fix(voice-call): drop dangling surrogate in partial-transcript tail slice

wangmiao0668000666 · wangmiao0668000666 · commit 3301ab096da4 · 2026-06-30T15:58:48.000+08:00
diff --git a/extensions/voice-call/src/webhook/realtime-handler.transcript-utf16.test.ts b/extensions/voice-call/src/webhook/realtime-handler.transcript-utf16.test.ts
@@ -0,0 +1,53 @@
+// Voice-call tests cover the UTF-16-safe partial-transcript tail slice in
+// webhook/realtime-handler.ts (limitPartialUserTranscript). Verifies that
+// `sliceUtf16Safe(text, -MAX_PARTIAL_USER_TRANSCRIPT_CHARS)` drops a surrogate
+// pair that straddles the tail boundary instead of leaving a lone high-
+// surrogate half in the partial transcript fed to the agent.
+import { describe, expect, it } from "vitest";
+import { sliceUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
+
+describe("voice-call partial-transcript tail UTF-16", () => {
+  // Mirrors MAX_PARTIAL_USER_TRANSCRIPT_CHARS in realtime-handler.ts. The
+  // exact cap is not exposed publicly, but the UTF-16-safe slicing contract
+  // is the same regardless of the numeric value, so we mirror a representative
+  // small cap here.
+  const MAX_PARTIAL_USER_TRANSCRIPT_CHARS = 200;
+  const emoji = "🎉";
+
+  it("sliceUtf16Safe drops a surrogate pair straddling the tail-start boundary", () => {
+    // Build a string of length 301 where the emoji sits at positions
+    // (100, 101). With sliceUtf16Safe(input, -200), `from = 301 - 200 = 101`,
+    // which is the low surrogate of the emoji, and position 100 is the high
+    // surrogate. The helper increments `from` past the high surrogate so the
+    // tail does not start with a lone surrogate half.
+    const input = "a".repeat(100) + emoji + "a".repeat(199);
+    const tail = sliceUtf16Safe(input, -MAX_PARTIAL_USER_TRANSCRIPT_CHARS);
+    // Tail was supposed to be 200 code units, but the dangling high surrogate
+    // at position 100 is dropped, so the tail is 199 code units.
+    expect(tail.length).toBe(199);
+    expect(tail.charCodeAt(0)).toBeLessThan(0xd800);
+  });
+
+  it("sliceUtf16Safe is a pass-through for plain ASCII partial transcript", () => {
+    const input = "hello world, this is a normal transcript";
+    expect(sliceUtf16Safe(input, -MAX_PARTIAL_USER_TRANSCRIPT_CHARS)).toBe(input);
+  });
+
+  it("sliceUtf16Safe preserves an emoji that sits entirely inside the tail window", () => {
+    // Input is exactly 200 chars. The emoji at position 100 is fully inside
+    // the tail window (no surrogate straddles the boundary).
+    const input = "a".repeat(100) + emoji + "a".repeat(98);
+    const tail = sliceUtf16Safe(input, -MAX_PARTIAL_USER_TRANSCRIPT_CHARS);
+    expect(tail.length).toBe(200);
+    expect(tail.includes(emoji)).toBe(true);
+  });
+
+  it("limitPartialUserTranscript-shaped behavior: short body passes through", () => {
+    // Mirror the production guard at the top of limitPartialUserTranscript:
+    // when text.length <= MAX_PARTIAL_USER_TRANSCRIPT_CHARS, the helper is
+    // not called (the production guard short-circuits first), so sliceUtf16Safe
+    // here is verifying a no-op for short input.
+    const input = "short";
+    expect(sliceUtf16Safe(input, -MAX_PARTIAL_USER_TRANSCRIPT_CHARS)).toBe(input);
+  });
+});
diff --git a/extensions/voice-call/src/webhook/realtime-handler.ts b/extensions/voice-call/src/webhook/realtime-handler.ts
@@ -27,6 +27,7 @@ import {
   type TalkSessionController,
 } from "openclaw/plugin-sdk/realtime-voice";
 import { createSubsystemLogger } from "openclaw/plugin-sdk/runtime-env";
+import { sliceUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 import WebSocket, { WebSocketServer } from "ws";
 import type { VoiceCallRealtimeConfig } from "../config.js";
 import type { CallManager } from "../manager.js";
@@ -154,7 +155,7 @@ function limitPartialUserTranscript(text: string): string {
   if (text.length <= MAX_PARTIAL_USER_TRANSCRIPT_CHARS) {
     return text;
   }
-  const tail = text.slice(-MAX_PARTIAL_USER_TRANSCRIPT_CHARS);
+  const tail = sliceUtf16Safe(text, -MAX_PARTIAL_USER_TRANSCRIPT_CHARS);
   return tail.replace(/^\S+\s+/, "").trimStart() || tail.trimStart();
 }
 
