fix(core): stop AbortSignal listener leak in long sessions (MaxListenersExceededWarning)

docs/verification/abort-controller-refactor/README.md

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+# AbortController refactor — verification plan
+
+Scenarios used to validate the change manually before opening the PR. Each
+scenario captures its tmux pane via `tmux pipe-pane -o 'cat >> <log>'`.
+
+## Setup once
+
+```sh
+# Point WT at your local checkout of the branch under review.
+WT=/path/to/qwen-code/worktree
+LOGDIR=$WT/docs/verification/abort-controller-refactor/logs
+mkdir -p "$LOGDIR"
+
+# Build the CLI once (skip sandbox image, skip vscode).
+( cd "$WT" && npm run build:packages )
+```
+
+## Scenarios
+
+For each scenario:
+
+```sh
+tmux new-session -d -s qwen-verify-XX
+tmux pipe-pane -t qwen-verify-XX -o "cat >> $LOGDIR/XX-name.log"
+tmux send-keys -t qwen-verify-XX "cd /path/to/your/test/workspace && exec node $WT/packages/cli/dist/index.js" C-m
+tmux attach -t qwen-verify-XX
+```
+
+Then drive the session manually per the matrix below. Hit `C-b d` to detach
+when done; `tmux kill-session -t qwen-verify-XX` to stop the pane.
+
+### 00 — Baseline (PRE-fix)
+
+- **Setup:** check out `main`, build, run with `NODE_OPTIONS=--trace-warnings`.
+- **Input:** long 50-round mixed-tool session (shell + edit + grep + agent).
+- **Expected:** after ~30–40 rounds, `MaxListenersExceededWarning: ... 1500+ abort listeners added to [AbortSignal]` printed to stderr.
+- **Log:** `00-baseline-reproduction.log`.
+
+### 01 — Long-session, DEBUG mode (this branch)
+
+- **Setup:** `NODE_OPTIONS=--trace-warnings DEBUG=1 qwen`.
+- **Input:** same 50-round script as #00.
+- **Expected:** no `MaxListenersExceededWarning` printed; any other warnings still print.
+- **Log:** `01-long-session-debug.log`.
+
+### 02 — Long-session, prod mode (this branch)
+
+- **Setup:** `qwen` (no debug env).
+- **Input:** same 50-round script.
+- **Expected:** clean output; a temporary `console.error` probe inside the handler (added then removed) confirms the filter fires.
+- **Log:** `02-long-session-prod.log`.
+
+### 03 — Ctrl-C mid-stream abort
+
+- **Setup:** this branch, interactive.
+- **Input:** ask for a long generation (>30s); press Ctrl-C mid-stream.
+- **Expected:** stream stops within ~200ms, "Cancelled" banner shown, next prompt accepts input. `process._getActiveHandles()` count returns to baseline (use `:debug handles`).
+- **Log:** `03-ctrlc-streaming.log`.
+
+### 04 — Cancel long-running shell
+
+- **Setup:** this branch.
+- **Input:** run `sleep 60` via the shell tool; cancel mid-execution.
+- **Expected:** child process killed (verify with `pgrep -f sleep` returning empty), tool result shows cancellation, agent accepts next prompt.
+- **Log:** `04-shell-cancel.log`.
+
+### 05 — Subagent cancellation
+
+- **Setup:** this branch.
+- **Input:** spawn a long agent task via the agent tool; cancel from parent.
+- **Expected:** subagent's in-flight tool calls abort, subagent's model stream stops, parent receives cancellation event.
+- **Log:** `05-subagent-cancel.log`.
+
+### 06 — Headless / non-interactive abort
+
+- **Setup:** `qwen --prompt "do a long task"`; send `SIGINT` from outside via `kill -INT <pid>`.
+- **Expected:** clean shutdown, exit code 130, no warnings.
+- **Log:** `06-headless-abort.log`.
+
+### 07 — Background agent flow
+
+- **Setup:** interactive.
+- **Input:** spawn a background agent (`run_in_background: true`); let it complete; spawn a second one; cancel the second mid-flight.
+- **Expected:** first agent completes normally; second aborts cleanly; no listener leak across the two.
+- **Log:** `07-background-agent.log`.
+
+### 08 — Memory baseline
+
+- **Setup:** `qwen --inspect`, attach Chrome devtools.
+- **Input:** 100-round session.
+- **Expected:** heap snapshots at round 0/50/100. `AbortSignal` instance count and per-signal listener count stable (no monotonic growth).
+- **Log:** `08-memory-snapshots/`.
+
+### 09 — Existing combinedAbortSignal consumer
+
+- **Setup:** trigger an HTTP hook with both an external signal and timeout.
+- **Input:** (a) cancel external signal mid-hook; (b) let timeout fire in a separate run.
+- **Expected:** hook aborts cleanly in both cases; deprecation shim path is exercised.
+- **Log:** `09-http-hook-shim.log`.
+
+## Automated (non-interactive) verifications
+
+The automated checks below were run during development and recorded in
+`automated-results.md`:
+
+- All abortController unit tests pass (`abortController.test.ts`, 18 tests + 1 GC test skipped under non-`--expose-gc`).
+- All warningHandler tests pass (`warningHandler.test.ts`, 9 tests).
+- Existing combinedAbortSignal tests pass against the deprecation shim (8 tests).
+- All agent runtime / followup / openaiContentGenerator / hooks tests pass.
+- Migration completeness: `grep -rn "new AbortController" packages/core/src --include="*.ts" | grep -v test | grep -v abortController.ts` returns **empty**.
+- TypeScript strict-mode typecheck passes for both `packages/core` and `packages/cli`.
+- Prettier check passes on all modified files.
+
+See `automated-results.md` for the actual command output.
+
+## How to capture the artifacts for the PR body
+
+After running each scenario, attach the transcript file (or relevant excerpt)
+to the PR. For #08 (memory), export the heap snapshots and include the
+listener-count delta between snapshots.

docs/verification/abort-controller-refactor/automated-results.md

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+# Automated verification results
+
+Captured 2026-05-20 during the AbortController refactor.
+
+## 1. Listener-accumulation reproducer
+
+Direct simulation of the listener-accumulation pattern observed in long
+sessions (1500+ abort listeners on a single AbortSignal). The script lives
+at `listener-accumulation-repro.mjs`.
+
+```text
+$ node docs/verification/abort-controller-refactor/listener-accumulation-repro.mjs
+Simulating 2000 rounds for each pattern.
+
+OLD pattern listener count on long-lived parent: 2000
+NEW pattern listener count on long-lived parent: 0
+PASS: OLD pattern accumulated >1500 listeners (reproduces the bug).
+PASS: NEW pattern kept listener count at 0 — the helper prevents accumulation.
+```
+
+This is a self-contained proof: the OLD pattern (raw `addEventListener`
+without `{once:true}` or reverse cleanup) accumulates 2000 listeners over
+2000 rounds — well past the 1500 threshold the user observed. The NEW
+pattern (`createChildAbortController` from `packages/core/src/utils/abortController.ts`)
+keeps the parent listener count at 0 across 2000 rounds because each child's
+reverse-cleanup listener removes the parent listener when the child aborts.
+
+## 2. Migration completeness
+
+```sh
+$ grep -rn "new AbortController" packages/core/src --include="*.ts" \
+    | grep -v test | grep -v abortController.ts
+(no output)
+```
+
+Every production `new AbortController()` call in `packages/core/src` (outside
+the helper module itself and outside test files) has been migrated to use
+`createAbortController` / `createChildAbortController`. See
+`migration-completeness.txt` for the captured grep.
+
+## 3. Affected test suites
+
+All 71 affected test files / 2085 tests pass (3 skipped — 1 is the GC test
+that requires `--expose-gc`, 2 are pre-existing skips in the headless suite).
+
+```text
+ Test Files  71 passed (71)
+      Tests  2085 passed | 3 skipped (2088)
+   Duration  16.71s
+```
+
+Coverage:
+
+- `packages/core/src/utils/abortController.test.ts` — 26 tests: factory cap (default + custom), child propagation, reverse cleanup, fast path, undefined parent, custom-maxListeners passthrough, `combineAbortSignals` semantics (incl. cleanup-cancels-timeout, timeout-cleans-input-listeners, `timeoutMs <= 0` boundary, mid-iteration defensive check), GC safety (best-effort).
+- `packages/cli/src/utils/warningHandler.test.ts` — 13 tests: idempotency, AbortSignal suppression (including `[AbortSignal{...}]` shape), generic EventTarget NOT suppressed, debug-mode passthrough, fan-out to prior listeners, spawned-child end-to-end stderr integration.
+- `packages/core/src/hooks/httpHookRunner.test.ts` — covers the migrated `combineAbortSignals` consumer (the deprecated `createCombinedAbortSignal` shim plus its test file were removed once the lone caller migrated).
+- `packages/core/src/agents/runtime/{agent-core,agent-interactive,agent-headless,agent-context,agent-statistics}.test.ts` — 102 tests covering the high-impact migrated files.
+- `packages/core/src/core/openaiContentGenerator/**` — 280+ tests including the pipeline that lost the `raiseAbortListenerCap` band-aid.
+- `packages/core/src/followup/**` — 100+ tests including the migrated speculation controller.
+- `packages/core/src/tools/agent/**`, `packages/core/src/tools/shell.test.ts`, `packages/core/src/services/**`, `packages/core/src/hooks/**`, `packages/core/src/confirmation-bus/**` — all migrated tool/hook/service files.
+
+## 4. TypeScript strict-mode typecheck
+
+```sh
+$ node_modules/.bin/tsc -p packages/core/tsconfig.json --noEmit
+(no output, exit 0)
+
+$ node_modules/.bin/tsc -p packages/cli/tsconfig.json --noEmit
+(no output, exit 0)
+```
+
+## 5. Prettier formatting
+
+```sh
+$ node_modules/.bin/prettier --check packages/core/src/agents/runtime/agent-core.ts \
+    packages/core/src/agents/runtime/agent-headless.ts \
+    packages/cli/src/utils/warningHandler.ts \
+    packages/cli/src/utils/warningHandler.test.ts \
+    packages/core/src/utils/abortController.ts \
+    packages/core/src/utils/abortController.test.ts
+Checking formatting...
+All matched files use Prettier code style!
+```
+
+## 6. Build + binary smoke test
+
+```sh
+$ npm run build:packages
+(succeeds for all 5 workspace packages)
+
+$ NODE_OPTIONS=--trace-warnings node packages/cli/dist/index.js --version
+0.15.11
+EXIT=0
+
+$ node packages/cli/dist/index.js --help
+Usage: qwen [options] [command]
+...
+```
+
+No warnings emitted during boot with `--trace-warnings`.
+
+## 7. Codex independent review
+
+Two full passes via the `codex:codex-rescue` agent (independent context each
+time). First pass surfaced 3 issues — all addressed in subsequent commits:
+
+1. **Throw between controller creation and explicit abort leaks listener** in
+   `agent-core.ts`'s per-iteration body and `agent-headless.ts`'s
+   pre-try-block setup. Fixed by wrapping each in `try { ... } finally {
+abortController.abort(); }`.
+2. **Warning suppressor regex `EventTarget` too broad**. Tightened to match
+   only `AbortSignal` (any shape Node ≥20 produces).
+3. **`process.removeAllListeners('warning')` strips third-party listeners**.
+   Removed — rely on Node's "no listeners → default printer fires" semantics
+   so adding our handler implicitly disables the default print path while
+   keeping third-party telemetry listeners intact.
+
+Second pass confirmed all fixes correct, no further blockers.
+
+## What remains for interactive verification
+
+The scenarios in `README.md` numbered 00–09 require a real interactive
+session against the model API (long mixed-tool conversations, Ctrl-C
+mid-stream, subagent cancellation, heap snapshots). Those are documented
+for human execution and the transcripts should be attached to the PR body
+when run.

docs/verification/abort-controller-refactor/listener-accumulation-repro.mjs

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+#!/usr/bin/env node
+/**
+ * Direct simulation of the listener-accumulation pattern the agent runtime
+ * exhibits in long sessions. Builds a deep parent → child chain to a depth
+ * the user observed (>1500 listeners) and asserts:
+ *
+ * 1. The OLD pattern (plain new AbortController + manual addEventListener
+ *    without {once:true} or reverse cleanup) accumulates listeners on the
+ *    long-lived parent — reproducing the warning.
+ *
+ * 2. The NEW pattern (createChildAbortController from the helper) keeps the
+ *    parent listener count bounded by 1, regardless of how many short-lived
+ *    children come and go.
+ *
+ * Run:
+ *   node docs/verification/abort-controller-refactor/listener-accumulation-repro.mjs
+ */
+
+import { getEventListeners, setMaxListeners } from 'node:events';
+
+// Inline copy of the production helper (packages/core/src/utils/abortController.ts)
+// so this script has no build-step dependency on @qwen-code/qwen-code-core.
+// Kept in sync — the child is held STRONGLY by the parent's listener closure
+// (no WeakRef on child) so propagation works even when a caller drops the
+// controller and keeps only the signal. WeakRef is used only on the PARENT,
+// to keep child cleanup from pinning a long-lived parent in memory.
+function createAbortController(maxListeners = 50) {
+  const c = new AbortController();
+  setMaxListeners(maxListeners, c.signal);
+  return c;
+}
+function createChildAbortController(parent) {
+  const child = createAbortController();
+  if (!parent) return child;
+  const parentSignal = parent.signal ?? parent;
+  if (parentSignal.aborted) {
+    child.abort(parentSignal.reason);
+    return child;
+  }
+  const weakParent = new WeakRef(parentSignal);
+  const handler = () => {
+    child.abort(weakParent.deref()?.reason);
+  };
+  parentSignal.addEventListener('abort', handler, { once: true });
+  child.signal.addEventListener(
+    'abort',
+    () => {
+      weakParent.deref()?.removeEventListener('abort', handler);
+    },
+    { once: true },
+  );
+  return child;
+}
+
+const ROUNDS = 2000;
+
+console.log(`Simulating ${ROUNDS} rounds for each pattern.\n`);
+
+// ─── OLD pattern: plain new AbortController + manual addEventListener ───
+const oldParent = new AbortController();
+setMaxListeners(0, oldParent.signal); // disable warning so we can measure cleanly
+for (let i = 0; i < ROUNDS; i++) {
+  const child = new AbortController();
+  // No {once:true}, no reverse cleanup — accumulates on oldParent.
+  oldParent.signal.addEventListener('abort', () => child.abort());
+}
+const oldCount = getEventListeners(oldParent.signal, 'abort').length;
+
+// ─── NEW pattern: createChildAbortController ───
+const newParent = createAbortController();
+for (let i = 0; i < ROUNDS; i++) {
+  const child = createChildAbortController(newParent);
+  child.abort(); // simulate end-of-round cleanup via try/finally
+}
+const newCount = getEventListeners(newParent.signal, 'abort').length;
+
+console.log(`OLD pattern listener count on long-lived parent: ${oldCount}`);
+console.log(`NEW pattern listener count on long-lived parent: ${newCount}`);
+
+const expectations = {
+  oldShouldExceed: 1500,
+  newMustBe: 0,
+};
+
+let pass = true;
+if (oldCount <= expectations.oldShouldExceed) {
+  console.error(
+    `FAIL: OLD pattern should accumulate >${expectations.oldShouldExceed} listeners; got ${oldCount}`,
+  );
+  pass = false;
+} else {
+  console.log(
+    `PASS: OLD pattern accumulated >${expectations.oldShouldExceed} listeners (reproduces the bug).`,
+  );
+}
+if (newCount !== expectations.newMustBe) {
+  console.error(
+    `FAIL: NEW pattern must have exactly ${expectations.newMustBe} listeners; got ${newCount}`,
+  );
+  pass = false;
+} else {
+  console.log(
+    `PASS: NEW pattern kept listener count at ${expectations.newMustBe} — the helper prevents accumulation.`,
+  );
+}
+
+process.exit(pass ? 0 : 1);

docs/verification/abort-controller-refactor/migration-completeness.txt

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+$ grep -rn "new AbortController" packages/core/src --include="*.ts" \
+    | grep -v test | grep -v abortController.ts
+(no output)

docs/verification/abort-controller-refactor/scripts/02-lite.sh

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+#!/usr/bin/env bash
+# Scenario 02-lite — single real-Qwen prompt under --trace-warnings.
+# Demonstrates the steady-state path emits no MaxListenersExceededWarning.
+set -uo pipefail
+WT="${WT:-$(git rev-parse --show-toplevel)}"
+LOG="$WT/docs/verification/abort-controller-refactor/logs/02-lite-short-prompt.log"
+mkdir -p "$(dirname "$LOG")"
+
+NODE_OPTIONS=--trace-warnings node "$WT/packages/cli/dist/index.js" \
+  --prompt "Reply with exactly 'OK' and nothing else." > "$LOG" 2>&1 &
+PID=$!
+for i in $(seq 1 90); do
+  if ! kill -0 $PID 2>/dev/null; then break; fi
+  sleep 1
+done
+if kill -0 $PID 2>/dev/null; then kill -9 $PID; echo "TIMEOUT"; exit 1; fi
+wait $PID 2>/dev/null
+EC=$?
+
+echo "EXIT=$EC"
+echo "MaxListenersExceededWarning count: $(grep -c MaxListenersExceededWarning "$LOG")"
+echo "--- log ---"
+cat "$LOG"