fix(server): imported thread titles no longer end in a broken emoji

apps/server/src/project/AgentSessionScanner.test.ts

@@ -2861,6 +2861,25 @@ describe("parseAgentSessionTranscript", () => {
     expect(thread?.messages.map((message) => message.text)).toEqual([prompt]);
   });
 
+  it("does not split an emoji when shortening a long first message into a title", () => {
+    const prompt = `${"a".repeat(99)}🚀 then deploy`;
+    const thread = AgentSessionScanner.parseAgentSessionTranscript({
+      contents: [
+        encodeTranscriptRecord({ type: "session_meta", payload: { id: "codex-session" } }),
+        encodeTranscriptRecord({
+          type: "event_msg",
+          payload: { type: "user_message", message: prompt },
+        }),
+      ].join("\n"),
+      source: "codex",
+      providerInstanceId: ProviderInstanceId.make("codex"),
+      fallbackSessionId: "fallback",
+      lastActiveAtMs: Date.parse("2026-08-25T08:00:00.000Z"),
+    });
+
+    expect(thread?.title).toBe("a".repeat(99));
+  });
+
   it("skips sessions without a visible user message", () => {
     const thread = AgentSessionScanner.parseAgentSessionTranscript({
       contents: JSON.stringify({

apps/server/src/project/AgentSessionScanner.ts

@@ -366,9 +366,16 @@ function codexHistoryBase(records: ReadonlyArray<DecodedTranscriptRecord>) {
     : undefined;
 }
 
+const MAX_DERIVED_TITLE_LENGTH = 100;
+
 function deriveTitle(source: AgentSessionSource, text: string): string | undefined {
   const request = source === "codex" ? text.replace(CODEX_TITLE_PREAMBLE, "") : text;
-  return request.trim().split("\n")[0]?.slice(0, 100).trim() || undefined;
+  const line = request.trim().split("\n")[0] ?? "";
+  // Cutting between an emoji's surrogates leaves a lone half that persists as U+FFFD.
+  const last = line.charCodeAt(MAX_DERIVED_TITLE_LENGTH - 1);
+  const end =
+    last >= 0xd800 && last <= 0xdbff ? MAX_DERIVED_TITLE_LENGTH - 1 : MAX_DERIVED_TITLE_LENGTH;
+  return line.slice(0, end).trim() || undefined;
 }
 
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