feat: add on-demand residency foundation

[schickling-assistant]

Problem

Agent desired state currently implies continuous process residency. There is no durable model for an agent that remains desired but can be cold between work bursts.

Goal

Add the typed foundation for on-demand residency without changing host orchestration yet.

Decisions

• Keep desired state (running | suspended | retired) separate from residency policy (always | on-demand).
• Model runtime residency as a durable tagged state machine.
• Key the canonical ledger by host, immutable agent ID, and generation.
• Keep the delivery ledger as the only message-delivery authority.
• Fail closed on ambiguous inventory or transition evidence.

Verification

• Agent Spec discovery and KDL round-trip tests cover residency on-demand.
• Residency unit tests cover legal transitions, stale generations, stop ordering, and persistence.
• Task inventory tests cover policy and runtime-residency wire shapes.
• cargo check --workspace passes on the complete stack.

Complexity

The large addition is the explicit ledger and transition model. Later PRs consume this model instead of duplicating provider-specific lifecycle state.

Concerns

This PR intentionally does not suspend or wake processes. Host policy arrives in PR #494.

Friction & bottlenecks

None specific to this layer.

Follow-ups

• PR feat: require exact Codex residency resume #491 adds exact Codex resume.
• PR feat: require exact OMP residency resume #492 adds exact OMP resume.
• PR feat: require exact Claude residency resume #493 adds exact Claude resume.
• PR feat: orchestrate on-demand runtime residency #494 adds host policy, demand, teardown, launch fencing, and wake commands.

References

Part of stack #495.

Posted on behalf of @schickling

field	value
agent_identity	mbp2025.direct.omp.bn5hrz39
session	mbp2025.bn5hrz39
agent_persona	generalist
agent_supervisor	unavailable
agent_tool	OMP
agent_tool_version	18.1.7
agent_runtime	OMP 18.1.7
tooling_profile	dotfiles@4816a7a