fix(skills): keep history scans UTF-16 safe (#107720)

src/skills/workshop/history-scan-transcript-content.ts

@@ -1,3 +1,4 @@
+import { sliceUtf16Safe, truncateUtf16Safe } from "@openclaw/normalization-core/utf16-slice";
 import { filterHeartbeatTranscriptTurns } from "../../auto-reply/heartbeat-transcript-turns.js";
 import { redactSensitiveText } from "../../logging/redact.js";
 import { formatSkillExperienceReviewTranscript } from "./experience-review-prompt.js";
@@ -20,12 +21,12 @@ function capSessionTranscript(transcript: string, maxChars: number): string {
   }
   const omission = "\n\n[older session content omitted]\n\n";
   if (maxChars <= omission.length) {
-    return transcript.slice(0, maxChars);
+    return truncateUtf16Safe(transcript, maxChars);
   }
   const contentBudget = Math.max(0, maxChars - omission.length);
   const headLength = Math.min(2_000, Math.floor(contentBudget / 2));
-  const head = transcript.slice(0, headLength);
-  const tail = transcript.slice(-(contentBudget - headLength));
+  const head = truncateUtf16Safe(transcript, headLength);
+  const tail = sliceUtf16Safe(transcript, -(contentBudget - head.length));
   return `${head}${omission}${tail}`;
 }
 

src/skills/workshop/history-scan.test.ts

@@ -48,6 +48,10 @@ function summary(sessionKey: string, overrides: Partial<SessionEntrySummary["ent
   >;
 }
 
+function hasDanglingSurrogate(value: string): boolean {
+  return /[\uD800-\uDBFF](?![\uDC00-\uDFFF])|(?<![\uD800-\uDBFF])[\uDC00-\uDFFF]/u.test(value);
+}
+
 describe("Skill Workshop history scan", () => {
   it("keeps interactive sessions and excludes system-owned work", () => {
     expect(isSkillHistoryScanSessionEligible(summary("agent:main:main"))).toBe(true);
@@ -244,6 +248,33 @@ describe("Skill Workshop history scan", () => {
     expect(transcript).toContain("…redacted…");
   });
 
+  it.each([
+    {
+      name: "a prefix-only budget",
+      content: "😀tail",
+      maxChars: 8,
+      includesOmission: false,
+    },
+    {
+      name: "the retained head",
+      content: `😀${"a".repeat(80)}`,
+      maxChars: 51,
+      includesOmission: true,
+    },
+    {
+      name: "the retained tail",
+      content: `${"a".repeat(60)}😀${"x".repeat(7)}`,
+      maxChars: 51,
+      includesOmission: true,
+    },
+  ])("keeps $name UTF-16 safe", ({ content, maxChars, includesOmission }) => {
+    const transcript = formatSkillHistoryScanTranscript([{ role: "user", content }], maxChars);
+
+    expect(transcript.length).toBeLessThanOrEqual(maxChars);
+    expect(transcript.includes("[older session content omitted]")).toBe(includesOmission);
+    expect(hasDanglingSurrogate(transcript)).toBe(false);
+  });
+
   it("continues before the oldest cursor and can return to new work", () => {
     const candidates = [
       { instanceId: "new", sessionKey: "main", updatedAtMs: 300, entry: summary("new").entry },