Derived Config ownership

Config derivation is a state-ownership operation, not a clone. deriveConfig keeps the existing prototype overlay model behind one boundary while production callers are migrated incrementally.

State	Ownership	Contract
workspace path and context	shared until explicitly overlaid	Worktree profiles must override the paired public getters and private reads together.
file service and discovery	shared until explicitly overlaid	Worktree profiles rebind both to the target workspace.
tool registry	shared or explicitly replaced	Agent profiles that rebuild it own cleanup of the replacement registry.
permission manager	shared or explicitly replaced	Agent profiles preserve the existing strip/restore lifecycle.
approval mode	shared or explicitly copied	Bare derived profiles cannot mutate it; agent execution profiles own child-local state and preserve the canonical permission lifecycle.
file-read cache	child-local	The first getter call installs a fresh cache on the derived Config.
memory-pressure monitor	child-local	The first getter call installs a new monitor using the inherited configuration snapshot.
active todo state	child-local	The first mutation installs independent maps.
chat recording service	shared unless hidden	Scoped profiles may hide it through a getter override.
goal runtime	prohibited	A derived Config cannot resolve the parent conversation's runtime.
session writer state	prohibited	Writer ownership stays with the canonical session Config.
canonical lifecycle	prohibited	A derived Config cannot initialize, start a session, relocate the workspace, or clean up inherited Team/Arena runtime resources.
approval mode mutation	prohibited or explicitly copied	Only the approval-profile factory may install a child-local transition method and cleanup contract.

Migration order:

1. Worktree contexts.
2. Agent execution contexts.
3. Scoped memory/remember/skill-review profiles.
4. Enforce that production prototype derivation occurs only inside deriveConfig.

The generic factory intentionally accepts public getter overrides only. Named profiles keep private field rebinding and lifecycle management inside config.ts without exposing arbitrary Config mutation.

The approval profile owns child-local approval state and its parent permission-manager strip/restore contract. Callers remain responsible for invoking its cleanup callback when the agent lifecycle ends.

Production core modules that import Config are linted against non-null Object.create(...) calls, keeping new prototype overlays behind the generic or named factories.