T10a feedback: toasts with undo and a hover-held clock, notifications and their center, alert, banner, callout, inline and status messages, empty state; root focus scopes take lost focus

AGENTS.md

@@ -38,9 +38,10 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - `svg()` paints only with its own `text_color`. `Icon` always sets one.
 - Buttons stay out of focus on click (`prevent_default` on mouse down). Tab still reaches them.
 - The focus ring is a 1px focus-colored border (`FocusRing`). gpui paints shadows under the element, so a shadow ring floods transparent elements. Focusable elements keep a 1px border, transparent at rest.
-- `ely_gpui_component::init` binds Tab and Shift-Tab to `FocusNext` and `FocusPrev`. Wrap the root in `FocusScope` and focus its handle.
+- `ely_gpui_component::init` binds Tab and Shift-Tab to `FocusNext` and `FocusPrev`. Wrap the root in `FocusScope` with `.root()` and focus its handle. A root scope takes focus when the focused element leaves the tree, as a toast's or an alert's button does.
 - gpui's `Window::dispatch_event` returns a private type, so the gallery scripts mouse input by posting `NSEvent`s to its own queue.
 - `hover()` needs an element id.
+- `occlude()` blocks the pointer for everything painted before it, its own ancestors too. Put it on the outermost box that should stop the pointer, as the toast stack does, or the ancestors' hover never fires.
 - gpui sends a drag's moves to every listener of its type. Each drag payload carries its owner's `EntityId`, and handlers check it.
 - A component that takes a starting value from its owner keeps it in `layout::seeded`: a new value from the owner replaces local drags.
 - The capture harness finds gpui windows by handle through `raw-window-handle`. AppKit popups, which gpui does not own, come from the window list by process and level.
@@ -71,6 +72,7 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - Thumbs stay inside their component's box: the track is padded by half a thumb (`Slider`, `ColorPicker`, `GradientEditor`).
 - gpui's `Hsla::opacity` scales alpha; `alpha` sets it.
 - A rounded box does not clip its children. Each layer inside takes the radius itself; `checker` takes one.
+- A window keeps one `feedback::Toaster` and renders one `ToastViewport`; anything holding the entity pushes to it. Messages share `primitives::Severity`.
 - Only gpui can build `ExternalPaths` with paths, so drop rules live in `forms::files::dropped`, where tests reach them.
 - gpui runs key bindings before key listeners. A container takes a child's bound key through the action with `capture_action`, as `Form` takes `Submit`.
 - `ScrollHandle::scroll_to_item` runs in the container's prepaint before its bounds are stored, so a first-frame call misfires. Call it from a child's prepaint once the handle has bounds, then request one frame (`navigation::editor_tabs`). Never poll layout with `request_animation_frame`.