Add Activity and ViewTransition components

Activity (React 19.2 stable):
- Type-safe bindings to React.Activity
- ActivityMode type (Visible/Hidden)
- Real tests against React 19.2

ViewTransition (React canary, experimental):
- Bindings to React.unstable_ViewTransition
- AnimationValue type, ViewTransitionInstance opaque type
- viewTransitionDefaults for ergonomic record updates
- Correct callback signatures (cleanup return, instance arg)

Author: i-am-the-slime

README.md

@@ -16,6 +16,8 @@ If we prefer this API over the existing react-basic API, we may eventually repla
 - **React 16.8+**: Core hooks (useState, useEffect, useReducer, useRef, useContext, useMemo, useDebugValue, useLayoutEffect)
 - **React 18+**: useId, useTransition, useDeferredValue, useSyncExternalStore, useInsertionEffect
 - **React 19+**: useOptimistic, useActionState, useEffectEvent (experimental)
+- **React 19.2+**: Activity component
+- **React canary**: ViewTransition component (experimental)
 
 ## Example
 
@@ -125,20 +127,65 @@ mkComponent :: Component Props
 mkComponent = do
   component "Component" \{ url, onSuccess } -> React.do
     count /\ setCount <- useState 0
-    
+
     -- onSuccess can use the latest count without re-running the effect
     onSuccessEvent <- useEffectEvent \data -> do
       onSuccess data count
-    
+
     -- Effect only re-runs when url changes, not when count changes
     useEffect url do
       response <- fetchData url
       onSuccessEvent response
       pure mempty
-    
+
     pure $ R.div_ [ ... ]
 ```
 
+## React 19.2 Components
+
+### Activity
+
+The `Activity` component lets you hide and restore the UI and internal state of its children while preserving their state and DOM. Available in `React.Basic.Hooks.Activity`. Requires React 19.2+.
+
+```purs
+import React.Basic.Hooks.Activity (activity, ActivityMode(..))
+
+mkTabPanel :: Component Props
+mkTabPanel = do
+  component "TabPanel" \{ activeTab } -> React.do
+    pure $ R.div_
+      [ activity
+          { mode: if activeTab == "tab1" then Visible else Hidden
+          , children: [ tab1Content ]
+          }
+      , activity
+          { mode: if activeTab == "tab2" then Visible else Hidden
+          , children: [ tab2Content ]
+          }
+      ]
+```
+
+### ViewTransition (Experimental)
+
+The `ViewTransition` component animates DOM elements when they update inside a Transition. Available in `React.Basic.Hooks.ViewTransition`. Requires React canary — this API is unstable and may change.
+
+```purs
+import React.Basic.Hooks.ViewTransition (viewTransition, viewTransitionDefaults, AnimationValue(..))
+
+mkAnimatedList :: Component Props
+mkAnimatedList = do
+  component "AnimatedList" \{ items } -> React.do
+    _isPending /\ startTransition <- useTransition
+
+    pure $ R.div_ $ items <#> \item ->
+      viewTransition $ viewTransitionDefaults
+        { children = [ renderItem item ]
+        , enter = Just (ClassName "slide-in")
+        , exit = Just (ClassName "slide-out")
+        , name = Just ("item-" <> item.id)
+        }
+```
+
 ## Available Hooks
 
 ### Core Hooks (React 16.8+)
@@ -169,4 +216,6 @@ mkComponent = do
 - Custom hooks via `React.Basic.Hooks.Aff` for async effects
 - `React.Basic.Hooks.Suspense` for Suspense support
 - `React.Basic.Hooks.ErrorBoundary` for error boundaries
+- `React.Basic.Hooks.Activity` for hiding/showing UI while preserving state (React 19.2)
+- `React.Basic.Hooks.ViewTransition` for animated transitions (React canary, experimental)
 ```

package-lock.json

@@ -5,8 +5,8 @@
   "main": "index.js",
   "module": "true",
   "dependencies": {
-    "react": "19.0.0",
-    "react-dom": "19.0.0"
+    "react": "^19.2.0",
+    "react-dom": "^19.2.0"
   },
   "devDependencies": {
     "@testing-library/react": "^16.0.0",

package.json

@@ -14,6 +14,7 @@ You can edit this file as you like.
   , "either"
   , "exceptions"
   , "foldable-traversable"
+  , "foreign-object"
   , "functions"
   , "indexed-monad"
   , "integers"

spago.dhall

@@ -0,0 +1,3 @@
+import React from "react";
+
+export const activity_ = React.Activity;

src/React/Basic/Hooks/Activity.js

@@ -0,0 +1,18 @@
+module React.Basic.Hooks.Activity
+  ( activity
+  , ActivityMode(..)
+  ) where
+
+import React.Basic.Hooks (JSX, ReactComponent, element)
+
+data ActivityMode
+  = Visible
+  | Hidden
+
+activity :: { mode :: ActivityMode, children :: Array JSX } -> JSX
+activity props = element activity_ { mode: modeToString props.mode, children: props.children }
+  where
+  modeToString Visible = "visible"
+  modeToString Hidden = "hidden"
+
+foreign import activity_ :: ReactComponent { mode :: String, children :: Array JSX }

src/React/Basic/Hooks/Activity.purs

@@ -0,0 +1,12 @@
+import React from "react";
+
+export const viewTransition_ = React.unstable_ViewTransition;
+
+export const mkClassName = (str) => str;
+
+export const mkAnimationMap = (obj) => obj;
+
+export const toCallback_ = (fn) => (instance, types) => {
+  const cleanup = fn(instance)(types)();
+  return cleanup;
+};