fix(ui): keep workboard capture text truncation UTF-16 safe (#102544)

* fix(ui): keep workboard capture text truncation UTF-16 safe

Replace raw .slice(0, N - 3) with truncateUtf16Safe in
clampSessionCaptureText and clampSessionCaptureTitle to prevent
lone surrogates when emoji cross the truncation boundary.

Completes the UTF-16 hardening started in #101685, which added the
import but only covered buildCardSessionLabel.

* test(ui): cover workboard UTF-16 boundaries

* docs(changelog): note Workboard UTF-16 fix

* docs(changelog): leave release notes to release flow

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

ui/src/lib/workboard/index.ts

@@ -2909,7 +2909,7 @@ function clampSessionCaptureText(value: string): string {
   if (compact.length <= SESSION_CAPTURE_TEXT_MAX_CHARS) {
     return compact;
   }
-  return `${compact.slice(0, SESSION_CAPTURE_TEXT_MAX_CHARS - 3).trimEnd()}...`;
+  return `${truncateUtf16Safe(compact, SESSION_CAPTURE_TEXT_MAX_CHARS - 3).trimEnd()}...`;
 }
 
 function clampSessionCaptureTitle(value: string): string {
@@ -2917,7 +2917,7 @@ function clampSessionCaptureTitle(value: string): string {
   if (compact.length <= WORKBOARD_CAPTURE_TITLE_MAX_CHARS) {
     return compact;
   }
-  return `${compact.slice(0, WORKBOARD_CAPTURE_TITLE_MAX_CHARS - 3).trimEnd()}...`;
+  return `${truncateUtf16Safe(compact, WORKBOARD_CAPTURE_TITLE_MAX_CHARS - 3).trimEnd()}...`;
 }
 
 function sessionTitle(session: GatewaySessionRow, recentUserText: string | null): string {

ui/src/pages/workboard/data.test.ts

@@ -3440,18 +3440,21 @@ describe("workboard controller", () => {
     );
   });
 
-  it("clamps long session labels before creating captured cards", async () => {
+  it("clamps captured session fields without splitting surrogate pairs", async () => {
     const host = {};
-    const longLabel = "x".repeat(220);
+    const titlePrefix = "x".repeat(176);
+    const textPrefix = "y".repeat(696);
     const client = createClient((method) => {
       if (method === "workboard.cards.list") {
         return { cards: [], statuses: ["todo"] };
       }
       if (method === "chat.history") {
-        return { messages: [] };
+        return {
+          messages: [{ role: "user", content: [{ type: "text", text: `${textPrefix}😀tail` }] }],
+        };
       }
       if (method === "workboard.cards.create") {
-        return { card: { ...sampleCard, title: `${"x".repeat(177)}...` } };
+        return { card: { ...sampleCard, title: `${titlePrefix}...` } };
       }
       return {};
     });
@@ -3459,14 +3462,17 @@ describe("workboard controller", () => {
     await captureSessionToWorkboard({
       host,
       client: client as never,
-      session: { ...sampleSession, label: longLabel },
+      session: { ...sampleSession, label: `${titlePrefix}😀tail` },
     });
 
     expect(client.request).toHaveBeenNthCalledWith(
       3,
       "workboard.cards.create",
       expect.objectContaining({
-        title: `${"x".repeat(177)}...`,
+        title: `${titlePrefix}...`,
+        notes: [`Session: ${sampleSession.key}`, "", `Recent user prompt: ${textPrefix}...`].join(
+          "\n",
+        ),
       }),
     );
   });