chore(agent-policy): rollback channel revision 15

[hv-agent-promoter]

Automated protected policy-channel transition.

• Action: rollback
• Revision: 15
• Evidence SHA-256: 0ccdc732f3127f330232a7e825d05f65b22a2d5185f85bb7ec1bfe62c1758ee6
• Signed bundle SHA-256: 8ed02bee19b02b1b622ea872546090c6b0cc8abd8ca4dbb822d69e24b9d42753

Closes #76

[willgriffin]

Closing without merging. This rollback was proposed because the smoke ring failed on happyvertical/pdf and happyvertical/ocr — both reported selected_artifact: null because their vendored agent-policy.yml still failed its own drift self-audit:

ERROR .github/workflows/agent-policy.yml: missing or differs from the canonical lifecycle workflow

That was stale vendoring, not a defect in generation 16. sdk, .github and smrt all passed smoke against sha256:78e729c3….

Both repositories have since been re-vendored to canonical — happyvertical/ocr#129 and happyvertical/pdf#110 are merged — so the condition that produced this rollback no longer holds. Re-running the smoke ring should now yield finalize instead.

Rolling stable back to generation 15 would discard a promotion whose canary evidence is recorded and valid (e3a09da0…, revision 14).