fix(agents): harden tool search child streams

steipete · steipete · commit b41bd6d6d346 · 2026-07-06T22:34:34.000-04:00
diff --git a/scripts/proof/tool-search-code-mode-stream-errors.mts b/scripts/proof/tool-search-code-mode-stream-errors.mts
diff --git a/src/agents/tool-search.stream-errors.test.ts b/src/agents/tool-search.stream-errors.test.ts
@@ -4,7 +4,6 @@ import { EventEmitter } from "node:events";
 import { afterEach, beforeAll, describe, expect, it, vi } from "vitest";
 
 type MockSpawnChild = EventEmitter & {
-  stdout?: EventEmitter & { setEncoding?: (enc: string) => void };
   stderr?: EventEmitter & { setEncoding?: (enc: string) => void };
   send?: (message: unknown, callback?: (error?: Error | null) => void) => boolean;
   connected?: boolean;
@@ -13,16 +12,13 @@ type MockSpawnChild = EventEmitter & {
 
 function createMockSpawnChild() {
   const child = new EventEmitter() as MockSpawnChild;
-  const stdout = new EventEmitter() as MockSpawnChild["stdout"];
-  stdout!.setEncoding = vi.fn();
   const stderr = new EventEmitter() as MockSpawnChild["stderr"];
   stderr!.setEncoding = vi.fn();
-  child.stdout = stdout;
   child.stderr = stderr;
   child.connected = true;
   child.kill = vi.fn();
   child.send = vi.fn(() => true);
-  return { child, stdout, stderr };
+  return { child, stderr };
 }
 
 vi.mock("node:child_process", async () => {
@@ -43,42 +39,52 @@ vi.mock("node:child_process", async () => {
 
 const spawnMock = vi.mocked(spawn);
 
-let testing: typeof import("./tool-search.js").testing;
+let toolSearch: typeof import("./tool-search.js");
 
 describe("tool-search code-mode stream errors", () => {
   beforeAll(async () => {
-    testing = (await import("./tool-search.js")).testing;
+    toolSearch = await import("./tool-search.js");
   });
 
   afterEach(() => {
-    testing.setToolSearchCodeModeSupportedForTest(undefined);
-    testing.setToolSearchMinCodeTimeoutMsForTest(undefined);
+    toolSearch.testing.setToolSearchCodeModeSupportedForTest(undefined);
+    toolSearch.testing.setToolSearchMinCodeTimeoutMsForTest(undefined);
   });
 
-  it("rejects when the code-mode child stderr emits an error", async () => {
-    testing.setToolSearchCodeModeSupportedForTest(true);
-    testing.setToolSearchMinCodeTimeoutMsForTest(1000);
+  it("rejects stderr errors and leaves the unused stdout unpiped", async () => {
+    toolSearch.testing.setToolSearchCodeModeSupportedForTest(true);
+    toolSearch.testing.setToolSearchMinCodeTimeoutMsForTest(1000);
 
+    let spawnedChild: MockSpawnChild | undefined;
     spawnMock.mockImplementationOnce(
       (_command: string, _args: readonly string[], _options: SpawnOptions): ChildProcess => {
         const { child, stderr } = createMockSpawnChild();
+        spawnedChild = child;
         process.nextTick(() => {
           stderr?.emit("error", new Error("stderr read failed"));
         });
         return child as unknown as ChildProcess;
       },
     );
 
-    const runtime = new testing.ToolSearchRuntime({}, testing.resolveToolSearchConfig({}));
+    const runtime = new toolSearch.ToolSearchRuntime(
+      {},
+      toolSearch.testing.resolveToolSearchConfig({}),
+    );
 
     await expect(
-      testing.runCodeModeChild({
+      toolSearch.testing.runCodeModeChild({
         code: "return 1;",
-        config: testing.resolveToolSearchConfig({}),
+        config: toolSearch.testing.resolveToolSearchConfig({}),
         logs: [],
         parentToolCallId: "call-stderr-error",
         runtime,
       }),
     ).rejects.toThrow("stderr read failed");
+    expect(spawnMock).toHaveBeenCalledOnce();
+    expect(spawnMock.mock.calls[0]?.[2]).toMatchObject({
+      stdio: ["ignore", "ignore", "pipe", "ipc"],
+    });
+    expect(spawnedChild?.kill).toHaveBeenCalledOnce();
   });
 });
diff --git a/src/agents/tool-search.ts b/src/agents/tool-search.ts
@@ -2111,7 +2111,9 @@ function runCodeModeChild(params: {
     const child = spawn(process.execPath, buildCodeModeChildArgs(), {
       cwd: os.tmpdir(),
       env: {},
-      stdio: ["ignore", "pipe", "pipe", "ipc"],
+      // The worker returns logs/results over IPC and never writes stdout.
+      // Ignore it so an unused pipe cannot fill or surface unhandled errors.
+      stdio: ["ignore", "ignore", "pipe", "ipc"],
     });
     let stderrTail = "";
     let settled = false;
@@ -2361,6 +2363,5 @@ export const testing = {
   addClientToolsToToolSearchCatalog,
   appendToolSearchCodeStderrTail,
   runCodeModeChild,
-  ToolSearchRuntime,
 };
 export { testing as __testing };
