* test(kms): add a scripted loopback Vault for policy wiring tests
A minimal HTTP/1.1 responder that serves canned Vault responses in order
and records the method/path sequence, so wiring tests can assert exactly
how many requests a code path performed (retries, read-confirm) without
a live Vault server.
* feat(kms): route Vault operations through the retry policy engine
Wire every outbound vaultrs call in the KV2 and Transit backends through
policy::execute, completing the wiring half of the operation policy work
(the engine landed separately):
- Reads (KV2 read/read_metadata/read_version/list, transit read/list/
encrypt/decrypt, health checks) run as ReadIdempotent: bounded retries
with exponential backoff and jitter on 429, recoverable 5xx, and
connection-level failures; 400/401/403/404 stay fatal.
- Writes (KV2 set/CAS set/delete_metadata, transit create/update/rotate/
delete, metadata writes) run as MutatingNonIdempotent: exactly one
attempt under the per-attempt timeout, never replayed. CAS conflicts
in the rotation protocol pass through unchanged as the concurrency
signal they are.
- Each attempt takes a fresh credential snapshot, so a retry after a
credential rotation uses the new token.
- Read-confirm recovery for lost create responses: when a create finds
an existing key that is exactly what it would have produced (same
algorithm, enabled, usable material, and for request-level creates the
same usage/description/tags), it reports the stored key as the create
result instead of KeyAlreadyExists. Any divergence keeps failing.
- Deletes treat already-deleted records as completed deletes (KV2
version records; transit metadata already did), so re-running an
interrupted deletion converges.
- A failed existence pre-check inside create now fails the create
instead of falling through to a blind overwrite (fail closed).
- The policy module sheds its allow(dead_code) now that it is wired.
Wiring tests run against a scripted loopback Vault and assert request
counts and endpoints for the retry, single-attempt, CAS-conflict, and
read-confirm paths.
Refs rustfs/backlog#1569 (part of rustfs/backlog#1562)
Zhengchao An