fix(09): WR-02 make initOutboxTrigger idempotent and retain the unsubscribe handle via stopOutboxTrigger

apps/api/src/broker/outboxWorker.ts

@@ -850,9 +850,27 @@ export async function runOutboxDrain(): Promise<void> {
  * T-09-02: initOutboxTrigger is called only under isMainModule() in index.ts;
  * tests import runOutboxDrain/scheduleOutboxDrain directly and never register
  * a listener — no open-handle leak preventing process exit.
+ *
+ * WR-02: idempotent. The unsubscribe handle is retained so a duplicate call is a
+ * no-op (never double-registers the 'drain' listener) and stopOutboxTrigger() can
+ * remove it for a clean teardown (tests, graceful shutdown).
  */
+let unsubscribeDrain: (() => void) | null = null;
+
 export function initOutboxTrigger(): void {
-  onOutboxDrain(() => scheduleOutboxDrain());
+  if (unsubscribeDrain) return; // idempotent — never double-register
+  unsubscribeDrain = onOutboxDrain(() => scheduleOutboxDrain());
+}
+
+/**
+ * Remove the 'drain' listener registered by initOutboxTrigger() and reset the
+ * idempotency guard so a later initOutboxTrigger() can re-register cleanly.
+ * Used by the test suite's afterAll teardown (WR-03) and available for graceful
+ * shutdown.
+ */
+export function stopOutboxTrigger(): void {
+  unsubscribeDrain?.();
+  unsubscribeDrain = null;
 }
 
 /**