Connectivity + session probes

sequenceDiagram autonumber participant UI as Page / Bootstrapping participant Probe as testConnection / checkSession participant HC as httpClient (Axios) participant BE as Backend API alt Connectivity UI->>Probe: testConnection() Probe->>HC: GET /api/health/db HC->>BE: request BE-->>HC: 200 or error alt 200 HC-->>Probe: status=200 Probe-->>UI: true else error HC-->>Probe: error Probe-->>UI: false end end alt Session validity UI->>Probe: checkSession() Probe->>HC: GET /api/me HC->>BE: request BE-->>HC: 200 (profile) or 401 alt 200 HC-->>Probe: profile Probe-->>UI: AppUserProfile else 401/other HC-->>Probe: error Probe-->>UI: null end end