fix: pr-bug-scan validated finding from #4518

[buf0-bot]

Automated fix-PR from pr-bug-scan for parent #4518.

Fixer status: FIXED_WITH_CODE_PROOF
Summary: Serialize show/dismiss per (hostId, notificationId) so a dismiss arriving while schedule is awaiting cannot no-op against an empty map.
Blocked proof link: mobile/src/notifications/mobile-notifications.ts:114-117
Typecheck: skipped

Proof (from validator)

• C1 — proof_type: code_analysis
  • trigger: Two desktop events arrive on the same RPC stream for the same notificationId in rapid succession: a 'notification' event (re-fire/replace) followed by a 'dismiss' event, while the first 'notification' event for that id is also still in-flight.
  • observable: Local push notification persists on the device even though the desktop already acknowledged/dismissed the corresponding agent state; tapping it routes to a stale worktree.
  • path:
    • mobile/src/notifications/mobile-notifications.ts:159 — subscribe callback dispatches both events without awaiting: void showLocalNotification(...) and void dismissLocalNotification(...)
    • mobile/src/notifications/mobile-notifications.ts:88-91 — second showLocalNotification deletes the existing identifier from scheduledNotificationIdsByHostAndNotificationId BEFORE awaiting scheduleNotificationAsync
    • mobile/src/notifications/mobile-notifications.ts:93 — control yields at await Notifications.scheduleNotificationAsync(...); map has no entry for storedKey
    • mobile/src/notifications/mobile-notifications.ts:114-117 — dismissLocalNotification runs in this gap, scheduledNotificationIdsByHostAndNotificationId.get(storedKey) is undefined, returns early without calling Notifications.dismissNotificationAsync
    • mobile/src/notifications/mobile-notifications.ts:102-104 — showLocalNotification resumes and writes the new scheduledIdentifier into the map, leaving a live OS notification with no pending dismiss

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Generated by pr-bug-scan (proof-machine architecture). Human approval required before merge.

[pullfrog]

✅ No new issues found.

Reviewed changes — serializes show/dismiss operations per (hostId, notificationId) key so a dismiss event arriving while a show is in-flight cannot no-op against an empty tracking map, closing the race condition from #4518.

• Add runSerializedByStoredKey — chains per-key operations via .then() on a Map<string, Promise<void>>; cleans up entries when the chain settles with no newer operation pending.
• Wrap showLocalNotification schedule logic — runs through the serializer when storedKey exists, preserving the existing fast path for notifications without ids.
• Wrap dismissLocalNotification — routes the identifier lookup, map delete, and platform dismiss through the serializer.

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