From c58d1cc4ce2955468b8479ca1d669665ba2f5d01 Mon Sep 17 00:00:00 2001
From: Alex Southwell <4596216+saphid@users.noreply.github.com>
Date: Tue, 3 Nov 2026 07:32:21 +1100
Subject: [PATCH] fix(cli): t3 thread start titles no longer end in a broken
 character

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 apps/server/src/cli/thread.test.ts |  7 ++++++-
 apps/server/src/cli/thread.ts      | 13 +++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/apps/server/src/cli/thread.test.ts b/apps/server/src/cli/thread.test.ts
index e09f3be00312b..1fab7881bcbb5 100644
--- a/apps/server/src/cli/thread.test.ts
+++ b/apps/server/src/cli/thread.test.ts
@@ -2,7 +2,7 @@ import { assert, it } from "@effect/vitest";
 import { RunId, ThreadId } from "@t3tools/contracts";
 import * as Effect from "effect/Effect";
 
-import { readLatestMessages, type ThreadTools, waitForRun } from "./thread.ts";
+import { readLatestMessages, type ThreadTools, titleFromMessage, waitForRun } from "./thread.ts";
 
 const threadId = ThreadId.make("thread-1");
 const runId = RunId.make("run-1");
@@ -160,3 +160,8 @@ it.effect("show returns a --messages count larger than one call can spread", ()
     );
   }),
 );
+
+it("titles from a long first line without splitting an emoji", () => {
+  const title = titleFromMessage(`${"a".repeat(78)}😀 and the rest of a long first line`);
+  assert.strictEqual(title, `${"a".repeat(78)}…`);
+});
diff --git a/apps/server/src/cli/thread.ts b/apps/server/src/cli/thread.ts
index 5d944e2723ee4..7bfddda4723a2 100644
--- a/apps/server/src/cli/thread.ts
+++ b/apps/server/src/cli/thread.ts
@@ -508,11 +508,16 @@ const finishRun = Effect.fn("cli.thread.finishRun")(function* (
   }
 });
 
-const titleFromMessage = (message: string) => {
+export const titleFromMessage = (message: string) => {
   const firstLine = message.trim().split("\n")[0]?.trim() ?? "";
-  return firstLine.length > TITLE_MAX_CHARS
-    ? `${firstLine.slice(0, TITLE_MAX_CHARS - 1).trimEnd()}…`
-    : firstLine;
+  if (firstLine.length <= TITLE_MAX_CHARS) return firstLine;
+  let end = TITLE_MAX_CHARS - 1;
+  const previous = firstLine.charCodeAt(end - 1);
+  const next = firstLine.charCodeAt(end);
+  if (previous >= 0xd800 && previous <= 0xdbff && next >= 0xdc00 && next <= 0xdfff) {
+    end -= 1;
+  }
+  return `${firstLine.slice(0, end).trimEnd()}…`;
 };
 
 const launchWorkspaceStrategy = (input: {