fix(cli): t3 thread start titles no longer end in a broken character

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)}…`);
+});

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: {