feat(01KVTB3Z): resolve each target repo's own build toolchain structurally instead of hardcoding pnpm at plugins/flow

plugins/flow/mcp-server/src/__tests__/dev-pre-pr-gate.test.ts

@@ -87,6 +87,24 @@ async function setupRepo(): Promise<TestContext> {
   const srcDir = path.join(repoRoot, "src");
   await fs.mkdir(srcDir, { recursive: true });
   await atomicWriteFile(path.join(srcDir, "index.ts"), "export const x = 1;\n");
+
+  // Flow-SHAPED build home so the structural toolchain resolver (Story
+  // native:01KVTB3Z) resolves cwd=plugins/flow + packageManager=pnpm + a knip
+  // script (so the bloat gate runs) PURELY from on-disk structure — no
+  // `.flow/config.yaml`. Mirrors the real Flow repo's dogfood path.
+  const flowDir = path.join(repoRoot, "plugins", "flow");
+  await fs.mkdir(flowDir, { recursive: true });
+  await atomicWriteFile(
+    path.join(flowDir, "package.json"),
+    JSON.stringify(
+      { name: "flow", private: true, scripts: { build: "pnpm -r build", test: "pnpm -r test", knip: "knip --no-progress" } },
+      null,
+      2,
+    ),
+  );
+  await atomicWriteFile(path.join(flowDir, "pnpm-workspace.yaml"), "packages:\n  - mcp-server\n");
+  await atomicWriteFile(path.join(flowDir, "pnpm-lock.yaml"), "lockfileVersion: '9.0'\n");
+
   await realExeca("git", ["-C", repoRoot, "add", "."]);
   await realExeca("git", ["-C", repoRoot, "commit", "-m", "chore: initial commit"]);
 

plugins/flow/mcp-server/src/__tests__/inline-ac-extraction.test.ts

@@ -106,6 +106,17 @@ async function setupRepo(): Promise<TestContext> {
   const srcDir = path.join(repoRoot, "src");
   await fs.mkdir(srcDir, { recursive: true });
   await atomicWriteFile(path.join(srcDir, "index.ts"), "export const x = 1;\n");
+  // Flow-shaped build home (Story native:01KVTB3Z) so the structural toolchain
+  // resolver lands on plugins/flow + pnpm. NO `knip` script here, so the bloat
+  // gate is SKIPPED (knipCmd null) — this fixture's stub only handles build/test.
+  const flowDir = path.join(repoRoot, "plugins", "flow");
+  await fs.mkdir(flowDir, { recursive: true });
+  await atomicWriteFile(
+    path.join(flowDir, "package.json"),
+    JSON.stringify({ name: "flow", private: true, scripts: { build: "pnpm -r build", test: "pnpm -r test" } }, null, 2),
+  );
+  await atomicWriteFile(path.join(flowDir, "pnpm-workspace.yaml"), "packages:\n  - mcp-server\n");
+  await atomicWriteFile(path.join(flowDir, "pnpm-lock.yaml"), "lockfileVersion: '9.0'\n");
   await realExeca("git", ["-C", repoRoot, "add", "."]);
   await realExeca("git", ["-C", repoRoot, "commit", "-m", "chore: initial commit"]);
 

plugins/flow/mcp-server/src/errors.ts

@@ -52,6 +52,32 @@ export class InvalidWorkspaceConfigError extends DomainError {
   }
 }
 
+/**
+ * `.flow/config.yaml` carries a `build:` block (the toolchain escape hatch) that
+ * failed schema validation — e.g. an unrecognised `packageManager` value, or a
+ * non-string command field. The resolver surfaces this TYPED error rather than
+ * silently falling back to structural detection, so a deliberate-but-malformed
+ * override is loud (the operator fixes the block) instead of being quietly
+ * ignored. (Story native:01KVTB3Z AC3.)
+ */
+export class ToolchainConfigError extends DomainError {
+  readonly configPath: string;
+  readonly yamlPath: string;
+  readonly detail: string;
+
+  constructor(opts: { configPath: string; yamlPath: string; detail: string }) {
+    super(
+      `${opts.configPath} has an invalid 'build:' block at '${opts.yamlPath}': ${opts.detail}. ` +
+        `Fix the build override (or remove it to fall back to structural toolchain ` +
+        `detection). Recognised packageManager values: pnpm | npm | yarn | bun. ` +
+        `See mcp-server/src/lib/resolve-project-toolchain.ts.`,
+    );
+    this.configPath = opts.configPath;
+    this.yamlPath = opts.yamlPath;
+    this.detail = opts.detail;
+  }
+}
+
 /**
  * `.flow/config.yaml` declares an `adapter:` name that does not match
  * any registered adapter. The user must either install the matching

plugins/flow/mcp-server/src/lib/__tests__/flow-shaped-build-home.ts

@@ -0,0 +1,54 @@
+/**
+ * Test helper: seed a Flow-SHAPED build home under a tmpdir repo root.
+ *
+ * Story native:01KVTB3Z made the dev pre-PR gates and the reviewer derive their
+ * build/test/bloat toolchain from `resolveProjectToolchain`, which detects the
+ * build home STRUCTURALLY (a pnpm-workspace.yaml whose root package.json owns a
+ * `build` script → `plugins/flow`, pnpm). Tests that previously relied on the
+ * hardcoded `<repo>/plugins/flow` + `pnpm` assumption must now seed that on-disk
+ * structure so the resolver lands on the same place — mirroring the real Flow
+ * repo's dogfood path on a clean worktree (where `.flow/config.yaml`, being
+ * gitignored, is absent).
+ *
+ * Writes:
+ *   <repoRoot>/plugins/flow/package.json        (scripts: build/test/knip)
+ *   <repoRoot>/plugins/flow/pnpm-workspace.yaml (packages: [mcp-server])
+ *   <repoRoot>/plugins/flow/pnpm-lock.yaml      (so PM detects pnpm)
+ */
+
+import * as path from "node:path";
+import { promises as fs } from "node:fs";
+
+/** Seed the Flow-shaped build home at `<repoRoot>/plugins/flow`. */
+export async function seedFlowShapedBuildHome(repoRoot: string): Promise<string> {
+  const flowDir = path.join(repoRoot, "plugins", "flow");
+  await fs.mkdir(flowDir, { recursive: true });
+  await fs.writeFile(
+    path.join(flowDir, "package.json"),
+    JSON.stringify(
+      {
+        name: "flow",
+        private: true,
+        scripts: {
+          build: "pnpm -r build",
+          test: "pnpm -r test",
+          knip: "knip --no-progress",
+        },
+      },
+      null,
+      2,
+    ),
+    "utf8",
+  );
+  await fs.writeFile(
+    path.join(flowDir, "pnpm-workspace.yaml"),
+    "packages:\n  - mcp-server\n",
+    "utf8",
+  );
+  await fs.writeFile(
+    path.join(flowDir, "pnpm-lock.yaml"),
+    "lockfileVersion: '9.0'\n",
+    "utf8",
+  );
+  return flowDir;
+}