docs: enforce repository-wide YAML governance

[huangzesen]

Summary

• add root docs.yaml as the single machine-readable contract for repository Markdown metadata
• migrate all 244 current Markdown documents to nonempty repo-relative related_files plus a document-specific maintenance rule, with no path-level content exemptions
• add scripts/check_docs_governance.py and regression coverage for strict frontmatter/YAML, maintenance placeholders and the exact 19/20 boundary, unsafe paths including Windows drive designators, specialized-owner boundaries, package/runtime consumers, and byte-exact notification bodies
• preserve existing Anatomy/Contract, prompt-crawl, glossary, session-journal, PR-template, and raw-consumer ownership semantics
• reconcile the reviewed V6R governance candidate onto live main a2b7d729: 167 files remain byte-identical to the reviewed candidate, while four overlapping manuals preserve the intervening fix(daemon): enforce explicit preset allowlist #917/fix: preserve timely-transient metadata during full replay #918 content and add only the exact reviewed governance blocks
• add an optional lifecycle: temporary marker with a required, concrete temporary_until exit condition; the marker adds obligations and never exempts maintenance or related_files
• mark exactly one evidence-backed transitional document, docs/plans/2026-06-25-fsutil-migration.md, while leaving durable/history documents unclassified by default

Validation

Current head f4163f2e9d2780d3d7a694b331b6f3b03e9aa670:

python scripts/check_docs_governance.py --check
OK: 244 documents (+ docs.yaml itself) validated.

python -m pytest -q -p no:cacheprovider --basetemp <scratch> \
  tests/test_docs_governance.py \
  tests/test_tool_glossary.py \
  tests/test_architecture_documents.py \
  tests/test_mcp_capability.py
288 passed in 1.83s

Earlier reconciled V6R full-suite baseline, before the lifecycle-only follow-up:

python -m pytest -q -p no:cacheprovider --basetemp <scratch>
4 failed, 5374 passed, 3 skipped in 240.78s (0:04:00)
# exact failed-node set matches the prior four classified baseline cases; candidate-specific failures: 0

Additional exact-candidate checks:

• scratch simulated post-commit: 881 tracked files, 244 Markdown documents, 0 untracked files; git diff --cached --check passed; real worktree index remained byte-identical
• initial reconciled candidate tree: bac66b18c2a7c8d55881c017e7f1516c19e617e2
• independently applied scratch-index tree: bac66b18c2a7c8d55881c017e7f1516c19e617e2
• initial exact live packet patch SHA-256: 0e3003629670b56d0d0197bf9a1fd69213d05d487ff9cbe6fba2ca1e51f524ce
• lifecycle follow-up exact diff SHA-256: 96167b10d8109a28d58cb9f375e1dc99281a04beb8255176886a2cd65a4b448e
• canonical pool Terra initial governance review: PASS, 0 blocker / 0 important / 0 NIT after its two bounded quality repairs
• capability-enforced and mechanically verified claude-opus-4-8 initial governance review: PASS, 0 blocker / 0 important / 1 cosmetic non-blocking NIT (three stale “V5” labels in test comments/docstrings only)
• lifecycle follow-up Terra exact review: PASS, 0 blocker / 0 important / 0 NIT after closing its anti-placeholder finding and non-whitespace-count NIT
• lifecycle follow-up no-tools, mechanically verified claude-opus-4-8 final review: PASS, 0 blocker / 0 important; two observational non-blocking NITs, with no candidate change required

Scope notes

• related_files remains a safe repo-relative logical/crawl-link field; deeper existence and graph semantics stay with their existing specialized owners.
• lifecycle_contract supplies only a small mechanical floor. It rejects placeholder tokens and bare generic “when done” / “after migration” conditions, but owners and review remain responsible for semantic concreteness.
• The read-only expiry audit found zero deletion-ready stale documents. This PR does not delete, archive, or move any document.
• Two stale related_files entries discovered in src/lingtai/kernel/i18n/ANATOMY.md are reported separately and deliberately not mixed into this PR.
• The HTML explainer is local-only and is not included in this PR.
• This PR does not add or claim a new hosted CI workflow.