fix(qdrant-backup-restore): SPHER-7668 capacity gate warns instead of…

[ddakv]

What

recover_snap_shards refused every collection whose write_consistency_factor exceeded the target's peer count (capacity gate failed: write_consistency_factor=2 > target peers=1). On CST-397 this skipped all 69 collections when restoring into a single-node target: our document-index chart sets write_consistency_factor: 2 server-wide, so every manifest carries 2.

The premise was wrong. Qdrant places min(RF, peers) replicas per shard and requires min(wcf, placed replicas) acks per write (shard_distribution.rs, replica_set/update.rs, identical in 1.15.1, 1.16.0 and dev), so the collection is created writable. The gate now warns and proceeds, mirroring the existing peers < replication_factor branch.

How it works

One file, +3/−4: the wcf > peers branch of check_capacity_gate prints a WARNING instead of return 8; the function header comment states the real semantics. rc 8 remains for non-numeric input. Restored collections keep the manifest's replication_factor/write_consistency_factor, so the intended durability applies once peers are added.

Guarantees & caveats

• Gate order unchanged: still before the state gate, so nothing is created or deleted before it runs.
• On a peer-short target the restored data sits on min(RF, peers) replicas until peers join; both shortfalls are logged as WARNINGs.
• Not in scope: the ConfigMap copy (regenerated by the CI injector on push) and the unit assertion on the test branch (tests/test_gates.sh expects rc 8 for check_capacity_gate 4 3 3; one-line flip prepared).

Testing

• Unfixed script from main vs a one-peer qdrant/qdrant:v1.15.1 (cluster mode on) with a wcf=2, rf=2 backup: reproduces the customer's exact error, exit 1, target untouched.
• Fixed script, same set, same target: both WARNINGs, VERIFIED (points=300, manifest=300), exit 0; collection green, rf/wcf preserved, payload index restored, both shards Active, upsert accepted.
• 18/18 compose drills PASS on the 3-node lab; unit suite unchanged (only the 3 pre-existing failures from the test branch predating the round-2 refactor); shellcheck clean.