Web source: CSS reset per document + (0,0) anchor — kill box-vs-content padding

HANDOFF.md

@@ -44,6 +44,7 @@ Build: 0 warnings, 0 errors. User verified it renders correctly.
 - No `CODING.md`; conventions live in `AGENTS.md` + `ai.md`.
 
 ## Next steps
-1. Await creator comments on the committed rendering fix; address what he raises.
+1. Await creator comments on the committed rendering fix; address what he raises; also testing
+   the box-vs-content padding fix (CSS reset + (0,0) anchor) just committed.
 2. Follow-up only if the creator asks: graceful handling of navigation errors / invalid URIs (TASK 17 ×9).
 3. Continue queue: TASK 18 local recording, TASK 21 media source, TASK 22 audio sync offset.

MainWindow.xaml

@@ -857,6 +857,8 @@
                                                                      <DataTrigger Binding="{Binding IsWebSource}" Value="True">
                                                                          <Setter Property="Visibility" Value="Visible"/>
                                                                          <Setter Property="Stretch" Value="Uniform"/>
+                                                                         <Setter Property="HorizontalAlignment" Value="Left"/>
+                                                                         <Setter Property="VerticalAlignment" Value="Top"/>
                                                                      </DataTrigger>
                                                                      <MultiDataTrigger>
                                                                         <MultiDataTrigger.Conditions>

Services/WebView2Manager.cs

@@ -15,6 +15,20 @@ namespace ytLive.Services;
 
 public sealed class WebView2Manager : IDisposable
 {
+    // Eliminates the wrapper padding/whitespace between the box and the page:
+    // clears UA margins/paddings, forces html/body to fill the viewport and
+    // anchors content at (0,0) so the rendered frame matches the widget's size.
+    private const string CssResetInjection =
+        "(function(){" +
+        "var s=document.createElement('style');" +
+        "s.textContent='html,body{margin:0!important;padding:0!important;" +
+        "width:100%!important;height:100%!important;overflow:hidden!important;" +
+        "background:transparent!important}';" +
+        "(document.head||document.documentElement).appendChild(s);" +
+        "if(document.documentElement)document.documentElement.style.background='transparent';" +
+        "if(document.body)document.body.style.background='transparent';" +
+        "})();";
+
     private readonly Panel _hostPanel;
     private readonly Dispatcher _dispatcher;
     private readonly Dictionary<string, WebSourceSession> _sessions = new();
@@ -108,18 +122,11 @@ public sealed class WebView2Manager : IDisposable
 
             var cws = session.Control.CoreWebView2!;
 
-            cws.NavigationStarting += (_, e) =>
+            await cws.AddScriptToExecuteOnDocumentCreatedAsync(CssResetInjection);
-            {
-                _ = cws.ExecuteScriptAsync(
-                    "document.documentElement.style.background='transparent';" +
-                    "document.body.style.background='transparent';");
-            };
 
             cws.NavigationCompleted += (_, _) =>
             {
-                _ = cws.ExecuteScriptAsync(
+                _ = cws.ExecuteScriptAsync(CssResetInjection);
-                    "document.documentElement.style.background='transparent';" +
-                    "document.body.style.background='transparent';");
                 _ = CaptureFrame(source.Id);
             };
 

TASKS.md

@@ -923,6 +923,13 @@ canvas size (1920×1080) in `Register`, never tracking the element box — the O
 box-sized viewport was the truncation bug. Display `Stretch`: web → `Uniform` (no crop),
 everything else → `UniformToFill`. Graceful-error handling (item 9) is a follow-up.
 
+**Box-vs-content padding (2026-08-28):** whitespace gaps between the bounding box and the web
+content were the page's own UA margins/padding + body sizing to content instead of the viewport.
+Fixed by injecting a CSS reset into every document via
+`CoreWebView2.AddScriptToExecuteOnDocumentCreatedAsync` (margin/padding 0, html/body 100% of
+viewport, overflow hidden, transparent bg) and anchoring the web `<Image>` at (0,0)
+(`HorizontalAlignment/VerticalAlignment=Left/Top`) inside the element box.
+
 ### Design decisions
 
 - WebView2 is the only option for Windows — it's pre-installed on Windows 10 20H2+ and Windows 11