diff --git a/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.ts b/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.ts
index 51a0d542d7f..b1508e9d02f 100644
--- a/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.ts
+++ b/packages/paperclip-runner/src/drivers/acpx/codex-runtime-adapter.ts
@@ -87,6 +87,8 @@ interface AcpxRuntimeGoalState {
 
 interface AcpxRuntimeExtensionTurn {
   nativeTurnToken?: string;
+  nativeTurnReady: Promise<void>;
+  acknowledgeNativeTurn(): void;
   requestId: string;
   sessionId: string;
   controller: AbortController;
@@ -352,6 +354,7 @@ export async function openQualifiedAcpxRuntime(
       if (options.profile.agent === "hermes" && method === "_hermes/turn_started") {
         if (!active || !ownsExtensionTurn(active, params) || params.version !== 1 || typeof params.turnToken !== "string" || !/^[0-9a-f-]{36}$/.test(params.turnToken) || active.nativeTurnToken) throw new Error("Invalid Hermes turn binding");
         active.nativeTurnToken = params.turnToken;
+      active.acknowledgeNativeTurn();
         return;
       }
       if (!extensionNotifications.has(method) || !active?.onNotification || !ownsExtensionTurn(active, params)) return;
@@ -1045,7 +1048,11 @@ function runtimePort(
       await abortableExtensionResult(active.promptStarted, active.signal);
       active.signal.throwIfAborted();
       if (extensionBoundary.active !== active) throw new Error("ACPX extension control turn expired");
-      if (method === "_hermes/steer" && !active.nativeTurnToken) throw new Error("Hermes has not acknowledged an active turn");
+      if (method === "_hermes/steer") {
+        await waitForHermesNativeTurn(active);
+        active.signal.throwIfAborted();
+        if (extensionBoundary.active !== active) throw new Error("ACPX extension control turn expired");
+      }
       const response = await abortableExtensionResult(runtime.requestExtension!({
         handle, method, params: { sessionId: identity.backendSessionId, message: text,
           ...(method === "_hermes/steer" ? { version: 1, turnToken: active.nativeTurnToken } : {}),
@@ -1392,7 +1399,10 @@ function runtimePort(
       if (extensionBoundary.active) throw new Error("ACPX runtime already has an active turn");
       const approval = new AbortController();
       const controller = new AbortController();
+      let acknowledgeNativeTurn!: () => void;
+      const nativeTurnReady = new Promise<void>(resolve => { acknowledgeNativeTurn = resolve; });
       const extensionTurn: AcpxRuntimeExtensionTurn = {
+        nativeTurnReady, acknowledgeNativeTurn,
         requestId: input.requestId, sessionId: identity.backendSessionId, controller,
         signal: input.signal ? AbortSignal.any([controller.signal, input.signal, approval.signal]) : AbortSignal.any([controller.signal, approval.signal]),
         promptStarted: Promise.resolve(),
@@ -2025,6 +2035,17 @@ async function abortableExtensionResult<T>(result: Promise<T>, signal: AbortSign
   finally { if (rejectAbort) signal.removeEventListener("abort", rejectAbort); }
 }
 
+async function waitForHermesNativeTurn(active: AcpxRuntimeExtensionTurn): Promise<void> {
+  if (active.nativeTurnToken) return;
+  let timer: ReturnType<typeof setTimeout> | undefined;
+  try {
+    await abortableExtensionResult(Promise.race([active.nativeTurnReady, new Promise<never>((_resolve, reject) => {
+      timer = setTimeout(() => reject(new Error("Hermes native turn acknowledgement timed out")), 5_000);
+      timer.unref();
+    })]), active.signal);
+  } finally { if (timer) clearTimeout(timer); }
+}
+
 function goalCapabilityFromAcpMessage(
   message: unknown,
 ): AcpxRuntimeGoalCapability | null {
diff --git a/packages/paperclip-runner/src/drivers/acpx/hermes-extensions.test.ts b/packages/paperclip-runner/src/drivers/acpx/hermes-extensions.test.ts
index e6ae3da9de6..265dccafc64 100644
--- a/packages/paperclip-runner/src/drivers/acpx/hermes-extensions.test.ts
+++ b/packages/paperclip-runner/src/drivers/acpx/hermes-extensions.test.ts
@@ -30,11 +30,35 @@ describe("Hermes native extensions", () => {
     const response = (value: string) => ({ action: "submit" as const, response: { schema: "paperclip.question_response.v1" as const,
       answers: { q0: answerMode === "text" ? { text: value } : { customText: value } },
     } });
-    expect(result.input.resolve(response("😀".repeat(32_768)))).toMatchObject({ outcome: "answered" });
-    for (const value of ["x".repeat(65_537), "x".repeat(70_000), "😀".repeat(32_769)]) {
-      expect(() => result.input.resolve(response(value))).toThrow("at most 65536 characters");
+    const limit = result.input.questionSet.questions[0]!.textValidation!.maxLength!;
+    expect(limit).toBeLessThan(65_536);
+    expect(result.input.resolve(response("😀".repeat(Math.floor(limit / 2))))).toMatchObject({ outcome: "answered" });
+    for (const value of ["x".repeat(limit + 1), "x".repeat(70_000), "😀".repeat(Math.floor(limit / 2) + 1)]) {
+      expect(() => result.input.resolve(response(value))).toThrow(`at most ${limit} characters`);
     }
   });
+  it.each(["text", "single_select", "multi_select"])("keeps all accepted %s answers inside ACPX's encoded response bound", async answerMode => {
+    const result = await adapter().request("_hermes/ask_questions", { version: 1, sessionId: "session", input: {
+      schema: "paperclip.question_set.v1", questions: Array.from({ length: 5 }, (_, i) => ({
+        id: `q${i}` + "\u0000".repeat(158), prompt: "Why?", required: true, answerMode,
+        textValidation: { maxLength: 65_536 },
+        ...(answerMode === "text" ? {} : { options: Array.from({ length: 4 }, (_, j) => ({
+          id: `o${j}` + "\u0000".repeat(158), label: `Choice ${j}`,
+        })), customAnswer: { enabled: true } }),
+      })),
+    } });
+    if (!("input" in result)) throw new Error("Missing canonical question form");
+    const answers = Object.fromEntries(result.input.questionSet.questions.map(question => [question.id, {
+      selectedOptionIds: answerMode === "multi_select" ? question.options!.map(option => option.id) : [],
+      [answerMode === "text" ? "text" : "customText"]: "\u0000".repeat(question.textValidation!.maxLength!),
+    }]));
+    const response = result.input.resolve({ action: "submit", response: { schema: "paperclip.question_response.v1", answers } });
+    expect(Buffer.byteLength(JSON.stringify(response))).toBeLessThanOrEqual(256 * 1024);
+    const oversized = Object.fromEntries(result.input.questionSet.questions.map(question => [question.id, {
+      [answerMode === "text" ? "text" : "customText"]: "x".repeat(60_000),
+    }]));
+    expect(() => result.input.resolve({ action: "submit", response: { schema: "paperclip.question_response.v1", answers: oversized } })).toThrow("at most");
+  });
   it("preserves estimated-cost provenance without inventing billed cost", async () => {
     const events = await adapter().notification("_hermes/usage", { version: 1, sessionId: "session", tokens: "reported", cost: "estimated", estimatedUsd: 0.012 });
     events.forEach(validateAcpxRichEvent);
diff --git a/packages/paperclip-runner/src/drivers/acpx/profile-extensions.ts b/packages/paperclip-runner/src/drivers/acpx/profile-extensions.ts
index 9bbf64099ca..4922a042d41 100644
--- a/packages/paperclip-runner/src/drivers/acpx/profile-extensions.ts
+++ b/packages/paperclip-runner/src/drivers/acpx/profile-extensions.ts
@@ -33,6 +33,28 @@ export interface AcpxProfileExtensionContext {
   turnId: string;
 }
 
+/** ACPX 0.13.1 bounds the complete encoded extension response at 256 KiB.
+ * Reserve its fixed fields and every selectable ID, then budget text for the
+ * worst JSON escape (six bytes per JavaScript string code unit). The persisted
+ * form and response validator must share this limit before a human submits.
+ */
+function boundedHermesQuestionSet(value: unknown): PaperclipQuestionSet {
+  const input = parsePaperclipQuestionSet(value);
+  const largestEmptyAnswers = Object.fromEntries(input.questions.map(question => [question.id, {
+    selectedOptionIds: (question.options ?? []).map(option => option.id),
+    ...(question.answerMode === "text" ? { text: "" }
+      : question.customAnswer?.enabled ? { customText: "" } : {}),
+  }]));
+  const overhead = Buffer.byteLength(JSON.stringify({ outcome: "answered", answers: largestEmptyAnswers }));
+  const maxLength = Math.min(65_536, Math.floor((256 * 1024 - overhead) / (6 * input.questions.length)));
+  if (maxLength < 1) throw new Error("Hermes question answers exceed the encoded response limit");
+  return parsePaperclipQuestionSet({ ...input, questions: input.questions.map(question => ({
+    ...question, textValidation: { ...question.textValidation,
+      maxLength: Math.min(question.textValidation?.maxLength ?? maxLength, maxLength),
+    },
+  })) });
+}
+
 /** Provider branches install their closed, pinned adapters here after qualification research. */
 export function createAcpxProfileExtensionAdapter(
   agent: QualifiedAcpxAgent,
@@ -42,7 +64,7 @@ export function createAcpxProfileExtensionAdapter(
   if (agent === "hermes") return {
     async request(method, params) {
       if (method !== "_hermes/ask_questions" || params.version !== 1 || params.sessionId !== context.sessionId) throw new Error("Unsupported Hermes question extension");
-      const questionSet = parsePaperclipQuestionSet(params.input);
+      const questionSet = boundedHermesQuestionSet(params.input);
       return { input: {
         method, questionSet,
         resolve(resolution) {