fix: notification config not broadcast to swarm nodes

[amir20]

Summary

• Swarm agent server was created with nil notification handler (main.go:98), so gRPC config broadcasts were silently dropped on all swarm nodes
• EventExpression was missing from subscription broadcast conversion, breaking event-based alerts on agent nodes
• Headers was missing from dispatcher broadcast conversion, breaking webhook dispatchers with custom headers on agent nodes

Fixes #4562

Test plan

• Deploy in swarm mode with multiple nodes
• Add a notification rule and verify it triggers on containers running on remote swarm nodes
• Verify event-based alerts (container start/stop) work on agent nodes
• Verify webhook dispatchers with custom headers work on agent nodes

🤖 Generated with Claude Code

[claude]

Clean, minimal fix. All three issues are legitimate bugs.

• EventExpression and Headers were both present in HandleNotificationConfig / LoadConfig but missing from broadcastNotificationConfig — copy-paste omissions confirmed.
• Manager correctly implements the agent.NotificationConfigHandler interface (HandleNotificationConfig + GetNotificationStats).
• NotificationHandler() accessor is safe — notificationManager is set at construction, no race risk.

No issues found.

[claude]

• Fix is correct — nil handler was silently dropping all notification config broadcasts to swarm nodes
• EventExpression and Headers omissions are straightforward copy bugs; worth double-checking no other fields are missing in broadcastNotificationConfig (e.g. compare all fields in notification.Subscription and Dispatcher structs vs what's copied)
• NotificationHandler() returning concrete *notification.Manager is fine if agent.NewServer accepts it; minor nit — naming it NotificationManager() would match what it returns
• protoc version bump in generated files is noise but harmless

[claude]

Three targeted fixes, all correct:

• main.go:97: Passing NotificationHandler() instead of nil is the right fix. The TODO was a known gap.
• multi_host_service.go:256: EventExpression omission was a bug — event-based alerts would silently not work on remote nodes.
• multi_host_service.go:271: Headers omission broke webhook dispatchers with auth headers on agents.

One concern: NotificationHandler() exposes the internal *notification.Manager directly. If the agent server only needs agent.NotificationConfigHandler, returning the concrete type leaks internals. Minor, but worth considering if the interface is already defined.

Otherwise the fix is minimal, correct, and well-scoped.

[claude]

Code review:

• server.go:394 / 447: log.Fatal() inside a gRPC handler is too aggressive — it kills the entire process if a client calls these RPCs on a server where the handler isn't registered. Should return a gRPC error instead (e.g. status.Error(codes.Internal, "...")), or at minimum keep the original warn+return pattern. Fatal is appropriate at startup, not at request time.

• multi_host_service.go:296-301: NotificationHandler() returns the concrete *notification.Manager type — consider whether the agent.NotificationConfigHandler interface would be more appropriate here to avoid coupling.

• The EventExpression and Headers fixes look correct and the main.go nil→handler fix addresses the root cause cleanly.

• Protoc version bump (v7.34.0→v7.34.1) in generated files is fine noise.

[claude]

Clarifying on the log.Fatal() concern raised in prior reviews: the nil check + fatal was moved from the request handlers to the constructor newServer(). Fatal at construction time (startup) is correct behavior — it surfaces the misconfiguration immediately rather than silently ignoring config updates at runtime. No issue here.

The three substantive fixes (nil handler, EventExpression, Headers) are all correct. LGTM.

[claude]

Review

• server.go: Moving nil check to newServer with log.Fatal() is correct — programmer error at startup, not a runtime condition. Good call.
• main.go:97: Fix looks correct. TODO resolved.
• multi_host_service.go: Missing EventExpression and Headers fields — straightforward fix.
• NotificationHandler() returns *notification.Manager — confirm it implements agent.NotificationConfigHandler (not visible in diff, but assumed from compilation).

Test plan gap: Two items unchecked — event-based alerts and webhook custom headers on agent nodes. These are the exact scenarios being fixed; should be verified before merge.

Minor: Whitespace-only alignment change in GetNotificationStats is noise in the diff.