diff --git a/AGENTS.md b/AGENTS.md
index 4fdd9adb..96dd1663 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -175,3 +175,34 @@ a separate inventory and authorization.
 When recommending a task or writing a prompt or handover, state the model,
 effort, new or existing session and Plan or Build mode, with a brief reason.
 A recommendation does not mean any setting was changed automatically.
+
+## SAM_UI dialog conventions
+
+`CLAUDE.md` imports this file, so these are the only copy; do not restate them elsewhere.
+The reference is the Part O windows (`WPF/SAM.Analytical.UI.WPF/Windows/PartO*Window.xaml`);
+do not invent a parallel design system and do not restyle Part O when touching other dialogs.
+
+- Merge `Themes/PartOStyles.xaml` and use its resources: `PartO.Brush.*` colours (no literal hex for text,
+  borders, surfaces or status), `PartO.SectionHeading`, `PartO.Caption` for secondary text,
+  `PartO.PrimaryButton` for the one action a dialog wants, `PartO.StatusGlyph` beside a status label.
+- Window: `FontFamily="Roboto Light"`, `WindowStartupLocation="CenterOwner"`, `Owner` set by the caller,
+  `ShowInTaskbar="False"` for a modal dialog, `SizeToContent="Height"` with a `Width`/`MinWidth` for forms,
+  `ResizeMode="CanResizeWithGrip"` only where content can grow. Content margin `16,14`.
+- Buttons: bottom-right, `Height="28"`, `MinWidth` 90 (or `Padding="12,0"`), 8 px apart; one primary
+  with `IsDefault`, Cancel/Close with `IsCancel`. A disabled choice keeps a tooltip saying why
+  (`ToolTipService.ShowOnDisabled`).
+- Status is never colour alone: pair colour with a glyph or words. Warning is amber, failure red, success
+  green (`PartO.Brush.Warning/Danger/Success`). Long operations use the shared progress window
+  (`documentation/ProgressDialogPattern.md`), not an ad-hoc bar.
+- Restyling is XAML-only: keep element names, handlers, cancellation, diagnostics and result logic as they are.
+
+## Validation policy
+
+Size validation to the change; do not run the full 26-repository BuildAll or the licensed simulation suite
+for styling changes unless a concrete dependency or regression risk requires it.
+
+- Documentation change: documentation review (links, accuracy, no internal files promoted to `master`).
+- UI-only change: build the affected SAM_UI project(s) and run the targeted tests that cover the changed code;
+  compare the window against the Part O reference (ownership, resize, DPI scaling, buttons, error and cancel paths).
+- Simulation logic change: focused unit tests plus the relevant workflow checks.
+- Installer change: packaging and deployment validation.
diff --git a/WPF/SAM.Analytical.UI.WPF/Windows/EngineComparisonWindow.xaml b/WPF/SAM.Analytical.UI.WPF/Windows/EngineComparisonWindow.xaml
index 42d087e9..e302bdef 100644
--- a/WPF/SAM.Analytical.UI.WPF/Windows/EngineComparisonWindow.xaml
+++ b/WPF/SAM.Analytical.UI.WPF/Windows/EngineComparisonWindow.xaml
@@ -1,10 +1,15 @@
 <Window x:Class="SAM.Analytical.UI.WPF.EngineComparisonWindow"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        Title="Compare Tas / OpenStudio" Height="780" Width="1180" MinWidth="760" MinHeight="480" WindowStartupLocation="CenterOwner">
+        Title="Compare Tas / OpenStudio" Height="780" Width="1180" MinWidth="760" MinHeight="480"
+        FontFamily="Roboto Light" WindowStartupLocation="CenterOwner">
     <!-- SAM_UI#231, Phase 1: a lightweight view over SAM_Validation's comparison of two B1a documents. Every value, difference,
          band and note shown is SAM_Validation's; this window only lays them out. No charts in Phase 1. -->
     <Window.Resources>
+        <ResourceDictionary>
+        <ResourceDictionary.MergedDictionaries>
+            <ResourceDictionary Source="/SAM.Analytical.UI.WPF;component/Themes/PartOStyles.xaml"/>
+        </ResourceDictionary.MergedDictionaries>
         <Style x:Key="Style_Row" TargetType="DataGridRow">
             <Style.Triggers>
                 <DataTrigger Binding="{Binding Status}" Value="NotEquivalent">
@@ -90,8 +95,9 @@
             <Setter Property="TextTrimming" Value="CharacterEllipsis"/>
             <Setter Property="ToolTip" Value="{Binding StatusText}"/>
         </Style>
+        </ResourceDictionary>
     </Window.Resources>
-    <Grid Margin="10">
+    <Grid Margin="16,14,16,14">
         <Grid.RowDefinitions>
             <RowDefinition Height="Auto"/>
             <RowDefinition Height="Auto"/>
@@ -99,7 +105,10 @@
             <RowDefinition Height="Auto"/>
         </Grid.RowDefinitions>
 
-        <GroupBox Grid.Row="0" Header="Runs (B1a documents)" Padding="6">
+        <GroupBox Grid.Row="0" Padding="8">
+            <GroupBox.Header>
+                <TextBlock Text="Runs (B1a documents)" Style="{StaticResource PartO.SectionHeading}" Margin="0"/>
+            </GroupBox.Header>
             <Grid>
                 <Grid.ColumnDefinitions>
                     <ColumnDefinition Width="Auto"/>
@@ -118,14 +127,14 @@
                 <TextBox x:Name="TextBox_OpenStudio" Grid.Row="1" Grid.Column="1" IsReadOnly="True" Margin="0,0,6,4"/>
                 <Button x:Name="Button_BrowseOpenStudio" Grid.Row="1" Grid.Column="2" Content="Browse..." Width="90" Margin="0,0,0,4"/>
                 <StackPanel Grid.Row="2" Grid.Column="0" Grid.ColumnSpan="3" Orientation="Horizontal" Margin="0,4,0,0">
-                    <Button x:Name="Button_Run" Content="Run Tas + OpenStudio..." Padding="10,3" Margin="0,0,8,0" ToolTipService.ShowOnDisabled="True"/>
-                    <Button x:Name="Button_LoadFolder" Content="Load run folder..." Padding="10,3" Margin="0,0,8,0"/>
-                    <Button x:Name="Button_Compare" Content="Compare" Padding="10,3"/>
+                    <Button x:Name="Button_Run" Content="Run Tas + OpenStudio..." Height="28" Padding="12,0" Margin="0,0,8,0" Style="{StaticResource PartO.PrimaryButton}" ToolTipService.ShowOnDisabled="True"/>
+                    <Button x:Name="Button_LoadFolder" Content="Load run folder..." Height="28" Padding="12,0" Margin="0,0,8,0"/>
+                    <Button x:Name="Button_Compare" Content="Compare" Height="28" Padding="12,0"/>
                 </StackPanel>
             </Grid>
         </GroupBox>
 
-        <Border x:Name="Border_Banner" Grid.Row="1" Margin="0,8,0,8" Padding="8,6" Background="#F2F2F2">
+        <Border x:Name="Border_Banner" Grid.Row="1" Margin="0,8,0,8" Padding="10,8" Background="{StaticResource PartO.Brush.Surface}" BorderBrush="{StaticResource PartO.Brush.Border}" BorderThickness="1">
             <TextBlock x:Name="TextBlock_Banner" TextWrapping="Wrap" Text="Choose a Tas and an OpenStudio B1a document, load a comparison run folder, or run both engines on the open model."/>
         </Border>
 
@@ -224,16 +233,16 @@
                 <RowDefinition Height="Auto"/>
             </Grid.RowDefinitions>
             <StackPanel Grid.Row="0">
-                <TextBlock TextWrapping="Wrap" Foreground="#6A6A6A"
+                <TextBlock Style="{StaticResource PartO.Caption}"
                            Text="Normalized difference (%) = 100 × |OpenStudio − TAS| / max(|TAS|, |OpenStudio|, applicable near-zero floor). It is unsigned and is not percentage change against TAS; peak hours use circular hours and no percentage. Bands are provisional tolerance bands, not engineering verdicts."/>
-                <TextBlock TextWrapping="Wrap" Foreground="#6A6A6A" Margin="0,3,0,0"
+                <TextBlock Style="{StaticResource PartO.Caption}" Margin="0,3,0,0"
                            Text="Values, differences, bands and notes are SAM_Validation's (benchmark-compare). Missing values are never shown as zero. Unit mismatches and informational rows are labelled; informational rows keep their band but are excluded from the numerical status."/>
             </StackPanel>
             <WrapPanel Grid.Row="1" Orientation="Horizontal" HorizontalAlignment="Right" Margin="0,6,0,0">
-                <Button x:Name="Button_OpenReport" Content="Open report" Padding="10,3" Margin="6,0,0,0" IsEnabled="False"/>
-                <Button x:Name="Button_Export" Content="Export reports..." Padding="10,3" Margin="6,0,0,0" IsEnabled="False"/>
-                <Button x:Name="Button_OpenFolder" Content="Open run folder" Padding="10,3" Margin="6,0,0,0" IsEnabled="False"/>
-                <Button x:Name="Button_Close" Content="Close" Padding="10,3" Margin="6,0,0,0" IsCancel="True"/>
+                <Button x:Name="Button_OpenReport" Content="Open report" Height="28" Padding="12,0" Margin="6,0,0,0" IsEnabled="False"/>
+                <Button x:Name="Button_Export" Content="Export reports..." Height="28" Padding="12,0" Margin="6,0,0,0" IsEnabled="False"/>
+                <Button x:Name="Button_OpenFolder" Content="Open run folder" Height="28" Padding="12,0" Margin="6,0,0,0" IsEnabled="False"/>
+                <Button x:Name="Button_Close" Content="Close" Height="28" Padding="12,0" Margin="6,0,0,0" IsCancel="True"/>
             </WrapPanel>
         </Grid>
     </Grid>
diff --git a/WPF/SAM.Analytical.UI.WPF/Windows/RunSimulationWindow.xaml b/WPF/SAM.Analytical.UI.WPF/Windows/RunSimulationWindow.xaml
index b97012fb..da031442 100644
--- a/WPF/SAM.Analytical.UI.WPF/Windows/RunSimulationWindow.xaml
+++ b/WPF/SAM.Analytical.UI.WPF/Windows/RunSimulationWindow.xaml
@@ -1,34 +1,46 @@
 <Window x:Class="SAM.Analytical.UI.WPF.RunSimulationWindow"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        Title="Run Simulation" Width="560" SizeToContent="Height" ResizeMode="NoResize" WindowStartupLocation="CenterOwner" ShowInTaskbar="False">
+        Title="Run Simulation" Width="600" SizeToContent="Height" MinWidth="480" ResizeMode="NoResize"
+        FontFamily="Roboto Light" WindowStartupLocation="CenterOwner" ShowInTaskbar="False">
+    <Window.Resources>
+        <ResourceDictionary>
+            <ResourceDictionary.MergedDictionaries>
+                <ResourceDictionary Source="/SAM.Analytical.UI.WPF;component/Themes/PartOStyles.xaml"/>
+            </ResourceDictionary.MergedDictionaries>
+            <!-- An engine's explanation sits under its radio button, indented to the label (the Part O caption look). -->
+            <Style x:Key="Style_EngineCaption" TargetType="TextBlock" BasedOn="{StaticResource PartO.Caption}">
+                <Setter Property="Margin" Value="20,0,0,12"/>
+            </Style>
+        </ResourceDictionary>
+    </Window.Resources>
     <!-- SAM_UI#231: the unified Run Simulation command. It only chooses the engine; each choice runs the existing workflow for it
          (Tas: Energy Simulation, unchanged; OpenStudio: SAM_UI#229; Both: one frozen snapshot, both producers in turn, SAM_Validation's
          comparison). -->
-    <StackPanel Margin="12">
-        <TextBlock Text="Simulate the open model with:" FontWeight="SemiBold" Margin="0,0,0,8"/>
+    <StackPanel Margin="16,14,16,14">
+        <TextBlock Text="Simulate the open model with:" Style="{StaticResource PartO.SectionHeading}" Margin="0,0,0,8"/>
 
         <RadioButton x:Name="RadioButton_Tas" GroupName="Engine" IsChecked="True" Margin="0,0,0,2" ToolTipService.ShowOnDisabled="True">
             <TextBlock Text="Tas only" FontWeight="SemiBold"/>
         </RadioButton>
-        <TextBlock Margin="20,0,0,10" TextWrapping="Wrap" Foreground="#555555"
+        <TextBlock Style="{StaticResource Style_EngineCaption}"
                    Text="The existing Energy Simulation, unchanged: its own settings dialog, results written back into the open model as before."/>
 
         <RadioButton x:Name="RadioButton_OpenStudio" GroupName="Engine" Margin="0,0,0,2" ToolTipService.ShowOnDisabled="True">
             <TextBlock Text="OpenStudio/EnergyPlus only" FontWeight="SemiBold"/>
         </RadioButton>
-        <TextBlock Margin="20,0,0,10" TextWrapping="Wrap" Foreground="#555555"
+        <TextBlock Style="{StaticResource Style_EngineCaption}"
                    Text="An annual OpenStudio/EnergyPlus run of a frozen copy of the open model. Its results and diagnostics are saved as a separate model in a new run folder; the open model is not changed. Needs OpenStudio 3.10."/>
 
         <RadioButton x:Name="RadioButton_Both" GroupName="Engine" Margin="0,0,0,2" ToolTipService.ShowOnDisabled="True">
             <TextBlock Text="Both - Tas + OpenStudio/EnergyPlus" FontWeight="SemiBold"/>
         </RadioButton>
-        <TextBlock Margin="20,0,0,10" TextWrapping="Wrap" Foreground="#555555"
+        <TextBlock Style="{StaticResource Style_EngineCaption}"
                    Text="One read-only snapshot of the model and one weather file; Tas then OpenStudio run on it (benchmark-tas and benchmark-openstudio, with their fixed workflow settings), each keeping its own outputs. When both complete, SAM_Validation compares them and the comparison window opens. If one engine fails, the other's results are kept and shown as partially completed - nothing is compared or filled in. The open model is not changed."/>
 
-        <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" Margin="0,6,0,0">
-            <Button x:Name="Button_Run" Content="Run" Width="80" IsDefault="True" Margin="0,0,8,0"/>
-            <Button x:Name="Button_Cancel" Content="Cancel" Width="80" IsCancel="True"/>
+        <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" Margin="0,8,0,0">
+            <Button x:Name="Button_Run" Content="Run" MinWidth="90" Height="28" IsDefault="True" Margin="0,0,8,0" Style="{StaticResource PartO.PrimaryButton}"/>
+            <Button x:Name="Button_Cancel" Content="Cancel" MinWidth="90" Height="28" IsCancel="True"/>
         </StackPanel>
     </StackPanel>
 </Window>
diff --git a/documentation/evidence/sim-dialog-consistency/README.md b/documentation/evidence/sim-dialog-consistency/README.md
new file mode 100644
index 00000000..3140cb0e
--- /dev/null
+++ b/documentation/evidence/sim-dialog-consistency/README.md
@@ -0,0 +1,13 @@
+# SAM_UI#246 visual acceptance evidence (2026-10-20)
+
+Rendered from the isolated worktree build (Release, tested head = the PR's XAML commit) by a temporary,
+uncommitted WPF test harness: each real window instance, fabricated SAM_Validation comparison documents,
+no simulation. Captures are window content only (no title bar), at 100% (`-100`) and 150% (`-150`) scale.
+Roboto Light is not installed on this machine, so all windows (Part O reference included) fall back to the
+same system font.
+
+- partO-100: Part O reference (Previous result found)
+- run-both-100/150: Run Simulation, Both selected (longest explanation)
+- run-disabled-150: Run Simulation with OpenStudio/Both disabled
+- compare-model-1180-100: Compare Tas / OpenStudio, Model grid
+- compare-spaces-760-150: Compare, Spaces grid at minimum width (horizontal scroll)
diff --git a/documentation/evidence/sim-dialog-consistency/compare-model-1180-100.png b/documentation/evidence/sim-dialog-consistency/compare-model-1180-100.png
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