arch: stop exporting makeEventBus from public @vibest/server/events

[cursor]

Problem

Architecture requires a single EventBusLayer reference because Effect memoizes layers by reference; a second bus silently drops events.

Production wiring in runtime.ts is correct, but @vibest/server/events publicly exports makeEventBus, and unit tests already construct standalone buses via makeEventBus() instead of sharing EventBusLayer. New code could repeat that in production layers.

Severity

P3

Affected files

• packages/server/src/events/index.ts
• packages/server/src/events/event-bus.ts
• Correct production pattern: packages/server/src/rpc/runtime.ts
• Test footgun examples: packages/server/test/harness/session-manager.test.ts, session-service.test.ts

Suggested fix

Stop exporting makeEventBus from the public @vibest/server/events entry; keep it module-private to event-bus.ts. Tests that need an isolated bus can import from the internal path or use Layer.build(EventBusLayer) as turn-log.test.ts already does.