Simplify the resource-refresh pass: drop mounted-output snapshots

CHANGELOG.md

@@ -91,7 +91,9 @@ Conventions for contributors:
   that cache only on a theme or palette change, so such an edit was invisible to `ThemeRef`
   modifiers, overrides and `ThemeRef.Resolve`. The call clears the cache and re-renders
   every live host past memoization and the skip of unchanged elements. Callable from
-  any thread (issue #1327).
+  any thread (issue #1327). A brush resolved eagerly and kept (`ThemeRef.Resolve` inside a
+  memo factory, or stored in state) is a fixed value and is not refreshed; bind it with
+  `Theme.Ref` instead.
 
 - **Getting Started documents the single-file path.** A Reactor app does not need
   a `.csproj`: .NET 10 runs a lone `.cs` file whose `#:package` / `#:property`

docs/_pipeline/templates/styling.md.dt

@@ -277,6 +277,12 @@ new value, memoized subtrees included. It is safe to call from any
 thread; await a host's `WaitForIdleAsync()` to observe the result.
 Mutating an existing brush's `Color` in place does not need it.
 
+A brush you resolve *eagerly* and keep is not refreshed: a
+`ThemeRef.Resolve(...)` inside a `UseMemo` or `Memo(key, ...)` factory, or a
+resolved brush stored in state, is a fixed value Reactor can't trace back
+to its key. Bind it instead (`.Foreground(Theme.Ref(key))`), or resolve it
+in `Render` outside the memo.
+
 ### Per-element theme override scope
 
 Pin one panel to a different scheme while the rest of the app follows

docs/guide/styling.md

@@ -460,6 +460,12 @@ new value, memoized subtrees included. It is safe to call from any
 thread; await a host's `WaitForIdleAsync()` to observe the result.
 Mutating an existing brush's `Color` in place does not need it.
 
+A brush you resolve *eagerly* and keep is not refreshed: a
+`ThemeRef.Resolve(...)` inside a `UseMemo` or `Memo(key, ...)` factory, or a
+resolved brush stored in state, is a fixed value Reactor can't trace back
+to its key. Bind it instead (`.Foreground(Theme.Ref(key))`), or resolve it
+in `Render` outside the memo.
+
 ### Per-element theme override scope
 
 Pin one panel to a different scheme while the rest of the app follows

src/Reactor/Core/Reconciler.Mount.cs

@@ -119,7 +119,7 @@ public sealed partial class Reconciler
             // factory output) when it changes, so the mounted inner is never re-derived from
             // the old factory. Any modifiers on the wrapper itself are applied by the
             // post-dispatch ApplyModifiers below, exactly like any other element.
-            KeyedMemoElement km => MountKeyedMemo(km, requestRerender),
+            KeyedMemoElement km => Mount(WithWrapperKey(km.Factory() ?? EmptyElement.Instance, km.Key), requestRerender),
             // EmptyElement is a no-op sentinel — callers (Reconcile, panel
             // children loops, ChildReconciler) already filter it before
             // reaching Mount, but MountContext.MountChild does not, so a V1
@@ -277,86 +277,6 @@ private static Element WithWrapperKey(Element inner, string? wrapperKey) =>
             ? inner
             : inner with { Key = wrapperKey };
 
-    private UIElement? MountKeyedMemo(KeyedMemoElement km, Action requestRerender)
-    {
-        var inner = WithWrapperKey(km.Factory() ?? EmptyElement.Instance, km.Key);
-        var control = Mount(inner, requestRerender);
-        // Nested memos share the realized control, so each layer records its own output. On a
-        // fresh control the layers inside this one have already recorded; this one goes on top.
-        if (control is FrameworkElement fe)
-        {
-            var state = GetOrCreateReactorState(fe);
-            SetKeyedMemoOutput(state, km.MemoKey, CountKeyedMemoOutputs(state, km.MemoKey), inner);
-        }
-        return control;
-    }
-
-    // The outputs recorded on a control are kept in the order their layers mounted, innermost
-    // first; layers with an equal MemoKey are told apart by that order (nth among the key's
-    // entries). RefreshKeyedMemo walks them outermost first.
-
-    internal static int CountKeyedMemoOutputs(ReactorState state, object memoKey)
-    {
-        int count = state.KeyedMemoKey is { } first && first.Equals(memoKey) ? 1 : 0;
-        if (state.MoreKeyedMemoOutputs is { } more)
-            count += more.Count(entry => entry.Key.Equals(memoKey));
-        return count;
-    }
-
-    /// <summary>The <paramref name="nth"/> output recorded for <paramref name="memoKey"/>, or null.</summary>
-    internal static Element? GetKeyedMemoOutput(ReactorState state, object memoKey, int nth)
-    {
-        if (state.KeyedMemoKey is { } first && first.Equals(memoKey))
-        {
-            if (nth == 0) return state.KeyedMemoOutput;
-            nth--;
-        }
-        if (state.MoreKeyedMemoOutputs is { } more)
-        {
-            foreach (var entry in more.Where(entry => entry.Key.Equals(memoKey)))
-            {
-                if (nth == 0) return entry.Value;
-                nth--;
-            }
-        }
-        return null;
-    }
-
-    /// <summary>
-    /// Replaces the <paramref name="nth"/> output recorded for <paramref name="memoKey"/>, or
-    /// appends one when fewer are recorded.
-    /// </summary>
-    internal static void SetKeyedMemoOutput(ReactorState state, object memoKey, int nth, Element output)
-    {
-        if (state.KeyedMemoKey is null)
-        {
-            state.KeyedMemoKey = memoKey;
-            state.KeyedMemoOutput = output;
-            return;
-        }
-        if (state.KeyedMemoKey.Equals(memoKey))
-        {
-            if (nth == 0)
-            {
-                state.KeyedMemoOutput = output;
-                return;
-            }
-            nth--;
-        }
-        var more = state.MoreKeyedMemoOutputs ??= new();
-        for (int i = 0; i < more.Count; i++)
-        {
-            if (!more[i].Key.Equals(memoKey)) continue;
-            if (nth == 0)
-            {
-                more[i] = new(memoKey, output);
-                return;
-            }
-            nth--;
-        }
-        more.Add(new(memoKey, output));
-    }
-
     /// <summary>
     /// Final dispatch arm: the four resolution arms in <see cref="Mount"/>
     /// (per-host <c>_v1Handlers</c>, per-host <c>_typeRegistry</c>, global