Add SimulatedMaster test helper + 20 assignment sequence tests (8 sequence,
5 failover, 5 adversarial, 2 status). Add BlockVolumeStatus struct and
Status() method. Includes QA test files for CP1-CP4a. 940 total unit tests.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Primary ships WAL entries to replica over TCP (data channel), confirms
durability via barrier RPC (control channel). SyncCache runs local fsync
and replica barrier in parallel via MakeDistributedSync. When replica is
unreachable, shipper enters permanent degraded mode and falls back to
local-only sync (Phase 3 behavior).
Key design: two separate TCP ports (data+control), contiguous LSN
enforcement, epoch equality check, WAL-full retry on replica,
cond.Wait-based barrier with configurable timeout, BarrierFsyncFailed
status code. Close lifecycle: shipper → receiver → drain → committer →
flusher → fd.
New files: repl_proto.go, wal_shipper.go, replica_apply.go,
replica_barrier.go, dist_group_commit.go
Modified: blockvol.go, blockvol_test.go
27 dev tests + 21 QA tests = 48 new tests; 889 total (609 engine + 280
iSCSI), all passing.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
