clientauth: nonexistent pgtle.clientauth_db_name causes indefinite login hang

[zjyzh]

Description

If pgtle.clientauth_db_name names a database that does not exist, every login hangs forever. The clientauth background workers FATAL on startup, the postmaster respawns them once per second, and clientauth_hook waits on a shared-memory rendezvous no live worker ever completes. The GUC is PGC_POSTMASTER, so no one can log in to fix it.

Steps to reproduce

1. Fresh cluster with pg_tle in shared_preload_libraries.
2. Set pgtle.enable_clientauth = 'on' and pgtle.clientauth_db_name = 'ghost_db_does_not_exist'.
3. Restart, then run psql -c 'SELECT 1'.

Expected outcome

Connection succeeds (matching the existing "pg_tle not installed" fallback under on), or is cleanly rejected under require.

Actual outcome

psql hangs indefinitely. Killed by timeout 10 with exit 124 and no output.

Analysis

Have each worker bump a workers_ready counter after BackgroundWorkerInitializeConnection() succeeds. clientauth_hook waits briefly on it before enqueuing, and on timeout falls back to can_allow_without_executing / can_reject_without_executing.

Logs

FATAL:  database "ghost_db_does_not_exist" does not exist
LOG:  background worker "pg_tle_clientauth worker" (PID ...) exited with exit code 1
[repeats every second, forever]