[HTExplicit]

Changes

Maintenance documentation repeated current behavior and retained obsolete recovery and testing instructions. Compact the downstream contracts and historical reviews, add a repository-local AGENTS entry, and make the developer guide select checks for the actual change.

Replace unconditional historical CI suites with one changed-risk plan and shared execution action. Keep all ten protected check names and the existing branch protection. Unknown executable inputs fail classification; required jobs report applicable execution, verified reuse, or explicit non-applicability. Receipt reuse verifies the complete tested tree, concrete targets, workflow definitions, environment and original successful execution. Preserve upstream dispatch, the macOS shell runner, scheduled security scans, and runtime checks when their actual inputs change. Release and production workflows are unchanged.

Validation

• Changed-document static checks and affected local anchors passed.
• Offline classification (22), receipt (17), runner (9), workflow (4), and the modified existing workflow contract (1) passed; fixes were rechecked only for their direct impact.
• Changed YAML parsing, Python syntax and diff formatting passed.
• No business, database, race, stress or real-model tests were run locally. This PR's selected CI work is static documentation and offline CI/upstream workflow contracts.