Architecture

File	Responsibility
`src/note.rs`	The data, the inputs and their rules, and the two boundary traits
`src/memory.rs`	A volatile in-process repository
`src/service.rs`	The application boundary over any repository
`src/routes.rs`	The only Axum module: parsing, status codes, JSON
`src/main.rs`	The composition root and host

Reading the wiring

The adapter (routes.rs) depends on the service; the service depends on the NoteRepository port; the memory store implements that port. Nothing else knows that HTTP exists, and the store is replaceable without touching either the rules or the transport. That is the same shape the application model describes — with one slice instead of three.