Expand signed ledger event coverage beyond route_audit

[coreytshaffer]

Summary

Follow-up from #4.

The persistent identity foundation is MVP-complete for local agent identities, Ed25519 signing, capability checks, revocation, signed route_audit events, and verification. This issue tracks any deliberate expansion of signed ledger event coverage beyond route_audit.

Candidate event types

• taskpacket_created
• route_decision
• validation_result
• project_steward_decision

Constraints

• Do not sign or persist raw sensitive prompt/data content.
• Do not treat a valid signature as approval, safety, or correctness.
• Keep event-specific capability checks, such as validation_result:sign.
• Preserve existing human review and admission gates.

Acceptance criteria

• Document which event types are intentionally signed and which remain unsigned.
• Any new signed event path has explicit capability checks.
• Tests cover success, tampering, unknown agent, revoked agent, and unauthorized capability.
• Verification output remains operator-facing and does not expose private keys or raw sensitive content.

[coreytshaffer]

CR-078 and CR-079 complete the first signed-event expansion path beyond route_audit.

Completed:

• signed validation_result ledger event append path
• explicit validation_result:sign capability
• operator-facing verification via tc audit --verify-signatures --kind validation_result
• metadata-only pass/fail readout
• safe failure reasons for mismatch, unknown agent, and revoked agent

Remaining future work under this issue:

• decide whether to sign additional event types such as route_decision, taskpacket_created, or project_steward_decision
• avoid treating signatures as approval, safety, or correctness
• avoid expanding event coverage before verification/readout behavior remains stable