feat(event-bus): wire SSE broadcast strategy into event bus lifecycle

[pedrofrxncx]

What is this contribution about?

This PR wires the SSE (Server-Sent Events) broadcast strategy into the event bus lifecycle, ensuring that:

• SSE hub is properly initialized with the appropriate broadcast strategy when the event bus is created
• Cross-pod SSE event replication works correctly with NATS
• Single-pod deployments use local in-memory broadcasting
• SSE hub can be hot-swapped for HMR support and test isolation

Key changes:

1. Event Bus Lifecycle Integration: Start SSE hub as part of createEventBus() and when custom EventBus is provided
2. Flexible Strategy Swapping: Updated SSEHub.start() to support replacing strategies without memory leaks
3. Race Condition Prevention: Added start promise memoization in NatsSSEBroadcast to prevent concurrent initialization
4. Input Validation: Strengthened message validation in NATS subscriber to handle malformed payloads safely
5. Resource Efficiency: Reuse TextEncoder instance in NatsSSEBroadcast

Screenshots/Demonstration

N/A

How to Test

1. Start the development server with bun run dev
2. Verify SSE hub initialization logs appear in console:
   • Single pod: [SSEHub] Using local SSE broadcast (single-pod)
   • Multi-pod with NATS: [SSEHub] Using NATS SSE broadcast (cross-pod)
3. Create event subscriptions and publish events to verify delivery
4. In multi-pod setup, verify events replicate across pods via NATS
5. Run tests: bun test (ignoring pre-existing Playwright e2e infrastructure issues)

Migration Notes

N/A - No database migrations or configuration changes required.

Review Checklist

• PR title is clear and descriptive
• Changes are tested and working
• No breaking changes
• Code formatted with Biome (bun run fmt)
• Linting passes (bun run lint)
• Type checking passes (bun run check:ci)
• Unused exports removed (bun run knip)

---

Summary by cubic

Wires a pluggable SSE broadcast strategy into the event bus so SSE events fan out across pods via NATS when available, with a local fallback. The SSE hub now starts/stops with the bus and supports hot-swapping for HMR.

• New Features

  • Start SSE hub in createEventBus with NatsSSEBroadcast when NATS_URL is set; otherwise use LocalSSEBroadcast.
  • Initialize SSE hub even when a custom EventBus is provided.
  • Stop SSE hub during HMR cleanup to avoid leaked connections.
  • SSEHub now uses a pluggable SSEBroadcastStrategy; sseHub and SSEEvent are exported for consumers.
  • Logs clearly indicate single-pod vs cross-pod mode.

• Bug Fixes

  • Prevent concurrent NATS initialization by memoizing start.
  • Validate and safely ignore malformed NATS messages.

^{Written for commit 3d7c4f9. Summary will update on new commits.}

[github-actions]

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[github-actions]

Release Options

Should a new version be published when this PR is merged?

React with an emoji to vote on the release type:

Reaction	Type	Next Version
👍	Prerelease	2.116.1-alpha.1
🎉	Patch	2.116.1
❤️	Minor	2.117.0
🚀	Major	3.0.0

Current version: 2.116.0

Deployment

• Deploy to production (triggers ArgoCD sync after Docker image is published)

[cubic-dev-ai]

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