fix(toast): clear a toast's auto-dismiss timer before re-arming it (C-3.25)

A coalesced repeat re-surfaced the toast and armed a new dismiss timer without
clearing the old one, so it vanished at the ORIGINAL deadline (6s not the expected
11s). Timers are now tracked in a Map<id> and cleared before re-arming (and on
manual dismiss).

frontend/src/lib/notifications.ts

@@ -129,6 +129,20 @@ let items: Notification[] = load();
 let listeners: Array<() => void> = [];
 let counter = items.reduce((m, n) => Math.max(m, n.id), 0) + 1;
 
+// Per-toast auto-dismiss timers. Keyed by id so re-arming (a coalesced repeat re-surfacing the same
+// toast) can CLEAR the previous timer first — otherwise the old one still fires at the original
+// deadline and dismisses the re-surfaced toast early (C-3.25).
+const dismissTimers = new Map<number, ReturnType<typeof setTimeout>>();
+
+function armDismiss(id: number, duration: number): void {
+  const existing = dismissTimers.get(id);
+  if (existing) clearTimeout(existing);
+  dismissTimers.set(
+    id,
+    setTimeout(() => dismiss(id), duration),
+  );
+}
+
 // Cached derived snapshots — useSyncExternalStore needs stable references between
 // emits, so we recompute these only when `items` changes.
 let cachedActive: Notification[] = [];
@@ -243,7 +257,7 @@ export function notify(input: NotifyInput): number {
           : n,
       );
       emit();
-      if (duration) setTimeout(() => dismiss(prior.id), duration);
+      if (duration) armDismiss(prior.id, duration);
       // Deliberately no re-beep: the first occurrence already sounded; a loop must stay quiet.
       return prior.id;
     }
@@ -275,12 +289,17 @@ export function notify(input: NotifyInput): number {
   ) {
     beep();
   }
-  if (duration) setTimeout(() => dismiss(id), duration);
+  if (duration) armDismiss(id, duration);
   return id;
 }
 
 /** Close the transient toast surface; the entry stays in the center's history. */
 export function dismiss(id: number): void {
+  const t = dismissTimers.get(id);
+  if (t) {
+    clearTimeout(t);
+    dismissTimers.delete(id);
+  }
   items = items.map((n) => (n.id === id ? { ...n, dismissed: true } : n));
   emit();
 }