fix(slack): keep inbound message preview truncation UTF-16 safe

NIO · cursoragent · NIO · commit a9b3c61d5686 · 2026-07-08T12:32:59.000+08:00
Replace raw .slice(0, 160) inbound preview truncation with truncateUtf16Safe
so emoji straddling the cap are dropped whole instead of leaving unpaired
surrogates in Slack inbound message previews.

Co-authored-by: Cursor &lt;cursoragent@cursor.com&gt;
diff --git a/extensions/slack/src/monitor/message-handler/prepare.test.ts b/extensions/slack/src/monitor/message-handler/prepare.test.ts
@@ -187,6 +187,15 @@ describe("slack prepareSlackMessage inbound contract", () => {
     expect(prepared.ctxPayload.BodyForAgent).toContain(body);
   });
 
+  it("truncates inbound preview on a surrogate boundary", async () => {
+    const body = `${"a".repeat(159)}🐱`;
+    const prepared = await prepareWithDefaultCtx(createSlackMessage({ text: body }));
+
+    assertPrepared(prepared);
+    expect(prepared.preview).toBe("a".repeat(159));
+    expect(/[\uD800-\uDBFF](?![\uDC00-\uDFFF])/.test(prepared.preview)).toBe(false);
+  });
+
   it("logs inbound metadata without logging message content", async () => {
     const body = "confidential acquisition target: northstar; do not include this text in logs";
     shouldLogVerboseMock.mockReturnValue(true);
diff --git a/extensions/slack/src/monitor/message-handler/prepare.ts b/extensions/slack/src/monitor/message-handler/prepare.ts
@@ -35,6 +35,7 @@ import {
   normalizeOptionalString,
 } from "openclaw/plugin-sdk/string-coerce-runtime";
 import { enqueueSystemEvent } from "openclaw/plugin-sdk/system-event-runtime";
+import { truncateUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 import { resolveSlackReplyToMode } from "../../account-reply-mode.js";
 import type { ResolvedSlackAccount } from "../../accounts.js";
 import { reactSlackMessage } from "../../actions.js";
@@ -1178,7 +1179,7 @@ export async function prepareSlackMessage(params: {
 
   const roomLabel = channelName ? `#${channelName}` : `#${message.channel}`;
   const senderName = await resolveSenderName();
-  const preview = rawBody.replace(/\s+/g, " ").slice(0, 160);
+  const preview = truncateUtf16Safe(rawBody.replace(/\s+/g, " "), 160);
   const inboundLabel = isDirectMessage
     ? `Slack DM from ${senderName}`
     : `Slack message in ${roomLabel} from ${senderName}`;
