Add active-turn steering (#3394)

* feat(agents): add active-turn steering

Let users choose whether an immediate prompt interrupts or joins the active turn. The daemon owns exact-turn admission, provider delivery, safe fallback, and canonical timeline identity while queueing remains client-side.

* fix(agents): stabilize steering history and replay QA

* fix(agents): preserve steering timeline order

* fix(agents): reconcile resumed provider history

* fix(agents): serialize steering with cancellation

* test(agents): prove Claude multi-tool steering

* test(agents): force explicit history hydration

* fix(agents): flush output before steer admission

packages/app/src/composer/actions.test.ts

@@ -179,6 +179,7 @@ interface FakeSendCall {
   text: string;
   options: {
     messageId: string;
+    activeTurnBehavior?: "interrupt" | "steer";
     images: Array<{ data: string; mimeType: string }>;
     attachments: AgentAttachment[];
   };
@@ -417,6 +418,50 @@ describe("pickAndPersistImages", () => {
 });
 
 describe("dispatchComposerAgentMessage", () => {
+  it("forwards the configured active-turn intent without provider capability checks", async () => {
+    const client = createFakeSendClient();
+    const stream = createFakeStream();
+
+    await dispatchComposerAgentMessage({
+      client,
+      agentId: "agent",
+      text: "steer this turn",
+      attachments: [],
+      encodeImages: async () => [],
+      submission: stream,
+      activeTurnBehavior: "steer",
+    });
+
+    expect(client.calls[0]?.options.activeTurnBehavior).toBe("steer");
+  });
+
+  it("stamps only a steer optimistic row with the daemon active turn ID", async () => {
+    const client = createFakeSendClient();
+    const stream = createFakeStream();
+    await dispatchComposerAgentMessage({
+      client,
+      agentId: "agent",
+      text: "hello",
+      attachments: [],
+      encodeImages: async () => [],
+      submission: stream,
+      activeTurnBehavior: "steer",
+      activeTurnId: "turn-1",
+    });
+    expect(stream.tail.get("agent")?.[0]).toMatchObject({ turnId: "turn-1" });
+    const legacy = createFakeStream();
+    await dispatchComposerAgentMessage({
+      client,
+      agentId: "legacy",
+      text: "hello",
+      attachments: [],
+      encodeImages: async () => [],
+      submission: legacy,
+      activeTurnBehavior: "steer",
+    });
+    expect(legacy.tail.get("legacy")?.[0]?.turnId).toBeUndefined();
+  });
+
   it("removes the submitted prompt when the host rejects it", async () => {
     const rejection = new Error("Host rejected prompt");
     const client = createFakeSendClient({ rejection });
@@ -477,6 +522,28 @@ describe("dispatchComposerAgentMessage", () => {
     ).rejects.toBe(transportError);
   });
 
+  it("surfaces an ambiguous failure even when a concurrent canonical echo was observed", async () => {
+    const transportError = new Error("Connection lost after delivery may have occurred");
+    const client = createFakeSendClient({ rejection: transportError });
+    const submission: MessageSubmissionWriter = {
+      begin: () => {},
+      accept: () => {},
+      reject: () => "accepted",
+    };
+
+    await expect(
+      dispatchComposerAgentMessage({
+        client,
+        agentId: "agent",
+        text: "ambiguous steer",
+        attachments: [],
+        encodeImages: passthroughEncodeImages,
+        submission,
+        activeTurnBehavior: "steer",
+      }),
+    ).rejects.toBe(transportError);
+  });
+
   it("sends text + image data + structured attachments and appends user_message to the tail when head is empty", async () => {
     const client = createFakeSendClient();
     const stream = createFakeStream();