Interaction · Keys, scroll and focus: roving focus, scroll sync, type-ahead

RovingFocus keeps a row or column of items behind one Tab stop: the
arrows walk focus, Home and End reach the ends, Enter or Space presses,
and a press moves the stop without taking focus. ScrollSync keeps boxes
at one place along an axis: the pane a wheel turned leads, and a canvas
ahead of the panes copies its place before they draw. SelectableList
moves its cursor to the row that starts with the letters typed, the
letters joining within a pause and a Command letter left to the app.
forms::History becomes public as the undo manager. The gallery shows
gpui's own key bindings, a two-stroke chord waiting on its first
stroke, uniform_list, autofocus and the focus ring.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

AGENTS.md

@@ -53,6 +53,7 @@ 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. An svg turns to any angle through its `Transformation`, so a control that turns shows one (`interaction::Rotatable`).
 - A box that keeps a cursor over its items rings the item the cursor is on, not the box, as SelectableList marks its row (`interaction::SelectionArea`).
+- Boxes that scroll together go through `interaction::ScrollSync`: the pane a wheel turned leads, and a canvas laid before the panes copies its place in prepaint, before they draw, so no frame shows them apart.
 - A component that takes a starting value from its owner keeps it in `layout::seeded`: a new value from the owner replaces local drags. A field that reports its words as they change keeps what it sent, so the owner's echo leaves the caret alone (`mail::SignatureEditor`). A cursor inside a seeded view stays while it lies in what is shown, so the owner's echo of a turn leaves it (`calendar::CalendarMonthView`, `YearView`).
 - 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.
@@ -141,7 +142,7 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - A mode that leaves on Escape holds its own focus through `primitives::hold_focus`: turned on while focus is elsewhere, it takes focus so Escape reaches it, and `hand_back` returns it (`documents::ZenMode`, `collab::FollowMode`).
 - A chat holds at its newest message through gpui's `list` with `ListAlignment::Bottom`: it sticks while scrolled to the end, and `scroll_to` one past the last item sticks it again; that call sends no scroll event, so the owner clears its own away state (`chat::MessageList`).
 - Anything pressable is a Tab stop: a row, card or toggle takes `tab_index(0)` and `focus_ring`, with a 1px border that stays transparent where it shows none; gpui presses it on the release of Enter or Space.
-- A list of pressable rows goes through `lists::SelectableList`, whose cursor reaches them by key: Up and Down move, Enter or a double press activates (`media::Playlist`). Enter activates on its release, armed by its own press, so an activation that moves focus leaves the release nothing to press (`onboarding::HelpPanel`). A bare `ListItem` press is the pointer's only. Titled sections of such lists go through `lists::Sections`, for ChannelList, MemberList and MailboxList; each owner builds its rows and keeps its own checks.
+- A list of pressable rows goes through `lists::SelectableList`, whose cursor reaches them by key: Up and Down move, Enter or a double press activates (`media::Playlist`). Enter activates on its release, armed by its own press, so an activation that moves focus leaves the release nothing to press (`onboarding::HelpPanel`). Typing a row's first letters moves the cursor there, the letters joining within a pause on the executor's clock; a letter held with Command, Control or Alt stays the app's. A bare `ListItem` press is the pointer's only. Titled sections of such lists go through `lists::Sections`, for ChannelList, MemberList and MailboxList; each owner builds its rows and keeps its own checks.
 - Columns that must line up across rows sit absolutely at fractions of their row, as the bars over them do (`calendar::CalendarMonthView`): with real text, gpui 0.2.2 lets a `flex_1` cell's text widen it, and the test platform's fixed advances hide it.
 - A row that holds text beside fixed parts lets the text give way: the text takes `flex_1().min_w_0()` and an `Ellipsis`; counts, icons, dates and chevrons take `flex_none`. A label that must stay whole wraps in that block instead, as `forms::Checkbox`'s does.
 - A mark over a text field reads the field at paint time, from a canvas laid over it (`collab::RemoteCursor`): by then `TextInput::bounds_for` holds this frame's layout, and a still page never renders again to catch up.