Standards

Preserve existing behavior, controller orchestration, TUI interactions, and on-disk .md and .toon controller formats throughout the refactor.
Prefer focused directory modules when a file mixes responsibilities or grows past roughly 300 lines, and keep mod.rs files as thin facades or reexport surfaces.
Keep public call sites stable unless a narrower API is clearly better, using pub use reexports to avoid unnecessary churn.
Split code by ownership boundary: model/state/schema concerns, process execution and parsing, TOON persistence and controller discovery, app runtime lifecycle, workspace input handling, and UI rendering helpers.
Move or add focused tests with the code they protect, especially around model schemas, session grouping and selection, process parsing, storage discovery and id generation, runtime event handling, workspace commands, and UI rendering helpers.
Remove dead helpers, stale imports, and compatibility layers that only mirror the old file layout.
Finish with cargo fmt --check, cargo test -q, and cargo clippy -q --all-targets --all-features passing.