docs: explain versioned Codex receipts and ready-trigger reviews #42

Source engine PR: RandomDevelopment/ci-fleet#149
Reviewed engine PR head: 846c2a4829d2c88bdda113fe5bb2d76e78700dd3.
Merged engine commit: 4467042bad40fcf1530840b8b4454d88ed526a21. Its tree matches the reviewed head. All eight PR validation stages, independent source review and the exact-head bot receipt passed. Main-push run40131398318, attempt1, passed both jobs and all seven applicable full stages on the actual merged source. This issue does not claim template publication or adopter host acceptance.

The existing Codex review guidance in docs/UPDATING.md lists an unversioned receipt opening and only Manual request or PR opened summary triggers. The provider now emits an exact v1 receipt marker and can use Draft marked ready. Core PR149 adds narrowly recognized compatibility with those records and the finite verified current opening variants, preserving exact reviewer/head binding and all conflicting, edited, stale, incomplete and unknown-format rejection. Completed summaries with null findings remain rejected, and a dashboard alone remains insufficient.

Update docs/UPDATING.md and its supporting immutable engine-contract reference after the actual engine merge. Check README if it repeats that contract link. Describe the exact v1 header, recognized finite suffixes and ready trigger without implying arbitrary prose acceptance. Preserve existing root-owned policy selection, separate standalone receipt, false/false finding flags, null security state, exact commit resolution and manager/checkpoint compatibility requirements.

No template schema, initializer, validator or capability field changes are needed. This is operator guidance for the existing opt-in configuration_codex_reviews capability. Adopters must select a compatible reviewed merged engine and complete their own validation/recovery/host acceptance. Preserve published release tags and historical release records; no engine pin, template release, private configuration or live host changes follow from this issue.

Acceptance: documentation matches the reviewed merged engine grammar; immutable links resolve; template documentation checks pass; no unsupported format or null-summary approval is documented. Prior template issue30 is closed and covers the older contract, so this new format gap needs separate tracking.