Documentation invariant (maintainer)

Documentation is checksum-tracked and test-enforced.

Invariant

1. Every docs/**/*.md file MUST appear in docs/doc_checksums.json.
2. Every tracked file MUST be listed in docs/index.md as a - docs/... bullet.
3. Each tracked file’s SHA-256 MUST match the value in docs/doc_checksums.json.

Workflow when editing docs

1. Edit docs.
2. Regenerate docs/doc_checksums.json (SHA-256 per file).
3. Ensure docs/index.md lists all tracked files.

The test enforcing this lives at tests/invariants/test_documentation_invariant.py.