fix(notifications): preserve in-flight outbox events

Reserve the actively delivered outbox event while the external sender is pending so concurrent persistence cannot evict it through expiry or capacity enforcement. Apply the delivery outcome under the exclusive chain before normal cleanup resumes, preserving retry state, delivery acknowledgements, and cooldown timing without duplicate sends. Add deterministic concurrency regressions for expiry-success and capacity-failure races.

src/main/notification-outbox.ts

@@ -173,6 +173,7 @@ export class NotificationOutbox {
   private retryTimer: NodeJS.Timeout | null = null;
   private shutdownRequested = false;
   private drainOperation: Promise<void> | null = null;
+  private inFlightEvent: NotificationEvent | null = null;
 
   public constructor(options: NotificationOutboxOptions) {
     this.filePath = options.filePath;
@@ -257,6 +258,7 @@ export class NotificationOutbox {
           }
           return null;
         }
+        this.inFlightEvent = next;
         return next;
       });
       if (!current) {
@@ -270,7 +272,8 @@ export class NotificationOutbox {
       }
       const outcomeAt = finiteInteger(this.clock(), currentNow);
       const delivered = await this.runExclusive(async () => {
-        const index = this.events.findIndex((event) => event.id === current.id);
+        const index = this.events.indexOf(current);
+        this.inFlightEvent = null;
         if (index < 0) {
           return false;
         }
@@ -346,10 +349,15 @@ export class NotificationOutbox {
   }
 
   private enforceLimits(now: number): void {
-    this.events = this.events.filter((event) => event.expiresAt > now);
+    this.events = this.events.filter((event) => event === this.inFlightEvent || event.expiresAt > now);
     while (this.events.length > MAX_EVENTS) {
-      const successIndex = oldestIndex(this.events, (event) => event.priority === "success");
-      const removeIndex = successIndex >= 0 ? successIndex : oldestIndex(this.events, () => true);
+      const successIndex = oldestIndex(this.events, (event) => event !== this.inFlightEvent && event.priority === "success");
+      const removeIndex = successIndex >= 0
+        ? successIndex
+        : oldestIndex(this.events, (event) => event !== this.inFlightEvent);
+      if (removeIndex < 0) {
+        break;
+      }
       this.events.splice(removeIndex, 1);
     }
   }