feat(ui): view tab strip with keep-alive and open-in-tab links (RIG-4444)

[rigel-mintaka]

This PR is part of a stack containing 7 PRs:

1. main
2. refactor(ui): extract parseRoute and add ViewScope with useView (RIG-4439) #1652
3. refactor(ui): move routed surfaces and agent-workspace state onto the view scope (RIG-4442) #1675
4. feat(ui): window layout model, hash sync and session persistence (RIG-4443) #1743
5. "feat(ui): view tab strip with keep-alive and open-in-tab links (RIG-4444)" (this PR)
6. feat(ui): W leader chords and palette commands for tabs and panes (RIG-4445) #1770
7. feat(ui): two-pane split with a resizable splitter (RIG-4446) #1780
8. fix(ui): chrome cleanup: drop ADE and usage bar, Session Log naming, pane edges, row re-measure (RIG-4771) #1811

Tabs T4 of docs/designs/ui/compass-in-window-tabs/design.md §T4 (RIG-4444), stacked on T3 #1743.

• components/TabStrip.tsx + design/components/tab-strip.css:
  • A .cx-tab-strip[role=tablist] over store.layout(). It dispatches only LayoutActions: focusTab, close (the close button or Delete), and move (drag).
  • Arrow keys, Home and End rove through createRovingGroup in the topbar zone. Agent tabs lead with a StateDot.
• route-title.ts: routeTitle (§A3) gives tab labels and document.title.
• App.tsx, keep-alive (§A4):
  • The tab strip replaces nav.view-tabs.
  • Each view instance gets one [role=tabpanel], which wraps its ViewHost.
  • Inactive panels are hidden and stay mounted. Focus moves into the shown view, to its last-focused element, before the old view hides.
  • .view-panel takes over sizing from .main, so view bodies don't move.
• open-link.ts (OQ-2): a plain click navigates in place, as before. Mod+click and middle-click dispatch open. This is wired on the sidebar tree, channel, topic and nav rows, the Bridge swimlane gutters, and the right-sidebar "Open agent" buttons.
• Bridge registers its board.*/list.* commands only while its view is focused. A cleanup removes only the registration it added. This fixes the case where closing one of two Bridge tabs dropped the other tab's commands.
• store.ts: exposes viewScopes. Adds channelPath and topicPath, so the in-place and new-tab paths are the same.

Readings:

• There is one ViewHost per view instance, so split panes stay alive too.
• Roving focus never activates a tab; Enter or a click does.
• Delete on a focused tab closes it.

Two topbar Bridge-tab tooltip tests were deleted from App.test.tsx. §A7 removes the pinned Bridge tab, and the sidebar Bridge link keeps its own chord-tooltip test.

Review fixes (de33726 → 624e1da, four rounds, now clean)

• A redirect from a hidden view applies to its own view, not the focused one.
• Closing a tab leaves focus on the new active tab.
• Focus only lands on visible, focusable elements; otherwise on the panel (tabindex=-1).
• An 11th tab shows a notice (§A3). It is an inline chip in the topbar after the strip, in an always-mounted role=status region, with a repeat counter, Dismiss and a 5s timeout. The timeout pauses while the chip has focus or hover and keeps pausing through a window blur. When the chip unmounts with focus inside it, focus returns to the active tab.
• The topbar search fills its flex box (240px, shrinking to 180px), so it no longer overflows onto the daemon pill when the strip is full.
• A conversation mounted while hidden scrolls to the latest message on its first show only. Later tab returns keep the user scroll position.
• Remembered focus targets must still be focusable; each focus move is checked, with fallback to a candidate, then the panel.
• Every view of the active tab is shown, ready for T6 splits.
• Backspace closes a tab on mac.
• Middle-button mousedown is cancelled, so no autoscroll.
• Bridge drops each of its commands before re-registering it.

Close buttons stay in the tablist; it is the usual closable-tabs pattern, and each has a label.

Visual baselines

These shots are local captures under the pinned dev shell, per DL-399 (#1644). The baseline commit depends on #1644 merging first.

• tab-strip: a new shot.
• agent: a refresh. Only the topbar row changes, because one agent tab replaces Bridge + agent. I checked agent-diff.png: no body pixels moved.

All other baselines are unchanged.

Tests

• New: TabStrip.test.tsx (6), tab-keep-alive.test.tsx (5, including two Bridge tabs where one closes), and a 6-case LeftSidebar open-modes block. All were red first.
• New e2e e2e/tab-strip.spec.ts: a draft survives switching tabs and back, and both tabs restore after a reload.
• moon run compass-ui:test: 1270 pass, 0 fail. Typecheck, stylelint and biome are clean.
• Playwright visual-smoke (13) + dev-boot + tab-strip all pass.

Spec-impact: none.
Ledger-impact: none

Co-authored-by: Matt Wilkinson matt@rigel.build

[linear-code]

RIG-4444

[github-actions]

Compass engineering docs preview: https://compass-ui-rig-4444-tab-stri.compass-eng-docs.pages.dev

Deployed from compass-ui/rig-4444-tab-strip at 624e1da.

[trunk-io]

This pull request is queued for merge as part of 1798, which will merge 1652, 1675, 1743, 1755, 1770, 1780, 1787, 1798.

[trunk-io]

This pull request was merged into main as part of stacked PR 1798.