fix(api): bound the SSE per-connection seen-set (#183 follow-up)

[brownjuly2003-code]

What

/v1/stream/events kept a bare per-connection set that grows one entry per distinct event for as long as the SSE connection stays open — the same disease as #183, scoped to a connection. Hours of sustained traffic mean hundreds of MB per open stream.

Fix

• BoundedSeenSet (from fix(api): bound journal scans and seen-sets — API RSS no longer grows with the journal #184) at SEEN_CACHE_SIZE = 10_000 per connection.
• Eviction cannot re-emit an event: the scan window is the newest limit (10) rows, so an id leaves the window after 10 newer events but leaves the cache only after 10 000 newer distinct ids — by then it can never re-enter the window.

Tests

• Spy test pins that the generator builds a BoundedSeenSet(maxlen=SEEN_CACHE_SIZE) — reverting to a bare set fails it.
• Behavioral test with a tiny cache (3) drives 5 distinct ids through eviction and asserts every id is emitted exactly once.
• Docs: CHANGELOG + serving-bridge.md §Journal scans are bounded gets the SSE bullet.

🤖 Generated with Claude Code

[github-actions]

DORA Metrics

• Window: last 30 days
• Branch: main
• Deployment frequency: 105 total / 24.5 per week
• Lead time for changes: avg 0.37h / median 0.0h
• Change failure rate: 64.76% (68/105)
• MTTR: 2.56h across 1 incident(s)