From 461faef584791e6d1d44aa3da23842f59d58cab9 Mon Sep 17 00:00:00 2001
From: Koi <helzky@proton.me>
Date: Thu, 12 Nov 2026 17:54:45 -0500
Subject: [PATCH] fix(web): reply labels no longer cut an emoji in half

Replying to an assistant response sliced the label to 64 UTF-16 units
before sanitizing it, so an emoji at that boundary left a lone high
surrogate in the label, the sent reference and the provider prompt.
Back off one unit when the cut lands inside a surrogate pair.

Refs #35660
---
 .../src/lib/composerContextRecords.test.ts    | 22 +++++++++++++++++++
 apps/web/src/lib/composerContextRecords.ts    | 10 ++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/apps/web/src/lib/composerContextRecords.test.ts b/apps/web/src/lib/composerContextRecords.test.ts
index 4f119f1b45573..dff3f83a59554 100644
--- a/apps/web/src/lib/composerContextRecords.test.ts
+++ b/apps/web/src/lib/composerContextRecords.test.ts
@@ -4,6 +4,7 @@ import {
   MessageId,
   OrchestrationMessageContext,
   ThreadId,
+  TurnItemId,
   type PreviewAnnotationPayload,
 } from "@t3tools/contracts";
 import * as Schema from "effect/Schema";
@@ -24,6 +25,7 @@ import {
   previewAnnotationFromRecord,
   pullRequestContextKindLabel,
   resolveUserMessageContext,
+  responseContextRecord,
   reviewCommentContextLabel,
   selectedMessageContextFragment,
   reviewCommentContextRecord,
@@ -227,6 +229,26 @@ describe("composerContextRecords", () => {
     expect(record.label).toBe(`${"a".repeat(46)}…`);
   });
 
+  it("shortens a long reply label without splitting an emoji", () => {
+    const text = `${"a".repeat(63)}😀 trailing`;
+    const record = responseContextRecord({
+      citation: {
+        version: 1,
+        environmentId: EnvironmentId.make("environment-1"),
+        threadId: ThreadId.make("thread-1"),
+        messageId: MessageId.make("message-1"),
+        text,
+        start: 0,
+        end: text.length,
+        prefix: "",
+        suffix: "",
+      },
+      itemId: TurnItemId.make("item-1"),
+      subagents: [],
+    });
+    expect(record.label).toBe("a".repeat(63));
+  });
+
   it("restores multiple edits on one target without parsing display strings", () => {
     const styleChanges = [
       ...annotation.styleChanges,
diff --git a/apps/web/src/lib/composerContextRecords.ts b/apps/web/src/lib/composerContextRecords.ts
index ac4256da894cf..a7ae316b5c865 100644
--- a/apps/web/src/lib/composerContextRecords.ts
+++ b/apps/web/src/lib/composerContextRecords.ts
@@ -48,6 +48,7 @@ import {
 import type { ReviewCommentContext } from "~/reviewCommentContext";
 
 const PREVIEW_LABEL_MAX_CHARS = 48;
+const RESPONSE_LABEL_MAX_CHARS = 64;
 
 // Truncate selections to wire bounds before persistence to avoid send-time encoding failures.
 const TRUNCATION_MARKER = "\n… truncated …";
@@ -178,6 +179,13 @@ export function responseContextReference(record: ResponseContextRecord): Compose
   return { kind: "response", contextId: record.contextId, label: record.label };
 }
 
+function responseContextLabel(text: string): string {
+  const last = text.charCodeAt(RESPONSE_LABEL_MAX_CHARS - 1);
+  const end =
+    last >= 0xd800 && last <= 0xdbff ? RESPONSE_LABEL_MAX_CHARS - 1 : RESPONSE_LABEL_MAX_CHARS;
+  return sanitizeComposerContextLabel(text.slice(0, end), "response");
+}
+
 /** One record per response, so replying to it again reuses the same reference. */
 export function responseContextRecord(
   input: Pick<ResponseContextRecord, "citation" | "itemId"> & {
@@ -192,7 +200,7 @@ export function responseContextRecord(
     version: 1,
     kind: "response",
     contextId: toKindScopedComposerContextId("response", input.citation.messageId),
-    label: sanitizeComposerContextLabel(input.citation.text.slice(0, 64), "response"),
+    label: responseContextLabel(input.citation.text),
     citation: input.citation,
     itemId: input.itemId,
     ...(input.subagents.length > 0