Codex: add agent execution registry readiness and suite integration contract

[mdheller]

Mission

Prepare agentplane to participate in the Prophet suite as the execution and evidence substrate for governed agents.

Context

The product suite now has:

• prophet-cli as façade command surface.
• SocioProphet/agent-registry for governed agent specs and identities.
• SocioProphet/mcp-a2a-zero-trust for zero-trust MCP/A2A patterns.
• SourceOS-Linux/sourceos-model-carry for on-device carry references.

agentplane should remain execution-focused: bundle -> validate -> run -> evidence -> replay.

Required work

Add a repo-local suite integration contract documenting:

• how prophet agent ... should delegate to agentplane;
• how agentplane consumes AgentSpec, AgentIdentity, ToolGrant, and PolicyBundle references;
• required evidence outputs for execution and replay;
• allowed and forbidden authority boundaries;
• how Codex/agent work should be scoped and reported.

If the repo already has similar docs, extend them rather than duplicating.

Acceptance criteria

• Add or update docs for prophet agent / suite delegation.
• Add a small machine-readable example execution contract under examples/ or contracts/.
• Add or update validation to check the example.
• Ensure make validate or the repo’s equivalent validation command covers the example.
• Document that model routing, guardrails, and SourceOS carry are delegated surfaces, not owned here.

Out of scope

• Do not implement full agent registry here.
• Do not implement model routing here.
• Do not embed tool secrets or broad runtime authority.
• Do not modify unrelated execution semantics.

Codex instructions

Open a focused PR with summary, changed files, validation output, and boundaries honored.