Pass optimistic user ids to turn start

src/app-server/client.ts

@@ -326,6 +326,7 @@ export class AppServerClient {
     threadId: string,
     cwd: string,
     input: string | UserInput[],
+    clientUserMessageId?: string | null,
     serviceTier?: ServiceTierRequest,
     collaborationMode?: CollaborationMode | null,
     model?: string | null,
@@ -335,6 +336,7 @@ export class AppServerClient {
     const params: ClientRequestParams<"turn/start"> & { collaborationMode?: CollaborationMode | null } = {
       threadId,
       cwd,
+      ...(clientUserMessageId !== undefined ? { clientUserMessageId } : {}),
       ...(serviceTier !== undefined ? { serviceTier } : {}),
       input: toUserInput(input),
     };

src/features/chat/controllers/submission/turn-submission-controller.ts

@@ -66,7 +66,7 @@ export class TurnSubmissionController {
       this.host.setDraft("");
       this.host.render();
 
-      const response = await client.startTurn(activeThreadId, this.host.vaultPath, codexInput);
+      const response = await client.startTurn(activeThreadId, this.host.vaultPath, codexInput, optimisticUserId);
       const pendingStart = this.state.pendingTurnStart;
       if (
         shouldAcknowledgeTurnStart({

tests/app-server/app-server-client.test.ts

@@ -229,13 +229,14 @@ describe("AppServerClient", () => {
     transport.emitLine({ id: 2, result: { thread: { id: "thread-1", title: null }, serviceTier: "fast" } });
     await startingThread;
 
-    const startingTurn = client.startTurn("thread-1", "/vault", "hello", null);
+    const startingTurn = client.startTurn("thread-1", "/vault", "hello", "local-user-1", null);
     expect(transport.sent[3]).toMatchObject({
       id: 3,
       method: "turn/start",
       params: {
         threadId: "thread-1",
         cwd: "/vault",
+        clientUserMessageId: "local-user-1",
         serviceTier: null,
         input: [{ type: "text", text: "hello", text_elements: [] }],
       },
@@ -251,7 +252,7 @@ describe("AppServerClient", () => {
       { type: "mention" as const, name: "Alpha", path: "thoughts/Alpha.md" },
     ];
 
-    const startingTurn = client.startTurn("thread-1", "/vault", input, null);
+    const startingTurn = client.startTurn("thread-1", "/vault", input);
     expect(transport.sent[2]).toMatchObject({
       method: "turn/start",
       params: {
@@ -292,7 +293,7 @@ describe("AppServerClient", () => {
   it("sends collaboration mode only for Plan turns", async () => {
     const { client, transport } = await connectedClient();
 
-    const defaultTurn = client.startTurn("thread-1", "/vault", "default", null, null);
+    const defaultTurn = client.startTurn("thread-1", "/vault", "default", undefined, null, null);
     expect(transport.sent[2]).toMatchObject({
       method: "turn/start",
       params: {
@@ -305,7 +306,7 @@ describe("AppServerClient", () => {
     transport.emitLine({ id: 2, result: { turn: { id: "turn-default" } } });
     await defaultTurn;
 
-    const planTurn = client.startTurn("thread-1", "/vault", "plan", null, {
+    const planTurn = client.startTurn("thread-1", "/vault", "plan", undefined, null, {
       mode: "plan",
       settings: {
         model: "gpt-5.5",
@@ -336,7 +337,7 @@ describe("AppServerClient", () => {
   it("sends model and effort turn overrides when provided", async () => {
     const { client, transport } = await connectedClient();
 
-    const startingTurn = client.startTurn("thread-1", "/vault", "override", null, null, "gpt-5.5", "high");
+    const startingTurn = client.startTurn("thread-1", "/vault", "override", undefined, null, null, "gpt-5.5", "high");
     expect(transport.sent[2]).toMatchObject({
       method: "turn/start",
       params: {
@@ -350,7 +351,7 @@ describe("AppServerClient", () => {
     transport.emitLine({ id: 2, result: { turn: { id: "turn-override" } } });
     await startingTurn;
 
-    const resetTurn = client.startTurn("thread-1", "/vault", "reset", null, null, null, null);
+    const resetTurn = client.startTurn("thread-1", "/vault", "reset", undefined, null, null, null, null);
     expect(transport.sent[3]).toMatchObject({
       method: "turn/start",
       params: {
@@ -368,7 +369,17 @@ describe("AppServerClient", () => {
   it("sends approval reviewer turn overrides when provided", async () => {
     const { client, transport } = await connectedClient();
 
-    const autoReviewTurn = client.startTurn("thread-1", "/vault", "review this", null, null, undefined, undefined, "auto_review");
+    const autoReviewTurn = client.startTurn(
+      "thread-1",
+      "/vault",
+      "review this",
+      undefined,
+      null,
+      null,
+      undefined,
+      undefined,
+      "auto_review",
+    );
     expect(transport.sent[2]).toMatchObject({
       method: "turn/start",
       params: {
@@ -381,7 +392,7 @@ describe("AppServerClient", () => {
     transport.emitLine({ id: 2, result: { turn: { id: "turn-auto-review" } } });
     await autoReviewTurn;
 
-    const userReviewTurn = client.startTurn("thread-1", "/vault", "ask me", null, null, undefined, undefined, "user");
+    const userReviewTurn = client.startTurn("thread-1", "/vault", "ask me", undefined, null, null, undefined, undefined, "user");
     expect(transport.sent[3]).toMatchObject({
       method: "turn/start",
       params: {

tests/features/chat/controllers/submission/turn-submission-controller.test.ts

@@ -88,7 +88,7 @@ describe("TurnSubmissionController", () => {
     expect(host.startThread).toHaveBeenCalledWith("hello");
     expect(host.notifyActiveThreadIdentityChanged).toHaveBeenCalledOnce();
     expect(host.resetThreadTurnPresence).toHaveBeenCalledWith(false);
-    expect(startTurn).toHaveBeenCalledWith("thread", "/vault", textInput("hello"));
+    expect(startTurn).toHaveBeenCalledWith("thread", "/vault", textInput("hello"), expect.stringMatching(/^local-user-\d+$/));
     expect(stateStore.getState().turnLifecycle).toEqual({ kind: "running", turnId: "turn" });
     expect(host.setDraft).toHaveBeenCalledWith("");
     expect(host.setStatus).toHaveBeenCalledWith("Turn running...");

tests/features/chat/view-connection.test.ts

@@ -365,7 +365,12 @@ describe("CodexChatView connection lifecycle", () => {
     await (view as unknown as { submitComposerAction: () => Promise<void> }).submitComposerAction();
 
     expect(client.resumeThread).toHaveBeenCalledWith("thread-1", "/vault");
-    expect(client.startTurn).toHaveBeenCalledWith("thread-1", "/vault", [{ type: "text", text: "hello", text_elements: [] }]);
+    expect(client.startTurn).toHaveBeenCalledWith(
+      "thread-1",
+      "/vault",
+      [{ type: "text", text: "hello", text_elements: [] }],
+      expect.stringMatching(/^local-user-\d+$/),
+    );
     expect(view.getState()).toEqual({ version: 1, threadId: "thread-1", threadTitle: "Restored thread" });
   });