Summary

Implements CR-078 as the first narrow expansion of signed ledger event coverage beyond route_audit.

This slice adds signed validation_result ledger events while preserving the core boundary that signatures provide provenance only, not approval, safety, or correctness.

Scope

• Adds signed validation_result ledger event append/verification helpers
• Requires explicit validation_result:sign capability
• Adds tests for:
  • valid signed validation result
  • tampering rejection
  • revoked agent rejection
  • unauthorized capability rejection
• Updates CR docs, backlog, and changelog

Non-goals

• Does not sign all ledger event types
• Does not implement runtime key rotation
• Does not treat signatures as approval or safety
• Does not persist raw sensitive prompt/data content

Validation

• python -m py_compile triage_core\task_ledger.py tests\test_task_ledger.py
• python -m pytest tests\test_task_ledger.py tests\test_agent_identity.py -q
• python -m pytest tests -q
• git diff --check