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## Problem
`test_nip29_announce_channel_wire` flaked in CI (9/30 local solo runs
failed). `emit_group_discovery_events` read the channel, its members and
the latest live `created_at` *before* taking the coordinate's
replacement lock, and only locked for the write. Two publishers for one
channel could therefore store in the reverse order of their reads, or
land on the same second where NIP-16's lower-id tie-break picks a random
winner. Either way a kind:39000/39001 built from stale state could stay
live.
In the test, the relay owner reconnects to send an `auto_join=false`
edit, gets auto-joined into the channel, and the join's kind:39000 —
built from the old `auto_join=true` state — replaces the edit's.
## Fix
- **buzz-db:** `lock_group_state_snapshot` takes the replacement lock
first, then reads the channel, the members the kind actually publishes
(full roster for a DM's kind:39000, owners/admins for kind:39001, none
otherwise) and the latest timestamp; `LockedGroupStateSnapshot::replace`
stores on the same transaction. This is the fence kind:39002 already had
via `LockedMemberSnapshot`. The lock is taken once per write
(`take_replacement_lock`), and the write keeps its
`ReplaceAddressableEvent` transaction timer and writer population so
metrics stay continuous.
- **buzz-relay:** `emit_addressable_discovery_event` builds tags and
`created_at` (live + 1s) from that snapshot.
## Tests
- buzz-db: `group_state_snapshot_reads_behind_the_replacement_lock`,
`group_state_snapshot_reads_the_members_its_kind_publishes`,
`group_state_replacement_takes_its_lock_once`.
- buzz-relay: `a_publisher_that_read_before_an_edit_cannot_replace_it`,
with `BeforeLock` and `AfterRead` legs driven by new
`nip_fi_test_hooks`.
- Every new assertion was confirmed to fail when its guard is reverted.
- `test_nip29_announce_channel_wire` solo against a relay built from
this tree: 30/30 passed (9/30 failed before).
Merged with current `main`; the only conflict kept main's bounded
`channel state write failed: {kind}` error mapping on the new snapshot
write.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Signed-off-by: Matt Toohey <contact@matttoohey.com>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>