diff --git a/Sources/TUIkit/Core/Lock.swift b/Sources/TUIkit/Core/Lock.swift
new file mode 100644
index 0000000..3e77bcb
--- /dev/null
+++ b/Sources/TUIkit/Core/Lock.swift
@@ -0,0 +1,60 @@
+//  TUIKit - Terminal UI Kit for Swift
+//  Lock.swift
+//
+//  Created by LAYERED.work
+//  License: MIT
+
+import Foundation
+
+#if canImport(os)
+import os
+#endif
+
+/// A cross-platform lock wrapper that uses the best available implementation.
+///
+/// On Apple platforms, uses `OSAllocatedUnfairLock` for optimal performance
+/// (unfair lock with no syscall in the uncontended case). On Linux, falls back
+/// to `NSLock`.
+///
+/// This type is `@unchecked Sendable` because the underlying lock implementations
+/// are thread-safe by design.
+final class Lock<State: Sendable>: @unchecked Sendable {
+    #if canImport(os)
+    private let _lock: OSAllocatedUnfairLock<State>
+
+    /// Creates a lock with the given initial state.
+    ///
+    /// - Parameter initialState: The initial protected state.
+    init(initialState: State) {
+        _lock = OSAllocatedUnfairLock(initialState: initialState)
+    }
+
+    /// Executes the closure while holding the lock and returns the result.
+    ///
+    /// - Parameter body: The closure to execute with exclusive access to the state.
+    /// - Returns: The value returned by the closure.
+    func withLock<R: Sendable>(_ body: @Sendable (inout State) throws -> R) rethrows -> R {
+        try _lock.withLock(body)
+    }
+    #else
+    private let _lock = NSLock()
+    private var _state: State
+
+    /// Creates a lock with the given initial state.
+    ///
+    /// - Parameter initialState: The initial protected state.
+    init(initialState: State) {
+        _state = initialState
+    }
+
+    /// Executes the closure while holding the lock and returns the result.
+    ///
+    /// - Parameter body: The closure to execute with exclusive access to the state.
+    /// - Returns: The value returned by the closure.
+    func withLock<R>(_ body: (inout State) throws -> R) rethrows -> R {
+        _lock.lock()
+        defer { _lock.unlock() }
+        return try body(&_state)
+    }
+    #endif
+}
diff --git a/Sources/TUIkit/Core/TupleViews.swift b/Sources/TUIkit/Core/TupleViews.swift
index bcaa205..57d5345 100644
--- a/Sources/TUIkit/Core/TupleViews.swift
+++ b/Sources/TUIkit/Core/TupleViews.swift
@@ -17,7 +17,7 @@
 ///   `@ViewBuilder`. Do not instantiate directly.
 public struct TupleView<each V: View>: View {
     /// The packed child views.
-    nonisolated(unsafe) let children: (repeat each V)
+    let children: (repeat each V)
 
     /// Creates a tuple view from a parameter pack of child views.
     ///
@@ -34,7 +34,7 @@ public struct TupleView<each V: View>: View {
 // MARK: - Equatable Conformance
 
 extension TupleView: @preconcurrency Equatable where repeat each V: Equatable {
-    public nonisolated static func == (lhs: TupleView, rhs: TupleView) -> Bool {
+    public static func == (lhs: TupleView, rhs: TupleView) -> Bool {
         func isEqual<T: Equatable>(_ left: T, _ right: T) -> Bool { left == right }
         var result = true
         repeat result = result && isEqual(each lhs.children, each rhs.children)
diff --git a/Sources/TUIkit/State/State.swift b/Sources/TUIkit/State/State.swift
index efa9d4a..8e838ae 100644
--- a/Sources/TUIkit/State/State.swift
+++ b/Sources/TUIkit/State/State.swift
@@ -22,15 +22,15 @@ import Foundation
 /// - Important: This is framework infrastructure. Prefer using ``State`` for reactive state
 ///   management in your views. Direct use of `AppState` is only necessary in advanced scenarios
 ///   where you manage state outside the view hierarchy.
-public final class AppState: @unchecked Sendable {
+public final class AppState: Sendable {
+    /// Internal state protected by a lock.
+    private struct StateData: Sendable {
+        var needsRender = false
+        var observers: [@Sendable () -> Void] = []
+    }
+
     /// Lock protecting all mutable state.
-    private let lock = NSLock()
-
-    /// Whether state has changed since last render.
-    private var _needsRender = false
-
-    /// Observers to notify on state change.
-    private var _observers: [@Sendable () -> Void] = []
+    private let lock = Lock(initialState: StateData())
 
     /// Creates a new app state instance.
     public init() {}
@@ -48,11 +48,10 @@ public extension AppState {
     /// automatically detects environment changes via ``EnvironmentSnapshot``
     /// comparison and clears the cache when needed.
     func setNeedsRender() {
-        let observers: [@Sendable () -> Void]
-        lock.lock()
-        _needsRender = true
-        observers = _observers
-        lock.unlock()
+        let observers = lock.withLock { state -> [@Sendable () -> Void] in
+            state.needsRender = true
+            return state.observers
+        }
         // Call observers outside the lock to avoid potential deadlocks
         for observer in observers {
             observer()
@@ -65,32 +64,30 @@ public extension AppState {
 extension AppState {
     /// Whether state has changed since last render.
     var needsRender: Bool {
-        lock.lock()
-        defer { lock.unlock() }
-        return _needsRender
+        lock.withLock { $0.needsRender }
     }
 
     /// Registers an observer to be notified of state changes.
     ///
     /// - Parameter callback: The callback to invoke on state change.
     func observe(_ callback: @escaping @Sendable () -> Void) {
-        lock.lock()
-        _observers.append(callback)
-        lock.unlock()
+        lock.withLock { state in
+            state.observers.append(callback)
+        }
     }
 
     /// Clears all observers.
     func clearObservers() {
-        lock.lock()
-        _observers.removeAll()
-        lock.unlock()
+        lock.withLock { state in
+            state.observers.removeAll()
+        }
     }
 
     /// Resets the needs render flag.
     func didRender() {
-        lock.lock()
-        _needsRender = false
-        lock.unlock()
+        lock.withLock { state in
+            state.needsRender = false
+        }
     }
 }