CultMeshQuicRealtimeProvider now keeps a `retained` map of the newest
latest-only frame per (channel, body) key, updated on broadcast using the
same generation comparison the receive-side filter already uses. Every peer
attached after that point is seeded with the retained frames before it is
added to the peer set, so a StreamPixels overlay that connects or reconnects
after state was published converges on it instead of waiting for the next
change. Reliable-ordered frames are events and are never retained.
Operator ruling (2026-09-23, OQ1 = A): the provider retains, not a service
heartbeat or a per-peer attach hook.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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