# §92 — The navigator

A nav rail down the left, routed views on the right, and lists you control the timing of.

This is the `sidebar` template, and it is the one to read to understand how the pieces fit. A `Route` enum with a stable id per destination, `atlas::shell::Nav` rendering the rail, and one view per surface reading the signals it cares about.

The rail collapses to icons and remembers that it did. A preference that has to be re-applied every launch is not a preference.

## What you are carrying

- `model + store` — Types and local persistence.
- `host` — The async facade behind every list.
- `atlas::shell::Nav` — The collapsing rail.
- `atlascore::Load` — Loading, ready, and failed as three screens.

## Start it

```bash
scripts/new.sh Acme ~/Dev/acme --template sidebar
```

## What it looks like

`crates/app/src/root.rs`

```rust
let nav = Nav::new(Route::nav(), route.id())
    .title("Acme")
    .collapsed(collapsed)
    .on_select(move |id, cx| {
        if let Some(next) = Route::from_id(&id) { route_signal.set(cx, next); }
    })
    .on_toggle(move |cx| collapse.toggle(cx));

// gpui dispatches actions along the focus path. With nothing focused the
// menu bar greys out and swallows its own shortcuts.
focus::claim(window, cx, &self.focus);

div().track_focus(&self.focus).flex().child(nav).child(content)
```

## Where now

- Sign it and ship it — turn to §101 (Appendix B)
- Hand it to an agent — turn to §102 (Appendix C)
- Walk it again from the start — turn to §1