refactor: shorten file mentions in thread titles

apps/web/src/components/ChatView.tsx

@@ -73,7 +73,7 @@ import {
   proposedPlanTitle,
   resolvePlanFollowUpSubmission,
 } from "../proposedPlan";
-import { truncateTitle } from "../truncateTitle";
+import { buildThreadTitle } from "../threadTitle";
 import {
   DEFAULT_INTERACTION_MODE,
   DEFAULT_RUNTIME_MODE,
@@ -2341,7 +2341,7 @@ export default function ChatView({ threadId }: ChatViewProps) {
           titleSeed = "New thread";
         }
       }
-      const title = truncateTitle(titleSeed);
+      const title = buildThreadTitle(titleSeed);
       let threadCreateModel: ModelSlug =
         selectedModel || (activeProject.model as ModelSlug) || DEFAULT_MODEL_BY_PROVIDER.codex;
 
@@ -2768,7 +2768,7 @@ export default function ChatView({ threadId }: ChatViewProps) {
     const nextThreadId = newThreadId();
     const planMarkdown = activeProposedPlan.planMarkdown;
     const implementationPrompt = buildPlanImplementationPrompt(planMarkdown);
-    const nextThreadTitle = truncateTitle(buildPlanImplementationThreadTitle(planMarkdown));
+    const nextThreadTitle = buildThreadTitle(buildPlanImplementationThreadTitle(planMarkdown));
     const nextThreadModel: ModelSlug =
       selectedModel ||
       (activeThread.model as ModelSlug) ||

apps/web/src/threadTitle.test.ts

@@ -0,0 +1,53 @@
+import { describe, expect, it } from "vitest";
+
+import { buildThreadTitle } from "./threadTitle";
+
+describe("buildThreadTitle", () => {
+  it("trims surrounding whitespace", () => {
+    expect(buildThreadTitle("   hello world   ")).toBe("hello world");
+  });
+
+  it("returns trimmed text when within max length", () => {
+    expect(buildThreadTitle("alpha", 10)).toBe("alpha");
+  });
+
+  it("appends ellipsis when text exceeds max length", () => {
+    expect(buildThreadTitle("abcdefghij", 5)).toBe("abcde...");
+  });
+
+  it("shortens a single file mention to its basename while keeping the marker", () => {
+    expect(buildThreadTitle("Inspect @apps/web/src/components/ChatView.tsx please")).toBe(
+      "Inspect @ChatView.tsx please",
+    );
+  });
+
+  it("shortens multiple file mentions independently", () => {
+    expect(buildThreadTitle("Compare @apps/web/src/a.ts with @packages/shared/src/b.ts now")).toBe(
+      "Compare @a.ts with @b.ts now",
+    );
+  });
+
+  it("shortens mentions before truncating the title", () => {
+    const title = buildThreadTitle(
+      "@apps/web/src/components/ChatView.tsx investigate header layout",
+      20,
+    );
+
+    expect(title).toBe("@ChatView.tsx invest...");
+    expect(title).not.toContain("apps/web/src/components");
+  });
+
+  it("leaves incomplete trailing mentions unchanged", () => {
+    expect(buildThreadTitle("Inspect @apps/web/src/components/ChatView.tsx")).toBe(
+      "Inspect @apps/web/src/components/ChatView.tsx",
+    );
+  });
+
+  it("preserves punctuation and whitespace around mention segments", () => {
+    expect(
+      buildThreadTitle(
+        "Review @apps/web/src/components/ChatView.tsx ; then ping @README.md please",
+      ),
+    ).toBe("Review @ChatView.tsx ; then ping @README.md please");
+  });
+});

apps/web/src/threadTitle.ts

@@ -0,0 +1,17 @@
+import { splitPromptIntoComposerSegments } from "./composer-editor-mentions";
+import { basenameOfPath } from "./vscode-icons";
+
+export function buildThreadTitle(text: string, maxLength = 50): string {
+  const normalized = splitPromptIntoComposerSegments(text)
+    .map((segment) =>
+      segment.type === "mention" ? `@${basenameOfPath(segment.path)}` : segment.text,
+    )
+    .join("")
+    .trim();
+
+  if (normalized.length <= maxLength) {
+    return normalized;
+  }
+
+  return `${normalized.slice(0, maxLength)}...`;
+}