Redeeming an invite read uses_count, checked the cap in JS, then did a
non-atomic uses_count = uses_count + 1 write AFTER creating the membership.
Two concurrent redemptions of a max_uses=1 invite both passed the check and
both created a member, and the counter under-counted.
Fix: claim a use ATOMICALLY before creating the membership via a
compare-and-swap on uses_count (lib/invite-claim.ts) — the UPDATE only writes
when uses_count still equals the value the cap decision was based on, so of two
racing claims exactly one wins. The loser re-reads and retries while capacity
remains (multi-use invites unaffected). On a failed membership insert the claim
is rolled back so a slot is not burned.
Extracted to lib/invite-claim.ts (out of the 'use server' surface, unit-tested).
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Moheeb ZaraandClaude Opus 4.8
2ee929658e