- wal.h/wal.c: wo_wal_fold_row_at — THE fold. Walks BACKWARD from an
offset through WO_WAL_DELTA records, remembering the first value
seen per field index (newest wins, since newest is seen first),
stops at the first INSERT/UPDATE, decodes it, overlays resolved
fields. Returns ENGINE-owned values so reads, replay, and
compaction (Tasks 3/5) can all build on the same output.
- Cycle guard: caps the walk at what the log up to the starting
offset could possibly hold (13 = scan_record's own record-size
floor), so a corrupt or malicious back-pointer fails loudly
instead of spinning.
- table.c: wo_row_borrow's keys arm now calls the fold instead of
wo_wal_read_row_at directly, then VM-decodes the result — same
two-stage pattern wo_wal_read_row_at used internally. Per-table
scratch, scratch_busy nested-borrow refusal, and the cid/id
identity check all preserved unchanged.
- resident: all path (wo_row_ptr) untouched.
- test_wal.c: two new tests — deltas on two different fields (changed
fields take the new value, the untouched field keeps its original)
and two deltas on the SAME field (the newer wins, pinning direction
— a reversed fold would pass with the older value instead).
Verified failing pre-implementation (wo_row_borrow returned NULL
since a delta record isn't INSERT/UPDATE) and passing after.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
(cherry picked from commit a60231cde1d49d74743cedbd134d2da11158b70b)
shoney.arickathil
4f3f71e003