diff --git a/HellionChat/Ui/Components/MessageList.cs b/HellionChat/Ui/Components/MessageList.cs
index 80e55c7..b0499b1 100644
--- a/HellionChat/Ui/Components/MessageList.cs
+++ b/HellionChat/Ui/Components/MessageList.cs
@@ -30,14 +30,9 @@ internal sealed class MessageList
     // B2: the height cache is only valid while these inputs are unchanged.
     // FontManager's own fingerprint covers font sizes only, not density / the two
     // name-display modes / width — a stale height would misplace the clipper dummies.
-    private (
-        float Global,
-        float Symbols,
-        bool Compact,
-        int NameForm,
-        int WorldSuffix,
-        float Width
-    ) _lastLayoutFingerprint;
+    // Per tab, not per list: the old single field let a width change in tab A mark
+    // itself applied, so tab B kept measuring against the previous width.
+    private readonly Dictionary<Guid, LayoutFingerprintGate> _fingerprintGates = [];
 
     // §6.2: setter-injection breaks the PayloadHandler → MainWindow → MessageList → PayloadHandler 3-cycle.
     // Wired by PayloadHandlerInitHostedService.StartAsync after both singletons exist.
@@ -84,29 +79,37 @@ internal sealed class MessageList
     }
 
     // Width is passed in (ContentRegionAvail is only valid inside the draw child);
-    // enum modes widened to int so the tuple stays comparable.
-    private (float, float, bool, int, int, float) BuildLayoutFingerprint(float contentWidth)
+    // enum modes widened to int so the record stays comparable. UiScale is in here
+    // because it feeds CalcWordWrapPositionA -- a scale change rewraps every row.
+    private LayoutFingerprint BuildLayoutFingerprint(float contentWidth)
     {
         var (global, symbols) = _fonts.EffectiveFontFingerprint();
-        return (
+        return new LayoutFingerprint(
             global,
             symbols,
             Plugin.Config.UseCompactDensity,
             (int)Plugin.Config.NameFormMode,
             (int)Plugin.Config.WorldSuffixMode,
-            contentWidth
+            contentWidth,
+            ImGuiHelpers.GlobalScale
         );
     }
 
-    // Drop the tab's cached heights when the layout fingerprint changed — one
-    // tuple compare per frame, a clear only on a real settings/resize change.
+    // Drop the tab's cached heights once the layout fingerprint has settled — one
+    // record compare per frame, a clear only after a real settings/resize change
+    // stopped moving. The gate is what keeps a slider drag from rebuilding the
+    // whole tab on every frame.
     private void InvalidateHeightCacheIfLayoutChanged(Tab tab, float contentWidth)
     {
-        var fingerprint = BuildLayoutFingerprint(contentWidth);
-        if (fingerprint.Equals(_lastLayoutFingerprint))
+        if (!_fingerprintGates.TryGetValue(tab.Identifier, out var gate))
+        {
+            gate = new LayoutFingerprintGate();
+            _fingerprintGates[tab.Identifier] = gate;
+        }
+
+        if (!gate.ShouldInvalidate(BuildLayoutFingerprint(contentWidth), Environment.TickCount64))
             return;
 
-        _lastLayoutFingerprint = fingerprint;
         using var messages = tab.Messages.GetReadOnly(3);
         foreach (var msg in messages)
         {
diff --git a/HellionChat/Util/LayoutFingerprint.cs b/HellionChat/Util/LayoutFingerprint.cs
new file mode 100644
index 0000000..54d295d
--- /dev/null
+++ b/HellionChat/Util/LayoutFingerprint.cs
@@ -0,0 +1,56 @@
+namespace HellionChat.Util;
+
+// Layout inputs that make a tab's cached row heights stale. Kept as a plain
+// value type so the build suite can pin the settle logic without an ImGui frame.
+internal readonly record struct LayoutFingerprint(
+    float FontGlobal,
+    float FontSymbols,
+    bool Compact,
+    int NameForm,
+    int WorldSuffix,
+    float Width,
+    float UiScale
+);
+
+// Dragging a window edge or the Dalamud UI-scale slider moves the fingerprint on
+// every single frame. Acting on each one drops the height cache, which sends the
+// whole tab through the linear measure path (up to Config.MaxLinesToRender rows,
+// default 2500). Waiting for the value to settle turns that into one rebuild per
+// drag instead of one per frame.
+internal sealed class LayoutFingerprintGate
+{
+    internal const long SettleMs = 200;
+
+    private LayoutFingerprint? _applied;
+    private LayoutFingerprint _pending;
+    private long _pendingSinceMs;
+
+    internal bool ShouldInvalidate(LayoutFingerprint current, long nowMs)
+    {
+        // First sight of this tab: nothing is cached yet, so there is nothing to
+        // drop and nothing to wait for.
+        if (_applied is null)
+        {
+            _applied = current;
+            _pending = current;
+            _pendingSinceMs = nowMs;
+            return false;
+        }
+
+        if (current.Equals(_applied.Value))
+            return false;
+
+        if (!current.Equals(_pending))
+        {
+            _pending = current;
+            _pendingSinceMs = nowMs;
+            return false;
+        }
+
+        if (nowMs - _pendingSinceMs < SettleMs)
+            return false;
+
+        _applied = current;
+        return true;
+    }
+}