fix(ui): stop cropping Nexus mod thumbnails (#244)

## Summary

- display Detailed-row Nexus thumbnails in responsive 16:9 frames
- fit complete source images and increase decode sizing for 2x displays
- add regression coverage and synchronize the UI architecture and
reference docs

## Validation

- `dotnet build src/modificus-curator.sln --configuration Release`
- `dotnet test src/modificus-curator.sln --configuration Release` (2,445
passed)
- `dotnet format src/modificus-curator.sln --verify-no-changes`
- operator visual verification

Fixes #243

Author: ModifAmorphic

AGENTS.md

@@ -625,11 +625,14 @@ src/        Modificus Curator -- the mod manager app (.NET 10 + Avalonia 12)
                           the automation name always carries the displayed
                           summary/fallback), and row 2
                           is a single `WrapPanel` action strip. Wide (card width
-                          greater than 680 DIP): a 112-DIP rounded `UniformToFill`
-                          thumbnail spans all three rows (column 1, `RowSpan=3`)
-                          and the action strip occupies only the content column.
+                          greater than 680 DIP): a 192x108 DIP rounded 16:9
+                          thumbnail (`Stretch=Uniform`, so the complete source
+                          image shows with the frame's neutral background
+                          letterboxing/pillarboxing non-16:9 assets) spans
+                          all three rows (column 1, `RowSpan=3`) and the
+                          action strip occupies only the content column.
                           Constrained (card width at or below 680 DIP): the
-                          thumbnail shrinks to 72 DIP spanning only name +
+                          thumbnail shrinks to 128x72 DIP spanning only name +
                           summary (`RowSpan=2`) and the same action strip moves to
                           a full-width row beneath all three columns
                           (`Grid.ColumnSpan=3`, via the

docs/architecture/MODIFICUS-CURATOR.md

@@ -650,10 +650,13 @@ is in [UI reference](../reference/ui.md).
   drag-reorder grip, column 1 is the thumbnail/placeholder slot, column 2
   holds the name + source badge (row 0) and a two-line summary (row 1), and
   row 2 is the action strip. When the card
-  is wide (greater than 680 DIP) a 112-DIP thumbnail spans all three rows and
-  the action strip occupies only the content column; when constrained (at or
-  below 680 DIP) the thumbnail shrinks to 72 DIP spanning name + summary and
-  the action strip moves to a full-width row beneath all three columns. The action
+  is wide (greater than 680 DIP) a 192x108 DIP 16:9 thumbnail (stretched
+  `Uniform`, so the complete source image shows with the frame's neutral
+  background letterboxing/pillarboxing non-16:9 assets) spans all three rows
+  and the action strip occupies only the content column; when constrained (at
+  or below 680 DIP) the thumbnail shrinks to 128x72 DIP spanning name +
+  summary and the action strip moves to a full-width row beneath all three
+  columns. The action
   strip is a right-aligned `WrapPanel` that wraps at the edge (no horizontal
   scrolling); width, height, row span, and the action column/span are driven by
   styles so the breakpoint changes them. The summary is plain text with `CharacterEllipsis` trimming and the full

docs/architecture/ui-architecture.md

@@ -1085,11 +1085,13 @@ subscription re-hydrates from the store when the result lands.
   holds the name + source badge (row 0) and a two-line plain-text summary
   (row 1, `MaxLines=2`, `TextWrapping=Wrap`, `TextTrimming=CharacterEllipsis`,
   full text in the tooltip and the automation name), and row 2 is the action
-  strip. When the card is wide (greater than 680 DIP) a 112-DIP
-  `UniformToFill` thumbnail spans all three rows and the action strip occupies
-  only the right column; when constrained (at or below 680 DIP) the thumbnail
-  shrinks to 72 DIP spanning name + summary and the action strip moves to a
-  full-width row beneath both columns. Width, height, row span, and action
+  strip. When the card is wide (greater than 680 DIP) a 192x108 DIP 16:9
+  `Uniform` thumbnail (the complete source image; the frame's neutral
+  background letterboxes/pillarboxes non-16:9 assets) spans all three rows and
+  the action strip occupies only the right column; when constrained (at or
+  below 680 DIP) the thumbnail shrinks to 128x72 DIP spanning name + summary
+  and the action strip moves to a full-width row beneath both columns. Width,
+  height, row span, and action
   column/span that change at the breakpoint are driven by styles (not local
   values, which would outrank styles); constant row/column positions stay
   local. Both roots bind the exact same per-row state and route to the exact

docs/reference/ui.md

@@ -1955,11 +1955,12 @@ feature).
   card-width breakpoint. Column 0 is the drag-reorder grip, column 1 is the
   thumbnail/placeholder slot, column 2
   holds the name + source badge (row 0) and the summary (row 1), and row 2 is
-  the action strip. Wide (card width greater than 680 DIP): a 112-DIP
-  `UniformToFill` thumbnail spans all three rows (`RowSpan=3`) and the action
-  strip occupies only the content column. Constrained (at or below 680 DIP): the
-  thumbnail shrinks to 72 DIP spanning only name + summary (`RowSpan=2`) and the
-  action strip moves to a full-width row beneath all three columns
+  the action strip. Wide (card width greater than 680 DIP): a 192x108 DIP
+  rounded 16:9 thumbnail spans all three rows (`RowSpan=3`) and the action
+  strip occupies only the content column. Constrained (at or below 680 DIP):
+  the thumbnail shrinks to 128x72 DIP spanning only name + summary
+  (`RowSpan=2`) and the action strip moves to a full-width row beneath all
+  three columns
   (`Grid.ColumnSpan=3`, driven by the `ContentControl.detailedActions` styles).
   Width, height, row span, and action column/span that
   change at the breakpoint are style-driven (default wide styles + the
@@ -1971,7 +1972,10 @@ feature).
 - **Summary.** `MaxLines="2"` + `TextWrapping="Wrap"` + `TextTrimming="CharacterEllipsis"`; the full text is retained in `ToolTip.Tip` (when non-null) + `AutomationProperties.Name` (always, so the fallback stays reachable by assistive tech).
 - **Thumbnail area.** A rounded `Border` with `ClipToBounds`; the `Image` shows
   only when `HasThumbnail`, otherwise a neutral drawn-geometry placeholder
-  (Material `image`) fills the box. The placeholder scales with the slot through
+  (Material `image`) fills the box. The `Image` stretches `Uniform` so the
+  complete source image is always visible; the frame's neutral background
+  supplies the letterbox/pillarbox space for non-16:9 assets. The placeholder
+  scales with the slot through
   the same styles as the thumbnail (36 DIP wide; 28 DIP constrained). Adult rows
   never receive a thumbnail (the coordinator skips them), so they fall through
   to the placeholder.
@@ -2135,10 +2139,10 @@ Cache + failure behavior (`ModThumbnailService`):
 - **Atomic write.** Download to a sibling temp file, then same-volume `File.Move`
   into place. A download failure returns `null` without creating the final file.
 - **Decode.** Production uses `Bitmap.DecodeToWidth(stream,
-  ModThumbnailService.DecodeWidth, BitmapInterpolationMode.HighQuality)` (256 px,
-  sized for the 112-DIP detailed-row thumbnail on scaled displays) on a
-  background thread; the render size is responsive (112 DIP wide, 72 DIP
-  constrained). The 256-px constant is the single named literal
+  ModThumbnailService.DecodeWidth, BitmapInterpolationMode.HighQuality)` (384 px,
+  sized for the 192-DIP detailed-row thumbnail frame at 2x display scaling) on a
+  background thread; the render size is responsive (192 DIP wide, 128 DIP
+  constrained). The 384-px constant is the single named literal
   (`ModThumbnailService.DecodeWidth`) referenced from the DI wiring.
 - **Four-slot load bound.** A `SemaphoreSlim(4)` bounds concurrent distinct-key
   fetch/decode work.

src/tests/Modificus.Curator.UI.Tests/ModRowSharedTemplatesTests.cs

@@ -164,6 +164,37 @@ public void The_680dip_breakpoint_still_moves_the_strip_and_thumbnail()
         Assert.Contains("Path.detailedPlaceholder", selectors);
     }
 
+    [Fact]
+    public void Detailed_thumbnail_frames_are_16by9_and_the_image_never_crops()
+    {
+        var xaml = LoadStrippedXaml("src/ui/Views/ModListView.axaml");
+
+        // The detailed thumbnail is a fixed 16:9 frame, never a square and
+        // never a cropping stretch: wide cards carry 192x108 DIP (RowSpan 3)
+        // and constrained cards (the 680-DIP container query) carry 128x72 DIP
+        // (RowSpan 2), so an ordinary 16:9 Nexus image renders uncropped.
+        var wide = Assert.Single(
+            Elements(xaml.Root!, "Style"),
+            s => A(s, "Selector") == "Border.detailedThumb"
+                && s.Parent?.Name.LocalName != "ContainerQuery");
+        AssertThumbFrame(wide, width: 192, height: 108, rowSpan: 3);
+
+        var query = Assert.Single(Elements(xaml.Root!, "ContainerQuery"));
+        var constrained = Assert.Single(
+            query.Descendants().Where(e => e.Name.LocalName == "Style"),
+            s => A(s, "Selector") == "Border.detailedThumb");
+        AssertThumbFrame(constrained, width: 128, height: 72, rowSpan: 2);
+
+        // The thumbnail Image must fit the whole source inside the frame
+        // (Uniform). UniformToFill fills the frame and hides roughly 44% of
+        // the width of a 16:9 source, so it is banned here; the frame's
+        // neutral background supplies the letterbox/pillarbox space instead.
+        var image = Assert.Single(
+            Elements(xaml.Root!, "Image"),
+            i => A(i, "Source") == "{Binding Thumbnail}");
+        Assert.Equal("Uniform", A(image, "Stretch"));
+    }
+
     [Fact]
     public void The_edit_band_is_one_definition_leading_both_row_roots()
     {
@@ -215,6 +246,28 @@ private static void AssertMargin(XDocument xaml, string selector, string margin)
         Assert.Equal(margin, A(setter, "Value"));
     }
 
+    /// <summary>
+    /// Asserts one <c>Border.detailedThumb</c> style pins an exactly 16:9
+    /// frame of the given DIP size with the given grid row span. The ratio is
+    /// checked from the parsed setters (not the expected literals) so an edit
+    /// that changes one dimension alone fails even if the literals are updated
+    /// with it.
+    /// </summary>
+    private static void AssertThumbFrame(XElement style, int width, int height, int rowSpan)
+    {
+        var actualWidth = int.Parse(SetterValue(style, "Width"));
+        var actualHeight = int.Parse(SetterValue(style, "Height"));
+        Assert.Equal(width, actualWidth);
+        Assert.Equal(height, actualHeight);
+        Assert.Equal(width * 9, actualHeight * 16);
+        Assert.Equal(rowSpan.ToString(), SetterValue(style, "Grid.RowSpan"));
+    }
+
+    private static string SetterValue(XElement style, string property) =>
+        style.Descendants()
+            .Single(e => e.Name.LocalName == "Setter" && A(e, "Property") == property)
+            .Attribute("Value")?.Value ?? string.Empty;
+
     private static string RequireSourceFile(string relativeFromRepo)
     {
         var path = Path.Combine(

src/tests/Modificus.Curator.UI.Tests/ModThumbnailServiceTests.cs

@@ -18,7 +18,8 @@ namespace Modificus.Curator.UI.Tests;
 /// coalescing, four-slot concurrency bound, oversize rejection (declared +
 /// streamed), HTTP/I/O failure retryability, corrupt-entry delete + one
 /// re-download + one re-decode, cancellation propagation + cleanup + retry,
-/// 90-day prune boundary + failure isolation, and no ConfigureAwait(false).
+/// 90-day prune boundary + failure isolation, production decode sizing (the
+/// 2x-scaled 192-DIP frame floor), and no ConfigureAwait(false).
 /// </summary>
 public sealed class ModThumbnailServiceTests
 {
@@ -722,6 +723,20 @@ public async Task Prune_sweeps_multiple_stale_files()
         }
     }
 
+    // ---- production decode sizing ------------------------------------------
+
+    [Fact]
+    public void Production_decode_width_covers_the_widest_thumbnail_at_2x()
+    {
+        // The widest detailed-row thumbnail frame is 192 DIP; at 2x display
+        // scaling that is 384 physical pixels. A DecodeWidth below the frame's
+        // physical size would render upsampled (soft) on scaled displays.
+        Assert.True(
+            ModThumbnailService.DecodeWidth >= 384,
+            $"DecodeWidth {ModThumbnailService.DecodeWidth} cannot keep the 192-DIP " +
+            "detailed-row thumbnail frame sharp at 2x display scaling.");
+    }
+
     // ---- DI registration ---------------------------------------------------
 
     [Fact]

src/ui/CuratorComposition.cs

@@ -217,7 +217,7 @@ public static IServiceProvider Build()
         // (registered by AddIntegrations via AddHttpClient) for a plain factory-
         // created HttpClient per download; production decode uses
         // Bitmap.DecodeToWidth at ModThumbnailService.DecodeWidth px (sized for
-        // the 112-DIP detailed-row thumbnail on scaled displays). Registered
+        // the 192-DIP detailed-row thumbnail at 2x display scaling). Registered
         // before ModListViewModel and the later detailed-row coordinator so it is
         // available when they resolve.
         services.AddSingleton<IModThumbnailService>(sp => new ModThumbnailService(

src/ui/ModThumbnailService.cs

@@ -48,12 +48,12 @@ internal sealed class ModThumbnailService : IModThumbnailService
 {
     /// <summary>
     /// The physical-pixel width the production decode path targets. Large enough
-    /// for the widest detailed-row thumbnail (112 DIP) to stay sharp on scaled
-    /// displays. Referenced from the production DI wiring
+    /// for the widest detailed-row thumbnail frame (192 DIP, 16:9) to stay sharp
+    /// at 2x display scaling. Referenced from the production DI wiring
     /// (<see cref="CuratorComposition"/>) so the decode literal lives in one
     /// place. Tests inject their own decode seam and do not read this value.
     /// </summary>
-    internal const int DecodeWidth = 256;
+    internal const int DecodeWidth = 384;
     private const int MaxBytes = 8 * 1024 * 1024; // 8 MiB absolute maximum.
     private const int IoBufferSize = 81920;
     private static readonly TimeSpan PruneAge = TimeSpan.FromDays(90);

src/ui/Views/ModListView.axaml

@@ -586,16 +586,16 @@
       root (Border.detailedRow) carries Container.Name + Container.Sizing=Width
       so it measures its own width; repeated cards share the name. The card Grid
       has three columns (grip, thumbnail, content); these default (wide) styles
-      set the large-card state: a 112-DIP thumbnail spanning all three content
-      rows in the thumbnail column, and the right-column action strip in the
-      content column. Width, height, row span, action column, and action column
-      span are set HERE (not as local values on the elements) so the
+      set the large-card state: a 192x108 DIP 16:9 thumbnail spanning all three
+      content rows in the thumbnail column, and the right-column action strip
+      in the content column. Width, height, row span, action column, and action
+      column span are set HERE (not as local values on the elements) so the
       ContainerQuery below can override them; local values outrank styles and
       would defeat the query.
     -->
     <Style Selector="Border.detailedThumb">
-      <Setter Property="Width" Value="112" />
-      <Setter Property="Height" Value="112" />
+      <Setter Property="Width" Value="192" />
+      <Setter Property="Height" Value="108" />
       <Setter Property="Grid.RowSpan" Value="3" />
     </Style>
     <Style Selector="Path.detailedPlaceholder">
@@ -620,15 +620,16 @@
     </Style>
     <!--
       Constrained state (card width at or below 680 DIP): the thumbnail shrinks
-      to 72 DIP and spans only name + summary; the single action strip moves to
-      a full-width row beneath all three columns. The query targets descendants
+      to 128x72 DIP (still 16:9) and spans only name + summary; the single
+      action strip moves to a full-width row beneath all three columns. The
+      query targets descendants
       of the named card root, never the queried Border itself, so the card chrome
       is untouched. Declared after the wide defaults so its setters win while the
       query is active.
     -->
     <ContainerQuery Name="detailedModRow" Query="max-width:680">
       <Style Selector="Border.detailedThumb">
-        <Setter Property="Width" Value="72" />
+        <Setter Property="Width" Value="128" />
         <Setter Property="Height" Value="72" />
         <Setter Property="Grid.RowSpan" Value="2" />
       </Style>
@@ -1362,15 +1363,19 @@
                                       ContentTemplate="{StaticResource ModRowGripTemplate}" />
 
                       <!--
-                        Thumbnail area (column 1). A rounded, clipped square
-                        whose Width, Height, and Grid.RowSpan come from the
-                        Border.detailedThumb styles (112 DIP spanning all three
-                        rows when wide; 72 DIP spanning name + summary when
-                        constrained). Border implements
+                        Thumbnail area (column 1). A rounded, clipped 16:9
+                        frame whose Width, Height, and Grid.RowSpan come from the
+                        Border.detailedThumb styles (192x108 DIP spanning all
+                        three rows when wide; 128x72 DIP spanning name + summary
+                        when constrained). Border implements
                         IVisualWithRoundRectClip with ClipToBoundsRadius mapped
                         to CornerRadius, so ClipToBounds clips the child to the
-                        rounded boundary. The Image shows only when a thumbnail
-                        has been decoded; every no-image case (Untracked/Linked,
+                        rounded boundary. The Image stretches Uniform so the
+                        complete source image is always visible; the frame's
+                        neutral background supplies the letterbox/pillarbox
+                        space for non-16:9 assets. The Image shows only when a
+                        thumbnail has been decoded; every no-image case
+                        (Untracked/Linked,
                         missing metadata, no auth, offline, failed image, adult
                         flag, empty URL) shows the same neutral drawn-geometry
                         placeholder in the same box. Adult rows never receive a
@@ -1383,7 +1388,7 @@
                               HorizontalAlignment="Left" VerticalAlignment="Top"
                               Background="{DynamicResource SystemControlBackgroundBaseMediumLowBrush}">
                         <Panel>
-                          <Image Source="{Binding Thumbnail}" Stretch="UniformToFill"
+                          <Image Source="{Binding Thumbnail}" Stretch="Uniform"
                                  IsVisible="{Binding HasThumbnail}" />
                           <!--
                             Neutral placeholder (Material "image", 24x24 source):