diff --git a/packages/flow-schema/package.json b/packages/flow-schema/package.json
index c078cc7..397d85b 100644
--- a/packages/flow-schema/package.json
+++ b/packages/flow-schema/package.json
@@ -17,6 +17,10 @@
       "types": "./dist/index.d.ts",
       "import": "./dist/index.js"
     },
+    "./structure": {
+      "types": "./dist/structure.d.ts",
+      "import": "./dist/structure.js"
+    },
     "./schema/v1": "./dist/generated/flow.v1.schema.json"
   },
   "files": [
diff --git a/packages/flow-schema/src/index.ts b/packages/flow-schema/src/index.ts
index 137e41f..6700aa1 100644
--- a/packages/flow-schema/src/index.ts
+++ b/packages/flow-schema/src/index.ts
@@ -11,12 +11,15 @@
 // in-repo copy so the Phase 3 swap is a dependency change, not a code
 // change.
 
-import { Ajv2020 } from 'ajv/dist/2020.js';
-import type { ErrorObject } from 'ajv';
-
 // The schema as a generated TS module, not a JSON import: import
 // attributes (`with { type: 'json' }`) don't survive every consumer
 // bundler. The raw JSON is still shipped at the `./schema/v1` export.
+//
+// Note: Ajv-based structural validation (`validateStructure`) deliberately
+// does NOT live here — it compiles a schema via runtime code generation,
+// which crashes code-gen-disallowed runtimes (Cloudflare Workers) at
+// import time. It lives behind the `@wavekat/flow-schema/structure`
+// subpath so this barrel stays Ajv-free and safe to bundle on the edge.
 import schema from './generated/schema.js';
 
 // Model: generated types + hand-written constants & helpers.
@@ -50,20 +53,3 @@ export {
   setNodeValue,
   stampIdentity,
 } from './mutate.js';
-
-const ajv = new Ajv2020({ allErrors: true, strict: false });
-const validateFn = ajv.compile(schema);
-
-export type StructuralResult =
-  | { valid: true }
-  | { valid: false; errors: ErrorObject[] };
-
-/**
- * Validate an already-parsed document against the normative JSON Schema
- * (structure only — no reachability / exit-wiring / hours semantics; use
- * `checkFlow` / `validateFlow` for those).
- */
-export function validateStructure(doc: unknown): StructuralResult {
-  const valid = validateFn(doc);
-  return valid ? { valid: true } : { valid: false, errors: validateFn.errors ?? [] };
-}
diff --git a/packages/flow-schema/src/structure.ts b/packages/flow-schema/src/structure.ts
new file mode 100644
index 0000000..2d9cc2d
--- /dev/null
+++ b/packages/flow-schema/src/structure.ts
@@ -0,0 +1,40 @@
+// JSON-Schema structural validation — kept OUT of the package barrel.
+//
+// Ajv compiles a schema by *generating JavaScript source and `new
+// Function`-ing it* into a validator (its whole speed model is JIT). Any
+// runtime that disallows code-generation-from-strings — notably the
+// Cloudflare Workers isolate the platform API runs on — throws
+// `EvalError: Code generation from strings disallowed` the moment this
+// module is evaluated. Because the compile happens at import time, merely
+// importing the barrel used to crash such consumers at startup even when
+// they never called `validateStructure`.
+//
+// So this lives behind the `@wavekat/flow-schema/structure` subpath: the
+// main entry (`.`) stays pure hand-written code with no Ajv in its module
+// graph, and only Node-side consumers that actually want meta-schema
+// structural validation opt into the Ajv dependency. This subpath is NOT
+// safe to import from a Workers/edge bundle.
+
+import { Ajv2020 } from 'ajv/dist/2020.js';
+import type { ErrorObject } from 'ajv';
+
+import schema from './generated/schema.js';
+
+const ajv = new Ajv2020({ allErrors: true, strict: false });
+const validateFn = ajv.compile(schema);
+
+export type StructuralResult =
+  | { valid: true }
+  | { valid: false; errors: ErrorObject[] };
+
+/**
+ * Validate an already-parsed document against the normative JSON Schema
+ * (structure only — no reachability / exit-wiring / hours semantics; use
+ * `checkFlow` / `validateFlow` for those).
+ *
+ * Node-side only — see the module header on Workers incompatibility.
+ */
+export function validateStructure(doc: unknown): StructuralResult {
+  const valid = validateFn(doc);
+  return valid ? { valid: true } : { valid: false, errors: validateFn.errors ?? [] };
+}
diff --git a/packages/flow-schema/test/conformance.test.ts b/packages/flow-schema/test/conformance.test.ts
index 31b7656..ce64b23 100644
--- a/packages/flow-schema/test/conformance.test.ts
+++ b/packages/flow-schema/test/conformance.test.ts
@@ -13,7 +13,8 @@ import { fileURLToPath } from 'node:url';
 import { describe, expect, it } from 'vitest';
 import { parse } from 'yaml';
 
-import { checkFlow, validateStructure } from '../src/index.js';
+import { checkFlow } from '../src/index.js';
+import { validateStructure } from '../src/structure.js';
 
 const here = dirname(fileURLToPath(import.meta.url));
 const corpusRoot = resolve(here, '..', '..', '..', 'conformance', 'v1');