docs: define modular local agent contracts

docs/architecture/LOCAL_AGENT.md

@@ -66,6 +66,8 @@ For a connected run, service run identity, proposal revisions and acceptance rec
 
 Pin the installed pack snapshot for an active run. If that version is unavailable after an upgrade, pause with a compatibility finding or explicitly start a successor run. Reuse previous outputs only when their hashes, evidence bindings and new stage contracts still hold; revalidate downstream stages after changes. Install/version manifests alone cannot enforce this in arbitrary hosts; native workflow tests must demonstrate it.
 
+The pack manifest supplies per-module implementation and instruction-contract versions, dependencies, compatible checkpoint contracts and file hashes for the profile, shared protocols, skills and pipelines. Run checkpoints retain the snapshot digest and resolved module IDs/contracts/hashes. Its service-capability requirements remain explicitly unbound until wire schemas exist; empty capability arrays are not a declaration of compatibility. The draft checkpoint fields and snapshot calculation are specified in the pack README.
+
 A pipeline has a bounded work/correction budget, explicit coverage and a resumable stop. Two unchanged validation failures are a default stop for diagnosis, not permission to relax checks. Network uncertainty triggers status lookup, not a fresh proposal identity. Protected decisions leave the agent workflow for the separate human owner client. No continuous watcher, automatic external messaging or unbounded research loop is introduced.
 
 ## Acceptance and sequencing