feat(web-ui): add workspace session tabs and rolling text

[GCWing]

Summary

Keep one stable session tab per owning workspace and device surface. Opening another session replaces that workspace's reference, while other tabs retain their titles and order. Workspace activation, session hydration, history navigation, and close fallback share one navigation transaction, and all session tabs use a single presentation host.

Add the public RollingText component and TabGroup label transitions, reuse them in the welcome surface, keep sidebar ordering tied to execution activity, and simplify the auxiliary canvas empty state and workspace resource panel.

Type and Areas

Feature, UI/UX, refactor, docs, and tests. Areas: Web UI session navigation, design system, Design Lab, localized welcome copy, and generated Data Migrator theme tokens.

Motivation / Impact

Users can retain their current session in each workspace without background labels following the active session. Superseded asynchronous navigation cannot select a stale destination, and switching tabs preserves the existing file, terminal, voice, and customization scene contracts. Session title edits remain static; replacing the referenced session uses interruptible motion that respects reduced-motion preferences.

Verification

GitHub CI run 34216519048 passed for ae5e93cf4a9f4e36caa6ecfe70e4c6ba38d34c56, including the full Web UI suite/build and Rust/CLI checks on Linux, macOS, and Windows. Repository Object Sizes also passed. The two impact-selected packaging jobs were skipped by the existing workflow.

Passed locally on Windows with Node.js 22.18.0 and pnpm 10.15.0:

• pnpm run design-system:check
• pnpm run check:web
• pnpm run lint:web (0 errors; 11 existing warnings)
• pnpm run theme:color-audit:all (23 surfaces)
• pnpm run i18n:audit (0 warnings)
• pnpm run motion:audit (intent inventory)
• node scripts/check-git-object-sizes.mjs --base origin/main --head HEAD
• git diff --check origin/main...HEAD
• Session and creation bridge integration recheck: pnpm --dir src/web-ui exec vitest run --maxWorkers=50% src/flow_chat/services/openBtwSession.test.ts src/infrastructure/creation/creationBridge.test.ts src/flow_chat/services/sessionActivation.test.ts src/app/services/sessionSceneLifecycle.test.ts src/app/stores/sceneStore.test.ts (5 files, 57 tests passed).
• Navigation regression recheck after lint cleanup: 6 files, 73 tests passed.
• Focused Web UI regression suite: 18 files, 184 tests passed. Design-system packages were built by the checks above before this run.

Focused regression command

pnpm --dir src/web-ui exec vitest run --maxWorkers=50% src/app/services/sessionSceneLifecycle.test.ts src/flow_chat/services/sessionActivation.test.ts src/flow_chat/services/storeSync.test.ts src/app/stores/sceneStore.test.ts src/app/services/sessionSceneTarget.test.ts src/app/hooks/useSessionTabLabels.test.tsx src/app/components/NavPanel/workspaceSessionView.test.ts src/app/components/NavPanel/sections/sessions/sessionNavSelection.test.ts src/app/components/SceneBar/SceneBar.test.tsx src/app/scenes/SceneViewport.test.tsx src/app/scenes/workspace-resources/workspaceResources.test.ts src/app/global-search/globalSearchArchitecture.test.ts src/flow_chat/services/flow-chat-manager/SessionModule.test.ts src/flow_chat/services/sessionNavStatusService.test.ts src/flow_chat/utils/workspaceScope.test.ts src/flow_chat/utils/sessionNavOrdering.test.ts src/shared/services/sceneOpenTargetResolver.test.ts src/infrastructure/design-system/RollingTextIntegration.test.tsx

Reviewer Notes

AI-assisted; tested with local build, type, contract, and unit checks. Visual fidelity was not verified through browser automation or mock screenshots, in accordance with repository guidance. Native visual checks remain separate from these results.

Tests cover legacy workspace metadata, worktree ownership, SSH host/path identity, device-surface isolation, and superseded selection. No live Remote Workspace, Remote Control, Peer Device Mode, or Detached Dispatch integration scenario was exercised locally. Persisted session shapes and wire protocols are unchanged.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.