fix(store-and-forward): resolve S&F delivery + replication wiring (3 Critical findings)

Resolves StoreAndForward-001, ExternalSystemGateway-001, NotificationService-001
— one systemic gap where buffered messages were persisted but never delivered,
and the active node never replicated its buffer to the standby.

Delivery handlers (ExternalSystemGateway-001 / NotificationService-001):
- AkkaHostedService registers delivery handlers for the ExternalSystem,
  CachedDbWrite and Notification categories after StoreAndForwardService starts;
  each resolves its scoped consumer in a fresh DI scope.
- ExternalSystemClient, DatabaseGateway and NotificationDeliveryService each
  gain a DeliverBufferedAsync method: re-resolve the target and re-attempt
  delivery, returning true/false/throwing per the transient-vs-permanent contract.
- EnqueueAsync gains an attemptImmediateDelivery flag; CachedCallAsync and
  NotificationDeliveryService.SendAsync pass false (they already attempted
  delivery themselves) so registering a handler does not dispatch twice.

Replication (StoreAndForward-001):
- ReplicationService is injected into StoreAndForwardService; a new BufferAsync
  helper replicates every enqueue, and successful-retry removes and parks are
  replicated too. Fire-and-forget, no-op when replication is disabled.

Tests: StoreAndForwardReplicationTests (Add/Remove/Park observed),
attemptImmediateDelivery behaviour, and DeliverBufferedAsync paths for each
consumer. Full solution builds; StoreAndForward/ExternalSystemGateway/
NotificationService suites green.

code-reviews/StoreAndForward/findings.md

@@ -8,7 +8,7 @@
 | Last reviewed | 2026-05-16 |
 | Reviewer | claude-agent |
 | Commit reviewed | `9c60592` |
-| Open findings | 13 |
+| Open findings | 12 |
 
 ## Summary
 
@@ -53,7 +53,7 @@ replication and retry-count issues are functional defects against the design.
 |--|--|
 | Severity | Critical |
 | Category | Error handling & resilience |
-| Status | Open |
+| Status | Resolved |
 | Location | `src/ScadaLink.StoreAndForward/ReplicationService.cs:40`, `:53`, `:66`; `src/ScadaLink.StoreAndForward/StoreAndForwardService.cs:155`, `:212`, `:222`, `:236` |
 
 **Description**
@@ -81,7 +81,14 @@ asserts the replication handler observes each operation type.
 
 **Resolution**
 
-_Unresolved._
+Resolved 2026-05-16. `ReplicationService` is now injected into `StoreAndForwardService`
+(wired in `AddStoreAndForward`), and every buffer operation is forwarded to the standby:
+a new `BufferAsync` helper calls `ReplicateEnqueue` after each persist, `ReplicateRemove`
+runs after a successful retry removes a message, and `ReplicatePark` runs on both park
+paths. Replication stays fire-and-forget and is a no-op when `ReplicationEnabled` is
+false or no handler is wired. Regression tests `StoreAndForwardReplicationTests` assert
+the replication handler observes the Add, Remove and Park operations. Fixed by the
+commit whose message references `StoreAndForward-001`.
 
 ### StoreAndForward-002 — Messages enqueued with no registered handler are buffered but never deliverable