Fence startup recovery phases before entering live mode #1684

Audit reference: I40

What can go wrong

Startup phases could overlap: recovered events might run before effects were safely enabled, or live mode might begin before all recovery history was observed.

When it happens

The race sits between schema/snapshot recovery, EffectsEnabled, event replay, and SyncEnded during every restart.

What changed

The event system now flushes at each phase boundary: effects enablement, recovered history, then live synchronization completion.

Why the change works

A later phase cannot overtake queued work from the previous phase, so actors see one stable startup sequence.

Checks

The observable startup-phase ordering regression passes.