- row_apply_field_keys's shadow-check borrowed candidates via
wo_row_borrow, which shares ONE per-table scratch with the row already
borrowed for the update — every candidate borrow returned NULL, clash
was always false, `@unique` silently accepted duplicates on update
- idx_add_row's own internal check has the identical defect at the same
call site; discarding its result is now actually safe, since the fixed
shadow-check clears uniqueness before it ever runs
- fix: extracted keys_fold_into (fold+decode) out of wo_row_borrow so it
can target a throwaway per-call buffer instead of t->scratch; the
shadow-check probes candidates into that buffer — r is never
released-and-reborrowed (r IS t->scratch; that would overwrite it)
- wo_row_borrow itself is behavior-preserving: same checks, same order,
same messages, just factored
- test_wal.c: new test — genuine @unique index, update collides with an
existing row, asserts refusal (DB_ERR_UNIQUE) and both rows untouched;
verified failing (update wrongly succeeded) pre-fix, passing after
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
(cherry picked from commit 409186da51fec0042d8d1e3dcf9f69f704937823)
shoney.arickathil
d492d1fefb