Returns the local config after editing key to value, without mutating
the inputs. An edit that lands exactly on the inherited value (deep
equality) — or clears the field (undefined) — drops the key from local
config so the field stays inherited instead of pinning a redundant copy.
Returns the local config after editing
keytovalue, without mutating the inputs. An edit that lands exactly on the inherited value (deep equality) — or clears the field (undefined) — drops the key from local config so the field stays inherited instead of pinning a redundant copy.