feat: add runtime API registry for dynamic provider switching

packages/ui/src/contexts/RuntimeAPIProvider.tsx

@@ -2,10 +2,38 @@ import React, { type JSX, type ReactNode } from 'react';
 import { RuntimeAPIContext } from '@/contexts/runtimeAPIContext';
 import type { FilesAPI, RuntimeAPIs } from '@/lib/api/types';
 import { createContentCachedFiles } from '@/contexts/content-cache-owner';
+import {
+  resolveActiveRuntimeAPIs,
+  subscribeRuntimeProviderChanged,
+} from '@/lib/runtime-api-registry';
 
 type ContentCachedFiles = ReturnType<typeof createContentCachedFiles>;
 
-export function RuntimeAPIProvider({ apis, children }: { apis: RuntimeAPIs; children: ReactNode }): JSX.Element {
+interface RuntimeAPIProviderProps {
+  /** Runtime APIs to provide. Ignored when a registry provider is active. */
+  apis: RuntimeAPIs;
+  children: ReactNode;
+}
+
+/**
+ * Provides RuntimeAPIs to the React tree. When a provider is registered in
+ * the runtime API registry, the component automatically re-resolves the APIs
+ * on provider switches. Otherwise it uses the `apis` prop directly (legacy
+ * behaviour, fully backward compatible).
+ */
+export function RuntimeAPIProvider({ apis: fallbackApis, children }: RuntimeAPIProviderProps): JSX.Element {
+  const [registryApis, setRegistryApis] = React.useState<RuntimeAPIs | null>(() =>
+    resolveActiveRuntimeAPIs(),
+  );
+
+  React.useEffect(() => {
+    return subscribeRuntimeProviderChanged(() => {
+      setRegistryApis(resolveActiveRuntimeAPIs());
+    });
+  }, []);
+
+  const apis = registryApis ?? fallbackApis;
+
   // Effect-owned lifecycle: React Strict Mode dispose+remount must create a fresh
   // owner. useMemo + dispose reused a dead owner and broke text-file opens
   // (binaries skipped the pre-read, so they still appeared to work).