Implementing Core Exception Infrastructure

Current State

The solver has some exception usage, but it lacks a solver-wide infrastructure that would be useful for a modular FE plan.

• Most production code throws generic standard exceptions, predominantly std::runtime_error, spread across many modules. Examples include Code/Source/solver/Parameters.h:166, Code/Source/solver/Vector.h
• There is one localized custom exception family for boundary-condition handling in Code/Source/solver/BoundaryCondition.h, but it is subsystem-specific. It stores only a message string and is not tied to shared status codes, source locations, MPI context, or common solver macros.
• Some failure paths bypass exceptions entirely and terminate the process directly, for example Code/Source/solver/trilinos_impl.cpp.
• The solver execution path also does not currently have a consistent top-level exception boundary. The read_files() catch is commented out in Code/Source/solver/main.cpp, while the simulation loop proceeds without a surrounding catch in Code/Source/solver/main.cpp.

Solution

We want to implement a core exception system that can define failure handling into a set of shared contracts instead of a pile of unrelated strings and exits. This system will need to be able to accommodate the following:

• A types list that provides a common vocabulary: semantic index types like LocalIndex, GlobalIndex, an DofIndex etc,, plus a status taxonomy. The current solver mixes raw int/double, backend-native codes like PetscErrorCode, and subsystem-local conventions, so there is no single way to say “this is invalid input” versus “this is a backend failure” versus “this is a convergence failure.”
• FEException class to add a base exception carrying structured context: message, status, file/line/function, MPI rank, and optional debug stack trace. It also will define typed subclasses like InvalidArgumentException in and standardized throw/check macros.
• Against the current code, that would give three immediate benefits: failures become classifiable instead of string-only, tests can assert on error categories instead of exact text, and MPI/backend failures can be surfaced consistently instead of sometimes throwing, sometimes aborting, and sometimes just printing. This will be crucial for testing modular subsystems in the future.