# inset-shell/src
No Flutter counterpart. Dart has no type — the engine owns the isolate.
## lib.rs
- Change: `Shell` owns the `App` and is the `EmbedderClient` the host drives.
Reason: platform — the host must not name `App`, and a lower crate cannot name a higher binding.
Affect: there is no isolate-global binding a host can reach into; everything it does to the framework goes through the client it was handed.
- Change: the host delivers frames, pointer packets and key data as calls on `Shell` rather than by assigning handlers onto `PlatformDispatcher` callback fields, and `key_data` returns whether a `HardwareKeyboard` handler took the key.
Reason: platform — there is no isolate-global callback table, and the host reads the key answer from the call.
Affect: a host cannot swap the frame or pointer handler at run time, and learns from the `key_data` return whether to pass the key on.
- Change: `platform_brightness_changed` and `locales_changed` invoke the callbacks `WidgetsBinding` assigned on `App::platform_callbacks`, each in a turn of its own.
Reason: platform — the shell cannot name `WidgetsBinding`, which lives above it.
Affect: a host that reports a theme or locale change reaches `MediaQuery` observers without the shell knowing widgets.
- Change: `edit_command`, `menu_selected`, `dock_menu_selected` and `tray_icon_event` invoke the callbacks set on `App::platform_callbacks`, each in a turn of its own: the widgets binding sets the edit command's, the menu bar's and the tray icons', and the app the Dock menu's.
Reason: platform — the shell cannot name `WidgetsBinding` or the app, which live above it.
Affect: a choice in a menu with no callback set, such as the Dock menu of an app that set none, is dropped.
- Change: `open_requested` hands the request to `App::open_requested` in a turn of its own.
Reason: platform — the app's handler is set on the `App`, which the shell owns.
Affect: a request that comes before the app sets its handler waits there for it.
- Change: `notification_activated` hands the click to `App::notification_activated` in a turn of its own.
Reason: platform — the app's handler is set on the `App`, which the shell owns.
Affect: a click that comes before the app sets its handler waits there for it.
- Change: `system_fonts_changed` notifies `PaintingBinding.systemFonts` in a turn of its own.
Reason: platform — Dart's engine posts `fontsChange` on a system channel; here the host calls the client.
Affect: paragraphs listening to `systemFonts` relayout after the host loads faces.
- Change: `Shell::new` installs the platform's fonts into `PaintingBinding` before `setup` runs.
Reason: platform — Flutter's engine collects platform fonts on its own; here the shell asks `Platform::font_source` once.
Affect: text shapes against the OS fonts with no application code, while a test shell on the inert platform has an empty collection until `PaintingBinding::install_fonts`.
- Change: `Shell` keeps the app clock — `frame` and `wake` advance it to the platform's `elapsed` first, so due `Timer`s fire before the frame's scheduler phases.
Reason: platform — Dart's event loop runs timers between engine events; here the clock only moves when the host says so.
Affect: a `Timer` (and so `run_app`'s root attach) fires at the next wake or frame, never during `setup`.
- Change: `view_added` and `view_removed` invoke the callbacks `WidgetsBinding` assigned with the view's id and then report the metrics changed, and `view_close_requested`, `window_changed` and `view_request_failed` invoke theirs, where dart:ui's `_addView` and `_removeView` invoke only `onMetricsChanged` and Flutter's windowing hears a window's close request and its changes through a callback each controller registers with its runner.
Reason: platform — the shell cannot name `WidgetsBinding`, and the host reports every view, given or asked for, through the one client.
Affect: the binding hears which view came, went, is asked to close or had its window change, and the metrics observers still hear a view come and go as Flutter's do.