c-api: use safe enum conversion helpers instead of raw static_cast for C→C++ enum params

[fpelliccioni]

Problem

The C-API bindings use static_cast<CppEnum>(c_enum_value) to convert C enum integers to C++ enum class types. If a caller passes an out-of-range integer value, static_cast produces an unspecified enum value — undefined behavior in practice.

The codebase already has safe conversion helpers (e.g. kth::network_to_cpp(kth_network_t) in helpers.hpp) that map unknown values to a sensible default (typically mainnet). Hand-written C-API code uses these helpers consistently, but the generated bindings emit raw static_cast instead.

Current behavior (generated code)

auto const net_cpp = static_cast<kth::domain::config::network>(net);

Expected behavior

auto const net_cpp = kth::network_to_cpp(net);

Or a generic pattern that works for all registered enums.

Scope

This affects every generated function that takes a C enum parameter:

• kth_network_t → config::network (payment_address, get_blocks, get_headers, etc.)
• kth_script_flags_t → machine::script_flags
• Any future enum params

Possible fix

Option A: Register a safe conversion helper per enum in the generator's _ENUM_REGISTRY, and emit calls to it instead of static_cast.

Option B: Generate a generic helper template:

template<typename CppEnum, typename CEnum>
CppEnum safe_enum_cast(CEnum value, CppEnum default_value);

Option C: Add a default case to each switch that uses the enum, returning a sensible fallback. This is what network_to_cpp already does internally.

Flagged by

Cursor Bugbot on PR #241 (comment #8).