fix(acp): keep background-task summaries UTF-16 safe at truncation boundaries

MoerAI · MoerAI · commit 8c962438927b · 2026-07-08T11:42:09.000+09:00
The bounded task label and progress summary shown for child ACP background runs used raw String.slice, which can split a surrogate pair at the 160/240-char boundaries and surface U+FFFD in requester-facing task status. Part of the UTF-16 safety sweep.
diff --git a/src/acp/control-plane/manager.background-task.test.ts b/src/acp/control-plane/manager.background-task.test.ts
@@ -0,0 +1,67 @@
+/** Regression coverage for ACP background-task summary truncation boundaries. */
+import { describe, expect, it } from "vitest";
+import type { OpenClawConfig } from "../../config/types.openclaw.js";
+import {
+  appendBackgroundTaskProgressSummary,
+  resolveBackgroundTaskContext,
+} from "./manager.background-task.js";
+import type { AcpSessionManagerDeps } from "./manager.types.js";
+
+// U+1F99E (🦞) is a surrogate pair in UTF-16; a raw .slice() boundary can split it.
+const LOBSTER = "🦞";
+
+const HIGH_SURROGATE_WITHOUT_LOW = /[\uD800-\uDBFF](?![\uDC00-\uDFFF])/;
+
+function fakeDeps(): AcpSessionManagerDeps {
+  const readSessionEntry = (params: { sessionKey: string }) =>
+    params.sessionKey === "child-session"
+      ? { entry: { spawnedBy: "requester-session" } }
+      : { entry: {} };
+  return { readSessionEntry } as unknown as AcpSessionManagerDeps;
+}
+
+describe("appendBackgroundTaskProgressSummary", () => {
+  it("keeps surrogate pairs intact at the progress truncation boundary", () => {
+    // combined length 244 puts the pair astride the 239-char cut point.
+    const result = appendBackgroundTaskProgressSummary("x".repeat(238), `${LOBSTER}tail`);
+    expect(result).toBe(`${"x".repeat(238)}…`);
+    expect(HIGH_SURROGATE_WITHOUT_LOW.test(result)).toBe(false);
+    expect(result.length).toBeLessThanOrEqual(240);
+  });
+
+  it("still truncates plain ASCII exactly at the boundary", () => {
+    const result = appendBackgroundTaskProgressSummary("a".repeat(240), "b");
+    expect(result).toBe(`${"a".repeat(239)}…`);
+  });
+
+  it("returns short combined summaries unchanged", () => {
+    expect(appendBackgroundTaskProgressSummary("done: ", "ok")).toBe("done: ok");
+    expect(appendBackgroundTaskProgressSummary("", `  step ${LOBSTER}`)).toBe(`step ${LOBSTER}`);
+  });
+});
+
+describe("resolveBackgroundTaskContext", () => {
+  it("keeps surrogate pairs intact in the bounded task label", () => {
+    // normalized length 164 puts the pair astride the 159-char cut point.
+    const context = resolveBackgroundTaskContext({
+      deps: fakeDeps(),
+      cfg: {} as unknown as OpenClawConfig,
+      sessionKey: "child-session",
+      requestId: "run-1",
+      text: `${"y".repeat(158)}${LOBSTER}tail`,
+    });
+    expect(context?.task).toBe(`${"y".repeat(158)}…`);
+    expect(HIGH_SURROGATE_WITHOUT_LOW.test(context?.task ?? "")).toBe(false);
+  });
+
+  it("passes short task text through unchanged", () => {
+    const context = resolveBackgroundTaskContext({
+      deps: fakeDeps(),
+      cfg: {} as unknown as OpenClawConfig,
+      sessionKey: "child-session",
+      requestId: "run-2",
+      text: `summarize ${LOBSTER} feedback`,
+    });
+    expect(context?.task).toBe(`summarize ${LOBSTER} feedback`);
+  });
+});
diff --git a/src/acp/control-plane/manager.background-task.ts b/src/acp/control-plane/manager.background-task.ts
@@ -1,4 +1,5 @@
 /** Mirrors child ACP turns into detached-task status for requester-facing progress. */
+import { truncateUtf16Safe } from "@openclaw/normalization-core/utf16-slice";
 import type { OpenClawConfig } from "../../config/types.openclaw.js";
 import { logVerbose } from "../../globals.js";
 import {
@@ -32,7 +33,7 @@ function summarizeBackgroundTaskText(text: string): string {
   if (normalized.length <= ACP_BACKGROUND_TASK_TEXT_MAX_LENGTH) {
     return normalized;
   }
-  return `${normalized.slice(0, ACP_BACKGROUND_TASK_TEXT_MAX_LENGTH - 1)}…`;
+  return `${truncateUtf16Safe(normalized, ACP_BACKGROUND_TASK_TEXT_MAX_LENGTH - 1)}…`;
 }
 
 /** Appends bounded progress text while preserving a single-line task summary. */
@@ -49,7 +50,7 @@ export function appendBackgroundTaskProgressSummary(current: string, chunk: stri
   if (combined.length <= ACP_BACKGROUND_TASK_PROGRESS_MAX_LENGTH) {
     return combined;
   }
-  return `${combined.slice(0, ACP_BACKGROUND_TASK_PROGRESS_MAX_LENGTH - 1)}…`;
+  return `${truncateUtf16Safe(combined, ACP_BACKGROUND_TASK_PROGRESS_MAX_LENGTH - 1)}…`;
 }
 
 /** Maps ACP runtime failures to detached-task terminal states. */

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,5 @@`
`1`	`1`	`/** Mirrors child ACP turns into detached-task status for requester-facing progress. */`
	`2`	`+import { truncateUtf16Safe } from "@openclaw/normalization-core/utf16-slice";`
`2`	`3`	`import type { OpenClawConfig } from "../../config/types.openclaw.js";`
`3`	`4`	`import { logVerbose } from "../../globals.js";`
`4`	`5`	`import {`
`@@ -32,7 +33,7 @@ function summarizeBackgroundTaskText(text: string): string {`
`32`	`33`	`if (normalized.length <= ACP_BACKGROUND_TASK_TEXT_MAX_LENGTH) {`
`33`	`34`	`return normalized;`
`34`	`35`	`}`
`35`		- return `${normalized.slice(0, ACP_BACKGROUND_TASK_TEXT_MAX_LENGTH - 1)}…`;
	`36`	+ return `${truncateUtf16Safe(normalized, ACP_BACKGROUND_TASK_TEXT_MAX_LENGTH - 1)}…`;
`36`	`37`	`}`
`37`	`38`
`38`	`39`	`/** Appends bounded progress text while preserving a single-line task summary. */`
`@@ -49,7 +50,7 @@ export function appendBackgroundTaskProgressSummary(current: string, chunk: stri`
`49`	`50`	`if (combined.length <= ACP_BACKGROUND_TASK_PROGRESS_MAX_LENGTH) {`
`50`	`51`	`return combined;`
`51`	`52`	`}`
`52`		- return `${combined.slice(0, ACP_BACKGROUND_TASK_PROGRESS_MAX_LENGTH - 1)}…`;
	`53`	+ return `${truncateUtf16Safe(combined, ACP_BACKGROUND_TASK_PROGRESS_MAX_LENGTH - 1)}…`;
`53`	`54`	`}`
`54`	`55`
`55`	`56`	`/** Maps ACP runtime failures to detached-task terminal states. */`