The transaction-scoped TRY variant had no production callers — only the
conn-level try-lock (acquireAdvisoryLock) and the blocking xact variant
(acquireAdvisoryXactLockBlocking, used by the admin cancellation path) are in
use. Dropping the dead code removes a foot-gun: a try-lock that silently
fails to acquire inside a transaction would otherwise look like a safe option.
Downgrades routine sweep bookkeeping from CRITICAL to WARN (genuine post-charge manual-reconciliation branches keep CRITICAL) and replaces the per-attempt time.After in tryAdvisoryLock with a single reusable timer.
Introduce acquireAdvisoryLock (pg_try_advisory_lock with a ~3s bounded retry) and acquireAdvisoryXactLockBlocking (deliberately blocking for the cancellation-refund path where silently dropping a refund is worse than waiting). Convert ApplyLoyaltyRedemption to the bounded variant: concurrent redemptions during an in-flight payment return 409 instead of pinning a pool connection. Add uncontended + contended-timeout unit tests and a lock-contended 409 redemption test.
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