feat(messaging): validate op/v/deadline before knowledge job processing
- Add op/v envelope validation using envelope_reject_reason before job processing
- Add deadline check to discard expired messages before expensive job execution
- Add 3 test cases: op_mismatch, unsupported_version, deadline_exceeded discards
- All validations log content-free summaries for operational safety
Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com