The grouped vertical rail is now an ARIA tree with a tree keyboard model,
and tab rows are pinned as full-row activation targets whose controls keep
their own actions and stable hit targets.
Tree semantics (grouped vertical rail only):
- #sessionTabs becomes role=tree while grouped and returns to its shipped
role=tablist and label when grouping ends. The header strip, sidebar and
flat rail keep role=tablist / role=tab exactly as before (the flat rail's
markup is unchanged byte for byte).
- A named group's header is a level-1 treeitem with aria-expanded that
aria-owns its rows' role=group (rows are level 2). Ungrouped rows and the
row a collapsed group keeps showing are level-1 items; a collapsed header
owns nothing, and the "Ungrouped" heading is a visual divider hidden from
assistive tech. aria-level, aria-setsize and aria-posinset are set on every
item, and aria-selected follows the selection without a rebuild.
- Exactly one treeitem carries tabindex=0 (roving). Controls inside rows
leave the tab order, so Shift+F10 / ContextMenu open a row's actions
(session action menu, web tab settings).
- Up/Down walk visible items, Home/End jump, Right expands a header or enters
it, Left collapses a header or climbs from a row to its header, Enter/Space
select a row or toggle a header. With the activity sort on, the walk follows
painted order within each group; the flat list keeps its whole-list walk.
- Focus survives a full re-render by identity (a row a collapse just hid hands
focus to its header), but a render never pulls focus into the rail.
- The group header is the treeitem itself (no nested button), still toggled by
click through the same onclick and still the lineage proxy anchor.
Full-row activation:
- Clicking a row's status dot, mode chip, name or padding already selected it
upstream; that is now pinned in real Chromium for the strip, the flat rail
and the grouped rail, together with every control (gear, detach, close,
overflow, web tab gear and close) running only its own action.
- The close control now shows a pointer like its siblings instead of the
default arrow.
- Enter/Space on a focused web tab in the flat list opens it; it used to call
selectSession(undefined).
- The action controls are pinned to stay under the pointer when a row is
hovered (no reflow-on-hover moving the gear out from under a click).
New Chromium suite test/tab-activation.browser.test.ts is listed in
BROWSER_TEST_GLOBS (run with npm run test:browser).
