Make release acceptance an executable freeze barrier

[TheGreenCedar]

Outcome

Replace the vague independently-accepted-head convention with an executable release freeze barrier and stop broad proof from running on support PRs or twice around a sole generated calibration freeze.

Deduplication completed before creation: open and closed issues, merged pull requests, and integration history contained no freeze-barrier implementation. #1590 covers release/calibration lineage, but not the pre-proof cleanliness, push, support-integration, mutation barrier, proof-trigger separation, cancellation contract, or handoff schema requested here.

Acceptance

• Add Albert's eight release-process rules to AGENTS.md: precise candidate acceptance; no broad proof on intermediate PR heads; mandatory freeze sequence; one full source proof around calibration; immediate cancellation of superseded runs; sub-90-second native probes after platform failures; deduplication before work creation; and one implementer plus one bounded adversarial verifier.
• Add the required release-handoff fields: final intended source head, known future source changes, proof-triggering labels/actions, reusable and invalidated evidence, currently running workflows, and next permitted mutation.
• Provide an executable barrier that pins commit and tree, checks a clean pushed branch, requires declared future source/workflow changes, and consumes exact-head hostile-mutation acceptance evidence before any gate expected to exceed five minutes.
• Separate support-PR review from release proof triggers. A support PR may run focused checks only; review acceptance must not start source, package, calibration, or hardware proof.
• Enforce the sequence: blockers integrated, focused checks, actual-host microprobes, hostile mutations, frozen pushed source head, calibration, sole generated constant-set change, one broad source proof on the frozen candidate, and qualification.
• Policy must reject two full source proofs for one candidate. A tree-preserving promotion may reuse the authenticated frozen-head source cell.
• Cancel queued or running proof when its head is superseded; pre-dispatch policy checks in-flight runs and known future source changes.
• Authenticate the complete parsed bodies of every acceptance job, including commands, shells, environment, conditions, dependencies, outputs, and step order. Reject variable, alias/function, delegated-script, chained-command, and alternate-shell mutations.
• Add workflow-policy regressions and executed hostile mutations for intermediate-PR proof triggers, dirty/unpushed/unmerged freeze declarations, later commits, duplicate source proofs, non-constant calibration lineage, failure to cancel superseded runs, and acceptance-job body substitutions.
• Any workflow edit updates check-workflow-policy.mjs and its tests; update release-claims.json when the DAG or claim graph changes.

Refs #1558 #1590

Release boundary

Work proceeds in parallel as a nonblocking follow-up. PR #1622 contains the frozen #1597 head plus later workflow/source changes, so it must not merge into the 0.16.3 lineage. It may land after release. This lane must not trigger calibration or broad proof.