When the restarted peer's dummy shard is auto-recovered by the
cluster's recovery loop before the test issues its manual
`replicate_shard` call, the manual call returns 400 "already involved
in transfer". Skip the manual call when a transfer is already in
flight — the existing wait_for / transfer-count / replica assertions
still verify the shard recovers.
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>