diff --git a/packages/core/src/loop/boringstack/gate-stages.ts b/packages/core/src/loop/boringstack/gate-stages.ts
index f39c54cd..952c8f92 100644
--- a/packages/core/src/loop/boringstack/gate-stages.ts
+++ b/packages/core/src/loop/boringstack/gate-stages.ts
@@ -146,7 +146,7 @@ function structuredSteerMessage(message: string, file: string): string {
   // emits json+multipart+text for EVERY route, scaffold ones included) — NOT a route/schema bug.
   // The model burned ~60 turns (build15) chasing it on the API side; steer to the consumer.
   if (message.includes("Readable<SuccessResponse")) {
-    return `${message}\n↳ \`Readable<SuccessResponse<…>>\` is the api-client's NORMAL, UNIVERSAL response type — Elysia's swagger emits three media types (json/multipart/text) for EVERY route (the scaffold's own auth/dashboard routes are identical), so you CANNOT remove it by editing the route or the \`response:\` schema — do NOT try. Fix it on the CONSUMER: the 'not assignable to Promise<IEntity>' error means you annotated the \`.queries.ts\`/\`.mutations.ts\` fn \`: Promise<IEntity>\` and did a bare \`return data\` — the fix is to REMOVE that return-type annotation and let TS INFER it (never \`as\`-cast). Then return the payload for THIS route's response shape: if it wraps \`{ data: … }\` (scaffold auth pattern) read \`data?.data\`; if it returns the object/array directly, just \`return data\` — match your \`response:\` schema, don't blindly add \`.data\`.`;
+    return `${message}\n↳ \`Readable<SuccessResponse<…>>\` is the api-client's NORMAL, UNIVERSAL response type — Elysia's swagger emits three media types (json/multipart/text) for EVERY route (the scaffold's own auth/dashboard routes are identical), so you CANNOT remove it by editing the route or the \`response:\` schema — do NOT try. Fix it on the CONSUMER by INFERRING, not annotating — it shows up two ways, BOTH fixed by removing an annotation (never \`as\`-cast): (a) \`not assignable to Promise<IEntity>\` = you annotated the \`.queries.ts\`/\`.mutations.ts\` fn \`: Promise<IEntity>\` with a bare \`return data\`; (b) \`UseMutationResult<Readable<…>> not assignable to UseMutationResult<IEntity>\` (or \`UseQueryResult\`) = you annotated the HOOK generic/return (\`useMutation<IEntity>\` / \`: UseMutationResult<IEntity>\`). REMOVE the annotation on the fn AND the hook and let TS INFER both. Then return the payload for THIS route's response shape: if it wraps \`{ data: … }\` (scaffold auth pattern) read \`data?.data\`; if it returns the object/array directly, just \`return data\` — match your \`response:\` schema, don't blindly add \`.data\`.`;
   }
 
   // A `PathsWithMethod<paths, …>` error means the path STRING doesn't match any generated key —
diff --git a/packages/core/src/loop/conventions.ts b/packages/core/src/loop/conventions.ts
index 787baf85..63895d36 100644
--- a/packages/core/src/loop/conventions.ts
+++ b/packages/core/src/loop/conventions.ts
@@ -74,6 +74,9 @@ export const TOPIC_RULES: Readonly<Record<ConventionTopic, readonly string[]>> =
       "no-conditional-expect",
       "no-real-network-in-unit-tests",
       "fake-timers-must-be-restored",
+      // build16's final blocker (9× in one row-hook test): empty placeholder callbacks. The
+      // testing guide teaches `vi.fn()` for these, so map the rule here to re-push it reactively.
+      "no-empty-function",
     ],
     // The audit-event rule is a boringstack-OWN eslint rule (not a tsforge meta-rule), so it
     // isn't keyed here for the reactive PUSH — the front-loaded guide is the delivery path.
@@ -185,9 +188,13 @@ const GUIDES: Readonly<Record<ConventionTopic, string>> = {
     "stream) for EVERY route — Elysia's swagger emits three media types (json/multipart/text) so " +
     "openapi-fetch unions them. This is EXPECTED and UNIVERSAL (the scaffold's own auth/dashboard " +
     "routes are identical); you CANNOT remove it from the route/response schema, so do NOT try. FIX " +
-    "IT ON THE CONSUMER. The error `Readable<…> not assignable to Promise<IEntity>` means you " +
-    "annotated the query/mutation fn `: Promise<IEntity>` and did a bare `return data` — the " +
-    "UNIVERSAL fix is to REMOVE that return-type annotation and let TS INFER it (never `as`-cast). " +
+    "IT ON THE CONSUMER by INFERRING, not annotating. The error appears two ways, BOTH fixed by " +
+    "removing a type annotation so TS infers from the unwrapped payload (never `as`-cast): " +
+    "(a) `Readable<…> not assignable to Promise<IEntity>` — you annotated the query/mutation fn " +
+    "`: Promise<IEntity>` and did a bare `return data`; (b) `UseMutationResult<Readable<…>> not " +
+    "assignable to UseMutationResult<IEntity>` (or `UseQueryResult<…>`) — you annotated the HOOK's " +
+    "generic/return type (`useMutation<IEntity>` / `: UseMutationResult<IEntity>`). Do NEITHER: " +
+    "leave the fn AND the hook UN-annotated and let TS INFER both. " +
     "Then return the payload for YOUR route's response SHAPE: if the response wraps `{ data: … }` " +
     '(the scaffold auth pattern), read `data?.data` — `const { data } = await apiClient.GET("/api/v1/' +
     'supplier/"); return data?.data ?? [];`; if the route returns the object/array DIRECTLY (no ' +
@@ -253,7 +260,9 @@ const GUIDES: Readonly<Record<ConventionTopic, string>> = {
     "• RULES the gate enforces: no `.only`/`.skip` (no-focused-tests); never put `expect` inside an " +
     "`if`/loop/`switch`/ternary — assert unconditionally (no-conditional-expect); if you use fake " +
     "timers, restore them in `afterEach` (fake-timers-must-be-restored); the test path/name mirrors " +
-    "its source (test-file-mirrors-source).\n" +
+    "its source (test-file-mirrors-source). A no-op/placeholder callback (e.g. an unused handler " +
+    "arg when testing ONE of a hook's callbacks) must be `vi.fn()`, NEVER an empty `() => {}` — an " +
+    "empty arrow/function body is a `no-empty-function` gate error (observed: 9 in one row-hook test).\n" +
     "• After you write a test the harness AUTO-FORMATS it (imports reordered, quotes/commas normalized), " +
     "so your next `edit` oldString won't match — RE-READ the file and copy oldString from its current " +
     "content; do NOT recreate the whole file.",
diff --git a/packages/core/tests/boringstack-conventions.test.ts b/packages/core/tests/boringstack-conventions.test.ts
index 2ed40e70..32242c7a 100644
--- a/packages/core/tests/boringstack-conventions.test.ts
+++ b/packages/core/tests/boringstack-conventions.test.ts
@@ -163,6 +163,10 @@ describe("convention registry", () => {
     expect(g).toContain("data?.data");
     expect(g).toContain("EXPECTED and UNIVERSAL");
     expect(g).toContain("not assignable to Promise<IEntity>");
+    // build16: the SAME over-annotation habit also hits the HOOK generic (useMutation/useQuery),
+    // not just the fn return — the guide must name that facet too.
+    expect(g).toContain("UseMutationResult<Readable");
+    expect(g).toContain("HOOK's");
     // The UNIVERSAL fix is infer-don't-annotate; data?.data is SHAPE-CONDITIONAL (panel: not
     // every response is {data:…} — a raw object/array returns `data` directly), so the guide
     // must NOT categorically prescribe .data.
@@ -202,6 +206,9 @@ describe("convention registry", () => {
     expect(g).toContain("no-focused-tests");
     expect(g).toContain("no-conditional-expect");
     expect(g).toContain("fake-timers-must-be-restored");
+    // build16 final blocker: empty placeholder callbacks in tests → no-empty-function; use vi.fn().
+    expect(g).toContain("no-empty-function");
+    expect(g).toContain("vi.fn()");
     // The auto-reformat re-read (the not-found edit-reject churn).
     expect(g).toContain("AUTO-FORMATS");
   });
@@ -209,7 +216,7 @@ describe("convention registry", () => {
 
 describe("topicForRule (testing)", () => {
   test("EVERY testing rule maps to the testing topic so its gate error pushes the guide", () => {
-    // Lock all six — a typo in any would silently disable the reactive PUSH for that error.
+    // Lock all — a typo in any would silently disable the reactive PUSH for that error.
     for (const rule of [
       "test-sibling-required",
       "test-file-mirrors-source",
@@ -217,6 +224,8 @@ describe("topicForRule (testing)", () => {
       "no-conditional-expect",
       "no-real-network-in-unit-tests",
       "fake-timers-must-be-restored",
+      // build16: the empty-placeholder-callback rule must re-push the testing guide too.
+      "no-empty-function",
     ]) {
       expect(topicForRule(rule)).toBe("testing");
     }
diff --git a/packages/core/tests/boringstack-gate-stages.test.ts b/packages/core/tests/boringstack-gate-stages.test.ts
index a1a8bd79..8b5339bf 100644
--- a/packages/core/tests/boringstack-gate-stages.test.ts
+++ b/packages/core/tests/boringstack-gate-stages.test.ts
@@ -183,6 +183,10 @@ describe("signatureToError", () => {
     // Universal move is infer-don't-annotate; unwrap is shape-conditional (not blind .data).
     expect(err.message).toContain("let TS INFER");
     expect(err.message).toContain("don't blindly add");
+    // Steer must name BOTH annotation sites — the fn AND the useMutation/useQuery HOOK generic
+    // (build16 oscillated on the hook one; guide + steer must agree).
+    expect(err.message).toContain("UseMutationResult<Readable");
+    expect(err.message).toContain("HOOK generic");
     // Must NOT tell the model to fix the route/schema for this.
     expect(err.message).toContain("CANNOT remove it by editing the route");
   });