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: parse_buffer classified /id/-prefixed task lines as headers
because '/' matches the '^%S' header pattern. Store timestamp test
was flaky when add and update ran within the same second.
Solution: check for task line patterns (id prefix or 2-space indent)
before falling through to the header branch. Backdate the initial
modified timestamp in the store update test.
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.
