Implement ACPX outbound extension delivery

Co-Authored-By: Paperclip <noreply@paperclip.ing>

doc/plans/2026-10-02-pi-production-readiness.md

@@ -42,6 +42,26 @@ prices are estimates. Unpriced usage must stay unpriced in the ledger and UI.
 
 ## Evidence so far
 
+- At `4237bc369`, the native turn-binding correction advances the steering
+  journey past `steering_stale_turn`, but the provider boundary still rejects
+  delivery. The real patched ACPX client lacks `requestExtension`: its types
+  and runtime callers declare it, while its implementation omits it. A real
+  package regression fails with that exact TypeError before the correction,
+  then passes steering and follow-up during an unanswered prompt afterward.
+  This is a separate runtime correction and needs a fresh installed journey.
+- The corrected Intel public package at `4237bc369` passes credential-free
+  closed startup in 37.8 seconds. Its CI typecheck, build, native tests and
+  browser shards pass. CI retains two failures: a resumed durability test
+  inherits the deliberately killed attempt's 500 ms timeout; the Linux public
+  Pi probe reaches `session_handshake_timeout`. The former gets an explicit
+  resumed-turn bound. The latter remains an admission blocker; accepting a
+  timeout as successful installation would weaken the release gate.
+- The local Linux image build at `4237bc369` fails before a provider starts
+  because the committed lock does not match the source patch configuration.
+  The official image workflow already regenerates its private build lock;
+  local builds must do the same and record that resolved lock's digest.
+  No repository lockfile or workflow changes are required.
+
 - `2b50801b2`: installed restart failed before native answer delivery. The
   durable request turn ID differs from the provider turn ID. The browser's
   issue-identifier route also differed from the matcher's UUID route.

packages/paperclip-runner/src/live/live-session.test.ts

@@ -1813,6 +1813,9 @@ describe("Capability live runnerd and Codex session", () => {
       sessionId: binding.sessionId,
       attemptId: "attempt-resumed",
       resumeOf: "attempt-killed",
+      // Only the killed attempt deliberately uses the short timeout. Allow
+      // durable disk writes to complete during the resumed successful turn.
+      turnTimeoutMs: 5_000,
     });
     expect(resumed.snapshot().providerThreadId).toBe(state.threadId);
     expect(resumed.snapshot().attempts).toMatchObject([

packages/paperclip-runner/test/acpx-rich-extensions-package-contract.test.mjs

@@ -25,6 +25,8 @@ readline.createInterface({input:process.stdin}).on('line',(line)=>{
   send({method:'fixture/ignored',params:{sessionId:'session-1'}});
   send({method:'fixture/activity',params:{sessionId:'wrong-session'}});
   send({id:0,method:mode==='unknown'?'fixture/not-enabled':'fixture/question',params:{sessionId:mode==='wrong-session'?'wrong-session':'session-1',value:'private-question'}});
+ } else if(message.method==='pi/steer' || message.method==='pi/follow_up') {
+  send({id:message.id,result:{accepted:true,sessionId:message.params.sessionId,disposition:'queued',message:message.params.message}});
  } else if(message.method==='session/cancel') { send({id:promptId,result:{stopReason:'cancelled'}}); promptId=undefined; }
  else if(message.id===0 && !message.method) {
   send({method:'session/update',params:{sessionId:'session-1',update:{sessionUpdate:'agent_message_chunk',content:{type:'text',text:JSON.stringify(message)}}}});
@@ -77,6 +79,29 @@ test("initialize retains mandatory capabilities while merging provider metadata"
   });
 });
 
+test("real patched client sends Pi steering and follow-up while its original prompt awaits input", { timeout: 10000 }, async () => {
+  let observe; const started = new Promise(resolve => { observe = resolve; });
+  await withClient({ onExtensionRequest: async () => { observe(); return await new Promise(() => {}); } }, async client => {
+    const pending = client.prompt("session-1", "question");
+    await started;
+    try {
+      for (const method of ["pi/steer", "pi/follow_up"]) {
+        assert.deepEqual(await client.requestExtension(method, { sessionId: "session-1", message: "Keep the original turn" }), {
+          accepted: true, sessionId: "session-1", disposition: "queued", message: "Keep the original turn",
+        });
+      }
+      for (const method of ["session/prompt", "fs/read_text_file", "initialize", "bad method/name"]) {
+        await assert.rejects(client.requestExtension(method, {}), /extension method/);
+      }
+      await assert.rejects(client.requestExtension("pi/steer", []), /payload must be an object/);
+      await assert.rejects(client.requestExtension("pi/steer", { message: "x".repeat(256 * 1024) }), /bounded size/);
+    } finally {
+      await client.cancel("session-1");
+      assert.equal((await pending).stopReason, "cancelled");
+    }
+  });
+});
+
 test("unknown methods and cross-session requests never reach the host callback", { timeout: 10000 }, async () => {
   let calls = 0;
   await withClient({ onExtensionRequest: async () => { calls++; return {}; } }, async (client) => {

patches/acpx@0.13.1.patch

@@ -523,7 +523,21 @@ index d454fd7c5..6eba74345 100644
  			}));
  			result = claudeAcp ? await withTimeout(createPromise, resolveClaudeAcpSessionCreateTimeoutMs()) : await createPromise;
  		} catch (error) {
-@@ -4864,7 +5099,7 @@ var AcpClient = class {
+@@ -4596,6 +4831,13 @@ var AcpClient = class {
+ 		}
+ 	}
++	async requestExtension(method, params) {
++		closedExtensionMethods([method]);
++		const payload = boundedExtensionRecord(params);
++		const connection = this.getConnection();
++		const result = await this.runConnectionRequest(() => connection.extMethod(method, payload));
++		return boundedExtensionRecord(result);
++	}
+ 	async setSessionModel(sessionId, modelId, controlOverride) {
+ 		const control = this.resolveModelControl(sessionId, controlOverride);
+ 		if (!control) throw new RequestedModelUnsupportedError(`Cannot set model "${modelId}": the ACP session did not advertise a model config option or legacy session/set_model support.`, "missing-capability");
+ 		const resolvedModelId = resolveRequestedModelId({
+@@ -4864,7 +5106,7 @@ var AcpClient = class {
  	}
  	selectAuthMethod(methods) {
  		for (const method of methods) {