Two-phase prepare/commit/cancel protocol ensures all replicas expand
atomically. Standalone volumes use direct-commit (unchanged behavior).
Engine: PrepareExpand/CommitExpand/CancelExpand with on-disk
PreparedSize+ExpandEpoch in superblock, crash recovery clears stale
prepare state on open, v.mu serializes concurrent expand operations.
Proto: 3 new RPCs (PrepareExpand/CommitExpand/CancelExpandBlockVolume).
Coordinator: expandClean flag pattern — ReleaseExpandInflight only on
clean success or full cancel. Partial replica commit failure calls
MarkExpandFailed (keeps ExpandInProgress=true, suppresses heartbeat
size updates). ClearExpandFailed for manual reconciliation.
Registry: AcquireExpandInflight records PendingExpandSize+ExpandEpoch.
ExpandFailed state blocks new expands until cleared.
Tests: 15 engine + 4 VS + 10 coordinator + heartbeat suppression
regression + updated QA CP82/durability tests with prepare/commit mocks.
Also includes CP11A-1 remaining: QA storage profile tests, QA
io_backend config tests, testrunner perf-baseline scenarios and
coordinated-expand actions.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
