Refactor: Extract shared hydration context setup into StateRegistration.withHydration

- Add StateRegistration.withHydration(context:_:) helper
- Replace duplicated save/set/restore pattern in renderToBuffer and measureChild
- Single source of truth for hydration context management

Sources/TUIkitView/Rendering/ChildInfo.swift

@@ -187,29 +187,10 @@ public func measureChild<V: View>(_ view: V, proposal: ProposedSize, context: Re
     // Skip Renderable views: their rendering logic (including environment
     // injection) lives in renderToBuffer, not in body. They fall through
     // to the render-to-measure fallback below, which runs the full pipeline.
-    //
-    // Must set up hydration context before evaluating body, just like
-    // renderToBuffer does. Otherwise @Environment(T.self) lookups and
-    // @State self-hydration crash because activeEnvironment/activeContext
-    // are nil.
     if !(view is Renderable), V.Body.self != Never.self {
-        let previousContext = StateRegistration.activeContext
-        let previousCounter = StateRegistration.counter
-        let previousEnvironment = StateRegistration.activeEnvironment
-
-        StateRegistration.activeContext = HydrationContext(
-            identity: context.identity,
-            storage: context.environment.stateStorage!
-        )
-        StateRegistration.counter = 0
-        StateRegistration.activeEnvironment = context.environment
-
-        let body = view.body
-
-        StateRegistration.activeContext = previousContext
-        StateRegistration.counter = previousCounter
-        StateRegistration.activeEnvironment = previousEnvironment
-
+        let body = StateRegistration.withHydration(context: context) {
+            view.body
+        }
         return measureChild(body, proposal: proposal, context: context)
     }
 

Sources/TUIkitView/Rendering/Renderable.swift

@@ -177,32 +177,16 @@ public func renderToBuffer<V: View>(_ view: V, context: RenderContext) -> FrameB
     if V.Body.self != Never.self {
         let childContext = context.withChildIdentity(type: V.Body.self)
 
-        // Save previous hydration state (supports nested composite views).
-        let previousContext = StateRegistration.activeContext
-        let previousCounter = StateRegistration.counter
-        let previousEnvironment = StateRegistration.activeEnvironment
-
-        // Activate hydration: @State.init will use this to look up persistent storage.
-        // Activate environment: @Environment reads from activeEnvironment during body.
-        StateRegistration.activeContext = HydrationContext(
-            identity: context.identity,
-            storage: context.environment.stateStorage!
-        )
-        StateRegistration.counter = 0
-        StateRegistration.activeEnvironment = context.environment
-
         // Wrap body evaluation in observation tracking so that any @Observable
         // property accessed during body triggers a re-render when mutated.
-        let body = withObservationTracking {
-            view.body
-        } onChange: {
-            AppState.shared.setNeedsRenderWithCacheClear()
+        let body = StateRegistration.withHydration(context: context) {
+            withObservationTracking {
+                view.body
+            } onChange: {
+                AppState.shared.setNeedsRenderWithCacheClear()
+            }
         }
 
-        // Restore previous hydration state and mark this identity as active for GC.
-        StateRegistration.activeContext = previousContext
-        StateRegistration.counter = previousCounter
-        StateRegistration.activeEnvironment = previousEnvironment
         context.environment.stateStorage!.markActive(context.identity)
 
         return renderToBuffer(body, context: childContext)

Sources/TUIkitView/State/State.swift

@@ -176,6 +176,40 @@ public enum StateRegistration {
     /// Used by `@Environment` to read environment values during `body` evaluation.
     /// Set alongside ``activeContext`` in `renderToBuffer(_:context:)`.
     nonisolated(unsafe) public static var activeEnvironment: EnvironmentValues?
+    /// Evaluates a closure with a hydration context active.
+    ///
+    /// Sets up `activeContext`, `counter`, and `activeEnvironment` before
+    /// calling the closure, then restores the previous state. This pattern
+    /// is needed whenever `view.body` is evaluated outside the normal
+    /// `renderToBuffer` dispatch (e.g., in `measureChild`).
+    ///
+    /// - Parameters:
+    ///   - context: The render context providing identity and environment.
+    ///   - block: The closure to execute with hydration active.
+    /// - Returns: The result of the closure.
+    public static func withHydration<R>(
+        context: RenderContext,
+        _ block: () -> R
+    ) -> R {
+        let previousContext = activeContext
+        let previousCounter = counter
+        let previousEnvironment = activeEnvironment
+
+        activeContext = HydrationContext(
+            identity: context.identity,
+            storage: context.environment.stateStorage!
+        )
+        counter = 0
+        activeEnvironment = context.environment
+
+        let result = block()
+
+        activeContext = previousContext
+        counter = previousCounter
+        activeEnvironment = previousEnvironment
+
+        return result
+    }
 }
 
 // MARK: - Binding