Cursor prompt: Implement Current Focus and FocusChanged

Prerequisites

Read:

• [ ] [ONTOUI.md](../WORKSPACE_RUNTIME.md`
• [ ] 0003-current-focus-central-ux.md
• [ ] ui/STATE_MANAGEMENT.md

Non-goals

• Cross-webview sync (separate webviews)
• AI context builder

Current state

• WorkspaceStore from prompt 02
• EntityInspector loads entity by IRI locally

Tasks

1. Add CurrentFocus type and setFocus action to workspaceStore
2. Create extension/webview-ui/src/store/events.ts with FocusChanged type
3. Add subscribe/emit helper (simple pub/sub in store module)
4. Update EntityInspector to call setFocus when entity loads
5. Add test: setFocus updates store and notifies subscriber

Acceptance criteria

• [ ] FocusChanged fires on entity selection
• [ ] Tests pass

Tests

• cd extension/webview-ui && npm test

Do not

• Do not implement cross-webview sync without extension host relay

References

• Cursor prompts index