fix(active-memory): bound timeout partials safely

steipete · zhangguiping-xydt · steipete · commit c0d70155b316 · 2026-07-09T16:05:22.000+01:00
Co-authored-by: 张贵萍0668001030 &lt;zhang.guiping@xydigit.com&gt;
diff --git a/extensions/active-memory/index.test.ts b/extensions/active-memory/index.test.ts
@@ -3201,6 +3201,47 @@ describe("active-memory plugin", () => {
     expect(readFileSpy).not.toHaveBeenCalled();
   });
 
+  it("keeps partial assistant transcript caps UTF-16 safe", async () => {
+    const sessionFile = path.join(stateDir, "surrogate-timeout-transcript.jsonl");
+    await writeTranscriptJsonl(sessionFile, [
+      {
+        type: "message",
+        message: {
+          role: "assistant",
+          content: `${"a".repeat(38)}🎉TAILWORD`,
+        },
+      },
+    ]);
+
+    const result = await testing.readPartialAssistantText(sessionFile, {
+      maxChars: 39,
+      maxLines: 10,
+    });
+
+    expect(result).toBe("a".repeat(38));
+  });
+
+  it("keeps joined partial assistant transcript caps UTF-16 safe", async () => {
+    const sessionFile = path.join(stateDir, "joined-surrogate-timeout-transcript.jsonl");
+    await writeTranscriptJsonl(sessionFile, [
+      {
+        type: "message",
+        message: { role: "assistant", content: "a".repeat(37) },
+      },
+      {
+        type: "message",
+        message: { role: "assistant", content: "🎉TAILWORD" },
+      },
+    ]);
+
+    const result = await testing.readPartialAssistantText(sessionFile, {
+      maxChars: 39,
+      maxLines: 10,
+    });
+
+    expect(result).toBe("a".repeat(37));
+  });
+
   it("skips malformed JSONL lines when reading partial assistant transcripts", async () => {
     const sessionFile = path.join(stateDir, "malformed-timeout-transcript.jsonl");
     await fs.mkdir(path.dirname(sessionFile), { recursive: true });
diff --git a/extensions/active-memory/index.ts b/extensions/active-memory/index.ts
@@ -2251,20 +2251,20 @@ async function readPartialAssistantText(
         if (remaining <= 0) {
           return true;
         }
-        const nextText = text.slice(0, remaining);
+        const nextText = truncateUtf16Safe(text, remaining);
+        if (!nextText) {
+          return true;
+        }
         texts.push(nextText);
         collectedChars += separatorChars + nextText.length;
-        return collectedChars >= resolvedLimits.maxChars;
+        // A surrogate backoff leaves spare code units; stop instead of skipping ahead.
+        return nextText.length < text.length || collectedChars >= resolvedLimits.maxChars;
       }
       return false;
     },
   });
-  const joined = texts
-    .map((text) => text.trim())
-    .filter(Boolean)
-    .join("\n")
-    .slice(0, resolvedLimits.maxChars)
-    .trim();
+  // Accepted chunks and separators are charged before append, so the join is already bounded.
+  const joined = texts.join("\n").trim();
   return joined || null;
 }
 
