T26b Media: crop and annotate

ImageCropper crops a picture by a box in shares of it: a press holds a
corner, a side or the body (crop::grip_at), a drag through gpui's drag
moves them (crop::dragged), kept inside the picture with a least side;
with an aspect only the corners size it and the box keeps its shape; the
arrows move it. The picture sits inset by half a handle, the focus border
outside it, so handles on its edge stay whole and it keeps its shape.
ImageUpload (T06e) takes pictures only, from a drop or the dialog
(forms::taken, DropZone::kinds), decodes the file for its shape, and with
no crop yet reports the largest centered box of its aspect once. The
annotator draws boxes, arrows, lines and numbered pins in chart colors
through forms::pen; Select chooses a mark, Delete removes it, and Cmd-Z
and Shift-Cmd-Z undo and redo through forms::History. theme.media() holds
their sizes.

AGENTS.md

@@ -51,7 +51,7 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - A drag that pans, turns or slides goes through gpui's drag, whose moves reach the owner in or out of its box; `on_mouse_move` stops at the box's edge. gpui sends a drag's moves to every listener of its type, so each payload carries its owner's `EntityId` and handlers check it.
 - gpui 0.2.2 paints pictures without a transform, so a picture turns by its pixels: `media::turn` turns decoded frames by quarter turns off the main thread, an asset keyed by the picture and the turn.
 - 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 turns on reduced motion, so shots are still: repeating motion rests on one frame, and a shimmer shows no band.
+- The capture harness turns on reduced motion, so shots are still: repeating motion rests on one frame, and a shimmer shows no band. gpui's mac window stops its display link while occluded, so a capture advances a moving picture only on the draws the harness forces.
 - Each capture pass starts its page fresh (`Gallery::fresh`): page state lives under the pass, so the dark pass runs its script from the same start as the light one.
 - 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.
 - Posted events cannot move a macOS window, so window drags are not scripted. `drag_region` follows Zed's title bar.
@@ -79,11 +79,11 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - A picker hands focus to its popup on open and back to its trigger on pick or Escape; it closes once focus leaves both (`forms::date::picker`).
 - Motion for a value change keys its animation on `motion::changes`, so it replays per change and stays still on first paint. Key only the part that moves: a keyed ancestor gives every descendant a new id, and focused buttons lose focus.
 - A spotlight or tour takes its target's box from `primitives::Measure`; the lit box glides between targets.
-- Thumbs stay inside their component's box: the track is padded by half a thumb (`Slider`, `ColorPicker`, `GradientEditor`).
+- Thumbs stay inside their component's box: the track is padded by half a thumb (`Slider`, `ColorPicker`, `GradientEditor`, `media::ImageCropper`).
 - 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.
+- Only gpui can build `ExternalPaths` with paths, so drop rules live in `forms::files::dropped`, where tests reach them. `taken` adds file kinds by extension, for drops and the dialog alike (`DropZone::kinds`).
 - A stroke drawn with the pointer goes through `forms::pen`: a press starts it, a drag extends it, and the lift hands it over, in or out of the pad (`SignaturePad`, `generative::InpaintCanvas`).
 - 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 against last frame's bounds and overflow, so a call before a list's first frame does nothing. Call it from a child's prepaint once the handle has bounds, then request one frame (`navigation::editor_tabs`). A floating list reveals its cursor, and a strip its focused item, through `forms::options::reveal` and `revealer`. A focused Tab stop deeper in a scroll box sets the box's offset whole from its own painted bounds in prepaint, once per focus, through `layout::bring_into_view`. Never poll layout with `request_animation_frame`.
@@ -146,7 +146,8 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - gpui takes a scroll box's reach from its direct children's bounds, and a block child stretches to the box. Content that scrolls sideways sets its least width on that child (`tables::body::least`).
 - gpui turns a wheel along the other axis onto a box that scrolls one way, and the page around it scrolls too. A box inside a scrolling page keeps its wheel to its axis with `layout::on_axis`, and so does the page.
 - The focus color belongs to the focus ring. A chosen or shown item takes accent, as `forms::glyphs` and `lists::ListItem` do.
-- A box that shows a host's picture takes the picture's shape from the host (`ratio`), so nothing is cropped and a point given as a share lands on the picture.
+- A box that shows a host's picture takes the picture's shape from the host (`ratio`), so nothing is cropped and a point given as a share lands on the picture. A focusable one keeps its focus border on an outer box, so the picture keeps that shape exactly (`media::ImageCropper`).
+- A default only the component can work out, such as a crop fitted to a picture it decodes, reaches the owner once through `window.defer` after render (`media::ImageUpload`).
 
 ## Decisions