {dist => ts/dist}/producer/model.d.ts (100%)
 rename {dist => ts/dist}/producer/model.js (100%)
 rename {dist => ts/dist}/producer/model.js.map (100%)
 rename {dist => ts/dist}/types.d.ts (100%)
 rename {dist => ts/dist}/types.js (100%)
 rename {dist => ts/dist}/types.js.map (100%)
 rename {dist => ts/dist}/watch.d.ts (100%)
 rename {dist => ts/dist}/watch.js (100%)
 rename {dist => ts/dist}/watch.js.map (100%)
 rename {model => ts/model}/.model-config/model-config.json (100%)
 rename {model => ts/model}/.model-config/model-config.jsonic (100%)
 rename {model => ts/model}/sys.json (100%)
 rename {model => ts/model}/sys.jsonic (100%)
 rename package.json => ts/package.json (98%)
 rename {src => ts/src}/build.ts (100%)
 rename {src => ts/src}/config.ts (100%)
 rename {src => ts/src}/model.ts (100%)
 rename {src => ts/src}/producer/local.ts (100%)
 rename {src => ts/src}/producer/model.ts (100%)
 rename {src => ts/src}/tsconfig.json (100%)
 rename {src => ts/src}/types.ts (100%)
 rename {src => ts/src}/watch.ts (100%)
 rename {test => ts/test}/build.test.ts (100%)
 rename {test => ts/test}/cli.test.ts (100%)
 rename {test => ts/test}/e01/doc.html (100%)
 rename {test => ts/test}/e01/model/config/config.jsonic (100%)
 rename {test => ts/test}/e01/model/config/model.json (100%)
 rename {test => ts/test}/e01/model/model.json (100%)
 rename {test => ts/test}/e01/model/model.jsonic (100%)
 rename {test => ts/test}/fix.test.ts (100%)
 rename {test => ts/test}/model.test.ts (100%)
 rename {test => ts/test}/p01/doc.html (100%)
 rename {test => ts/test}/p01/model/model.json (100%)
 rename {test => ts/test}/p01/model/model.jsonic (100%)
 rename {test => ts/test}/p01/model/zed.jsonic (100%)
 rename {test => ts/test}/perf-bench.js (100%)
 rename {test => ts/test}/quick.js (100%)
 rename {test => ts/test}/sys01/build/foo.js (100%)
 rename {test => ts/test}/sys01/build/pre.js (100%)
 rename {test => ts/test}/sys01/foo.txt (100%)
 rename {test => ts/test}/sys01/model/.model-config/model-config.json (100%)
 rename {test => ts/test}/sys01/model/.model-config/model-config.jsonic (100%)
 rename {test => ts/test}/sys01/model/color.jsonic (100%)
 rename {test => ts/test}/sys01/model/model.json (85%)
 rename {test => ts/test}/sys01/model/model.jsonic (100%)
 rename {test => ts/test}/sys01/model/pre.jsonic (100%)
 rename {test => ts/test}/sys01/pre.txt (100%)
 rename {test => ts/test}/t01.jsonic (100%)
 rename {test => ts/test}/t02.jsonic (100%)
 rename {test => ts/test}/t03.jsonic (100%)
 rename {test => ts/test}/tsconfig.json (100%)
 rename {test => ts/test}/util.js (100%)
 rename {test => ts/test}/w01/doc.html (100%)
 rename {test => ts/test}/w01/model/model.json (100%)
 rename {test => ts/test}/w01/model/model.jsonic (100%)
 rename {test => ts/test}/w01/model/zed.jsonic (100%)
 rename {test => ts/test}/watch-w01.js (100%)
 rename {test => ts/test}/watch.test.ts (100%)

diff --git a/.gitignore b/.gitignore
index 8ee4c30..d95345e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -105,10 +105,10 @@ typings/
 
 
 coverage
-test/cov
+ts/test/cov
 
 # Generated fixtures written by tests at runtime
-test/_gen
+ts/test/_gen
 
 package-lock.json
 yarn.lock
@@ -116,5 +116,5 @@ yarn.lock
 
 *~
 
-test/coverage.html
+ts/test/coverage.html
 
diff --git a/AGENTS.md b/AGENTS.md
index ca91a4b..bfb3d41 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -4,207 +4,172 @@ Guidance for AI coding agents (and humans) working **on** the `@voxgig/model`
 codebase. For using the tool, start at the [README](./README.md) and
 [docs/](./docs/). This file is about developing the package itself.
 
-Keep this file accurate: if you change the build, test layout, or a convention
-below, update it in the same change.
+This repository holds **two implementations** of the same tool:
 
+- **`ts/`** — the TypeScript package `@voxgig/model` (npm library + CLI).
+  **TypeScript is canonical.**
+- **`go/`** — the Go module `github.com/voxgig/model/go`, kept in architectural
+  parity with the TypeScript version.
 
-## What this project is
+Keep this file accurate: if you change the build, test layout, or a convention,
+update it in the same change.
 
-`@voxgig/model` unifies `.jsonic` source into a single JSON model (via the
-[aontu](https://github.com/voxgig/aontu) CUE-style engine) and runs generator
-"actions" over it. It can build once or watch and rebuild. It ships a library
-(`Model`) and a CLI (`voxgig-model`).
 
-A 90-second tour of how it fits together is in
-[docs/explanation.md](./docs/explanation.md#architecture-at-a-glance). Read that
-before making structural changes.
+## Layout
 
+```
+ts/                 TypeScript implementation (canonical)
+  src/              library source (model.ts, build.ts, watch.ts, ...)
+  test/             node:test suites
+  dist/ dist-test/  COMMITTED build output
+  bin/voxgig-model  CLI entry (plain JS)
+  model/            the package's own sample model
+  package.json
+go/                 Go implementation (parity)
+  *.go              package `model` (build.go, producer.go, watch.go, ...)
+  cmd/voxgig-model/ Go CLI entry
+  *_test.go         go test suites
+  go.mod  go.sum
+docs/               tutorial / how-to / reference / explanation
+Makefile            orchestrates both: `make build`, `make test`
+.github/workflows/  CI (a `ts` job and a `go` job)
+```
 
-## Environment
-
-- **Node.js 24** is the target (CI matrix). Node 20.19+ works; the `shape`
-  dependency declares `engines.node >= 24`, so older Node prints an
-  `EBADENGINE` warning — harmless here.
-- TypeScript, CommonJS output (`"type": "commonjs"`).
-- Install with `npm install`. No lockfile is committed (it is gitignored).
 
+## Build & test
 
-## Build, test, run
+From the repository root, `make` drives both implementations:
 
 ```bash
-npm install            # once
-npm run build          # tsc --build src test  -> dist/ and dist-test/
-npm test               # node --test dist-test/**/*.test.js
+make build     # build-ts + build-go
+make test      # test-ts + test-go
+make           # all: build then test
 ```
 
-```bash
-# a single suite / pattern
-TEST_PATTERN='watch' npm run test-some
+### TypeScript (run from `ts/`)
 
-# coverage (writes coverage/lcov.info)
+```bash
+cd ts
+npm install
+npm run build              # tsc --build src test  -> dist/ and dist-test/
+npm test                   # node --test dist-test/**/*.test.js
+TEST_PATTERN=watch npm run test-some
 npm run test-cov
+```
+
+**You must `npm run build` before `npm test`** — tests run against compiled
+output in `dist-test/` and import the library from `dist/`.
 
-# recompile on save
-npm run watch
+### Go (run from `go/`)
 
-# exercise the CLI against the bundled sample model
-npm run test-model     # build once on test/sys01/model/model.jsonic
-npm run model          # watch model/sys.jsonic
+```bash
+cd go
+go build ./...
+go vet ./...
+gofmt -l .                 # must print nothing
+go test ./...
 ```
 
-**You must `npm run build` before `npm test`.** Tests are TypeScript compiled to
-`dist-test/`, and they import the compiled library from `dist/`. Source edits do
-not take effect in tests until rebuilt. For a fully clean rebuild use
-`npx tsc --build src test --force`.
+Go **1.24+** is required (the `aontu/go` dependency declares `go 1.24.7`).
 
 
-## Critical gotchas
+## Critical gotchas (TypeScript)
 
-1. **Run commands from the repository root.** `tsc --build src test` resolves
-   `src` and `test` as project paths relative to the current directory. Running
-   it from a subdirectory fails with `TS5083: Cannot read file '.../src/
-   tsconfig.json'` and silently leaves `dist/` stale — so tests then run against
-   old code. If a build looks like it "passed" but tests don't reflect your
-   change, check your working directory.
+1. **Run TS commands from `ts/`.** `tsc --build src test` resolves `src` and
+   `test` as project paths relative to the current directory; from the wrong
+   directory it fails with `TS5083` and silently leaves `dist/` stale — so
+   tests then run against old code.
 
-2. **`dist/` and `dist-test/` are committed.** They are tracked in git (in the
-   `files` allowlist for publishing). After any source change, rebuild and
-   commit the regenerated `dist/`/`dist-test/` alongside the `.ts`. CI rebuilds
-   them, but the repo convention is to commit them.
+2. **`ts/dist/` and `ts/dist-test/` are committed.** After any source change,
+   rebuild and commit the regenerated output alongside the `.ts`.
 
-3. **The CLI (`bin/voxgig-model`) is plain JavaScript**, not compiled. Edits to
-   it take effect immediately (no build needed for the bin itself), but it
+3. **The CLI (`ts/bin/voxgig-model`) is plain JavaScript**, not compiled. It
    `require`s `dist/model.js`, so the library must be built.
 
-4. **`aontu` reads `opts.err`, not `opts.errs`.** When invoking
-   `aontu.generate(src, opts)`, set `opts.err = <array>` to enable collect mode
-   (errors gathered into the array instead of thrown). This is easy to get
-   wrong — see `src/build.ts: resolveModel`.
+4. **`aontu` (npm) reads `opts.err`, not `opts.errs`** — collect mode. See
+   `ts/src/build.ts: resolveModel`.
 
-5. **Generated test fixtures go in `test/_gen/`** (gitignored). Tests write their
-   own fixtures there at runtime; do not commit them. See "Writing tests".
+5. **Generated test fixtures go in `ts/test/_gen/`** (gitignored). Tests write
+   their own fixtures there at runtime; do not commit them.
 
 
-## Repository map
+## The Go port
 
-```
-src/
-  model.ts            Model: public entry; wires config build + model build
-  config.ts           Config: specialized build for .model-config
-  watch.ts            Watch: chokidar, debounce, rebuild queue, dep tracking
-  build.ts            BuildImpl/makeBuild: resolve model (aontu) + run producers
-  types.ts            shared interfaces (Build, BuildSpec, Producer, ...)
-  producer/
-    model.ts          model_producer: write the unified model as JSON
-    local.ts          local_producer: load & run actions declared in config
-  tsconfig.json       project config for src
-
-bin/voxgig-model      CLI entry (plain JS): arg parsing -> new Model().run/start
-
-test/
-  *.test.ts           node:test suites (compiled to dist-test/)
-  tsconfig.json       project config for tests
-  sys01/, p01/, e01/, w01/   committed fixtures
-  _gen/               GITIGNORED scratch fixtures written by tests at runtime
-
-model/                the package's own sample model (sys.jsonic + config)
-dist/, dist-test/     COMMITTED build output
-docs/                 tutorial / how-to / reference / explanation
-```
+The Go module ports the **architecture**, not every mechanism. The build
+lifecycle (pre → reload → post), producers, model output, dryrun, and watch
+semantics match TypeScript. Two things differ by necessity:
+
+- **Actions are a registry, not dynamic modules.** TypeScript declares actions
+  in a config file and loads them with `require()`. Go cannot load code at
+  runtime, so actions are registered programmatically via `ModelSpec.Actions`
+  (`map[string]ActionDef`) — see `go/producer.go`.
+- **Watching polls modification times** (`go/watch.go`) rather than using
+  chokidar.
 
-Data flow: `CLI/Model` → `Config` (resolves actions) + `Watch` → `BuildImpl`
-(`aontu` unify → producers). The model build runs `model_producer` then
-`local_producer`. Full detail:
-[docs/explanation.md](./docs/explanation.md).
+Other notes:
 
+- **Unification** uses the real Go aontu engine
+  (`github.com/rjrodger/aontu/go`). Its `Generate(src)` has no base parameter,
+  so `AontuResolver` briefly `chdir`s to the model base (guarded by a mutex)
+  so `@"..."` imports resolve. aontu/go does not report import deps, so the
+  watcher tracks `*.jsonic` files under the base directory.
+- **JSON key order** differs: Go's `encoding/json` sorts object keys;
+  TypeScript preserves insertion order. Content is otherwise equivalent — an
+  accepted cross-language difference.
+- **`const Version`** lives in `go/model.go`; `make publish-go V=x.y.z`
+  rewrites it and tags `go/vx.y.z`.
+- The Go port depends on **`aontu/go` only**; it does not use `util/go` (the
+  TypeScript `@voxgig/util` dependency is for pino logging, replaced here by a
+  minimal `Log` interface).
 
-## Code conventions
 
-Match the surrounding style; in this codebase that means:
+## Maintaining parity
 
-- **2-space indent, no semicolons, single quotes.**
-- Prefer `let`; use `const` where the existing file does.
-- Null checks as `null == x` / `null != x`. Comparisons are often "yoda"
-  (`'post' === ctx.step`). Follow the local file.
-- CommonJS modules. Keep imports grouped: node builtins, then deps, then local.
-- Keep the public type surface in `src/types.ts`. Many internal fields are typed
-  `any` by design; do not tighten them speculatively.
-- Logging goes through the pino logger (`build.log` / `this.log`) with a `point`
-  (short event name) and a human `note`. Do not `console.log` in library code.
-- Copyright header comment at the top of each source file (see existing files).
+TypeScript is canonical. When changing behavior:
+
+1. Change TypeScript first, with a test (`ts/test/*.test.ts`).
+2. Apply the equivalent change to Go, with a test (`go/*_test.go`).
+3. Rebuild TypeScript and commit the regenerated `ts/dist/`.
+4. Run both suites (`make test`); keep `gofmt`/`go vet` clean.
+5. Update `docs/` if the API changed.
 
 
 ## Writing tests
 
-- Use `node:test` (`describe`/`test`) and `node:assert`. Import the library from
-  `../dist/...` (compiled output), mirroring existing suites.
-- **Put runtime fixtures under `test/_gen/<name>/`** and create them in the test
-  (write `.jsonic`, config, and any action `.js`). This keeps fixtures
-  self-contained and out of git. Clean the dir at the start of the test
-  (`rm -rf` then `mkdir -p`).
-- **Watch-mode tests must call `model.stop()` in a `finally`.** `start()` opens
-  chokidar watchers (for both the model and the config); leaving them open hangs
-  the test process. Poll for the expected result with a timeout helper rather
-  than fixed sleeps (see `test/watch.test.ts`).
-- **CLI tests** spawn the built bin without a shell, for cross-platform
-  safety:
-  ```js
-  const { spawnSync } = require('node:child_process')
-  const res = spawnSync(process.execPath, [BIN, modelPath, '-b', '{a:1}'],
-                        { encoding: 'utf8' })
-  ```
-  Use jsonic barewords (`{a:b}`) to avoid embedded-quote escaping.
-- Make tests **meaningful guards**: when adding a test for a fix, confirm it
-  fails without the fix (temporarily revert, run, restore).
-
-Existing suites to model new ones on:
-
-| Suite | Covers |
-|-------|--------|
-| `test/build.test.ts` | end-to-end builds (`makeBuild`, `Model.run`) with the `p01`/`sys01` fixtures |
-| `test/fix.test.ts` | error recovery, unknown/misconfigured actions, dry-run filesystem |
-| `test/watch.test.ts` | watch rebuilds on model and config changes |
-| `test/cli.test.ts` | the CLI passes build args through to actions |
+**TypeScript:** `node:test` (`describe`/`test`), import from `../dist/...`.
+Runtime fixtures under `ts/test/_gen/<name>/`, created in the test. Watch tests
+must `await model.stop()` in a `finally`. CLI tests spawn the built bin without
+a shell.
+
+**Go:** standard `testing` with `t.TempDir()` fixtures. Watch tests must
+`defer m.Stop()`. Do **not** `t.Parallel()` resolver-using tests —
+`AontuResolver` changes the working directory.
 
 
 ## Common tasks (playbooks)
 
 ### Add a build action (product-level generator)
-Actions are user-space, not framework code — declare in a model's
-`.model-config/model-config.jsonic` and implement under `build/`. See
-[docs/how-to.md](./docs/how-to.md#write-a-build-action). No library change.
+User-space, not framework code. TypeScript: declare in
+`.model-config/model-config.jsonic`, implement under `build/`. Go: register an
+`ActionDef` in `ModelSpec.Actions`. See
+[docs/how-to.md](./docs/how-to.md#write-a-build-action).
 
 ### Add a built-in producer (framework-level)
-1. Create `src/producer/<name>.ts` exporting a `Producer`
-   `(build, ctx) => Promise<ProducerResult>` (see `src/producer/model.ts`).
-2. Add it to the pipeline in `src/model.ts` (`this.build.res`), or document it
-   for `makeBuild` users.
-3. Rebuild, add a test, commit `dist/` too.
-
-### Add or change a CLI flag
-Edit `bin/voxgig-model`: add to `resolveOptions` (`parseArgs` `options`) and
-`validateOptions` (the `Shape`), then include it in the `spec` passed to
-`new Model(spec)`. Thread the field through `ModelSpec` in `src/types.ts` and
-read it in the `Model` constructor. (The CLI maps `--build` → `buildargs`; keep
-spec keys aligned with `ModelSpec`.)
+TypeScript: add `ts/src/producer/<name>.ts`, wire it into `ts/src/model.ts`.
+Go: add a `Producer` func in `go/producer.go`, wire it into `go/model.go`.
+Rebuild and test both; commit `ts/dist/`.
 
 ### Change the model/build types
-Edit `src/types.ts`. Rebuild so `dist/*.d.ts` regenerates; commit them.
-
-### Touch the build/error/cache logic
-`src/build.ts`. Remember the `opts.err` collect-mode rule (gotcha #4) and that
-`this.errs` is reset per run so a reused build instance doesn't accumulate stale
-errors. Add a regression test in `test/fix.test.ts`.
+TypeScript: `ts/src/types.ts`. Go: `go/types.go`. Keep the two aligned.
 
 
 ## Before you commit
 
-- `npm run build` is clean (`tsc rc 0`) **from the repo root**.
-- `npm test` is green; add/adjust tests for behavior changes.
-- Regenerated `dist/` and `dist-test/` are staged with the source.
-- No `test/_gen/` artifacts are staged (they are gitignored — verify with
-  `git status`).
-- Keep this file and `docs/` in sync with any behavior or convention change.
+- `make build` is clean and `make test` is green (both languages).
+- Regenerated `ts/dist/` and `ts/dist-test/` are staged with the source.
+- `gofmt -l go` prints nothing; `cd go && go vet ./...` is clean.
+- No `ts/test/_gen/` artifacts are staged.
+- This file and `docs/` reflect any behavior or convention change.
 
 
 ## More documentation
diff --git a/CLAUDE.md b/CLAUDE.md
index 5d4f840..a14a818 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -2,36 +2,37 @@
 
 Guidance for Claude Code (and other AI agents) working in this repository.
 
-The full contributor/agent guide — environment, repository map, conventions,
-test patterns, and task playbooks — is in **@AGENTS.md**. Read it before making
-changes. The essentials:
+This repo has **two implementations**: `ts/` (TypeScript, canonical) and `go/`
+(Go, in parity). The full contributor/agent guide is in **@AGENTS.md** — read
+it before making changes. The essentials:
 
 ## Build & test
-- Run everything **from the repository root**.
-- `npm run build` (`tsc --build src test`) **before** `npm test`; tests run
-  against compiled output in `dist-test/` and import the library from `dist/`.
-- `dist/` and `dist-test/` are **committed** — rebuild and stage them with any
-  source change.
-- Single suite: `TEST_PATTERN='<name>' npm run test-some`. Coverage:
-  `npm run test-cov`.
+- From the root, `make build` and `make test` drive both languages.
+- **TypeScript** (`cd ts`): `npm run build` (`tsc --build src test`) **before**
+  `npm test`. `ts/dist/` and `ts/dist-test/` are **committed** — rebuild and
+  stage them with any source change.
+- **Go** (`cd go`): `go build ./...`, `go vet ./...`, `gofmt -l .`,
+  `go test ./...`. Go 1.24+.
 
 ## Watch out for
-- Stale `dist/` from a build that failed because it ran in a subdirectory
-  (`TS5083`) — tests then pass against old code. Verify cwd is the repo root.
-- Watch-mode tests must `await model.stop()` in a `finally`, or the process
-  hangs on open file watchers.
-- Runtime test fixtures belong in `test/_gen/` (gitignored); don't commit them.
-- `aontu.generate` collects errors only when given `opts.err` (not `opts.errs`).
+- Run TS commands **from `ts/`**: `tsc --build src test` resolves project paths
+  relative to cwd (`TS5083` otherwise), and a failed build leaves stale `dist/`.
+- Watch tests must release watchers (`await model.stop()` / `defer m.Stop()`),
+  or the process hangs.
+- TS runtime fixtures belong in `ts/test/_gen/` (gitignored).
+- TS: `aontu.generate` collects errors only with `opts.err` (not `opts.errs`).
+- Go: `AontuResolver` `chdir`s to the model base — don't `t.Parallel()` tests
+  that resolve.
 
-## Where things are
-- Library: `src/` (`model.ts`, `config.ts`, `watch.ts`, `build.ts`, `types.ts`,
-  `producer/`). CLI: `bin/voxgig-model` (plain JS). Docs: `docs/`.
-- Architecture overview: `docs/explanation.md`.
+## Parity
+TypeScript is canonical. Change TS (with a test) first, then mirror in Go (with
+a test), rebuild `ts/dist/`, and run `make test`. Keep the two in step.
 
 ## Style
-- 2-space indent, no semicolons, single quotes, CommonJS. Match the local file.
-- Log via the pino logger (`build.log`/`this.log`), never `console.log` in
-  library code.
+- TS: 2-space indent, no semicolons, single quotes, CommonJS. Match the file.
+- Go: standard `gofmt`; package `model`; `/* Copyright © ... */` header.
+- Never `console.log` in TS library code (use the pino logger); in Go log
+  through the `Log` interface.
 
 When you change behavior or a convention, update `@AGENTS.md` and the relevant
 file in `docs/` in the same change.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..5b1e801
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,51 @@
+.PHONY: all build test clean build-ts build-go test-ts test-go vet-go clean-ts clean-go publish-go tags-go reset
+
+all: build test
+
+build: build-ts build-go
+
+test: test-ts test-go
+
+clean: clean-ts clean-go
+
+# TypeScript (the npm package lives in ts/) — the canonical implementation.
+build-ts:
+	cd ts && npm run build
+
+test-ts:
+	cd ts && npm test
+
+cov-ts:
+	cd ts && npm run test-cov
+
+clean-ts:
+	rm -rf ts/dist ts/dist-test ts/node_modules
+
+# Go (the module lives in go/) — kept in parity with TypeScript.
+build-go:
+	cd go && go build ./...
+
+test-go:
+	cd go && go test ./...
+
+vet-go:
+	cd go && go vet ./... && gofmt -l .
+
+clean-go:
+	cd go && go clean
+
+# Publish the Go module: make publish-go V=0.1.1
+publish-go: vet-go test-go
+	@test -n "$(V)" || (echo "Usage: make publish-go V=x.y.z" && exit 1)
+	sed -i 's/^const Version = ".*"/const Version = "$(V)"/' go/model.go
+	git add go/model.go
+	git commit -m "go: v$(V)"
+	git tag go/v$(V)
+	git push origin HEAD go/v$(V)
+
+tags-go:
+	git tag -l 'go/v*' --sort=-version:refname
+
+reset:
+	cd ts && npm run reset
+	cd go && go clean -cache && go build ./... && go test ./...
diff --git a/README.md b/README.md
index 8d0e013..481ff7e 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,8 @@ once or watch and rebuild on change.
 
 ## Install
 
+The TypeScript package (npm):
+
 ```bash
 npm install @voxgig/model pino
 ```
@@ -22,6 +24,16 @@ npm install @voxgig/model pino
 `pino` is a peer dependency (logging). Requires Node.js — CI runs Node 24;
 Node 20.19+ generally works.
 
+The Go module:
+
+```bash
+go get github.com/voxgig/model/go
+```
+
+Both implementations live in this repository — `ts/` (TypeScript, canonical)
+and `go/` (Go, kept in parity). See [go/README.md](./go/README.md) for Go usage
+and [AGENTS.md](./AGENTS.md) for working on the repo.
+
 
 ## Quick start
 
diff --git a/docs/explanation.md b/docs/explanation.md
index 79c6695..05d3e1a 100644
--- a/docs/explanation.md
+++ b/docs/explanation.md
@@ -86,13 +86,13 @@ CLI (bin/voxgig-model)
 
 | Component | File | Responsibility |
 |-----------|------|----------------|
-| `Model` | `src/model.ts` | Public entry. Wires a config build and a model build together; exposes `run`/`start`/`stop`. |
-| `Config` | `src/config.ts` | A specialized build for `.model-config/model-config.jsonic`. |
-| `Watch` | `src/watch.ts` | File watching, debouncing, the rebuild queue, dependency tracking. |
-| `Build` / `BuildImpl` | `src/build.ts` | One build: resolve the model via aontu, run the producer pipeline, cache by mtime. |
-| `model_producer` | `src/producer/model.ts` | Serialize the unified model to JSON. |
-| `local_producer` | `src/producer/local.ts` | Load action modules from config and run them. |
-| types | `src/types.ts` | The shared interfaces (`Build`, `BuildSpec`, `Producer`, …). |
+| `Model` | `ts/src/model.ts` | Public entry. Wires a config build and a model build together; exposes `run`/`start`/`stop`. |
+| `Config` | `ts/src/config.ts` | A specialized build for `.model-config/model-config.jsonic`. |
+| `Watch` | `ts/src/watch.ts` | File watching, debouncing, the rebuild queue, dependency tracking. |
+| `Build` / `BuildImpl` | `ts/src/build.ts` | One build: resolve the model via aontu, run the producer pipeline, cache by mtime. |
+| `model_producer` | `ts/src/producer/model.ts` | Serialize the unified model to JSON. |
+| `local_producer` | `ts/src/producer/local.ts` | Load action modules from config and run them. |
+| types | `ts/src/types.ts` | The shared interfaces (`Build`, `BuildSpec`, `Producer`, …). |
 
 `aontu` (unification), `chokidar` (file watching), `memfs` (the dry-run
 filesystem), and `pino`/`@voxgig/util` (logging) are the external moving parts.
diff --git a/docs/reference.md b/docs/reference.md
index 87f1904..416fc11 100644
--- a/docs/reference.md
+++ b/docs/reference.md
@@ -585,8 +585,9 @@ notes are shown relative to the current working directory.
 
 ## npm scripts
 
-For working **on** this repository (see [AGENTS.md](../AGENTS.md) for the full
-contributor/agent guide):
+For working **on** the TypeScript package — run these from the `ts/` directory
+(see [AGENTS.md](../AGENTS.md) for the full contributor/agent guide, including
+the Go module and the root `Makefile` that builds and tests both):
 
 | Script | What it does |
 |--------|--------------|
@@ -602,7 +603,7 @@ contributor/agent guide):
 
 > Always `build` before `test`: tests run against compiled output in
 > `dist-test/`, importing the compiled library from `dist/`. Run these scripts
-> from the repository root.
+> from the `ts/` directory.
 
 
 ## Troubleshooting
diff --git a/go/README.md b/go/README.md
new file mode 100644
index 0000000..c33b384
--- /dev/null
+++ b/go/README.md
@@ -0,0 +1,72 @@
+# @voxgig/model (Go)
+
+A Go port of [@voxgig/model](https://github.com/voxgig/model): unify `.jsonic`
+source into a single model (via [aontu](https://github.com/rjrodger/aontu)) and
+run generator "actions" over it, once or in a rebuild-on-change watch loop. The
+TypeScript implementation in [`../ts`](../ts) is canonical; this module is kept
+in architectural parity.
+
+```bash
+go get github.com/voxgig/model/go
+```
+
+## Usage
+
+```go
+package main
+
+import (
+	"fmt"
+
+	model "github.com/voxgig/model/go"
+)
+
+func main() {
+	m := model.New(model.ModelSpec{
+		Path: "model/model.jsonic",
+		Base: "model",
+		Actions: map[string]model.ActionDef{
+			"summary": {Run: func(mod map[string]any, b *model.Build, ctx *model.BuildContext) model.ActionResult {
+				fmt.Printf("model has %d top-level keys\n", len(mod))
+				return model.ActionResult{OK: true}
+			}},
+		},
+	})
+
+	br := m.Run() // or m.Start() to watch, then m.Stop()
+	if !br.OK {
+		for _, e := range br.Errs {
+			fmt.Println("ERROR:", e)
+		}
+	}
+}
+```
+
+`model.New(...).Run()` resolves the model (applying aontu defaults, types and
+`@"..."` imports), writes `<base>/<name>.json`, then runs the registered
+actions whose step matches each build phase.
+
+## Differences from the TypeScript version
+
+This port mirrors the architecture — the build lifecycle (pre → reload →
+post), producers, dryrun, and watch semantics — but adapts a few mechanisms to
+Go:
+
+- **Actions are registered programmatically** (`ModelSpec.Actions`) instead of
+  being loaded from a config file: Go cannot `require()` code at runtime.
+- **Watching polls modification times** instead of using chokidar.
+- **Imports** resolve relative to the model base directory; the resolver
+  briefly changes the working directory because the Go aontu `Generate(src)`
+  API takes no base parameter.
+- **JSON object keys are emitted in sorted order** (Go's `encoding/json`),
+  where TypeScript preserves insertion order. The content is otherwise the
+  same.
+
+## CLI
+
+```bash
+go run github.com/voxgig/model/go/cmd/voxgig-model -w model/model.jsonic
+```
+
+Flags: `-w` watch, `-y` dryrun, `-g <level>` log level. The CLI writes the
+model JSON; for custom actions, embed the package and register them.
diff --git a/go/build.go b/go/build.go
new file mode 100644
index 0000000..66a06e9
--- /dev/null
+++ b/go/build.go
@@ -0,0 +1,251 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import (
+	"fmt"
+	"os"
+	"sync"
+
+	aontu "github.com/rjrodger/aontu/go"
+)
+
+// Resolver turns model source text into a unified model. The default
+// implementation uses the aontu CUE engine; callers may supply their own
+// (for example to unify from a non-file source, or in tests).
+type Resolver interface {
+	Resolve(src string) (model map[string]any, errs []error)
+}
+
+// chdirMu serializes the working-directory changes AontuResolver needs to
+// resolve @"..." imports relative to a model's base directory.
+var chdirMu sync.Mutex
+
+// AontuResolver resolves source with the aontu engine. The Go aontu API has
+// no base-directory parameter, so imports are resolved relative to Base by
+// briefly changing the working directory (serialized across builds).
+type AontuResolver struct {
+	Base string
+}
+
+// Resolve implements Resolver.
+func (r AontuResolver) Resolve(src string) (map[string]any, []error) {
+	chdirMu.Lock()
+	defer chdirMu.Unlock()
+
+	if r.Base != "" {
+		if prev, err := os.Getwd(); err == nil {
+			if cerr := os.Chdir(r.Base); cerr == nil {
+				defer func() { _ = os.Chdir(prev) }()
+			}
+		}
+	}
+
+	out, err := aontu.New().Generate(src)
+	if err != nil {
+		return nil, []error{err}
+	}
+	if out == nil {
+		return map[string]any{}, nil
+	}
+	m, ok := out.(map[string]any)
+	if !ok {
+		return nil, []error{fmt.Errorf("model did not resolve to an object (got %T)", out)}
+	}
+	return m, nil
+}
+
+// Build resolves a model and runs a producer pipeline over it.
+type Build struct {
+	ID     string
+	Path   string
+	Base   string
+	Model  map[string]any
+	Args   map[string]any
+	Dryrun bool
+	FS     FS
+	Log    Log
+	Use    map[string]any
+	Errs   []error
+	Ctx    BuildContext
+
+	spec     BuildSpec
+	pdef     []ProducerDef
+	resolver Resolver
+	cacheSig map[string]int64
+}
+
+var (
+	buildSeq   int64
+	buildSeqMu sync.Mutex
+)
+
+// NewBuild creates a Build from a spec, filling in defaults (an os- or
+// dryrun-backed FS, a no-op logger, and the aontu resolver).
+func NewBuild(spec BuildSpec) *Build {
+	buildSeqMu.Lock()
+	buildSeq++
+	id := buildSeq
+	buildSeqMu.Unlock()
+
+	fs := spec.FS
+	if fs == nil {
+		if spec.Dryrun {
+			fs = newDryFS()
+		} else {
+			fs = OSFS{}
+		}
+	}
+	log := spec.Log
+	if log == nil {
+		log = NopLog{}
+	}
+	resolver := spec.Resolver
+	if resolver == nil {
+		resolver = AontuResolver{Base: spec.Base}
+	}
+
+	return &Build{
+		ID:       fmt.Sprintf("%06d", id),
+		Path:     spec.Path,
+		Base:     spec.Base,
+		Args:     spec.Args,
+		Dryrun:   spec.Dryrun,
+		FS:       fs,
+		Log:      log,
+		Use:      map[string]any{},
+		spec:     spec,
+		pdef:     spec.Res,
+		resolver: resolver,
+	}
+}
+
+// Run performs one build: resolve the model, run the producer pipeline in
+// the pre phase, re-resolve if a producer requested a reload, then run the
+// pipeline in the post phase. Per-run error state is reset so a reused Build
+// does not carry failures between runs.
+func (b *Build) Run(watch bool) *BuildResult {
+	b.Errs = nil
+	b.Ctx = BuildContext{Step: StepPre, Watch: watch, State: map[string]any{}}
+
+	runlog := []string{}
+	var plog []ProducerResult
+	hasErr := false
+
+	runlog = append(runlog, "model:initial")
+	if b.resolveModel() {
+		hasErr = true
+	}
+
+	forceReload := false
+	if !hasErr {
+		for _, pd := range b.pdef {
+			pr := b.runProducer(pd)
+			plog = append(plog, pr)
+			forceReload = forceReload || pr.Reload
+			runlog = append(runlog, "producer:pre:"+pr.Name)
+			if !pr.OK {
+				hasErr = true
+				break
+			}
+		}
+	}
+
+	if forceReload && !hasErr {
+		runlog = append(runlog, "model:full")
+		if b.resolveModel() {
+			hasErr = true
+		}
+	}
+
+	if !hasErr {
+		b.Ctx.Step = StepPost
+		for _, pd := range b.pdef {
+			pr := b.runProducer(pd)
+			plog = append(plog, pr)
+			runlog = append(runlog, "producer:post:"+pr.Name)
+			if !pr.OK {
+				hasErr = true
+				break
+			}
+		}
+	}
+
+	return &BuildResult{
+		OK:        !hasErr,
+		Errs:      b.Errs,
+		Runlog:    runlog,
+		Producers: plog,
+		build:     b,
+	}
+}
+
+// runProducer runs a producer, converting a panic into a failed result so a
+// single misbehaving producer cannot crash the build.
+func (b *Build) runProducer(pd ProducerDef) (pr ProducerResult) {
+	defer func() {
+		if r := recover(); r != nil {
+			err, ok := r.(error)
+			if !ok {
+				err = fmt.Errorf("%v", r)
+			}
+			b.Errs = append(b.Errs, err)
+			pr = ProducerResult{OK: false, Step: b.Ctx.Step, Errs: []error{err}}
+		}
+	}()
+	pr = pd.Build(b, &b.Ctx)
+	if !pr.OK && len(pr.Errs) > 0 {
+		b.Errs = append(b.Errs, pr.Errs...)
+	}
+	return pr
+}
+
+// resolveModel reads and unifies the root model. A successful result is
+// cached by the root file's modification time and reused while unchanged.
+//
+// Note: the Go aontu engine does not report the imports it followed, so the
+// cache tracks only the root file. Watchers call InvalidateCache when any
+// watched source changes, so imported-file edits still rebuild.
+func (b *Build) resolveModel() (hasErr bool) {
+	if b.Model != nil && b.cacheSig != nil && b.cacheHit() {
+		return false
+	}
+
+	src, err := b.FS.ReadFile(b.Path)
+	if err != nil {
+		b.Errs = append(b.Errs, err)
+		b.cacheSig = nil
+		return true
+	}
+
+	model, errs := b.resolver.Resolve(string(src))
+	if len(errs) > 0 {
+		b.Errs = append(b.Errs, errs...)
+		b.cacheSig = nil
+		return true
+	}
+
+	b.Model = model
+	b.cacheSig = map[string]int64{b.Path: mtime(b.FS, b.Path)}
+	return false
+}
+
+// InvalidateCache forces the next resolveModel to re-read and re-unify.
+func (b *Build) InvalidateCache() { b.cacheSig = nil }
+
+func (b *Build) cacheHit() bool {
+	for path, prev := range b.cacheSig {
+		if mtime(b.FS, path) != prev {
+			return false
+		}
+	}
+	return true
+}
+
+func mtime(fs FS, path string) int64 {
+	info, err := fs.Stat(path)
+	if err != nil {
+		return -1
+	}
+	return info.ModTime().UnixNano()
+}
diff --git a/go/build_test.go b/go/build_test.go
new file mode 100644
index 0000000..65e34f6
--- /dev/null
+++ b/go/build_test.go
@@ -0,0 +1,87 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// A happy build resolves the model and exposes it to producers, with aontu
+// applying defaults and types (port defaults to 8080 as an integer).
+func TestRunHappy(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "service: { name: 'orders', port: *8080 | integer }\n")
+
+	var seen map[string]any
+	spec := BuildSpec{
+		Path: filepath.Join(dir, "m.jsonic"),
+		Base: dir,
+		Res: []ProducerDef{
+			{Path: "/", Build: func(b *Build, ctx *BuildContext) ProducerResult {
+				if ctx.Step == StepPost {
+					seen = b.Model
+				}
+				return ProducerResult{OK: true, Name: "capture", Step: ctx.Step, Active: true}
+			}},
+		},
+	}
+
+	br := NewBuild(spec).Run(false)
+	if !br.OK {
+		t.Fatalf("build failed: %v", br.Errs)
+	}
+	svc, _ := seen["service"].(map[string]any)
+	if svc["name"] != "orders" {
+		t.Fatalf("name = %#v", svc["name"])
+	}
+	if svc["port"] != int64(8080) {
+		t.Fatalf("port = %#v", svc["port"])
+	}
+}
+
+// A failed build must not stick to the next run on a reused Build.
+func TestErrorRecovery(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "m.jsonic")
+	writeFile(t, dir, "m.jsonic", "x: 1\nx: 2\n")
+
+	b := NewBuild(BuildSpec{Path: path, Base: dir})
+
+	bad := b.Run(false)
+	if bad.OK {
+		t.Fatal("expected failure on conflicting values")
+	}
+	if len(bad.Errs) == 0 {
+		t.Fatal("expected errors")
+	}
+
+	writeFile(t, dir, "m.jsonic", "x: 1\n")
+	good := b.Run(false)
+	if !good.OK {
+		t.Fatalf("expected recovery after fix: %v", good.Errs)
+	}
+	if len(good.Errs) != 0 {
+		t.Fatalf("errors leaked across runs: %v", good.Errs)
+	}
+}
+
+// A dryrun build runs fully but writes nothing to disk.
+func TestDryrunWritesNothing(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "m.jsonic")
+	writeFile(t, dir, "m.jsonic", "a: 1\n")
+
+	b := NewBuild(BuildSpec{
+		Path: path, Base: dir, Dryrun: true,
+		Res: []ProducerDef{{Path: "/", Build: ModelProducer}},
+	})
+	br := b.Run(false)
+	if !br.OK {
+		t.Fatalf("dryrun build failed: %v", br.Errs)
+	}
+	if _, err := os.Stat(filepath.Join(dir, "m.json")); !os.IsNotExist(err) {
+		t.Fatal("dryrun wrote m.json to disk")
+	}
+}
diff --git a/go/cmd/voxgig-model/main.go b/go/cmd/voxgig-model/main.go
new file mode 100644
index 0000000..21dffb5
--- /dev/null
+++ b/go/cmd/voxgig-model/main.go
@@ -0,0 +1,78 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+// Command voxgig-model unifies a .jsonic model and writes the resulting
+// model JSON. It mirrors the core of the TypeScript CLI. Custom build
+// actions — which the TypeScript CLI loads dynamically from a config file —
+// are not available here, because Go cannot load code at runtime; embed the
+// model package and register actions programmatically to use them.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"os/signal"
+	"path/filepath"
+	"syscall"
+
+	model "github.com/voxgig/model/go"
+)
+
+func main() {
+	watch := flag.Bool("w", false, "watch and rebuild on change")
+	dryrun := flag.Bool("y", false, "dry run (write nothing to disk)")
+	level := flag.String("g", "info", "log level: trace|debug|info|warn|error|silent")
+	flag.Usage = func() {
+		fmt.Fprintln(os.Stderr, "usage: voxgig-model [-w] [-y] [-g level] <root-file>")
+		flag.PrintDefaults()
+	}
+	flag.Parse()
+
+	path := flag.Arg(0)
+	if path == "" {
+		flag.Usage()
+		os.Exit(1)
+	}
+
+	abs, err := filepath.Abs(path)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "ERROR:", err)
+		os.Exit(1)
+	}
+	if _, serr := os.Stat(abs); serr != nil {
+		fmt.Fprintln(os.Stderr, "ERROR: model file does not exist:", path)
+		os.Exit(1)
+	}
+
+	m := model.New(model.ModelSpec{
+		Path:   abs,
+		Base:   filepath.Dir(abs),
+		Dryrun: *dryrun,
+		Log:    model.NewLog(*level),
+	})
+
+	if *watch {
+		br := m.Start()
+		reportErrs(br)
+		sig := make(chan os.Signal, 1)
+		signal.Notify(sig, os.Interrupt, syscall.SIGTERM)
+		<-sig
+		m.Stop()
+		return
+	}
+
+	br := m.Run()
+	if !br.OK {
+		reportErrs(br)
+		os.Exit(1)
+	}
+}
+
+func reportErrs(br *model.BuildResult) {
+	if br == nil {
+		return
+	}
+	for _, e := range br.Errs {
+		fmt.Fprintln(os.Stderr, "ERROR:", e)
+	}
+}
diff --git a/go/fs.go b/go/fs.go
new file mode 100644
index 0000000..ab05bba
--- /dev/null
+++ b/go/fs.go
@@ -0,0 +1,68 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import (
+	"os"
+	"path/filepath"
+	"sync"
+)
+
+// FS is the filesystem seam used by builds, producers and actions. Writing
+// through it (rather than the os package directly) lets a dryrun build
+// redirect writes away from disk. It mirrors the role of the swappable fs in
+// the TypeScript implementation.
+type FS interface {
+	ReadFile(name string) ([]byte, error)
+	WriteFile(name string, data []byte, perm os.FileMode) error
+	MkdirAll(path string, perm os.FileMode) error
+	Stat(name string) (os.FileInfo, error)
+}
+
+// OSFS is the real, disk-backed filesystem.
+type OSFS struct{}
+
+// ReadFile reads a file from disk.
+func (OSFS) ReadFile(name string) ([]byte, error) { return os.ReadFile(name) }
+
+// WriteFile writes a file to disk.
+func (OSFS) WriteFile(name string, data []byte, perm os.FileMode) error {
+	return os.WriteFile(name, data, perm)
+}
+
+// MkdirAll creates a directory and any parents.
+func (OSFS) MkdirAll(path string, perm os.FileMode) error { return os.MkdirAll(path, perm) }
+
+// Stat returns file info from disk.
+func (OSFS) Stat(name string) (os.FileInfo, error) { return os.Stat(name) }
+
+// dryFS reads from the real filesystem but keeps writes in memory, so a
+// dryrun build runs normally without touching disk.
+type dryFS struct {
+	mu  sync.Mutex
+	mem map[string][]byte
+}
+
+func newDryFS() *dryFS { return &dryFS{mem: map[string][]byte{}} }
+
+func (d *dryFS) ReadFile(name string) ([]byte, error) {
+	key := filepath.Clean(name)
+	d.mu.Lock()
+	data, ok := d.mem[key]
+	d.mu.Unlock()
+	if ok {
+		return append([]byte(nil), data...), nil
+	}
+	return os.ReadFile(name)
+}
+
+func (d *dryFS) WriteFile(name string, data []byte, _ os.FileMode) error {
+	d.mu.Lock()
+	d.mem[filepath.Clean(name)] = append([]byte(nil), data...)
+	d.mu.Unlock()
+	return nil
+}
+
+func (d *dryFS) MkdirAll(string, os.FileMode) error { return nil }
+
+func (d *dryFS) Stat(name string) (os.FileInfo, error) { return os.Stat(name) }
diff --git a/go/go.mod b/go/go.mod
new file mode 100644
index 0000000..cc8f74c
--- /dev/null
+++ b/go/go.mod
@@ -0,0 +1,13 @@
+module github.com/voxgig/model/go
+
+go 1.24.7
+
+require github.com/rjrodger/aontu/go v0.1.2
+
+require (
+	github.com/jsonicjs/directive/go v0.1.4 // indirect
+	github.com/jsonicjs/expr/go v0.1.3 // indirect
+	github.com/jsonicjs/jsonic/go v0.1.22 // indirect
+	github.com/jsonicjs/multisource/go v0.1.4 // indirect
+	github.com/jsonicjs/path/go v0.1.2 // indirect
+)
diff --git a/go/go.sum b/go/go.sum
new file mode 100644
index 0000000..ccc88e4
--- /dev/null
+++ b/go/go.sum
@@ -0,0 +1,12 @@
+github.com/jsonicjs/directive/go v0.1.4 h1:K7ai2ccoh8d23mjCK8/YMjEDbzb6+jWcepOL3YubpKo=
+github.com/jsonicjs/directive/go v0.1.4/go.mod h1:PMjJ3EulIhdo1R0o9bOUvSUOTCPvM/xCzo1O35VBiXs=
+github.com/jsonicjs/expr/go v0.1.3 h1:D7x+5AIM/CLX6A6VUiHBzfvRxufuGzXYB6gmPb1lv+A=
+github.com/jsonicjs/expr/go v0.1.3/go.mod h1:6kmd1o4p4/FL4DVuCxwYAqX5YRYjF20hbIrHQM81Qoc=
+github.com/jsonicjs/jsonic/go v0.1.22 h1:sam238fTyjDq0nby9TYS+aCCHprLl91ArQPWLCg2O0Y=
+github.com/jsonicjs/jsonic/go v0.1.22/go.mod h1:ObNKlCG7esWoi4AHCpdgkILvPINV8bpvkbCd4llGGUg=
+github.com/jsonicjs/multisource/go v0.1.4 h1:vTfr1pHNuKV6XBSErZpi2fA4SjVvX5DfoQs7nEoQzko=
+github.com/jsonicjs/multisource/go v0.1.4/go.mod h1:XzgM6nuW2MOAsVySsGtpp7fWSx9PTCXd4eIRSCAA/6o=
+github.com/jsonicjs/path/go v0.1.2 h1:Pk7PZIiRq64iodssEVtaJw+4jHiJe84aFtmKDUasXAo=
+github.com/jsonicjs/path/go v0.1.2/go.mod h1:ffXuSMg950pdfU3wapeK6QnyvZrV5yHFSj4ifwmsgmU=
+github.com/rjrodger/aontu/go v0.1.2 h1:vTStp1UIbTxGovcPH+29FwZ3eNwzaJUMV8PXEtz6Lmk=
+github.com/rjrodger/aontu/go v0.1.2/go.mod h1:Ejv19nAWPMFlzqc1rdkvIEjh1dihKf8S2uiGigyQyYE=
diff --git a/go/log.go b/go/log.go
new file mode 100644
index 0000000..7ac4a94
--- /dev/null
+++ b/go/log.go
@@ -0,0 +1,79 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+)
+
+// Log is a minimal leveled logger. Each entry carries a short point (event
+// name) and a human-readable note. It stands in for the pino logger used by
+// the TypeScript implementation.
+type Log interface {
+	Info(point, note string)
+	Debug(point, note string)
+	Error(point string, err error, note string)
+}
+
+const (
+	levelDebug = iota
+	levelInfo
+	levelError
+	levelSilent
+)
+
+// NewLog returns a Log writing to stderr at the given level: "debug",
+// "info" (the default), "error", or "silent".
+func NewLog(level string) Log {
+	return &stdLog{level: parseLevel(level), w: os.Stderr}
+}
+
+func parseLevel(level string) int {
+	switch strings.ToLower(level) {
+	case "debug", "trace":
+		return levelDebug
+	case "warn", "error", "fatal":
+		return levelError
+	case "silent":
+		return levelSilent
+	default:
+		return levelInfo
+	}
+}
+
+type stdLog struct {
+	level int
+	w     io.Writer
+}
+
+func (l *stdLog) Info(point, note string)  { l.emit(levelInfo, "INFO", point, note) }
+func (l *stdLog) Debug(point, note string) { l.emit(levelDebug, "DEBUG", point, note) }
+
+func (l *stdLog) Error(point string, err error, note string) {
+	if err != nil {
+		note = strings.TrimSpace(note + " " + err.Error())
+	}
+	l.emit(levelError, "ERROR", point, note)
+}
+
+func (l *stdLog) emit(level int, label, point, note string) {
+	if level < l.level {
+		return
+	}
+	fmt.Fprintf(l.w, "%-5s %-18s %s\n", label, point, note)
+}
+
+// NopLog discards all log entries.
+type NopLog struct{}
+
+// Info discards the entry.
+func (NopLog) Info(string, string) {}
+
+// Debug discards the entry.
+func (NopLog) Debug(string, string) {}
+
+// Error discards the entry.
+func (NopLog) Error(string, error, string) {}
diff --git a/go/model.go b/go/model.go
new file mode 100644
index 0000000..cf111c0
--- /dev/null
+++ b/go/model.go
@@ -0,0 +1,87 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+// Package model is a Go port of @voxgig/model. It unifies .jsonic source
+// into a single model (via the aontu engine) and runs generator "actions"
+// over it, once or in a rebuild-on-change watch loop.
+//
+// The TypeScript implementation in ts/ is canonical; this package is kept in
+// architectural parity. Two mechanisms differ by necessity: actions are
+// registered programmatically (Go cannot require() code at runtime), and
+// watching polls modification times (rather than using chokidar).
+package model
+
+import (
+	"path/filepath"
+	"time"
+)
+
+// Version is the released version of the Go module. It is rewritten by
+// `make publish-go V=x.y.z` to match the git tag (go/vx.y.z).
+const Version = "0.1.0"
+
+// DefaultIdle is the default watch debounce period.
+const DefaultIdle = 111 * time.Millisecond
+
+// Model unifies a .jsonic model and runs producers (the model writer and any
+// registered actions) over it. It can build once or watch and rebuild.
+type Model struct {
+	build *Build
+	watch *Watch
+	log   Log
+}
+
+// New creates a Model from a spec.
+func New(spec ModelSpec) *Model {
+	log := spec.Log
+	if log == nil {
+		log = NopLog{}
+	}
+
+	base := spec.Base
+	if base == "" && spec.Path != "" {
+		base = filepath.Dir(spec.Path)
+	}
+
+	idle := spec.Idle
+	if idle <= 0 {
+		idle = DefaultIdle
+	}
+
+	bspec := BuildSpec{
+		Name:     "model",
+		Path:     spec.Path,
+		Base:     base,
+		Args:     spec.Args,
+		Dryrun:   spec.Dryrun,
+		Resolver: spec.Resolver,
+		Actions:  spec.Actions,
+		Order:    spec.Order,
+		Idle:     idle,
+		Watch:    spec.Watch,
+		Log:      log,
+		Res: []ProducerDef{
+			{Path: "/", Build: ModelProducer},
+			{Path: "/", Build: LocalProducer},
+		},
+	}
+
+	build := NewBuild(bspec)
+	return &Model{
+		build: build,
+		watch: NewWatch(build, "model", idle),
+		log:   log,
+	}
+}
+
+// Run builds the model once and returns the result.
+func (m *Model) Run() *BuildResult { return m.watch.Run(false) }
+
+// Start builds once, then watches and rebuilds until Stop is called. It
+// returns the initial build result.
+func (m *Model) Start() *BuildResult { return m.watch.Start() }
+
+// Stop ends watching and releases the watcher.
+func (m *Model) Stop() { m.watch.Stop() }
+
+// Build returns the underlying Build (valid after Run or Start).
+func (m *Model) Build() *Build { return m.build }
diff --git a/go/model_test.go b/go/model_test.go
new file mode 100644
index 0000000..9b29b95
--- /dev/null
+++ b/go/model_test.go
@@ -0,0 +1,108 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+)
+
+func writeFile(t *testing.T, dir, name, content string) {
+	t.Helper()
+	if err := os.WriteFile(filepath.Join(dir, name), []byte(content), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func containsErr(errs []error, sub string) bool {
+	for _, e := range errs {
+		if strings.Contains(e.Error(), sub) {
+			return true
+		}
+	}
+	return false
+}
+
+// End-to-end: New().Run() unifies the model, writes the JSON, and runs a
+// registered action that sees the resolved model.
+func TestModelRun(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "service: { name: 'orders', port: *8080 | integer }\n")
+
+	var saw string
+	m := New(ModelSpec{
+		Path: filepath.Join(dir, "m.jsonic"),
+		Base: dir,
+		Actions: map[string]ActionDef{
+			"env": {Run: func(model map[string]any, b *Build, ctx *BuildContext) ActionResult {
+				svc := model["service"].(map[string]any)
+				saw = fmt.Sprintf("PORT=%v", svc["port"])
+				return ActionResult{OK: true}
+			}},
+		},
+	})
+	br := m.Run()
+	if !br.OK {
+		t.Fatalf("model run failed: %v", br.Errs)
+	}
+	if saw != "PORT=8080" {
+		t.Fatalf("action saw %q", saw)
+	}
+	if _, err := os.Stat(filepath.Join(dir, "m.json")); err != nil {
+		t.Fatalf("model JSON not written: %v", err)
+	}
+}
+
+// Watch mode rebuilds when an imported source file changes.
+func TestWatchRebuild(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "val: @\"./zed.jsonic\"\n")
+	writeFile(t, dir, "zed.jsonic", "2")
+
+	var mu sync.Mutex
+	var last any
+	m := New(ModelSpec{
+		Path: filepath.Join(dir, "m.jsonic"),
+		Base: dir,
+		Idle: 60 * time.Millisecond,
+		Actions: map[string]ActionDef{
+			"capture": {Step: StepPost, Run: func(model map[string]any, b *Build, ctx *BuildContext) ActionResult {
+				mu.Lock()
+				last = model["val"]
+				mu.Unlock()
+				return ActionResult{OK: true}
+			}},
+		},
+	})
+
+	br := m.Start()
+	defer m.Stop()
+	if !br.OK {
+		t.Fatalf("initial build failed: %v", br.Errs)
+	}
+
+	read := func() any { mu.Lock(); defer mu.Unlock(); return last }
+	if read() != int64(2) {
+		t.Fatalf("initial val = %#v", read())
+	}
+
+	// Let the watcher settle, then change the imported file.
+	time.Sleep(120 * time.Millisecond)
+	writeFile(t, dir, "zed.jsonic", "7")
+
+	deadline := time.Now().Add(4 * time.Second)
+	for time.Now().Before(deadline) {
+		if read() == int64(7) {
+			break
+		}
+		time.Sleep(30 * time.Millisecond)
+	}
+	if read() != int64(7) {
+		t.Fatalf("after change val = %#v", read())
+	}
+}
diff --git a/go/producer.go b/go/producer.go
new file mode 100644
index 0000000..8a5b11f
--- /dev/null
+++ b/go/producer.go
@@ -0,0 +1,107 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+// ModelProducer writes the unified model to <base>/<root-name>.json. It runs
+// in the post phase only, and skips the write when the output is byte-for-byte
+// unchanged (avoiding mtime churn that would re-trigger watchers).
+//
+// Go's encoding/json emits object keys in sorted order, where the TypeScript
+// implementation preserves insertion order; the JSON content is otherwise
+// equivalent. This is a known, accepted cross-language difference.
+func ModelProducer(b *Build, ctx *BuildContext) ProducerResult {
+	pr := ProducerResult{OK: true, Name: "model", Step: ctx.Step, Active: true}
+	if ctx.Step != StepPost {
+		return pr
+	}
+
+	data, err := json.MarshalIndent(b.Model, "", "  ")
+	if err != nil {
+		return fail("model", ctx.Step, err)
+	}
+
+	name := filepath.Base(b.Path)
+	if ext := filepath.Ext(name); ext != "" {
+		name = strings.TrimSuffix(name, ext)
+	}
+	file := filepath.Join(b.Base, name+".json")
+
+	if existing, rerr := b.FS.ReadFile(file); rerr == nil && bytes.Equal(existing, data) {
+		b.Log.Debug("write-model-skip", file+" (unchanged)")
+		return pr
+	}
+
+	if merr := b.FS.MkdirAll(filepath.Dir(file), 0o755); merr != nil {
+		return fail("model", ctx.Step, merr)
+	}
+	if werr := b.FS.WriteFile(file, data, 0o644); werr != nil {
+		return fail("model", ctx.Step, werr)
+	}
+	b.Log.Info("write-model", file)
+	return pr
+}
+
+// LocalProducer runs the registered actions whose step matches the current
+// phase, in the configured order (or sorted action names when no order is
+// given). An order entry naming an unregistered action fails the build.
+func LocalProducer(b *Build, ctx *BuildContext) ProducerResult {
+	pr := ProducerResult{OK: true, Name: "local", Step: ctx.Step, Active: true}
+
+	order := b.spec.Order
+	if len(order) == 0 {
+		for name := range b.spec.Actions {
+			order = append(order, name)
+		}
+		sort.Strings(order)
+	}
+
+	var ran []string
+	for _, name := range order {
+		def, ok := b.spec.Actions[name]
+		if !ok {
+			pr.OK = false
+			pr.Errs = append(pr.Errs,
+				fmt.Errorf("unknown model action %q referenced in order", name))
+			return pr
+		}
+
+		step := def.Step
+		if step == "" {
+			step = StepPost
+		}
+		if step != ctx.Step && step != StepAll {
+			continue
+		}
+		if def.Run == nil {
+			pr.OK = false
+			pr.Errs = append(pr.Errs, fmt.Errorf("model action %q has no Run function", name))
+			return pr
+		}
+
+		res := def.Run(b.Model, b, ctx)
+		ran = append(ran, name)
+		if res.Reload {
+			pr.Reload = true
+		}
+		if !res.OK {
+			pr.OK = false
+			break
+		}
+	}
+
+	b.Log.Info(string(ctx.Step)+"-actions", strings.Join(ran, ";"))
+	return pr
+}
+
+func fail(name string, step Step, err error) ProducerResult {
+	return ProducerResult{Name: name, Step: step, Active: true, OK: false, Errs: []error{err}}
+}
diff --git a/go/producer_test.go b/go/producer_test.go
new file mode 100644
index 0000000..3115ada
--- /dev/null
+++ b/go/producer_test.go
@@ -0,0 +1,102 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+// ModelProducer writes the model JSON and skips the write when unchanged.
+func TestModelProducerWritesAndSkips(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "m.jsonic")
+	writeFile(t, dir, "m.jsonic", "a: 1\nb: 2\n")
+
+	build := func() *Build {
+		return NewBuild(BuildSpec{Path: path, Base: dir,
+			Res: []ProducerDef{{Path: "/", Build: ModelProducer}}})
+	}
+
+	if br := build().Run(false); !br.OK {
+		t.Fatalf("build failed: %v", br.Errs)
+	}
+	out := filepath.Join(dir, "m.json")
+	data, err := os.ReadFile(out)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var got map[string]any
+	if err := json.Unmarshal(data, &got); err != nil {
+		t.Fatal(err)
+	}
+	if got["a"] != float64(1) || got["b"] != float64(2) {
+		t.Fatalf("unexpected model.json: %s", data)
+	}
+
+	info1, _ := os.Stat(out)
+	time.Sleep(15 * time.Millisecond)
+	if br := build().Run(false); !br.OK {
+		t.Fatalf("second build failed: %v", br.Errs)
+	}
+	info2, _ := os.Stat(out)
+	if !info1.ModTime().Equal(info2.ModTime()) {
+		t.Fatal("model.json rewritten despite unchanged content")
+	}
+}
+
+// Actions run in the configured order.
+func TestLocalProducerOrder(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "m.jsonic")
+	writeFile(t, dir, "m.jsonic", "x: 1\n")
+
+	var order []string
+	mk := func(name string) ActionDef {
+		return ActionDef{Run: func(model map[string]any, b *Build, ctx *BuildContext) ActionResult {
+			order = append(order, name)
+			return ActionResult{OK: true}
+		}}
+	}
+	b := NewBuild(BuildSpec{
+		Path: path, Base: dir,
+		Actions: map[string]ActionDef{"a": mk("a"), "b": mk("b"), "c": mk("c")},
+		Order:   []string{"c", "a", "b"},
+		Res:     []ProducerDef{{Path: "/", Build: LocalProducer}},
+	})
+	if br := b.Run(false); !br.OK {
+		t.Fatalf("build failed: %v", br.Errs)
+	}
+	if strings.Join(order, ",") != "c,a,b" {
+		t.Fatalf("action order = %v", order)
+	}
+}
+
+// An order entry naming an unregistered action fails clearly.
+func TestUnknownAction(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "m.jsonic")
+	writeFile(t, dir, "m.jsonic", "x: 1\n")
+
+	b := NewBuild(BuildSpec{
+		Path: path, Base: dir,
+		Actions: map[string]ActionDef{
+			"real": {Run: func(map[string]any, *Build, *BuildContext) ActionResult {
+				return ActionResult{OK: true}
+			}},
+		},
+		Order: []string{"real", "ghost"},
+		Res:   []ProducerDef{{Path: "/", Build: LocalProducer}},
+	})
+	br := b.Run(false)
+	if br.OK {
+		t.Fatal("expected failure for unknown action")
+	}
+	if !containsErr(br.Errs, "ghost") {
+		t.Fatalf("errors = %v", br.Errs)
+	}
+}
diff --git a/go/types.go b/go/types.go
new file mode 100644
index 0000000..d000d80
--- /dev/null
+++ b/go/types.go
@@ -0,0 +1,119 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import "time"
+
+// Step is a build phase.
+type Step string
+
+const (
+	// StepPre runs before the model is finalized.
+	StepPre Step = "pre"
+	// StepPost runs after the model is finalized.
+	StepPost Step = "post"
+	// StepAll runs in both phases.
+	StepAll Step = "all"
+)
+
+// BuildContext carries the current phase and shared state through one build.
+type BuildContext struct {
+	Step  Step
+	Watch bool
+	State map[string]any
+}
+
+// ProducerResult is what a producer reports for one phase.
+type ProducerResult struct {
+	OK     bool
+	Name   string
+	Step   Step
+	Active bool
+	Reload bool
+	Errs   []error
+	Runlog []string
+}
+
+// Producer transforms or emits output from the model during a build phase.
+type Producer func(b *Build, ctx *BuildContext) ProducerResult
+
+// ProducerDef pairs a producer with a (currently informational) path scope.
+type ProducerDef struct {
+	Path  string
+	Build Producer
+}
+
+// BuildResult summarizes one build.
+type BuildResult struct {
+	OK        bool
+	Errs      []error
+	Runlog    []string
+	Producers []ProducerResult
+
+	build *Build
+}
+
+// Build returns the underlying Build (may be nil for a synthesized result).
+func (r *BuildResult) Build() *Build {
+	if r == nil {
+		return nil
+	}
+	return r.build
+}
+
+// Action is a project-local generator run by LocalProducer. It receives the
+// unified model and the build, and reports whether it succeeded and whether
+// the model should be re-resolved.
+type Action func(model map[string]any, b *Build, ctx *BuildContext) ActionResult
+
+// ActionResult is what an Action reports.
+type ActionResult struct {
+	OK     bool
+	Reload bool
+}
+
+// ActionDef registers an Action to run in a given step. Unlike the
+// TypeScript port, which loads actions dynamically from a config file, Go
+// actions are registered programmatically (Go cannot load code at runtime).
+type ActionDef struct {
+	Run  Action
+	Step Step // StepPre, StepPost (the zero value defaults to post) or StepAll
+}
+
+// WatchModes selects which filesystem events trigger a rebuild.
+type WatchModes struct {
+	Mod bool
+	Add bool
+	Rem bool
+}
+
+// BuildSpec configures a Build.
+type BuildSpec struct {
+	Name     string
+	Path     string
+	Base     string
+	Res      []ProducerDef
+	Resolver Resolver
+	Args     map[string]any
+	Dryrun   bool
+	FS       FS
+	Actions  map[string]ActionDef
+	Order    []string
+	Idle     time.Duration
+	Watch    WatchModes
+	Log      Log
+}
+
+// ModelSpec configures a Model.
+type ModelSpec struct {
+	Path     string
+	Base     string
+	Args     map[string]any
+	Dryrun   bool
+	Resolver Resolver
+	Actions  map[string]ActionDef
+	Order    []string
+	Idle     time.Duration
+	Watch    WatchModes
+	Log      Log
+}
diff --git a/go/watch.go b/go/watch.go
new file mode 100644
index 0000000..fa9cb83
--- /dev/null
+++ b/go/watch.go
@@ -0,0 +1,166 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import (
+	"io/fs"
+	"os"
+	"path/filepath"
+	"sync"
+	"time"
+)
+
+// modelExts are the source extensions a watcher tracks. Generated output
+// (e.g. .json) is deliberately excluded so writing it cannot loop.
+var modelExts = map[string]bool{".jsonic": true, ".aon": true, ".aontu": true}
+
+// Watch rebuilds a Build when its source files change. It polls modification
+// times (stdlib only, no external dependency where the TypeScript port uses
+// chokidar) and debounces bursts of changes by an idle quiet period.
+type Watch struct {
+	build *Build
+	name  string
+	idle  time.Duration
+
+	mu      sync.Mutex
+	last    *BuildResult
+	sig     map[string]int64
+	stop    chan struct{}
+	done    chan struct{}
+	running bool
+}
+
+// NewWatch creates a watcher for a build. A non-positive idle defaults to
+// 111ms (matching the TypeScript default).
+func NewWatch(b *Build, name string, idle time.Duration) *Watch {
+	if idle <= 0 {
+		idle = 111 * time.Millisecond
+	}
+	if name == "" {
+		name = "model"
+	}
+	return &Watch{build: b, name: name, idle: idle}
+}
+
+// Run performs a single build and records the result.
+func (w *Watch) Run(watch bool) *BuildResult {
+	br := w.build.Run(watch)
+	w.mu.Lock()
+	w.last = br
+	w.mu.Unlock()
+	return br
+}
+
+// Last returns the most recent build result.
+func (w *Watch) Last() *BuildResult {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	return w.last
+}
+
+// Start runs an initial build, then watches the model's base directory and
+// rebuilds after each quiet period. Call Stop to release it.
+func (w *Watch) Start() *BuildResult {
+	br := w.Run(true)
+
+	w.mu.Lock()
+	w.sig = w.snapshot()
+	w.stop = make(chan struct{})
+	w.done = make(chan struct{})
+	w.running = true
+	w.mu.Unlock()
+
+	go w.loop()
+	return br
+}
+
+// Stop ends watching and waits for the watch loop to exit.
+func (w *Watch) Stop() {
+	w.mu.Lock()
+	running := w.running
+	w.running = false
+	stop := w.stop
+	done := w.done
+	w.mu.Unlock()
+	if !running {
+		return
+	}
+	close(stop)
+	<-done
+}
+
+func (w *Watch) loop() {
+	defer close(w.done)
+
+	tick := w.idle / 2
+	if tick <= 0 {
+		tick = 50 * time.Millisecond
+	}
+	t := time.NewTicker(tick)
+	defer t.Stop()
+
+	var changedAt time.Time
+	for {
+		select {
+		case <-w.stop:
+			return
+		case <-t.C:
+			now := w.snapshot()
+
+			w.mu.Lock()
+			prev := w.sig
+			w.mu.Unlock()
+
+			if !sameSig(now, prev) {
+				w.mu.Lock()
+				w.sig = now
+				w.mu.Unlock()
+				changedAt = time.Now()
+				continue
+			}
+
+			if !changedAt.IsZero() && time.Since(changedAt) >= w.idle {
+				changedAt = time.Time{}
+				w.build.InvalidateCache()
+				w.Run(true)
+				w.mu.Lock()
+				w.sig = w.snapshot()
+				w.mu.Unlock()
+			}
+		}
+	}
+}
+
+// snapshot records the modification times of model source files under the
+// build's base directory.
+func (w *Watch) snapshot() map[string]int64 {
+	sig := map[string]int64{}
+	base := w.build.Base
+	if base == "" {
+		base = filepath.Dir(w.build.Path)
+	}
+	_ = filepath.WalkDir(base, func(path string, d fs.DirEntry, err error) error {
+		if err != nil || d.IsDir() {
+			return nil
+		}
+		if modelExts[filepath.Ext(path)] {
+			if info, serr := os.Stat(path); serr == nil {
+				sig[path] = info.ModTime().UnixNano()
+			}
+		}
+		return nil
+	})
+	return sig
+}
+
+func sameSig(a, b map[string]int64) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for k, v := range a {
+		if b[k] != v {
+			return false
+		}
+	}
+	return true
+}
diff --git a/bin/voxgig-model b/ts/bin/voxgig-model
similarity index 100%
rename from bin/voxgig-model
rename to ts/bin/voxgig-model
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similarity index 100%
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diff --git a/model/.model-config/model-config.json b/ts/model/.model-config/model-config.json
similarity index 100%
rename from model/.model-config/model-config.json
rename to ts/model/.model-config/model-config.json
diff --git a/model/.model-config/model-config.jsonic b/ts/model/.model-config/model-config.jsonic
similarity index 100%
rename from model/.model-config/model-config.jsonic
rename to ts/model/.model-config/model-config.jsonic
diff --git a/model/sys.json b/ts/model/sys.json
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rename to ts/model/sys.json
diff --git a/model/sys.jsonic b/ts/model/sys.jsonic
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diff --git a/package.json b/ts/package.json
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rename to ts/package.json
index 93d8b5f..a4bad04 100644
--- a/package.json
+++ b/ts/package.json
@@ -43,7 +43,7 @@
     "LICENSE"
   ],
   "dependencies": {
-    "aontu": "0.44.0",
+    "aontu": "0.45.1",
     "chokidar": "5.0.0",
     "shape": "10.1.0",
     "memfs": "4.57.6"
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similarity index 100%
rename from test/model.test.ts
rename to ts/test/model.test.ts
diff --git a/test/p01/doc.html b/ts/test/p01/doc.html
similarity index 100%
rename from test/p01/doc.html
rename to ts/test/p01/doc.html
diff --git a/test/p01/model/model.json b/ts/test/p01/model/model.json
similarity index 100%
rename from test/p01/model/model.json
rename to ts/test/p01/model/model.json
diff --git a/test/p01/model/model.jsonic b/ts/test/p01/model/model.jsonic
similarity index 100%
rename from test/p01/model/model.jsonic
rename to ts/test/p01/model/model.jsonic
diff --git a/test/p01/model/zed.jsonic b/ts/test/p01/model/zed.jsonic
similarity index 100%
rename from test/p01/model/zed.jsonic
rename to ts/test/p01/model/zed.jsonic
diff --git a/test/perf-bench.js b/ts/test/perf-bench.js
similarity index 100%
rename from test/perf-bench.js
rename to ts/test/perf-bench.js
diff --git a/test/quick.js b/ts/test/quick.js
similarity index 100%
rename from test/quick.js
rename to ts/test/quick.js
diff --git a/test/sys01/build/foo.js b/ts/test/sys01/build/foo.js
similarity index 100%
rename from test/sys01/build/foo.js
rename to ts/test/sys01/build/foo.js
diff --git a/test/sys01/build/pre.js b/ts/test/sys01/build/pre.js
similarity index 100%
rename from test/sys01/build/pre.js
rename to ts/test/sys01/build/pre.js
diff --git a/test/sys01/foo.txt b/ts/test/sys01/foo.txt
similarity index 100%
rename from test/sys01/foo.txt
rename to ts/test/sys01/foo.txt
diff --git a/test/sys01/model/.model-config/model-config.json b/ts/test/sys01/model/.model-config/model-config.json
similarity index 100%
rename from test/sys01/model/.model-config/model-config.json
rename to ts/test/sys01/model/.model-config/model-config.json
diff --git a/test/sys01/model/.model-config/model-config.jsonic b/ts/test/sys01/model/.model-config/model-config.jsonic
similarity index 100%
rename from test/sys01/model/.model-config/model-config.jsonic
rename to ts/test/sys01/model/.model-config/model-config.jsonic
diff --git a/test/sys01/model/color.jsonic b/ts/test/sys01/model/color.jsonic
similarity index 100%
rename from test/sys01/model/color.jsonic
rename to ts/test/sys01/model/color.jsonic
diff --git a/test/sys01/model/model.json b/ts/test/sys01/model/model.json
similarity index 85%
rename from test/sys01/model/model.json
rename to ts/test/sys01/model/model.json
index 314b859..cab1b47 100644
--- a/test/sys01/model/model.json
+++ b/ts/test/sys01/model/model.json
@@ -2,15 +2,18 @@
   "main": {
     "srv": {
       "foo": {
+        "in": {},
+        "out": {},
+        "deps": {},
         "api": {
           "web": {
             "active": true,
+            "path": {
+              "prefix": "/api/"
+            },
             "method": "POST",
             "cors": {
               "active": false
-            },
-            "path": {
-              "prefix": "/api/"
             }
           }
         },
@@ -20,46 +23,43 @@
             "timeout": 30,
             "handler": {
               "path": {
-                "suffix": ".handler",
-                "prefix": "src/handler/lambda/"
+                "prefix": "src/handler/lambda/",
+                "suffix": ".handler"
               }
             },
             "kind": "standard"
           }
-        },
-        "in": {},
-        "out": {},
-        "deps": {}
+        }
       },
       "bar": {
+        "in": {},
+        "out": {},
+        "deps": {},
+        "api": {
+          "web": {
+            "active": true,
+            "path": {
+              "prefix": "/api/"
+            },
+            "method": "POST",
+            "cors": {
+              "active": false
+            }
+          }
+        },
         "env": {
           "lambda": {
             "active": true,
             "timeout": 30,
             "handler": {
               "path": {
-                "suffix": ".handler",
-                "prefix": "src/handler/lambda/"
+                "prefix": "src/handler/lambda/",
+                "suffix": ".handler"
               }
             },
             "kind": "standard"
           }
-        },
-        "api": {
-          "web": {
-            "active": true,
-            "method": "POST",
-            "cors": {
-              "active": false
-            },
-            "path": {
-              "prefix": "/api/"
-            }
-          }
-        },
-        "in": {},
-        "out": {},
-        "deps": {}
+        }
       }
     }
   },
diff --git a/test/sys01/model/model.jsonic b/ts/test/sys01/model/model.jsonic
similarity index 100%
rename from test/sys01/model/model.jsonic
rename to ts/test/sys01/model/model.jsonic
diff --git a/test/sys01/model/pre.jsonic b/ts/test/sys01/model/pre.jsonic
similarity index 100%
rename from test/sys01/model/pre.jsonic
rename to ts/test/sys01/model/pre.jsonic
diff --git a/test/sys01/pre.txt b/ts/test/sys01/pre.txt
similarity index 100%
rename from test/sys01/pre.txt
rename to ts/test/sys01/pre.txt
diff --git a/test/t01.jsonic b/ts/test/t01.jsonic
similarity index 100%
rename from test/t01.jsonic
rename to ts/test/t01.jsonic
diff --git a/test/t02.jsonic b/ts/test/t02.jsonic
similarity index 100%
rename from test/t02.jsonic
rename to ts/test/t02.jsonic
diff --git a/test/t03.jsonic b/ts/test/t03.jsonic
similarity index 100%
rename from test/t03.jsonic
rename to ts/test/t03.jsonic
diff --git a/test/tsconfig.json b/ts/test/tsconfig.json
similarity index 100%
rename from test/tsconfig.json
rename to ts/test/tsconfig.json
diff --git a/test/util.js b/ts/test/util.js
similarity index 100%
rename from test/util.js
rename to ts/test/util.js
diff --git a/test/w01/doc.html b/ts/test/w01/doc.html
similarity index 100%
rename from test/w01/doc.html
rename to ts/test/w01/doc.html
diff --git a/test/w01/model/model.json b/ts/test/w01/model/model.json
similarity index 100%
rename from test/w01/model/model.json
rename to ts/test/w01/model/model.json
diff --git a/test/w01/model/model.jsonic b/ts/test/w01/model/model.jsonic
similarity index 100%
rename from test/w01/model/model.jsonic
rename to ts/test/w01/model/model.jsonic
diff --git a/test/w01/model/zed.jsonic b/ts/test/w01/model/zed.jsonic
similarity index 100%
rename from test/w01/model/zed.jsonic
rename to ts/test/w01/model/zed.jsonic
diff --git a/test/watch-w01.js b/ts/test/watch-w01.js
similarity index 100%
rename from test/watch-w01.js
rename to ts/test/watch-w01.js
diff --git a/test/watch.test.ts b/ts/test/watch.test.ts
similarity index 100%
rename from test/watch.test.ts
rename to ts/test/watch.test.ts

From 127934bd465b78accee9d7e94cfa54be28bacbe3 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Mon, 8 Jun 2026 18:42:30 +0000
Subject: [PATCH 6/6] test: add cases for both languages; make the Go CLI
 testable

Go (model package 78% -> 94%, total 70% -> 91%):
- Refactor cmd/voxgig-model into a testable run() with a local FlagSet;
  add main_test.go (write, dryrun, missing file, bad model, no args).
- Add log_test.go (level parsing/filtering, silent, NopLog).
- Add extra_test.go: reload re-resolves, resolver error, missing root,
  non-object model, action steps (pre/post/all), failing action, action
  with no Run, recovered producer panic, write error, dryrun via Model,
  Build accessor, NewWatch defaults + Last.

TypeScript (93.3% -> 94.3%):
- extra.test.ts: producer throws (pre/post), producer returns ok:false
  (pre/post), missing root file, Promise-exported action, unresolved
  import.
- watch.test.ts: recover from a failed rebuild while watching.

make test is green for both languages (19 TS, 30 Go test cases).

https://claude.ai/code/session_01HxXpZNrKj3qonocwAtEP8r
---
 go/cmd/voxgig-model/main.go      |  57 ++++---
 go/cmd/voxgig-model/main_test.go |  79 ++++++++++
 go/extra_test.go                 | 254 +++++++++++++++++++++++++++++++
 go/log_test.go                   |  68 +++++++++
 ts/dist-test/extra.test.js       | 151 ++++++++++++++++++
 ts/dist-test/extra.test.js.map   |   1 +
 ts/dist-test/watch.test.js       |  25 +++
 ts/dist-test/watch.test.js.map   |   2 +-
 ts/test/extra.test.ts            | 181 ++++++++++++++++++++++
 ts/test/watch.test.ts            |  36 +++++
 10 files changed, 830 insertions(+), 24 deletions(-)
 create mode 100644 go/cmd/voxgig-model/main_test.go
 create mode 100644 go/extra_test.go
 create mode 100644 go/log_test.go
 create mode 100644 ts/dist-test/extra.test.js
 create mode 100644 ts/dist-test/extra.test.js.map
 create mode 100644 ts/test/extra.test.ts

diff --git a/go/cmd/voxgig-model/main.go b/go/cmd/voxgig-model/main.go
index 21dffb5..e4e8f05 100644
--- a/go/cmd/voxgig-model/main.go
+++ b/go/cmd/voxgig-model/main.go
@@ -10,6 +10,7 @@ package main
 import (
 	"flag"
 	"fmt"
+	"io"
 	"os"
 	"os/signal"
 	"path/filepath"
@@ -19,29 +20,40 @@ import (
 )
 
 func main() {
-	watch := flag.Bool("w", false, "watch and rebuild on change")
-	dryrun := flag.Bool("y", false, "dry run (write nothing to disk)")
-	level := flag.String("g", "info", "log level: trace|debug|info|warn|error|silent")
-	flag.Usage = func() {
-		fmt.Fprintln(os.Stderr, "usage: voxgig-model [-w] [-y] [-g level] <root-file>")
-		flag.PrintDefaults()
+	os.Exit(run(os.Args[1:], os.Stderr))
+}
+
+// run parses args and builds the model, returning a process exit code. It is
+// separated from main (which only adds os.Exit and signal handling) so the
+// behavior can be tested directly.
+func run(args []string, stderr io.Writer) int {
+	fs := flag.NewFlagSet("voxgig-model", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	watch := fs.Bool("w", false, "watch and rebuild on change")
+	dryrun := fs.Bool("y", false, "dry run (write nothing to disk)")
+	level := fs.String("g", "info", "log level: trace|debug|info|warn|error|silent")
+	fs.Usage = func() {
+		fmt.Fprintln(stderr, "usage: voxgig-model [-w] [-y] [-g level] <root-file>")
+		fs.PrintDefaults()
+	}
+	if err := fs.Parse(args); err != nil {
+		return 2
 	}
-	flag.Parse()
 
-	path := flag.Arg(0)
+	path := fs.Arg(0)
 	if path == "" {
-		flag.Usage()
-		os.Exit(1)
+		fs.Usage()
+		return 1
 	}
 
 	abs, err := filepath.Abs(path)
 	if err != nil {
-		fmt.Fprintln(os.Stderr, "ERROR:", err)
-		os.Exit(1)
+		fmt.Fprintln(stderr, "ERROR:", err)
+		return 1
 	}
 	if _, serr := os.Stat(abs); serr != nil {
-		fmt.Fprintln(os.Stderr, "ERROR: model file does not exist:", path)
-		os.Exit(1)
+		fmt.Fprintln(stderr, "ERROR: model file does not exist:", path)
+		return 1
 	}
 
 	m := model.New(model.ModelSpec{
@@ -52,27 +64,26 @@ func main() {
 	})
 
 	if *watch {
-		br := m.Start()
-		reportErrs(br)
+		reportErrs(m.Start(), stderr)
 		sig := make(chan os.Signal, 1)
 		signal.Notify(sig, os.Interrupt, syscall.SIGTERM)
 		<-sig
 		m.Stop()
-		return
+		return 0
 	}
 
-	br := m.Run()
-	if !br.OK {
-		reportErrs(br)
-		os.Exit(1)
+	if br := m.Run(); !br.OK {
+		reportErrs(br, stderr)
+		return 1
 	}
+	return 0
 }
 
-func reportErrs(br *model.BuildResult) {
+func reportErrs(br *model.BuildResult, stderr io.Writer) {
 	if br == nil {
 		return
 	}
 	for _, e := range br.Errs {
-		fmt.Fprintln(os.Stderr, "ERROR:", e)
+		fmt.Fprintln(stderr, "ERROR:", e)
 	}
 }
diff --git a/go/cmd/voxgig-model/main_test.go b/go/cmd/voxgig-model/main_test.go
new file mode 100644
index 0000000..a04d807
--- /dev/null
+++ b/go/cmd/voxgig-model/main_test.go
@@ -0,0 +1,79 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package main
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func write(t *testing.T, path, content string) {
+	t.Helper()
+	if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestCLIWritesModel(t *testing.T) {
+	dir := t.TempDir()
+	root := filepath.Join(dir, "m.jsonic")
+	write(t, root, "a: 1\nb: 2\n")
+
+	var out bytes.Buffer
+	if code := run([]string{"-g", "silent", root}, &out); code != 0 {
+		t.Fatalf("exit %d: %s", code, out.String())
+	}
+	if _, err := os.Stat(filepath.Join(dir, "m.json")); err != nil {
+		t.Fatalf("model JSON not written: %v", err)
+	}
+}
+
+func TestCLIDryrunWritesNothing(t *testing.T) {
+	dir := t.TempDir()
+	root := filepath.Join(dir, "m.jsonic")
+	write(t, root, "a: 1\n")
+
+	var out bytes.Buffer
+	if code := run([]string{"-y", "-g", "silent", root}, &out); code != 0 {
+		t.Fatalf("exit %d: %s", code, out.String())
+	}
+	if _, err := os.Stat(filepath.Join(dir, "m.json")); !os.IsNotExist(err) {
+		t.Fatal("dryrun wrote m.json to disk")
+	}
+}
+
+func TestCLIMissingFile(t *testing.T) {
+	var out bytes.Buffer
+	code := run([]string{filepath.Join(t.TempDir(), "nope.jsonic")}, &out)
+	if code == 0 {
+		t.Fatal("expected non-zero exit for missing file")
+	}
+	if !strings.Contains(out.String(), "does not exist") {
+		t.Fatalf("stderr = %q", out.String())
+	}
+}
+
+func TestCLINoArgs(t *testing.T) {
+	var out bytes.Buffer
+	if code := run(nil, &out); code != 1 {
+		t.Fatalf("exit %d, want 1", code)
+	}
+}
+
+func TestCLIBadModel(t *testing.T) {
+	dir := t.TempDir()
+	root := filepath.Join(dir, "m.jsonic")
+	write(t, root, "x: 1\nx: 2\n")
+
+	var out bytes.Buffer
+	code := run([]string{"-g", "silent", root}, &out)
+	if code != 1 {
+		t.Fatalf("exit %d, want 1", code)
+	}
+	if !strings.Contains(out.String(), "ERROR") {
+		t.Fatalf("stderr = %q", out.String())
+	}
+}
diff --git a/go/extra_test.go b/go/extra_test.go
new file mode 100644
index 0000000..31fcfa8
--- /dev/null
+++ b/go/extra_test.go
@@ -0,0 +1,254 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// countResolver records how many times it was asked to resolve, and returns
+// a fixed model. It exercises the Resolver seam without aontu.
+type countResolver struct {
+	model map[string]any
+	errs  []error
+	calls int
+}
+
+func (c *countResolver) Resolve(string) (map[string]any, []error) {
+	c.calls++
+	out := map[string]any{}
+	for k, v := range c.model {
+		out[k] = v
+	}
+	return out, c.errs
+}
+
+// A pre-action that invalidates the cache and requests a reload causes the
+// model to be re-resolved before the post phase.
+func TestReloadReResolves(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "a: 1\n")
+
+	r := &countResolver{model: map[string]any{"a": int64(1)}}
+	b := NewBuild(BuildSpec{
+		Path: filepath.Join(dir, "m.jsonic"), Base: dir, Resolver: r,
+		Actions: map[string]ActionDef{
+			"regen": {Step: StepPre, Run: func(_ map[string]any, b *Build, _ *BuildContext) ActionResult {
+				b.InvalidateCache() // a real pre-action would have rewritten source
+				return ActionResult{OK: true, Reload: true}
+			}},
+		},
+		Res: []ProducerDef{{Path: "/", Build: LocalProducer}},
+	})
+
+	br := b.Run(false)
+	if !br.OK {
+		t.Fatalf("build failed: %v", br.Errs)
+	}
+	if r.calls != 2 {
+		t.Fatalf("resolve calls = %d, want 2 (initial + reload)", r.calls)
+	}
+}
+
+// A custom resolver returning errors fails the build.
+func TestResolverError(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "a: 1\n")
+	r := &countResolver{errs: []error{errors.New("nope")}}
+	b := NewBuild(BuildSpec{Path: filepath.Join(dir, "m.jsonic"), Base: dir, Resolver: r})
+	br := b.Run(false)
+	if br.OK {
+		t.Fatal("expected failure from resolver error")
+	}
+	if !containsErr(br.Errs, "nope") {
+		t.Fatalf("errors = %v", br.Errs)
+	}
+}
+
+// A missing root file fails the build with the read error.
+func TestMissingRootFile(t *testing.T) {
+	dir := t.TempDir()
+	b := NewBuild(BuildSpec{Path: filepath.Join(dir, "nope.jsonic"), Base: dir})
+	br := b.Run(false)
+	if br.OK {
+		t.Fatal("expected failure for missing root file")
+	}
+	if len(br.Errs) == 0 {
+		t.Fatal("expected an error")
+	}
+}
+
+// A model that resolves to a non-object is rejected by AontuResolver.
+func TestNonObjectModel(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "5\n")
+	b := NewBuild(BuildSpec{Path: filepath.Join(dir, "m.jsonic"), Base: dir})
+	br := b.Run(false)
+	if br.OK {
+		t.Fatal("expected failure for non-object model")
+	}
+	if len(br.Errs) == 0 {
+		t.Fatal("expected an error")
+	}
+}
+
+// Actions run only in their declared step; StepAll runs in both phases.
+func TestActionSteps(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "x: 1\n")
+
+	var log []string
+	rec := func(name string) Action {
+		return func(_ map[string]any, _ *Build, ctx *BuildContext) ActionResult {
+			log = append(log, name+":"+string(ctx.Step))
+			return ActionResult{OK: true}
+		}
+	}
+	b := NewBuild(BuildSpec{
+		Path: filepath.Join(dir, "m.jsonic"), Base: dir,
+		Actions: map[string]ActionDef{
+			"pre":  {Step: StepPre, Run: rec("pre")},
+			"post": {Step: StepPost, Run: rec("post")},
+			"all":  {Step: StepAll, Run: rec("all")},
+		},
+		Order: []string{"pre", "post", "all"},
+		Res:   []ProducerDef{{Path: "/", Build: LocalProducer}},
+	})
+	if br := b.Run(false); !br.OK {
+		t.Fatalf("build failed: %v", br.Errs)
+	}
+	got := strings.Join(log, ",")
+	want := "pre:pre,all:pre,post:post,all:post"
+	if got != want {
+		t.Fatalf("action run log = %q, want %q", got, want)
+	}
+}
+
+// A failing action stops the build and skips later actions.
+func TestActionFailsBuild(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "x: 1\n")
+
+	var ran []string
+	mk := func(name string, ok bool) ActionDef {
+		return ActionDef{Run: func(_ map[string]any, _ *Build, _ *BuildContext) ActionResult {
+			ran = append(ran, name)
+			return ActionResult{OK: ok}
+		}}
+	}
+	b := NewBuild(BuildSpec{
+		Path: filepath.Join(dir, "m.jsonic"), Base: dir,
+		Actions: map[string]ActionDef{"a": mk("a", true), "b": mk("b", false), "c": mk("c", true)},
+		Order:   []string{"a", "b", "c"},
+		Res:     []ProducerDef{{Path: "/", Build: LocalProducer}},
+	})
+	br := b.Run(false)
+	if br.OK {
+		t.Fatal("expected build failure from failing action")
+	}
+	if strings.Join(ran, ",") != "a,b" {
+		t.Fatalf("ran %v, want [a b] (c skipped)", ran)
+	}
+}
+
+// An action whose step matches but has no Run function fails the build.
+func TestActionMissingRun(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "x: 1\n")
+	b := NewBuild(BuildSpec{
+		Path: filepath.Join(dir, "m.jsonic"), Base: dir,
+		Actions: map[string]ActionDef{"empty": {Step: StepPost}},
+		Order:   []string{"empty"},
+		Res:     []ProducerDef{{Path: "/", Build: LocalProducer}},
+	})
+	br := b.Run(false)
+	if br.OK {
+		t.Fatal("expected failure for action with no Run")
+	}
+	if !containsErr(br.Errs, "no Run") {
+		t.Fatalf("errors = %v", br.Errs)
+	}
+}
+
+// A producer that panics is converted to a failed build, not a crash.
+func TestProducerPanicRecovered(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "x: 1\n")
+	b := NewBuild(BuildSpec{
+		Path: filepath.Join(dir, "m.jsonic"), Base: dir,
+		Res: []ProducerDef{{Path: "/", Build: func(_ *Build, _ *BuildContext) ProducerResult {
+			panic("boom in producer")
+		}}},
+	})
+	br := b.Run(false)
+	if br.OK {
+		t.Fatal("expected failure from panicking producer")
+	}
+	if !containsErr(br.Errs, "boom in producer") {
+		t.Fatalf("errors = %v", br.Errs)
+	}
+}
+
+// A filesystem write error fails the model producer.
+type failWriteFS struct{ OSFS }
+
+func (failWriteFS) WriteFile(string, []byte, os.FileMode) error {
+	return errors.New("simulated write failure")
+}
+
+func TestModelProducerWriteError(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "a: 1\n")
+	b := NewBuild(BuildSpec{
+		Path: filepath.Join(dir, "m.jsonic"), Base: dir, FS: failWriteFS{},
+		Res: []ProducerDef{{Path: "/", Build: ModelProducer}},
+	})
+	br := b.Run(false)
+	if br.OK {
+		t.Fatal("expected failure when write fails")
+	}
+	if !containsErr(br.Errs, "write failure") {
+		t.Fatalf("errors = %v", br.Errs)
+	}
+}
+
+// Model.New honors dryrun and exposes the resolved build.
+func TestModelDryrunAndBuild(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "a: 1\n")
+	m := New(ModelSpec{Path: filepath.Join(dir, "m.jsonic"), Base: dir, Dryrun: true})
+
+	br := m.Run()
+	if !br.OK {
+		t.Fatalf("run failed: %v", br.Errs)
+	}
+	if _, err := os.Stat(filepath.Join(dir, "m.json")); !os.IsNotExist(err) {
+		t.Fatal("dryrun wrote m.json")
+	}
+	if m.Build() == nil || m.Build().Model["a"] != int64(1) {
+		t.Fatalf("Build() model = %#v", m.Build())
+	}
+	if br.Build() != m.Build() {
+		t.Fatal("BuildResult.Build() did not match Model.Build()")
+	}
+}
+
+// NewWatch applies defaults; Last returns the most recent result.
+func TestWatchRunAndLast(t *testing.T) {
+	dir := t.TempDir()
+	writeFile(t, dir, "m.jsonic", "a: 1\n")
+	b := NewBuild(BuildSpec{Path: filepath.Join(dir, "m.jsonic"), Base: dir})
+	w := NewWatch(b, "", 0) // defaults: name "model", idle 111ms
+
+	br := w.Run(false)
+	if !br.OK {
+		t.Fatalf("run failed: %v", br.Errs)
+	}
+	if w.Last() != br {
+		t.Fatal("Last did not return the latest result")
+	}
+}
diff --git a/go/log_test.go b/go/log_test.go
new file mode 100644
index 0000000..811a4c3
--- /dev/null
+++ b/go/log_test.go
@@ -0,0 +1,68 @@
+/* Copyright © 2021-2026 Voxgig Ltd, MIT License. */
+
+package model
+
+import (
+	"bytes"
+	"errors"
+	"strings"
+	"testing"
+)
+
+func TestParseLevel(t *testing.T) {
+	cases := map[string]int{
+		"debug": levelDebug, "trace": levelDebug,
+		"info": levelInfo, "": levelInfo, "nonsense": levelInfo,
+		"warn": levelError, "error": levelError, "fatal": levelError,
+		"silent": levelSilent,
+	}
+	for in, want := range cases {
+		if got := parseLevel(in); got != want {
+			t.Errorf("parseLevel(%q) = %d, want %d", in, got, want)
+		}
+	}
+}
+
+func TestStdLogRespectsLevel(t *testing.T) {
+	var buf bytes.Buffer
+	l := &stdLog{level: levelInfo, w: &buf}
+
+	l.Debug("dbg", "hidden") // below info -> suppressed
+	l.Info("inf", "shown")
+	l.Error("err", errors.New("boom"), "context")
+
+	out := buf.String()
+	if strings.Contains(out, "hidden") {
+		t.Error("debug entry leaked at info level")
+	}
+	if !strings.Contains(out, "inf") || !strings.Contains(out, "shown") {
+		t.Error("info entry not logged")
+	}
+	if !strings.Contains(out, "ERROR") || !strings.Contains(out, "boom") {
+		t.Errorf("error not logged with cause: %q", out)
+	}
+}
+
+func TestStdLogSilent(t *testing.T) {
+	var buf bytes.Buffer
+	l := &stdLog{level: levelSilent, w: &buf}
+	l.Info("a", "b")
+	l.Debug("a", "b")
+	l.Error("a", errors.New("x"), "b")
+	if buf.Len() != 0 {
+		t.Fatalf("silent log produced output: %q", buf.String())
+	}
+}
+
+func TestNewLogConstructs(t *testing.T) {
+	if NewLog("debug") == nil {
+		t.Fatal("NewLog returned nil")
+	}
+}
+
+func TestNopLog(t *testing.T) {
+	var l Log = NopLog{} // discards everything, must not panic
+	l.Info("a", "b")
+	l.Debug("a", "b")
+	l.Error("a", errors.New("x"), "b")
+}
diff --git a/ts/dist-test/extra.test.js b/ts/dist-test/extra.test.js
new file mode 100644
index 0000000..45be782
--- /dev/null
+++ b/ts/dist-test/extra.test.js
@@ -0,0 +1,151 @@
+"use strict";
+/* Copyright © 2021-2025 Voxgig Ltd, MIT License. */
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+const node_fs_1 = __importDefault(require("node:fs"));
+const promises_1 = require("node:fs/promises");
+const node_test_1 = require("node:test");
+const node_assert_1 = __importDefault(require("node:assert"));
+const util_1 = require("@voxgig/util");
+const build_1 = require("../dist/build");
+const model_1 = require("../dist/model");
+const GEN = __dirname + '/../test/_gen';
+function silentLog() {
+    return (0, util_1.prettyPino)('test', { debug: 'silent' });
+}
+function okResult(name) {
+    return { ok: true, name, step: '', active: true, reload: false, errs: [], runlog: [] };
+}
+(0, node_test_1.describe)('extra', () => {
+    // A producer that throws in the pre phase fails the build, and the error is
+    // collected rather than escaping.
+    (0, node_test_1.test)('producer-throws-in-pre', async () => {
+        const dir = GEN + '/ex-pre';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir, { recursive: true });
+        await (0, promises_1.writeFile)(dir + '/m.jsonic', 'a: 1\n');
+        const b = (0, build_1.makeBuild)({
+            fs: node_fs_1.default, base: dir, path: dir + '/m.jsonic',
+            res: [{
+                    path: '/', build: async function boom(_build, ctx) {
+                        if ('pre' === ctx.step) {
+                            throw new Error('pre-boom');
+                        }
+                        return okResult('boom');
+                    },
+                }],
+        }, silentLog());
+        const v = await b.run({ watch: false });
+        node_assert_1.default.strictEqual(v.ok, false);
+        node_assert_1.default.ok(v.errs.some((e) => String(e.message ?? e).includes('pre-boom')));
+    });
+    // A producer that throws in the post phase fails the build.
+    (0, node_test_1.test)('producer-throws-in-post', async () => {
+        const dir = GEN + '/ex-post';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir, { recursive: true });
+        await (0, promises_1.writeFile)(dir + '/m.jsonic', 'a: 1\n');
+        const b = (0, build_1.makeBuild)({
+            fs: node_fs_1.default, base: dir, path: dir + '/m.jsonic',
+            res: [{
+                    path: '/', build: async function boom(_build, ctx) {
+                        if ('post' === ctx.step) {
+                            throw new Error('post-boom');
+                        }
+                        return okResult('boom');
+                    },
+                }],
+        }, silentLog());
+        const v = await b.run({ watch: false });
+        node_assert_1.default.strictEqual(v.ok, false);
+        node_assert_1.default.ok(v.errs.some((e) => String(e.message ?? e).includes('post-boom')));
+    });
+    // A missing root file fails the build with the read error.
+    (0, node_test_1.test)('missing-root-file', async () => {
+        const b = (0, build_1.makeBuild)({
+            fs: node_fs_1.default, base: GEN, path: GEN + '/does-not-exist.jsonic', res: [],
+        }, silentLog());
+        const v = await b.run({ watch: false });
+        node_assert_1.default.strictEqual(v.ok, false);
+        node_assert_1.default.ok(0 < v.errs.length);
+    });
+    // An action module may export a Promise resolving to the action function;
+    // the local producer awaits it before running.
+    (0, node_test_1.test)('promise-exported-action', async () => {
+        const dir = GEN + '/ex-promise';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir + '/model/.model-config', { recursive: true });
+        await (0, promises_1.mkdir)(dir + '/build', { recursive: true });
+        await (0, promises_1.writeFile)(dir + '/model/m.jsonic', 'a: 1\n');
+        await (0, promises_1.writeFile)(dir + '/model/.model-config/model-config.jsonic', "sys: model: action: { p: load: 'build/p' }\n");
+        await (0, promises_1.writeFile)(dir + '/build/p.js', "const Path = require('node:path')\n" +
+            'module.exports = Promise.resolve(async function p(model, build) {\n' +
+            "  const root = Path.resolve(build.path, '..', '..')\n" +
+            "  build.fs.writeFileSync(Path.resolve(root, 'p.txt'), 'OK')\n" +
+            '  return { ok: true }\n' +
+            '})\n');
+        const model = new model_1.Model({
+            path: dir + '/model/m.jsonic', base: dir + '/model', debug: 'silent',
+        });
+        const br = await model.run();
+        node_assert_1.default.ok(br.ok, 'build failed: ' + JSON.stringify(br.errs));
+        node_assert_1.default.strictEqual(await (0, promises_1.readFile)(dir + '/p.txt', 'utf8'), 'OK');
+    });
+    // A producer that returns ok:false in the pre phase fails the build.
+    (0, node_test_1.test)('producer-returns-not-ok-pre', async () => {
+        const dir = GEN + '/ex-nokpre';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir, { recursive: true });
+        await (0, promises_1.writeFile)(dir + '/m.jsonic', 'a: 1\n');
+        const b = (0, build_1.makeBuild)({
+            fs: node_fs_1.default, base: dir, path: dir + '/m.jsonic',
+            res: [{
+                    path: '/', build: async function bad(_build, ctx) {
+                        return {
+                            ok: 'pre' !== ctx.step, name: 'bad', step: ctx.step,
+                            active: true, reload: false, errs: [], runlog: [],
+                        };
+                    },
+                }],
+        }, silentLog());
+        const v = await b.run({ watch: false });
+        node_assert_1.default.strictEqual(v.ok, false);
+    });
+    // A producer that returns ok:false in the post phase fails the build.
+    (0, node_test_1.test)('producer-returns-not-ok-post', async () => {
+        const dir = GEN + '/ex-nokpost';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir, { recursive: true });
+        await (0, promises_1.writeFile)(dir + '/m.jsonic', 'a: 1\n');
+        const b = (0, build_1.makeBuild)({
+            fs: node_fs_1.default, base: dir, path: dir + '/m.jsonic',
+            res: [{
+                    path: '/', build: async function bad(_build, ctx) {
+                        return {
+                            ok: 'post' !== ctx.step, name: 'bad', step: ctx.step,
+                            active: true, reload: false, errs: [], runlog: [],
+                        };
+                    },
+                }],
+        }, silentLog());
+        const v = await b.run({ watch: false });
+        node_assert_1.default.strictEqual(v.ok, false);
+    });
+    // An unresolved import makes aontu throw; the build collects it as an error
+    // rather than letting it escape.
+    (0, node_test_1.test)('unresolved-import-fails', async () => {
+        const dir = GEN + '/ex-import';
+        await (0, promises_1.rm)(dir, { recursive: true, force: true });
+        await (0, promises_1.mkdir)(dir, { recursive: true });
+        await (0, promises_1.writeFile)(dir + '/m.jsonic', 'top: @"./missing.jsonic"\n');
+        const b = (0, build_1.makeBuild)({
+            fs: node_fs_1.default, base: dir, path: dir + '/m.jsonic', res: [],
+        }, silentLog());
+        const v = await b.run({ watch: false });
+        node_assert_1.default.strictEqual(v.ok, false);
+        node_assert_1.default.ok(0 < v.errs.length);
+    });
+});
+//# sourceMappingURL=extra.test.js.map
\ No newline at end of file
diff --git a/ts/dist-test/extra.test.js.map b/ts/dist-test/extra.test.js.map
new file mode 100644
index 0000000..51cd058
--- /dev/null
+++ b/ts/dist-test/extra.test.js.map
@@ -0,0 +1 @@
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\ No newline at end of file
diff --git a/ts/dist-test/watch.test.js b/ts/dist-test/watch.test.js
index 2fd4946..af330a4 100644
--- a/ts/dist-test/watch.test.js
+++ b/ts/dist-test/watch.test.js
@@ -98,5 +98,30 @@ async function read(file) {
             await model.stop();
         }
     });
+    // A failed rebuild while watching is reported, and the watcher recovers when
+    // the model is fixed.
+    (0, node_test_1.test)('recovers-from-error-while-watching', async () => {
+        const base = GEN + '/wat03/model';
+        await (0, promises_1.rm)(GEN + '/wat03', { recursive: true, force: true });
+        await (0, promises_1.mkdir)(base + '/.model-config', { recursive: true });
+        await (0, promises_1.writeFile)(base + '/model.jsonic', 'val: 1\n');
+        await (0, promises_1.writeFile)(base + '/.model-config/model-config.jsonic', 'sys: model: action: {}\n');
+        const out = base + '/model.json';
+        const model = new model_1.Model({ path: base + '/model.jsonic', base, debug: 'silent' });
+        try {
+            await model.start();
+            node_assert_1.default.ok(await waitFor(async () => (await readVal(out)) === 1), 'initial build should produce val:1');
+            // Break the model: conflicting scalar values do not unify.
+            await new Promise(r => setTimeout(r, 200));
+            await (0, promises_1.writeFile)(base + '/model.jsonic', 'val: 1\nval: 2\n');
+            await new Promise(r => setTimeout(r, 400)); // let the failed rebuild run
+            // Fix it; the watcher should recover.
+            await (0, promises_1.writeFile)(base + '/model.jsonic', 'val: 9\n');
+            node_assert_1.default.ok(await waitFor(async () => (await readVal(out)) === 9), 'watcher should recover to val:9 after the model is fixed');
+        }
+        finally {
+            await model.stop();
+        }
+    });
 });
 //# sourceMappingURL=watch.test.js.map
\ No newline at end of file
diff --git a/ts/dist-test/watch.test.js.map b/ts/dist-test/watch.test.js.map
index 324f4d3..ed18a1d 100644
--- a/ts/dist-test/watch.test.js.map
+++ b/ts/dist-test/watch.test.js.map
@@ -1 +1 @@
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\ No newline at end of file
diff --git a/ts/test/extra.test.ts b/ts/test/extra.test.ts
new file mode 100644
index 0000000..282f54b
--- /dev/null
+++ b/ts/test/extra.test.ts
@@ -0,0 +1,181 @@
+/* Copyright © 2021-2025 Voxgig Ltd, MIT License. */
+
+import Fs from 'node:fs'
+import { mkdir, writeFile, readFile, rm } from 'node:fs/promises'
+import { test, describe } from 'node:test'
+import assert from 'node:assert'
+
+import { prettyPino } from '@voxgig/util'
+
+import { makeBuild } from '../dist/build'
+import { Model } from '../dist/model'
+import type { Build, BuildContext } from '../dist/types'
+
+
+const GEN = __dirname + '/../test/_gen'
+
+function silentLog() {
+  return prettyPino('test', { debug: 'silent' })
+}
+
+function okResult(name: string) {
+  return { ok: true, name, step: '', active: true, reload: false, errs: [], runlog: [] }
+}
+
+
+describe('extra', () => {
+
+  // A producer that throws in the pre phase fails the build, and the error is
+  // collected rather than escaping.
+  test('producer-throws-in-pre', async () => {
+    const dir = GEN + '/ex-pre'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir, { recursive: true })
+    await writeFile(dir + '/m.jsonic', 'a: 1\n')
+
+    const b = makeBuild({
+      fs: Fs, base: dir, path: dir + '/m.jsonic',
+      res: [{
+        path: '/', build: async function boom(_build: Build, ctx: BuildContext) {
+          if ('pre' === ctx.step) { throw new Error('pre-boom') }
+          return okResult('boom')
+        },
+      }],
+    }, silentLog())
+
+    const v = await b.run({ watch: false })
+    assert.strictEqual(v.ok, false)
+    assert.ok(v.errs.some((e: any) => String(e.message ?? e).includes('pre-boom')))
+  })
+
+
+  // A producer that throws in the post phase fails the build.
+  test('producer-throws-in-post', async () => {
+    const dir = GEN + '/ex-post'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir, { recursive: true })
+    await writeFile(dir + '/m.jsonic', 'a: 1\n')
+
+    const b = makeBuild({
+      fs: Fs, base: dir, path: dir + '/m.jsonic',
+      res: [{
+        path: '/', build: async function boom(_build: Build, ctx: BuildContext) {
+          if ('post' === ctx.step) { throw new Error('post-boom') }
+          return okResult('boom')
+        },
+      }],
+    }, silentLog())
+
+    const v = await b.run({ watch: false })
+    assert.strictEqual(v.ok, false)
+    assert.ok(v.errs.some((e: any) => String(e.message ?? e).includes('post-boom')))
+  })
+
+
+  // A missing root file fails the build with the read error.
+  test('missing-root-file', async () => {
+    const b = makeBuild({
+      fs: Fs, base: GEN, path: GEN + '/does-not-exist.jsonic', res: [],
+    }, silentLog())
+
+    const v = await b.run({ watch: false })
+    assert.strictEqual(v.ok, false)
+    assert.ok(0 < v.errs.length)
+  })
+
+
+  // An action module may export a Promise resolving to the action function;
+  // the local producer awaits it before running.
+  test('promise-exported-action', async () => {
+    const dir = GEN + '/ex-promise'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir + '/model/.model-config', { recursive: true })
+    await mkdir(dir + '/build', { recursive: true })
+
+    await writeFile(dir + '/model/m.jsonic', 'a: 1\n')
+    await writeFile(dir + '/model/.model-config/model-config.jsonic',
+      "sys: model: action: { p: load: 'build/p' }\n")
+    await writeFile(dir + '/build/p.js',
+      "const Path = require('node:path')\n" +
+      'module.exports = Promise.resolve(async function p(model, build) {\n' +
+      "  const root = Path.resolve(build.path, '..', '..')\n" +
+      "  build.fs.writeFileSync(Path.resolve(root, 'p.txt'), 'OK')\n" +
+      '  return { ok: true }\n' +
+      '})\n')
+
+    const model = new Model({
+      path: dir + '/model/m.jsonic', base: dir + '/model', debug: 'silent',
+    })
+    const br = await model.run()
+
+    assert.ok(br.ok, 'build failed: ' + JSON.stringify(br.errs))
+    assert.strictEqual(await readFile(dir + '/p.txt', 'utf8'), 'OK')
+  })
+
+
+  // A producer that returns ok:false in the pre phase fails the build.
+  test('producer-returns-not-ok-pre', async () => {
+    const dir = GEN + '/ex-nokpre'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir, { recursive: true })
+    await writeFile(dir + '/m.jsonic', 'a: 1\n')
+
+    const b = makeBuild({
+      fs: Fs, base: dir, path: dir + '/m.jsonic',
+      res: [{
+        path: '/', build: async function bad(_build: Build, ctx: BuildContext) {
+          return {
+            ok: 'pre' !== ctx.step, name: 'bad', step: ctx.step,
+            active: true, reload: false, errs: [], runlog: [],
+          }
+        },
+      }],
+    }, silentLog())
+
+    const v = await b.run({ watch: false })
+    assert.strictEqual(v.ok, false)
+  })
+
+
+  // A producer that returns ok:false in the post phase fails the build.
+  test('producer-returns-not-ok-post', async () => {
+    const dir = GEN + '/ex-nokpost'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir, { recursive: true })
+    await writeFile(dir + '/m.jsonic', 'a: 1\n')
+
+    const b = makeBuild({
+      fs: Fs, base: dir, path: dir + '/m.jsonic',
+      res: [{
+        path: '/', build: async function bad(_build: Build, ctx: BuildContext) {
+          return {
+            ok: 'post' !== ctx.step, name: 'bad', step: ctx.step,
+            active: true, reload: false, errs: [], runlog: [],
+          }
+        },
+      }],
+    }, silentLog())
+
+    const v = await b.run({ watch: false })
+    assert.strictEqual(v.ok, false)
+  })
+
+
+  // An unresolved import makes aontu throw; the build collects it as an error
+  // rather than letting it escape.
+  test('unresolved-import-fails', async () => {
+    const dir = GEN + '/ex-import'
+    await rm(dir, { recursive: true, force: true })
+    await mkdir(dir, { recursive: true })
+    await writeFile(dir + '/m.jsonic', 'top: @"./missing.jsonic"\n')
+
+    const b = makeBuild({
+      fs: Fs, base: dir, path: dir + '/m.jsonic', res: [],
+    }, silentLog())
+
+    const v = await b.run({ watch: false })
+    assert.strictEqual(v.ok, false)
+    assert.ok(0 < v.errs.length)
+  })
+
+})
diff --git a/ts/test/watch.test.ts b/ts/test/watch.test.ts
index d87261e..3fabf21 100644
--- a/ts/test/watch.test.ts
+++ b/ts/test/watch.test.ts
@@ -133,4 +133,40 @@ describe('watch', () => {
     }
   })
 
+
+  // A failed rebuild while watching is reported, and the watcher recovers when
+  // the model is fixed.
+  test('recovers-from-error-while-watching', async () => {
+    const base = GEN + '/wat03/model'
+    await rm(GEN + '/wat03', { recursive: true, force: true })
+    await mkdir(base + '/.model-config', { recursive: true })
+    await writeFile(base + '/model.jsonic', 'val: 1\n')
+    await writeFile(base + '/.model-config/model-config.jsonic',
+      'sys: model: action: {}\n')
+
+    const out = base + '/model.json'
+    const model = new Model({ path: base + '/model.jsonic', base, debug: 'silent' })
+
+    try {
+      await model.start()
+      assert.ok(
+        await waitFor(async () => (await readVal(out)) === 1),
+        'initial build should produce val:1')
+
+      // Break the model: conflicting scalar values do not unify.
+      await new Promise(r => setTimeout(r, 200))
+      await writeFile(base + '/model.jsonic', 'val: 1\nval: 2\n')
+      await new Promise(r => setTimeout(r, 400)) // let the failed rebuild run
+
+      // Fix it; the watcher should recover.
+      await writeFile(base + '/model.jsonic', 'val: 9\n')
+      assert.ok(
+        await waitFor(async () => (await readVal(out)) === 9),
+        'watcher should recover to val:9 after the model is fixed')
+    }
+    finally {
+      await model.stop()
+    }
+  })
+
 })