refactor(optim-config): split parsing (reading) from cross-validation

src/gems_craft/model/resolve_library.py

@@ -202,6 +202,8 @@ def _convert_port_type(port_type: PortTypeSchema) -> PortType:
     )
 
 
+# TODO: these _forbid_* checks are expression validation embedded in the
+# resolution pass — consider isolating them from the build logic below.
 def _forbid_nonlinear(expr: ExpressionNode, context: str) -> None:
     if not is_linear(expr):
         raise ValueError(f"Non-linear expression is not allowed in {context}.")

src/gems_craft/optim_config/__init__.py

@@ -19,8 +19,8 @@
     SolverOptionsConfig,
     TimeScopeConfig,
     load_optim_config,
-    validate_optim_config,
 )
+from .validation import validate_optim_config
 
 __all__ = [
     "ElementLocation",