Problem: parse_buffer matched the old ' text' indent pattern and
detected headers via '^%S'. Priority was read from a '[N] ' prefix.
apply() never reconciled status changes written into the buffer.
Solution: match '- [.] text' for tasks and '^## ' for headers.
Extract state char to derive priority (! -> 1) and status (x -> done).
apply() now reconciles status from the buffer, setting/clearing 'end'
timestamps — enabling the oil-style edit-checkbox-then-:w workflow.
Problem: several critical code paths had zero test coverage —
parse.resolve_date (relative date resolution), store.snapshot
(foundation of the undo stack), and the diff.apply invariant that
unchanged tasks do not get their modified timestamp bumped. The
diff.apply due/priority clearing paths were also untested.
Solution: add six targeted test blocks across parse_spec, store_spec,
and diff_spec: resolve_date happy/failure paths, parse.body with
relative due tokens, snapshot copy-semantics and deleted-task
exclusion, diff unchanged-modified invariant, due cleared on removal,
priority cleared on ! removal.
Problem: need test coverage for core data operations, inline
metadata parsing, and buffer diff algorithm.
Solution: add busted specs for store CRUD, round-trip
preservation, parse body/command_add with configurable date
syntax, and diff create/delete/update/copy/move operations.
