- wal/commit_queue.go: bounded buffered channel for write requests
- wal/writer.go: single-goroutine main loop implementing 11-step write flow
with group commit, sequence allocation, MemTable publish/abort, write-stopped
- wal/recovery.go: BatchReplayer interface, ReplayBatch, ReplaySegmentFile,
RecoverFromSegments with fragment reassembly and tail corruption handling
- Comprehensive tests for all modules, all pass with -race
