cardinal-errors

Centralised error definitions used across the workspace.

• CardinalError is the top-level error type exposed by public APIs.
• internal module holds more granular variants (InternalError::ProviderNotRegistered, InvalidWasmModule, etc.).
• Conversions are implemented so ? works seamlessly across crate boundaries.

When extending the system, add new variants here rather than inventing ad-hoc error enums in downstream crates.