fix(agents): keep exec auto-reviewer rationale truncation UTF-16 safe (#101513)

* fix(agents): keep exec auto-reviewer rationale truncation UTF-16 safe

String.prototype.slice at offset 500 can split surrogate pairs in
LLM-generated review rationale text, rendering broken U+FFFD in
exec approval UI payloads.

Replace raw slice(0, 500) with truncateUtf16Safe.

* fix(agents): keep exec reviewer rationale and prompt template description truncation UTF-16 safe

String.prototype.slice can split surrogate pairs at truncation boundaries,
producing broken U+FFFD in both exec approval rationale (500 chars) and
session prompt-template descriptions (60 chars).

Replace raw slice with truncateUtf16Safe in both locations.

* test(exec): cover UTF-16-safe reviewer rationale

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/agents/exec-auto-reviewer.test.ts

@@ -118,6 +118,24 @@ describe("parseExecAutoReviewResponse", () => {
       });
     }
   });
+
+  it("does not split surrogate pairs when truncating rationale", () => {
+    const rationale = "x".repeat(499) + "🚀tail";
+
+    expect(
+      parseExecAutoReviewResponse(
+        JSON.stringify({
+          decision: "ask",
+          risk: "medium",
+          rationale,
+        }),
+      ),
+    ).toEqual({
+      decision: "ask",
+      risk: "medium",
+      rationale: "x".repeat(499),
+    });
+  });
 });
 
 describe("createModelExecAutoReviewer", () => {

src/agents/exec-auto-reviewer.ts

@@ -6,6 +6,7 @@
  */
 import { resolveTimerTimeoutMs } from "@openclaw/normalization-core/number-coercion";
 import { normalizeOptionalString } from "@openclaw/normalization-core/string-coerce";
+import { truncateUtf16Safe } from "@openclaw/normalization-core/utf16-slice";
 import { z } from "zod";
 import type { AgentModelConfig } from "../config/types.agents-shared.js";
 import type { OpenClawConfig } from "../config/types.openclaw.js";
@@ -76,7 +77,7 @@ function buildReviewerUserPrompt(input: ExecAutoReviewInput): string {
 
 function normalizeRationale(value: unknown, fallback: string): string {
   const text = normalizeOptionalString(typeof value === "string" ? value : undefined);
-  return (text ?? fallback).slice(0, 500);
+  return truncateUtf16Safe(text ?? fallback, 500);
 }
 
 function textLooksLikeReviewerDirective(value: string): boolean {