Feat/cas

[lahiruudayakumara]

Summary

Validation

• cargo fmt --all --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace

Compatibility and security

• Documentation and compatibility matrix are updated if behavior changed.
• Threat model or security documentation is updated for new trust boundaries.
• Persistent format/API changes have an RFC and migration story.
• Performance claims include reproducible evidence.