T07b navigation places: nav item and group, navigation menu, back and forward history, table of contents with anchors, go to line; measuring canvases pinned to their parent

AGENTS.md

@@ -67,6 +67,7 @@ Ely GPUI Component. A component library for GPUI, in light and dark.
 - 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`.
 - The test platform never runs next-frame callbacks, and its text metrics are simplified: each character takes a fixed advance. Tests refresh the window in place of the display link, and click where layout does not hang on text, such as padding and slots.
+- An absolute element with no insets sits where it would flow: after the content in a block, inside the padding in a flex box. A canvas that measures its parent pins itself with `.top_0().left_0()`.
 - Long grids scroll in a `uniform_list`. gpui has no nearest scroll, so a key move up scrolls with `Top` and down with `Bottom` (`forms::glyphs`).
 - Masks reshape edits inside `TextInput::set_fit`, which sees the replaced range and the typed text. A diff after the fact cannot tell typed characters from kept ones.
 - Ids inside a reusable component carry its owner's id or `EntityId`, animation ids too. Twin ids share focus, click and animation state.