fix(agents): preserve UTF-16 tool summary truncation

ZengWen-DT · ZengWen-DT · commit 85572835ae46 · 2026-07-01T13:38:32.000Z
diff --git a/src/agents/tool-description-summary.test.ts b/src/agents/tool-description-summary.test.ts
@@ -0,0 +1,32 @@
+import { describe, expect, it } from "vitest";
+import {
+  describeToolForVerbose,
+  summarizeToolDescriptionText,
+} from "./tool-description-summary.js";
+
+function hasDanglingSurrogate(value: string): boolean {
+  return /[\uD800-\uDBFF](?![\uDC00-\uDFFF])|(?<![\uD800-\uDBFF])[\uDC00-\uDFFF]/u.test(value);
+}
+
+describe("tool description summaries", () => {
+  it("keeps compact summaries UTF-16 safe at truncation boundaries", () => {
+    const summary = summarizeToolDescriptionText({
+      displaySummary: "abcd😀 efgh",
+      maxLen: 8,
+    });
+
+    expect(summary).toBe("abcd...");
+    expect(hasDanglingSurrogate(summary)).toBe(false);
+  });
+
+  it("keeps verbose descriptions UTF-16 safe at truncation boundaries", () => {
+    const description = describeToolForVerbose({
+      rawDescription: "abcd😀 efgh",
+      fallback: "Tool",
+      maxLen: 8,
+    });
+
+    expect(description).toBe("abcd...");
+    expect(hasDanglingSurrogate(description)).toBe(false);
+  });
+});
diff --git a/src/agents/tool-description-summary.ts b/src/agents/tool-description-summary.ts
@@ -5,6 +5,7 @@
  */
 import { normalizeOptionalString } from "@openclaw/normalization-core/string-coerce";
 import { normalizeStringEntries } from "@openclaw/normalization-core/string-normalization";
+import { truncateUtf16Safe } from "../shared/utf16-slice.js";
 
 function normalizeSummaryWhitespace(value: string): string {
   return value.replace(/\s+/g, " ").trim();
@@ -14,7 +15,7 @@ function truncateSummary(value: string, maxLen = 120): string {
   if (value.length <= maxLen) {
     return value;
   }
-  const sliced = value.slice(0, maxLen - 3);
+  const sliced = truncateUtf16Safe(value, maxLen - 3);
   const boundary = sliced.lastIndexOf(" ");
   const trimmed = (boundary >= 48 ? sliced.slice(0, boundary) : sliced).trimEnd();
   return `${trimmed}...`;
@@ -136,7 +137,7 @@ export function describeToolForVerbose(params: {
   if (normalized.length <= maxLen) {
     return normalized;
   }
-  const sliced = normalized.slice(0, maxLen - 3);
+  const sliced = truncateUtf16Safe(normalized, maxLen - 3);
   const boundary = sliced.lastIndexOf(" ");
   return `${(boundary >= Math.floor(maxLen / 2) ? sliced.slice(0, boundary) : sliced).trimEnd()}...`;
 }
