GC race: dynamic pool can be removed before first connection

[vadv]

Problem

create_dynamic_pool() inserts a pool into POOLS with size == 0. Between insertion and the first server connection (created by get_server_parameters()), GC can remove the pool, causing No pool configured errors.

Currently mitigated with a 2-second grace period (created_at field on ConnectionPool, checked in gc.rs). This works but is a timing-based workaround.

Root cause

The pool is registered in POOLS before its first connection exists. GC sees size == 0 and removes it.

Failed structural fix

Attempted to split create_dynamic_pool into create + register phases (insert into POOLS only after get_server_parameters). This caused protocol hangs on second connection — root cause of the hang was not identified. Reverted in 760ac60.

Desired fix

Insert pool into POOLS only after the first connection is established, without breaking the auth flow for subsequent connections.

Reproduction

Only reproduced in CI (GitHub Actions runners). The SSLRequest roundtrip in prefer mode widens the GC window enough to trigger. With allow mode (default, no SSLRequest) the window is smaller but still exists in theory.

References

• PR Add server-side TLS (pg_doorman → PostgreSQL) #208 (server-side TLS)
• Grace period workaround: commit ad2fd7f
• Failed structural fix: commit 089fc22, reverted in 760ac60