sequenceDiagram
    participant Client as Frontend (React)
    participant MplSlot as MplInteractiveSlot
    participant MplComm as MplCommWebSocket
    participant Model as WidgetModel
    participant Backend as Python Kernel
    participant Registry as _FigureManagerRegistry
    participant Mgr as FigureManagerWebAgg
    participant Fig as matplotlib Figure

    Note over Client,Fig: INITIAL CELL EXECUTION
    
    Client->>MplSlot: mount (useEffect)
    MplSlot->>MplComm: new MplCommWebSocket(sendFn)
    MplSlot->>MplComm: create mpl.figure(id, ws, ondownload, container)
    MplSlot->>MplComm: trigger fakeWs.onopen()
    MplComm->>Model: model.send(msg) - handshake
    Model-->>MplComm: msg:custom events
    
    Note over Backend,Fig: Python side - manager acquisition
    
    Backend->>Registry: acquire(fig, factory)
    Registry->>Registry: check cache by id(fig)
    alt Cache miss (first time)
        Registry->>Mgr: factory() - new_figure_manager_given_figure()
        Mgr-->>Registry: manager
        Registry->>Registry: set_original_geometry(fig, dpi, size)
    else Cache hit (rerun)
        Registry-->>Backend: cached manager
        Backend->>Fig: root.set_canvas(manager.canvas) if needed
    end
    Registry-->>Backend: (manager, created)
    Backend->>Mgr: store as self._figure_manager
    
    Note over Backend: Create per-element comm & websocket
    
    Backend->>Mgr: add_web_socket(sync_ws)
    Mgr-->>Backend: websocket registered
    Backend->>Backend: register _MplCleanupHandle with ref to figure

    Note over Client,Fig: CELL RE-RUN (same figure)
    
    Client->>MplSlot: rerender with new modelId
    MplSlot->>MplSlot: read modelIdRef.current (skip first run)
    MplSlot->>MplComm: setSendHandler(newSendFn)
    MplComm-->>MplSlot: send handler updated
    MplSlot->>MplComm: trigger fakeWs.onopen() again
    MplComm->>Model: new handshake with current model
    Note over MplSlot: Figure DOM NOT rebuilt - toolbar state preserved

    alt Two cells sharing same figure
        Client->>MplSlot: second cell mounts with same figure
        Backend->>Registry: acquire(fig, factory)
        Registry-->>Backend: same cached manager (refcount=2)
        Backend->>Mgr: add_web_socket(second_sync_ws)
        Mgr-->>Backend: both websockets registered
    end

    Note over Client,Fig: CLEANUP / DISPOSE
    
    Backend->>Registry: release(fig) - decrement refcount
    alt Refcount > 0 (other consumers remain)
        Backend->>Mgr: remove_web_socket(sync_ws) only
        Registry-->>Backend: manager kept alive
    else Refcount = 0 (last consumer)
        Registry->>Registry: pop from _managers, _refcounts, _original_geometry
        Registry-->>Backend: return True (destroy)
        Backend->>Mgr: cleanup toolbar callbacks
        Backend->>Fig: restore original dpi & size_inches
        Backend->>Mgr: destroy manager
    end