1. ReadAsync (subscribe-once) now opens the early-event window around its
SubscribeBulk + registration; an initial value that overtook the reply was
dropped and the read returned BadTimeout.
2. Register/Rebind write the reverse map and promote parked events in ONE
critical section under the park gate, and ResolveOrPark resolves under that
gate whenever anything is held (lock-free fast path only when nothing is),
so a later live event can no longer overtake the parked initial value. A
resolved handle that still holds a parked list queues behind it.
3. Held events are fenced by a session epoch: each new EventPump calls
StartNewEpoch(), discarding parked AND promoted-but-unreplayed events; an
older pump can neither park nor replay. Item-handle reuse across a reconnect
can no longer put an old-session value on a new tag.
4. ResubscribeAllAsync opens one window per subscription, not across the whole
replay.
5. Promoted-but-unreplayed (ready) events count toward MaxParkedEvents.
6. Begin/End of a window run under the park gate, so N->0 discard and 0->1
open are atomic (no inherited leftovers).
Documented that ParkedEventsReady may run under _registryGate/_syncLock and
relies on the channel's AllowSynchronousContinuations=false.
Tests use TestWait (#858); each new test was checked red against a mutation
of the fix it pins.
Claude-Session: https://claude.ai/code/session_01GT67AD99zQQqpLCVm3p7xk
Joseph Doherty
f89e0cc04c