- persist_write_checkpoint_marker(): writes WAL_CHECKPOINT header entry
with CRC, increments current_lsn; never updates last_replicated_crc
(checkpoint markers are local-only, never replicated)
- write_snapshot(): atomic tmp→rename write of P0 sentinel snapshot
("XCESNAP\0" + checkpoint_lsn); full Cap'n Proto body in Task 11
- trim_wal_segments(): removes seg-*.wal files whose start LSN is
strictly less than checkpoint_lsn
- rotate_snapshots(): collects .capnp files, sorts by name (LSN order),
deletes oldest beyond snap_keep_n
- persist_checkpoint(): EBUSY guard via atomic_exchange, sequences
marker→lsn record→snapshot→trim→rotate, clears flag on exit
- 5 TDD tests in test_persist_checkpoint.c covering: snapshot file
creation, checkpoint_lsn advance, WAL lsn advance, EBUSY guard,
and rotation keeping at most snap_keep_n files
- All 18 controller unit tests pass (0 failures)
- In persist_wal_async(), check rotate_segment() return value and propagate -EIO on failure (MEDIUM)
- Change last_crc and last_replicated_crc fields from uint64_t to uint32_t to match CRC32 width (LOW)
Both fixes address code review issues in commit b0a5fbb.
- Expose persist_t struct concretely in persist.h (opaque pattern deferred)
- persist_set_workdir() derives wal/snap paths from workdir+name
- persist_init() creates WAL/snap directories, rejects NFS mounts
- persist_wal_async() writes WAL entries with chained CRC32 via zlib
- Dedicated fsync pthread fires every wal_sync_ms milliseconds
- persist_flush() forces fdatasync for tests and clean shutdown
- WAL_CHECKPOINT type rejected with -EINVAL (never written via async path)
- Stubs: persist_recover, persist_wal_sync_append, persist_checkpoint
- Add fsync_thread_running flag to guard persist_stop when thread not started
- Add zlib_dep to controller and unit test meson targets
- 3 new TDD tests: init_creates_directories, wal_async_writes_entry,
checkpoint_type_rejected — all GREEN
