Extends src/schema/controller.capnp with persistence structures needed
for WAL replication and snapshots:
- PersistConfig (8 fields, @0-@7): capnp-serialisable copy of the
persistence configuration; mapped to capnp_persist_cfg_t to avoid
collision with the plain-C persist_config_t in persist.h
- SnapshotHeader (9 fields, @0-@8): snapshot manifest with LSN, term,
timestamp, record counts and checksums; mapped to capnp_snap_hdr_t
- ReplEnvelope (6 fields, @0-@5): replication wire envelope (NOT the
on-disk format); named to avoid collision with wal_entry_hdr_t and
the WALEntry_ internal symbol c-capnproto generates; mapped to
capnp_repl_envelope_t
Also extends existing structs:
- Job.transientSince @11 (UInt64=0, mapname transient_since): set when
job enters JOB_STAT_TRANSIENT; also adds uint64_t transient_since to
xce_job_t in types.h
- Worker.deadSince @6 (UInt64=0, mapname dead_since): mirrors existing
time_t dead_since field in xce_worker_t
OPCode enum extended with 7 replication opcodes @22-@28:
replEntry, replAck, redirect, heartbeat, steppingDown,
replSnapshot, replCatchUpDone
New C typedefs (capnp_persist_cfg_t, capnp_snap_hdr_t,
capnp_repl_envelope_t) added to typemap.h for the encode/decode shims.
TDD: test_persist_schema.c added (6 tests, all GREEN). Controller test
suite remains 1/1 PASS.
- 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
