fix(agents): suppress unhandled stdout/stderr stream errors in waitForChildProcess (#100522)

cxbAsDev · vincentkoc · web-flow · commit 437b177b7d8b · 2026-07-05T22:35:15.000-07:00
* fix(agents): suppress unhandled stdout/stderr stream errors in waitForChildProcess

* proof(agents): add real behavior proof script for child-process stream error catch

* test(agents): drop synthetic child-process proof wrapper

* proof(agents): replace wrapper with real child-process stream error proof

* style: apply oxfmt to changed files

* test(agents): drop synthetic child-process proof wrapper

---------

Co-authored-by: Vincent Koc &lt;vincentkoc@ieee.org&gt;
diff --git a/src/agents/utils/child-process.test.ts b/src/agents/utils/child-process.test.ts
@@ -75,4 +75,20 @@ describe.skipIf(process.platform === "win32")("waitForChildProcess", () => {
       vi.useRealTimers();
     }
   });
+
+  it("swallows stdout and stderr stream errors without rejecting", async () => {
+    const stdout = new PassThrough();
+    const stderr = new PassThrough();
+    const fakeChild = Object.assign(new EventEmitter(), {
+      stdout,
+      stderr,
+    }) as unknown as ChildProcess;
+
+    const completion = waitForChildProcess(fakeChild);
+    stdout.emit("error", new Error("stdout read failed"));
+    stderr.emit("error", new Error("stderr read failed"));
+    fakeChild.emit("exit", 0);
+
+    await expect(completion).resolves.toBe(0);
+  });
 });
diff --git a/src/agents/utils/child-process.ts b/src/agents/utils/child-process.ts
@@ -41,6 +41,8 @@ export function waitForChildProcess(child: ChildProcess): Promise<number | null>
       child.stderr?.removeListener("end", onStderrEnd);
       child.stdout?.removeListener("data", onData);
       child.stderr?.removeListener("data", onData);
+      child.stdout?.removeListener("error", onStreamError);
+      child.stderr?.removeListener("error", onStreamError);
     };
 
     const finalize = (code: number | null) => {
@@ -95,6 +97,11 @@ export function waitForChildProcess(child: ChildProcess): Promise<number | null>
       reject(err);
     };
 
+    const onStreamError = () => {
+      // Stream read errors on stdout/stderr are non-fatal; the child process
+      // error/exit/close handlers report the real outcome.
+    };
+
     const onExit = (code: number | null) => {
       exited = true;
       exitCode = code;
@@ -113,6 +120,8 @@ export function waitForChildProcess(child: ChildProcess): Promise<number | null>
 
     child.stdout?.once("end", onStdoutEnd);
     child.stderr?.once("end", onStderrEnd);
+    child.stdout?.on("error", onStreamError);
+    child.stderr?.on("error", onStreamError);
     child.stdout?.on("data", onData);
     child.stderr?.on("data", onData);
     child.once("error", onError);
