When PresentationState storage is copied (COW), clear effectNavigationIDPath.

This signals that presentation was moved to a new parent context.
Detect this as parentContextChanged and recreate effect.

Author: Oguz Yuksel

Sources/ComposableArchitecture/Reducer/Reducers/PresentationReducer.swift

@@ -57,6 +57,8 @@ public struct PresentationState<State> {
 
   private var storage: Storage
   @usableFromInline var presentedID: NavigationIDPath?
+  // Tracks navigation path when effect was created. Cleared on COW to detect parent context changes.
+  @usableFromInline var effectNavigationIDPath: NavigationIDPath? = nil
 
   public init(wrappedValue: State?) {
     self.storage = Storage(state: wrappedValue)
@@ -67,6 +69,7 @@ public struct PresentationState<State> {
     set {
       if !isKnownUniquelyReferenced(&self.storage) {
         self.storage = Storage(state: newValue)
+        self.effectNavigationIDPath = nil  // Clear on COW to trigger effect recreation
       } else {
         self.storage.state = newValue
       }
@@ -586,6 +589,9 @@ public struct _PresentationReducer<Base: Reducer, Destination: Reducer>: Reducer
   public func reduce(into state: inout Base.State, action: Base.Action) -> Effect<Base.Action> {
     let initialPresentationState = state[keyPath: self.toPresentationState]
     let presentationAction = self.toPresentationAction.extract(from: action)
+    
+    // Capture the navigation ID BEFORE any state changes (like StackReducer does with idsBefore)
+    let navigationIDBeforeReduce = initialPresentationState.wrappedValue.map(self.navigationIDPath(for:))
 
     let destinationEffects: Effect<Base.Action>
     let baseEffects: Effect<Base.Action>
@@ -657,9 +663,24 @@ public struct _PresentationReducer<Base: Reducer, Destination: Reducer>: Reducer
       baseEffects = self.base.reduce(into: &state, action: action)
     }
 
+    let navigationIDAfterReduce = state[keyPath: self.toPresentationState].wrappedValue.map(self.navigationIDPath(for:))
+    let storedEffectPath = initialPresentationState.effectNavigationIDPath
+    
+    // Detect parent context change (e.g., enum case transition via COW)
+    let parentContextChanged: Bool
+    if let current = navigationIDAfterReduce {
+      if let stored = storedEffectPath {
+        parentContextChanged = stored != current
+      } else {
+        parentContextChanged = true  // nil path + existing presentation = COW occurred
+      }
+    } else {
+      parentContextChanged = false
+    }
+    let navigationContextChanged = navigationIDBeforeReduce != navigationIDAfterReduce
+
     let presentationIdentityChanged =
-      initialPresentationState.presentedID
-      != state[keyPath: self.toPresentationState].wrappedValue.map(self.navigationIDPath(for:))
+      initialPresentationState.presentedID != navigationIDAfterReduce
 
     let dismissEffects: Effect<Base.Action>
     if presentationIdentityChanged,
@@ -676,14 +697,24 @@ public struct _PresentationReducer<Base: Reducer, Destination: Reducer>: Reducer
 
     if presentationIdentityChanged, state[keyPath: self.toPresentationState].wrappedValue == nil {
       state[keyPath: self.toPresentationState].presentedID = nil
+      state[keyPath: self.toPresentationState].effectNavigationIDPath = nil
     }
 
     let presentEffects: Effect<Base.Action>
-    if presentationIdentityChanged || state[keyPath: self.toPresentationState].presentedID == nil,
+    // Recreate Empty effect if:
+    // - Parent context changed (e.g., enum case transition)
+    // - Navigation context changed (normal navigation)
+    // - Presentation identity changed
+    // - First time presenting (presentedID is nil)
+    if (parentContextChanged 
+      || navigationContextChanged 
+      || presentationIdentityChanged 
+      || state[keyPath: self.toPresentationState].presentedID == nil),
       let presentationState = state[keyPath: self.toPresentationState].wrappedValue,
       !isEphemeral(presentationState)
     {
       let presentationDestinationID = self.navigationIDPath(for: presentationState)
+      state[keyPath: self.toPresentationState].effectNavigationIDPath = presentationDestinationID
       state[keyPath: self.toPresentationState].presentedID = presentationDestinationID
       presentEffects = .concatenate(
         .publisher { Empty(completeImmediately: false) }