PDFCAB 1.21.0
Own-revision signature coverage fixture
Adds the 158th deterministic fixture pair, signature.own_revision_coverage_required, for PFP013.
Both PDFs retain an older semantic signature after a later incremental update, so neither range reaches the current physical end. Only the baseline reaches its own signing revision footer; the candidate stops before it. The public contract expects the own-revision inventory event and PFP013 only.
Validation: 88 tests, Ruff, reproducible wheel/sdist builds, and an exact 158/158 process-bound score against PDFFence 1.21.0. Public truth remains aggregate-only and does not disclose offsets, signature contents, certificates, or hashes.