The executable spec for BoardWriter's cross-cutting guarantees, in a
dedicated WriteFidelityTests.swift: minimal-touch verified down to
sibling mtimes across a seven-operation session; renumber pinned as
the sole exception (whole lane rewritten, board root / other lanes /
tombstones untouched); delete→restore byte-precise (only the modified
line differs, zero tombstone residue); unknown-key order preserved
with keys interleaved among schema-owned ones; and a composite
building a board purely through the writer, hand-editing a file like
an agent would, then moving/copying/deleting/renumbering to a
zero-warning reload. Guarantees already pinned by the per-operation
suites (atomicity, move/copy identity, body round-trip) are
referenced, not duplicated. Shared fixtures promoted to
WriterTestSupport.swift. README gains the write-side feature bullet.
5 new tests; 250 total green. Closes milestone m2-storage-write.
Claude-Session: https://claude.ai/code/session_018BjQRYBR6jQja3jCRi5S3A
rzen
328cfb629f