Nice project... the per-agent tool restriction is the same core insight (smaller tool space -> better reasoning)

The main difference with Statewright is that tool access changes over time within a single agent. Planning phase gets read-only tools, edit capability unlocks after the agent proves it has adequate understanding... test tools unlock after the fix. State machines handle the phase transitions, guards and retry loops.

Your multi-agent approach decomposes by role instead of by phase/state. Both are valid. Since you're already in Rust, the engine crate (crates/engine) is a pure library with no deps. It might be interesting to see if putting a state machine around your orchestration layer improves your observed performance