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.
