notescraft/scripts/waves/wave2/canvas-split.md

Crate: crates/canvas (notescraft-canvas). Pure refactor: src/lib.rs is ~1100 lines. Split it into modules by concern (suggested: error.rs, model.rs for types, read.rs, write.rs, validate.rs, id.rs), keeping lib.rs as module declarations plus re-exports so the public API (names, signatures, paths such as notescraft_canvas::Canvas) is IDENTICAL. No behaviour change, no new dependency, no test weakened or deleted (tests may move next to their code). Each file under ~400 lines. cargo test -p notescraft-canvas must pass with the same number of tests as before (31); report before/after counts.