Hard quota admission is owned by the durable reservation ledger (decision
D3, rustfs/backlog#2872), but the request-path quota check still read
scanner usage on every write and mapped `UsageUnavailable` to a retryable
503 even for buckets the ledger admits. For a durable quota the checker now
treats scanner usage as reporting input: an unavailable lookup yields
`current_usage = None` and `allowed = true`, counted and logged at debug
level, and admin quota stats report the usage as null instead of zero.
Buckets without a reservation protocol keep the fail-closed snapshot path.
Quotas saved before the reservation protocols are re-saved under protocol
v2 with the same limit, type and created_at. The write goes through a new
guarded save that keeps the admin save's lifecycle/transaction guards,
incarnation check and fleet capability proof and additionally refuses when
the quota revision moved since the cached read, so a concurrent quota edit
wins. It is triggered lazily from the quota read path (background, one
attempt per bucket with a retry interval, never blocking the read) and in
bulk by `POST /rustfs/admin/v3/quota-migration`, which reports every bucket.
The ADR's Consequences section inventories the remaining scanner-usage
"authority" consumers with their meaning after D3, retirement condition and
compatibility window; the operations guide documents the migration and the
report-only usage semantics.
Refs rustfs/backlog#2904, rustfs/backlog#2872, rustfs/rustfs#8678,
rustfs/rustfs#5716, rustfs/rustfs#7350
Co-authored-by: Hauser <housemecn@gmail.com>
Chris
9a1f3d2c4c