fix: fail closed v3 legacy semantic fallbacks

backend/test/workspaces-bindings.test.ts

@@ -31,6 +31,29 @@ semantic_index:
 llm_policy:
   allowed: [zai/glm-5.2]
 `);
+const workspaceV3 = parseWorkspaceYaml(`workspace:
+  schema_version: 3
+  id: psd-clinical
+  name: Policlinico San Donato
+  language: it
+dwh:
+  engine: postgres
+  database: postgres
+  schema: datawarehouse
+  supported_transports: [postgres_direct, rest_api]
+semantic_index:
+  vector_store:
+    engine: qdrant
+    collection: psd-clinical
+    dimensions: 1024
+    distance: cosine
+  embedding:
+    provider: ollama_internal
+    model: qwen3-embedding:0.6b
+    dimensions: 1024
+llm_policy:
+  allowed: [zai/glm-5.2]
+`);
 const temporaryRoots: string[] = [];
 
 afterEach(() => {
@@ -196,3 +219,12 @@ test("never treats a vector reader credential as the optional writer binding", (
     values: {},
   });
 });
+
+test("fails closed for v3 external semantic bindings", () => {
+  expect(() => resolveBinding(workspaceV3, "VECTOR", {}, ["/run/secrets"]))
+    .toThrow(/unsupported|schema version 3|semantic/i);
+  expect(() => resolveBinding(workspaceV3, "EMBEDDING", {}, ["/run/secrets"]))
+    .toThrow(/unsupported|schema version 3|semantic/i);
+  expect(() => resolveRuntimeBindings(workspaceV3, {}, ["/run/secrets"]))
+    .toThrow(/unsupported|schema version 3|semantic/i);
+});