Registry-native plan commands.
Purpose
-------
Expose plan lifecycle mutation and inspection commands beneath
``python -m oc_chat.registry plan``.
Responsibilities
----------------
- Parse plan domain command arguments.
- Resolve the registry and actor slot.
- Dispatch to domain API and reader helpers.
Diagnostics
-----------
Domain: OC_CHAT.MAIN
Levels:
L2 - lifecycle events
L3 - semantic details
L4 - deep tracing
Contracts
---------
- Mutating commands emit one operation-log row through the seam.
- ``show`` is read-only and returns the current projected plan row.
Dependencies
------------
- oc_diagnostics (structured debug logging via _dbg)
- oc_chat.registry.backends.sqlite (SQLite backend)
- oc_chat.registry.discovery (registry path discovery)
- oc_chat.registry.domain (plan mutation API)
- oc_chat.registry.readers (plan readers)
- oc_chat.registry (Registry facade for plan mutations and readers)