fix: use relayAbort helper for addEventListener to preserve AbortError reason

src/agents/pi-tools.abort.ts

@@ -1,4 +1,5 @@
 import type { AnyAgentTool } from "./pi-tools.types.js";
+import { bindAbortRelay } from "../utils/fetch-timeout.js";
 
 function throwAbortError(): never {
   const err = new Error("Aborted");
@@ -36,7 +37,7 @@ function combineAbortSignals(a?: AbortSignal, b?: AbortSignal): AbortSignal | un
   }
 
   const controller = new AbortController();
-  const onAbort = controller.abort.bind(controller);
+  const onAbort = bindAbortRelay(controller);
   a?.addEventListener("abort", onAbort, { once: true });
   b?.addEventListener("abort", onAbort, { once: true });
   return controller.signal;

src/infra/abort-pattern.test.ts

@@ -1,4 +1,5 @@
 import { describe, expect, it } from "vitest";
+import { bindAbortRelay } from "../utils/fetch-timeout.js";
 
 /**
  * Regression test for #7174: Memory leak from closure-wrapped controller.abort().
@@ -7,12 +8,13 @@ import { describe, expect, it } from "vitest";
  * surrounding lexical scope (controller, timer, locals).  In long-running
  * processes these closures accumulate and prevent GC.
  *
- * The fix is `controller.abort.bind(controller)` which creates a minimal
- * bound function with no scope capture.
- *
- * This test verifies the behavioral equivalence of .bind() for both the
- * setTimeout and addEventListener use-cases.
+ * The fix uses two patterns:
+ * - setTimeout: `controller.abort.bind(controller)` (safe, no args passed)
+ * - addEventListener: `bindAbortRelay(controller)` which returns a bound
+ *   function that ignores the Event argument, preserving the default
+ *   AbortError reason.
  */
+
 describe("abort pattern: .bind() vs arrow closure (#7174)", () => {
   it("controller.abort.bind(controller) aborts the signal", () => {
     const controller = new AbortController();
@@ -31,42 +33,64 @@ describe("abort pattern: .bind() vs arrow closure (#7174)", () => {
     clearTimeout(timer);
   });
 
-  it("bound abort works as addEventListener callback and can be removed", () => {
+  it("bindAbortRelay() preserves default AbortError reason when used as event listener", () => {
     const parent = new AbortController();
     const child = new AbortController();
-    const onAbort = child.abort.bind(child);
+    const onAbort = bindAbortRelay(child);
 
     parent.signal.addEventListener("abort", onAbort, { once: true });
-    expect(child.signal.aborted).toBe(false);
-
     parent.abort();
+
     expect(child.signal.aborted).toBe(true);
+    // The reason must be the default AbortError, not the Event object
+    expect(child.signal.reason).toBeInstanceOf(DOMException);
+    expect(child.signal.reason.name).toBe("AbortError");
   });
 
-  it("removeEventListener works with saved .bind() reference", () => {
+  it("raw .abort.bind() leaks Event as reason — bindAbortRelay() does not", () => {
+    // Demonstrates the bug: .abort.bind() passes the Event as abort reason
+    const parentA = new AbortController();
+    const childA = new AbortController();
+    parentA.signal.addEventListener("abort", childA.abort.bind(childA), { once: true });
+    parentA.abort();
+    // childA.signal.reason is the Event, NOT an AbortError
+    expect(childA.signal.reason).not.toBeInstanceOf(DOMException);
+
+    // The fix: bindAbortRelay() ignores the Event argument
+    const parentB = new AbortController();
+    const childB = new AbortController();
+    parentB.signal.addEventListener("abort", bindAbortRelay(childB), { once: true });
+    parentB.abort();
+    // childB.signal.reason IS the default AbortError
+    expect(childB.signal.reason).toBeInstanceOf(DOMException);
+    expect(childB.signal.reason.name).toBe("AbortError");
+  });
+
+  it("removeEventListener works with saved bindAbortRelay() reference", () => {
     const parent = new AbortController();
     const child = new AbortController();
-    const onAbort = child.abort.bind(child);
+    const onAbort = bindAbortRelay(child);
 
     parent.signal.addEventListener("abort", onAbort);
-    // Remove before parent aborts — child should NOT be aborted
     parent.signal.removeEventListener("abort", onAbort);
     parent.abort();
     expect(child.signal.aborted).toBe(false);
   });
 
-  it("bound abort forwards abort through combined signals", () => {
+  it("bindAbortRelay() forwards abort through combined signals", () => {
     // Simulates the combineAbortSignals pattern from pi-tools.abort.ts
     const signalA = new AbortController();
     const signalB = new AbortController();
     const combined = new AbortController();
 
-    const onAbort = combined.abort.bind(combined);
+    const onAbort = bindAbortRelay(combined);
     signalA.signal.addEventListener("abort", onAbort, { once: true });
     signalB.signal.addEventListener("abort", onAbort, { once: true });
 
     expect(combined.signal.aborted).toBe(false);
     signalA.abort();
     expect(combined.signal.aborted).toBe(true);
+    expect(combined.signal.reason).toBeInstanceOf(DOMException);
+    expect(combined.signal.reason.name).toBe("AbortError");
   });
 });

src/infra/fetch.ts

@@ -1,3 +1,5 @@
+import { bindAbortRelay } from "../utils/fetch-timeout.js";
+
 type FetchWithPreconnect = typeof fetch & {
   preconnect: (url: string, init?: { credentials?: RequestCredentials }) => void;
 };
@@ -42,7 +44,7 @@ export function wrapFetchWithAbortSignal(fetchImpl: typeof fetch): typeof fetch
       return fetchImpl(input, patchedInit);
     }
     const controller = new AbortController();
-    const onAbort = controller.abort.bind(controller);
+    const onAbort = bindAbortRelay(controller);
     if (signal.aborted) {
       controller.abort();
     } else {

src/infra/net/fetch-guard.ts

@@ -1,5 +1,6 @@
 import type { Dispatcher } from "undici";
 import { logWarn } from "../../logger.js";
+import { bindAbortRelay } from "../../utils/fetch-timeout.js";
 import {
   closeDispatcher,
   createPinnedDispatcher,
@@ -51,7 +52,7 @@ function buildAbortSignal(params: { timeoutMs?: number; signal?: AbortSignal }):
 
   const controller = new AbortController();
   const timeoutId = setTimeout(controller.abort.bind(controller), timeoutMs);
-  const onAbort = controller.abort.bind(controller);
+  const onAbort = bindAbortRelay(controller);
   if (signal) {
     if (signal.aborted) {
       controller.abort();

src/utils/fetch-timeout.ts

@@ -1,3 +1,16 @@
+/**
+ * Relay abort without forwarding the Event argument as the abort reason.
+ * Using .bind() avoids closure scope capture (memory leak prevention).
+ */
+function relayAbort(this: AbortController) {
+  this.abort();
+}
+
+/** Returns a bound abort relay for use as an event listener. */
+export function bindAbortRelay(controller: AbortController): () => void {
+  return relayAbort.bind(controller);
+}
+
 /**
  * Fetch wrapper that adds timeout support via AbortController.
  *