fix(slack): keep thread label snippet truncation UTF-16 safe

NIO · cursoragent · NIO · commit 7c3661dad298 · 2026-07-08T10:10:47.000+08:00
Replace raw .slice(0, 80) thread label snippets with truncateUtf16Safe so
emoji straddling the cap are dropped whole instead of leaving unpaired
surrogates in Slack thread labels.

Co-authored-by: Cursor &lt;cursoragent@cursor.com&gt;
diff --git a/extensions/slack/src/monitor/message-handler/prepare-thread-context-root.test.ts b/extensions/slack/src/monitor/message-handler/prepare-thread-context-root.test.ts
@@ -244,4 +244,11 @@ describe("formatSlackBotStarterThreadLabel", () => {
       }),
     ).toBe("Slack thread DM (assistant root): Line one Line two");
   });
+
+  it("drops a surrogate-pair emoji whole when it straddles the 80-char snippet limit", () => {
+    const starterText = `${"a".repeat(79)}🐱tail`;
+    const label = formatSlackBotStarterThreadLabel({ roomLabel: "DM", starterText });
+    expect(label).toBe(`Slack thread DM (assistant root): ${"a".repeat(79)}`);
+    expect(/[\uD800-\uDBFF](?![\uDC00-\uDFFF])/.test(label)).toBe(false);
+  });
 });
diff --git a/extensions/slack/src/monitor/message-handler/prepare-thread-context-root.ts b/extensions/slack/src/monitor/message-handler/prepare-thread-context-root.ts
@@ -1,4 +1,6 @@
 // Slack plugin module implements prepare thread context root behavior.
+import { truncateUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
+
 export type SlackBotAuthorIdentity = {
   botUserId?: string;
   botId?: string;
@@ -107,7 +109,7 @@ export function formatSlackBotStarterThreadLabel(params: {
   if (!params.starterText) {
     return base;
   }
-  const snippet = params.starterText.replace(/\s+/g, " ").slice(0, 80).trim();
+  const snippet = truncateUtf16Safe(params.starterText.replace(/\s+/g, " "), 80).trim();
   if (!snippet) {
     return base;
   }
diff --git a/extensions/slack/src/monitor/message-handler/prepare-thread-context.ts b/extensions/slack/src/monitor/message-handler/prepare-thread-context.ts
@@ -8,6 +8,7 @@ import {
   filterSupplementalContextItems,
   shouldIncludeSupplementalContext,
 } from "openclaw/plugin-sdk/security-runtime";
+import { truncateUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 import type { ResolvedSlackAccount } from "../../accounts.js";
 import type { SlackMessageEvent } from "../../types.js";
 import { resolveSlackAllowListMatch } from "../allow-list.js";
@@ -224,7 +225,7 @@ export async function resolveSlackThreadContextData(params: {
 
   if (starter?.text && includeStarterContext) {
     threadStarterBody = starter.text;
-    const snippet = starter.text.replace(/\s+/g, " ").slice(0, 80);
+    const snippet = truncateUtf16Safe(starter.text.replace(/\s+/g, " "), 80);
     threadLabel = `Slack thread ${params.roomLabel}${snippet ? `: ${snippet}` : ""}`;
     // Root media seeds a new thread session once. Rehydrating it later makes
     // old files look like current-turn uploads and repeats media processing.
