fix(joint-react): keep the diagram rendered and wired across dev-server hot reloads (HMR)

[samuelgja]

Description

Hot reloading on a dev server (Vite / any Fast Refresh HMR) could leave the diagram blank or unresponsive until a full page reload. Three root causes, all fixed:

1. GraphProvider kept publishing a destroyed store. A Fast Refresh re-runs all effects of the refreshed component (dependency arrays are ignored), so the provider's mount effect destroys and re-creates its GraphStore — but readiness was tracked as a boolean, so setIsReady(true) bailed out and consumers never learned about the new instance: the context kept handing out the destroyed store (cleared graph, dead subscriptions). useImperativeApi() now keeps the instance itself in React state and exposes it; the context value and the provider wiring effect are keyed on the instance identity, so a re-created store is published and re-wired (controlled cells re-applied included).

2. <Paper> never re-registered against a swapped store. The paper registration effect had [] dependencies, so it stayed bound to the destroyed store forever. It is now keyed on [graphStore, id], so a store re-created while the paper stays mounted gets a fresh registration (and a paper id change re-registers as well).

3. instanceof PaperView guards blanked all portals after a module re-evaluation. HMR re-evaluates mvc/paper.ts, producing a new PaperView class identity while live paper instances still come from the previous evaluation; the element/link portal guards rejected them and every portal rendered null. The guards now use a capability check (isPaperView()), which survives re-evaluation. This is the StrictMode-flavored variant of the bug: under StrictMode the strict double-render replay resets ignorePreviousDependencies, so the effect re-run path never fires and only the class-identity hazard remains.

Known behavior, unchanged by this fix (uncontrolled mode): a hot reload that re-creates the provider's store re-seeds the graph from initialCells, so runtime-only edits (cells added at runtime, dragged positions) reset — the same as a remount. This is inherent to the provider owning the store inside an effect. Controlled mode (cells) is re-applied to the new store, and an external graph prop is adopted without being cleared, so both preserve state across the reload. This PR targets the blank/broken canvas, not state round-tripping.

The regression tests drive the real react-refresh runtime against the real react-dom: the suite injects the refresh hook before react-dom loads, renders, re-evaluates only graph-provider.tsx with all its dependencies shared (the same module-graph shape a Vite HMR update produces), runs performReactRefresh(), and asserts the diagram stays rendered, does not remount, and remains live (an imperative graph.addCell() still paints). A second suite pins the cross-evaluation PaperView guard. react-refresh is added as a dev dependency for these tests.

Fixes #3483

Motivation and Context

Editing library source with the storybook/Vite dev server running would "sometimes" — depending on which module the edit invalidated — blank the canvas or freeze subscriptions, forcing a full page reload. This makes HMR reliable in both non-StrictMode apps (effect re-run path) and StrictMode apps (class-identity path).

Screenshots (if appropriate):