Emit fallback session titles

src/CodexAcpServer.ts

@@ -102,6 +102,8 @@ export interface SessionState {
     sessionMcpServers?: Array<string>;
     terminalOutputMode: TerminalOutputMode;
     currentGoal?: ThreadGoalSnapshot | null;
+    sessionTitle: string | null;
+    sessionTitleSource: "unset" | "fallback" | "explicit" | "unknown";
 }
 
 interface ActiveAuthState {
@@ -416,6 +418,8 @@ export class CodexAcpServer {
             currentModelSupportsFast: currentModelSupportsFast,
             sessionMcpServers: sessionMcpServers,
             terminalOutputMode: this.terminalOutputMode,
+            sessionTitle: null,
+            sessionTitleSource: "sessionId" in request ? "unknown" : "unset",
         };
         this.sessions.set(sessionId, sessionState);
         resumeSubscribed = false;
@@ -945,6 +949,8 @@ export class CodexAcpServer {
             currentModelSupportsFast: currentModelSupportsFast,
             sessionMcpServers: sessionMcpServers,
             terminalOutputMode: this.terminalOutputMode,
+            sessionTitle: null,
+            sessionTitleSource: "unset",
         };
         this.sessions.set(sessionId, sessionState);
         subscribed = false;
@@ -972,6 +978,7 @@ export class CodexAcpServer {
     private async streamThreadHistory(sessionId: string, thread: Thread): Promise<void> {
         const session = new ACPSessionConnection(this.connection, sessionId);
         const sessionState = this.getSessionState(sessionId);
+        await this.publishThreadHistoryTitle(session, sessionState, thread);
         const responseItemFallbackUpdates = await createResponseItemHistoryFallbackUpdates(
             thread,
             sessionState.terminalOutputMode,
@@ -993,6 +1000,67 @@ export class CodexAcpServer {
         }
     }
 
+    private async publishThreadHistoryTitle(
+        session: ACPSessionConnection,
+        sessionState: SessionState,
+        thread: Thread,
+    ): Promise<void> {
+        const explicitTitle = this.normalizeSessionTitle(thread.name);
+        if (explicitTitle) {
+            sessionState.sessionTitle = explicitTitle;
+            sessionState.sessionTitleSource = "explicit";
+            await session.update({
+                sessionUpdate: "session_info_update",
+                title: explicitTitle,
+            });
+            return;
+        }
+
+        const historyTitle = this.findFirstUserMessageTitle(thread)
+            ?? this.normalizeSessionTitle(thread.preview);
+        await this.publishFallbackSessionTitle(sessionState, historyTitle);
+    }
+
+    private findFirstUserMessageTitle(thread: Thread): string | null {
+        for (const turn of thread.turns) {
+            for (const item of turn.items) {
+                if (item.type !== "userMessage") continue;
+                const title = this.normalizeSessionTitle(item.content
+                    .filter((input): input is Extract<UserInput, {type: "text"}> => input.type === "text")
+                    .map(input => input.text)
+                    .join(" "));
+                if (title) return title;
+            }
+        }
+        return null;
+    }
+
+    private async publishFallbackSessionTitle(
+        sessionState: SessionState,
+        title: string | null,
+    ): Promise<void> {
+        if (sessionState.sessionTitleSource !== "unset" || !title) return;
+        sessionState.sessionTitle = title;
+        sessionState.sessionTitleSource = "fallback";
+        const session = new ACPSessionConnection(this.connection, sessionState.sessionId);
+        await session.update({
+            sessionUpdate: "session_info_update",
+            title,
+        });
+    }
+
+    private createPromptFallbackTitle(prompt: acp.ContentBlock[]): string | null {
+        return this.normalizeSessionTitle(prompt
+            .filter((block): block is Extract<acp.ContentBlock, {type: "text"}> => block.type === "text")
+            .map(block => block.text)
+            .join(" "));
+    }
+
+    private normalizeSessionTitle(title: string | null | undefined): string | null {
+        const normalized = title?.replace(/\s+/g, " ").trim() ?? "";
+        return normalized.length > 0 ? normalized : null;
+    }
+
     private async createHistoryUpdates(item: ThreadItem, sessionState: SessionState): Promise<UpdateSessionEvent[]> {
         switch (item.type) {
             case "userMessage":
@@ -1597,6 +1665,11 @@ export class CodexAcpServer {
                 throw error;
             }
 
+            await this.publishFallbackSessionTitle(
+                sessionState,
+                this.createPromptFallbackTitle(params.prompt),
+            );
+
             return {
                 stopReason: "end_turn",
                 usage: this.buildPromptUsage(sessionState.lastTokenUsage),

src/CodexEventHandler.ts

@@ -122,6 +122,10 @@ export class CodexEventHandler {
             case "thread/tokenUsage/updated":
                 return this.createUsageUpdate(notification.params);
             case "thread/name/updated":
+                this.sessionState.sessionTitle = notification.params.threadName ?? null;
+                this.sessionState.sessionTitleSource = notification.params.threadName == null
+                    ? "unset"
+                    : "explicit";
                 return {
                     sessionUpdate: "session_info_update",
                     title: notification.params.threadName ?? null,

src/__tests__/CodexACPAgent/data/load-session-history.json

@@ -64,6 +64,18 @@
     }
   ]
 }
+{
+  "method": "sessionUpdate",
+  "args": [
+    {
+      "sessionId": "session-1",
+      "update": {
+        "sessionUpdate": "session_info_update",
+        "title": "Saved title"
+      }
+    }
+  ]
+}
 {
   "method": "sessionUpdate",
   "args": [

src/__tests__/CodexACPAgent/data/load-session-response-item-history-fallback.json

@@ -64,6 +64,18 @@
     }
   ]
 }
+{
+  "method": "sessionUpdate",
+  "args": [
+    {
+      "sessionId": "session-legacy",
+      "update": {
+        "sessionUpdate": "session_info_update",
+        "title": "List the files"
+      }
+    }
+  ]
+}
 {
   "method": "sessionUpdate",
   "args": [

src/__tests__/CodexACPAgent/data/session-info-update-fallback-title.json

@@ -0,0 +1,12 @@
+{
+  "method": "sessionUpdate",
+  "args": [
+    {
+      "sessionId": "test-session-id",
+      "update": {
+        "sessionUpdate": "session_info_update",
+        "title": "Fix the flaky test in CI"
+      }
+    }
+  ]
+}

src/__tests__/CodexACPAgent/load-session.test.ts

@@ -66,7 +66,7 @@ describe("CodexACPAgent - loadSession", () => {
             agentNickname: null,
             agentRole: null,
             gitInfo: null,
-            name: null,
+            name: "Saved title",
             turns: [
                 {
                     id: "turn-1",

src/__tests__/CodexACPAgent/session-info-update-events.test.ts

@@ -5,6 +5,40 @@ import { setupPromptTestSession } from "../acp-test-utils";
 describe("CodexEventHandler - session info updates", () => {
     const sessionId = "test-session-id";
 
+    it("uses the first user prompt as a fallback session title", async () => {
+        const { mockFixture } = setupPromptTestSession({
+            sessionId,
+            sessionTitleSource: "unset",
+        });
+
+        await mockFixture.getCodexAcpAgent().prompt({
+            sessionId,
+            prompt: [
+                { type: "text", text: "  Fix the flaky\n test  " },
+                { type: "text", text: "in CI" },
+            ],
+        });
+
+        await expect(`${mockFixture.getAcpConnectionDump([])}\n`).toMatchFileSnapshot(
+            "data/session-info-update-fallback-title.json"
+        );
+    });
+
+    it("does not replace an explicit session title with the prompt fallback", async () => {
+        const { mockFixture } = setupPromptTestSession({
+            sessionId,
+            sessionTitle: "Explicit title",
+            sessionTitleSource: "explicit",
+        });
+
+        await mockFixture.getCodexAcpAgent().prompt({
+            sessionId,
+            prompt: [{ type: "text", text: "Fallback title" }],
+        });
+
+        expect(mockFixture.getAcpConnectionEvents([])).toEqual([]);
+    });
+
     it("maps thread name updates to ACP session info updates", async () => {
         const { mockFixture } = setupPromptTestSession({ sessionId });
 

src/__tests__/acp-test-utils.ts

@@ -386,6 +386,8 @@ export function createTestSessionState(overrides?: Partial<SessionState>): Sessi
         fastModeEnabled: false,
         currentModelSupportsFast: false,
         terminalOutputMode: "terminal_output_delta",
+        sessionTitle: null,
+        sessionTitleSource: "unknown",
         ...overrides,
     };
 }