src/frontmatter.py grows from a single-key reader into the full machine
contract: reader (read_frontmatter_value, unchanged), one parse primitive
(parse_frontmatter), writer (render/write_frontmatter), schema validator
(validate_schema/REQUIRED_FIELDS, warning-only by default) and a shared
strip_frontmatter helper. The five verdict gates (check_reviewer_verdict,
_parse_tests_verdict, _parse_deploy_status, _parse_staging_status,
parse_security_status) now read through the single parse_frontmatter point
instead of duplicated ad-hoc YAML logic; review_parse._strip_frontmatter and
security_gate.extract_security_findings reuse the shared helper.
Strictly backward compatible + never-raise: STAGE_TRANSITIONS, the QG_CHECKS
composition, verdict semantics (incl. ORCH-047 three-field tester + negative
token priority), reason-strings and worktree->origin/main fallback are 1:1.
The schema validator never influences a gate verdict by default; hard-fail is
reserved behind the frontmatter_validation_strict kill-switch (default False).
New formal handoff spec docs/_standards/HANDOFF_PROTOCOL.md ("stage -> required
output" + required frontmatter schema), aligned 1:1 with PIPELINE_DOCS.md.
Tests: test_frontmatter.py (TC-01..07), test_qg_verdicts.py (TC-08..15),
test_security_gate.py (TC-12), test_stages_invariants.py (TC-16). Full
tests/ green (1212).
Refs: ORCH-076
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
