fix(threads): preserve auto-title matching after prompt formatting

Author: maria-rcks

apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts

@@ -425,6 +425,58 @@ describe("ProviderCommandReactor", () => {
     expect(thread?.title).toBe("Keep this custom title");
   });
 
+  it("matches the client-seeded title even when the outgoing prompt is reformatted", async () => {
+    const harness = await createHarness();
+    const now = new Date().toISOString();
+    const seededTitle = "Fix reconnect spinner on resume";
+    harness.generateThreadTitle.mockReturnValue(
+      Effect.succeed({
+        title: "Reconnect spinner resume bug",
+      }),
+    );
+
+    await Effect.runPromise(
+      harness.engine.dispatch({
+        type: "thread.meta.update",
+        commandId: CommandId.makeUnsafe("cmd-thread-title-formatted-seed"),
+        threadId: ThreadId.makeUnsafe("thread-1"),
+        title: seededTitle,
+      }),
+    );
+
+    await Effect.runPromise(
+      harness.engine.dispatch({
+        type: "thread.turn.start",
+        commandId: CommandId.makeUnsafe("cmd-turn-start-title-formatted"),
+        threadId: ThreadId.makeUnsafe("thread-1"),
+        message: {
+          messageId: asMessageId("user-message-title-formatted"),
+          role: "user",
+          text: "[effort:high]\\n\\nFix reconnect spinner on resume",
+          attachments: [],
+        },
+        titleSeed: seededTitle,
+        textGenerationModel: "gpt-5.4-mini",
+        interactionMode: DEFAULT_PROVIDER_INTERACTION_MODE,
+        runtimeMode: "approval-required",
+        createdAt: now,
+      }),
+    );
+
+    await waitFor(() => harness.generateThreadTitle.mock.calls.length === 1);
+    await waitFor(async () => {
+      const readModel = await Effect.runPromise(harness.engine.getReadModel());
+      return (
+        readModel.threads.find((entry) => entry.id === ThreadId.makeUnsafe("thread-1"))?.title ===
+        "Reconnect spinner resume bug"
+      );
+    });
+
+    const readModel = await Effect.runPromise(harness.engine.getReadModel());
+    const thread = readModel.threads.find((entry) => entry.id === ThreadId.makeUnsafe("thread-1"));
+    expect(thread?.title).toBe("Reconnect spinner resume bug");
+  });
+
   it("reuses the text generation model for automatic worktree branch naming", async () => {
     const harness = await createHarness();
     const now = new Date().toISOString();

apps/server/src/orchestration/Layers/ProviderCommandReactor.ts

@@ -79,8 +79,16 @@ const DEFAULT_THREAD_TITLE = "New thread";
 function buildReplaceableThreadTitles(input: {
   readonly messageText: string;
   readonly attachments?: ReadonlyArray<ChatAttachment>;
+  readonly titleSeed?: string;
 }): ReadonlySet<string> {
   const titles = new Set<string>([DEFAULT_THREAD_TITLE]);
+  const trimmedTitleSeed = input.titleSeed?.trim();
+
+  if (trimmedTitleSeed) {
+    titles.add(trimmedTitleSeed);
+    return titles;
+  }
+
   const trimmedMessage = input.messageText.trim();
 
   if (trimmedMessage.length > 0) {
@@ -101,6 +109,7 @@ function isReplaceableThreadTitle(
   input: {
     readonly messageText: string;
     readonly attachments?: ReadonlyArray<ChatAttachment>;
+    readonly titleSeed?: string;
   },
 ): boolean {
   return buildReplaceableThreadTitles(input).has(currentTitle.trim());
@@ -565,6 +574,7 @@ const make = Effect.gen(function* () {
       const generationInput = {
         messageText: message.text,
         ...(message.attachments !== undefined ? { attachments: message.attachments } : {}),
+        ...(event.payload.titleSeed !== undefined ? { titleSeed: event.payload.titleSeed } : {}),
         ...(event.payload.textGenerationModel !== undefined
           ? { textGenerationModel: event.payload.textGenerationModel }
           : {}),

apps/server/src/orchestration/decider.ts

@@ -377,6 +377,7 @@ export const decideOrchestrationCommand = Effect.fn("decideOrchestrationCommand"
           ...(command.modelSelection !== undefined
             ? { modelSelection: command.modelSelection }
             : {}),
+          ...(command.titleSeed !== undefined ? { titleSeed: command.titleSeed } : {}),
           ...(command.textGenerationModel !== undefined
             ? { textGenerationModel: command.textGenerationModel }
             : {}),

apps/web/src/components/ChatView.tsx

@@ -2711,6 +2711,7 @@ export default function ChatView({ threadId }: ChatViewProps) {
           attachments: turnAttachments,
         },
         modelSelection: selectedModelSelection,
+        titleSeed: title,
         textGenerationModel: selectedTextGenerationModel,
         assistantDeliveryMode: settings.enableAssistantStreaming ? "streaming" : "buffered",
         runtimeMode,
@@ -2994,6 +2995,7 @@ export default function ChatView({ threadId }: ChatViewProps) {
             attachments: [],
           },
           modelSelection: selectedModelSelection,
+          titleSeed: activeThread.title,
           textGenerationModel: selectedTextGenerationModel,
           assistantDeliveryMode: settings.enableAssistantStreaming ? "streaming" : "buffered",
           runtimeMode,
@@ -3113,6 +3115,7 @@ export default function ChatView({ threadId }: ChatViewProps) {
             attachments: [],
           },
           modelSelection: selectedModelSelection,
+          titleSeed: nextThreadTitle,
           textGenerationModel: selectedTextGenerationModel,
           assistantDeliveryMode: settings.enableAssistantStreaming ? "streaming" : "buffered",
           runtimeMode,

packages/contracts/src/orchestration.test.ts

@@ -338,6 +338,25 @@ it.effect("accepts a text generation model in thread.turn.start", () =>
   }),
 );
 
+it.effect("accepts a title seed in thread.turn.start", () =>
+  Effect.gen(function* () {
+    const parsed = yield* decodeThreadTurnStartCommand({
+      type: "thread.turn.start",
+      commandId: "cmd-turn-title-seed",
+      threadId: "thread-1",
+      message: {
+        messageId: "msg-title-seed",
+        role: "user",
+        text: "hello",
+        attachments: [],
+      },
+      titleSeed: "Investigate reconnect failures",
+      createdAt: "2026-01-01T00:00:00.000Z",
+    });
+    assert.strictEqual(parsed.titleSeed, "Investigate reconnect failures");
+  }),
+);
+
 it.effect("accepts a source proposed plan reference in thread.turn.start", () =>
   Effect.gen(function* () {
     const parsed = yield* decodeThreadTurnStartCommand({
@@ -409,6 +428,18 @@ it.effect("decodes thread.turn-start-requested text generation model when presen
   }),
 );
 
+it.effect("decodes thread.turn-start-requested title seed when present", () =>
+  Effect.gen(function* () {
+    const parsed = yield* decodeThreadTurnStartRequestedPayload({
+      threadId: "thread-2",
+      messageId: "msg-2",
+      titleSeed: "Investigate reconnect failures",
+      createdAt: "2026-01-01T00:00:00.000Z",
+    });
+    assert.strictEqual(parsed.titleSeed, "Investigate reconnect failures");
+  }),
+);
+
 it.effect("decodes latest turn source proposed plan metadata when present", () =>
   Effect.gen(function* () {
     const parsed = yield* decodeOrchestrationLatestTurn({

packages/contracts/src/orchestration.ts

@@ -399,6 +399,7 @@ export const ThreadTurnStartCommand = Schema.Struct({
     attachments: Schema.Array(ChatAttachment),
   }),
   modelSelection: Schema.optional(ModelSelection),
+  titleSeed: Schema.optional(TrimmedNonEmptyString),
   textGenerationModel: Schema.optional(TrimmedNonEmptyString),
   assistantDeliveryMode: Schema.optional(AssistantDeliveryMode),
   runtimeMode: RuntimeMode.pipe(Schema.withDecodingDefault(() => DEFAULT_RUNTIME_MODE)),
@@ -420,6 +421,7 @@ const ClientThreadTurnStartCommand = Schema.Struct({
     attachments: Schema.Array(UploadChatAttachment),
   }),
   modelSelection: Schema.optional(ModelSelection),
+  titleSeed: Schema.optional(TrimmedNonEmptyString),
   textGenerationModel: Schema.optional(TrimmedNonEmptyString),
   assistantDeliveryMode: Schema.optional(AssistantDeliveryMode),
   runtimeMode: RuntimeMode,
@@ -716,6 +718,7 @@ export const ThreadTurnStartRequestedPayload = Schema.Struct({
   threadId: ThreadId,
   messageId: MessageId,
   modelSelection: Schema.optional(ModelSelection),
+  titleSeed: Schema.optional(TrimmedNonEmptyString),
   textGenerationModel: Schema.optional(TrimmedNonEmptyString),
   assistantDeliveryMode: Schema.optional(AssistantDeliveryMode),
   runtimeMode: RuntimeMode.pipe(Schema.withDecodingDefault(() => DEFAULT_RUNTIME_MODE)),