P1-tool-integrity: signed tool manifests + pinned runtime versions

[omarespejel]

Summary

Protect tool execution from silent drift or supply-chain mismatch.

Problem

Tool metadata/schema/runtime versions can drift across environments, weakening deterministic safety checks.

Scope

• Introduce signed tool manifest containing:
  • tool name
  • schema hash
  • implementation package/version
  • policy profile compatibility
• Enforce manifest verification at startup for production profile.
• Block execution when manifest signature invalid or version not allowlisted.
• Add explicit upgrade workflow docs (rotate manifest, review diff, re-sign).

Acceptance Criteria

• Startup fails closed on invalid manifest
• Policy layer can assert expected manifest digest in logs/artifacts
• CI includes manifest verification test
• Upgrade runbook documented