Web source: container == content — element grid + selection box sized to the cropped frame's canvas extent

- FindContentBounds already trimmed the bitmap; the grid/box still rendered at the uncropped user
  size, so Fill stretched the tight widget into a bigger frame = dead-between-content-and-border.
- ContentCanvasSize maps the crop rect to canvas units (1920/pixW per axis, DPI-correct) and the
  preview event now carries (bitmap, canvasW, canvasH).
- OnWebView2PreviewBitmapChanged sets the element Width/Height to that size; the grid and the
  SelectionOverlay (both bound to the element's Width/Height) now equal the widget exactly.
- IsPreviewDragging (set in MainWindow drag/resize) suppresses auto-fit mid-gesture.
- Tests 10/10 (alpha bounds, canvas-size mapping incl. DPI, control size); 0 warnings.

HANDOFF.md

@@ -6,36 +6,34 @@
 working). **NOT pushed — user rule: never push without explicit instruction (2026-08-24).** No feature
 branches pre-1.0: all work lands on `main` per work unit.
 
-## The web-source rendering work (2026-08-28) — CURRENT MODEL: canvas-size viewport + ALPHA-BBOX crop
+## The web-source rendering work (2026-08-28) — CURRENT MODEL: canvas-size viewport + alpha crop + container==content
 
-**History of failures (see MyMistakes.md for the full log):** box-size rendering clipped full-bleed
-widgets to their upper-left chunk (fixed — page renders at the master canvas 1920×1080, stable, the
-one render the creator confirmed solid). Then four crop attempts failed in different ways: (1) the
-`JSON.stringify` return double-encoded under `ExecuteScriptAsync`, silently disabling the crop;
-(2) `scrollWidth/scrollHeight` at canvas size returns the whole viewport for full-canvas wrapper
-bodies → no trim (ghost boundary); (3) union-of-DOM-elements measured an unsettled layout on
-NavigationCompleted and BROKE the image (creator's "don't break the rendering" boundary crossed).
-(4) Reverting to f39ebd9's scroll-crop was another dead end (#2 again).
+**History of failures (see MyMistakes.md for the full log):**
+1. box-sized viewport clipped full-bleed widgets to their upper-left chunk → render at the master
+   canvas 1920×1080 (stable), the only render the creator confirmed solid.
+2. `JSON.stringify` return double-encoded under `ExecuteScriptAsync` → crop silently disabled.
+3. `scrollWidth/scrollHeight` at canvas size = whole viewport for full-canvas wrapper bodies → no trim.
+4. DOM-element-union crop measured an unsettled layout on NavigationCompleted → BROKE the image.
+5. Alpha-bbox crop (from the frame itself) fixed the BITMAP but the grid/box stayed at the uncropped
+   user size → Fill stretched the tight widget into a big frame → dead space between content and border.
 
-**The CURRENT MODEL (this commit):**
+**The CURRENT MODEL (this change):**
 - `Services/WebView2Manager.cs` — page renders at 1920×1080 (stable, never tracked); `overflow:hidden`
-  + transparent-bg injection. `FindContentBounds` scans the Bgra32 capture per frame and crops to the
-  bounding box of NON-TRANSPARENT pixels — the widget's true rendered extent, measured from the frame
-  itself. No DOM query, no layout timing: it can never truncate visible content (worst case = full
-  frame = the confirmed-good image). `Stretch="Fill"` maps the cropped frame flush under the selection
-  box → the box hugs the widget on all four sides. `QueryContentBoundsAsync` + the JS script are
-  DELETED.
-- `MainWindow.xaml` — web `<Image>` Stretch set to Fill via the IsWebSource DataTrigger (unchanged).
-- Invariant: **render at canvas size; crop to the alpha extent; Fill to the box.**
-- Unit tests: 3 new for `FindContentBounds` (tight box, no-alpha no-crop, full-alpha no-crop).
+  + transparent-bg injection. `FindContentBounds` crops the Bgra32 capture to the bounding box of
+  non-transparent pixels each frame (immune to timing, can never truncate content). `ContentCanvasSize`
+  maps the crop rect to CANVAS UNITS (DPI-correct). Preview event now carries (bitmap, canvasW, canvasH).
+- `ViewModels/MainViewModel.cs` — `OnWebView2PreviewBitmapChanged` sets the element's Width/Height to
+  the cropped canvas size → the element grid AND the SelectionOverlay (both bound to element
+  Width/Height) EQUAL the widget. `IsPreviewDragging` suppresses the auto-fit during a drag gesture.
+- `MainWindow.xaml.cs` — sets/clears `IsPreviewDragging` at drag/resize start and end.
+- Invariant: **render at canvas size; crop to the alpha extent; SIZE THE BOX to the crop.**
+- Unit tests: 10/10 (alpha bounds ×3, canvas-size mapping ×3, control size ×4).
 
 **Property panel / sliders (2026-08-28):** web URI ✕ clears the textbox; web ✓/✕ icon buttons
-`IsTabStop="False"` so Tab walks X→Y→W→H→URI; Slider style `IsMoveToPointEnabled="True"`
-restores click-anywhere-on-bar. All three confirmed fixed by the creator.
+`IsTabStop="False"`; Slider style `IsMoveToPointEnabled="True"`. Confirmed fixed by the creator.
 
-Build: 0 warnings; tests 7/7 (WebView2Manager). Rejected for the record: box-sized viewport (upper-left
-truncation), fixed 1920×1080 + `Uniform` (letterbox dead space), CSS margin/100% reset (enlarged gap),
-viewport==box (reflow/truncation/scrollbars), DOM-union crop (broke the image).
+Build: 0 warnings; tests 10/10. Rejected for the record: box-sized viewport, `Uniform`, CSS reset,
+viewport==box, DOM-union crop (broke image), crop-without-container-size (left the gap).
 
 ## Key facts / landmines
 
@@ -52,8 +50,8 @@ viewport==box (reflow/truncation/scrollbars), DOM-union crop (broke the image).
 - No `CODING.md`; conventions live in `AGENTS.md` + `ai.md`.
 
 ## Next steps
-1. AWAIT creator's verdict on the ALPHA-BBOX crop — reload a widget URL at several box sizes; the
-   selection frame must snap flush to the widget with no dead space, image must stay identical for
-   full-bleed widgets. If an animated widget causes visible jitter, add crop hysteresis as a follow-up.
-2. Follow-up only if the creator asks: graceful handling of navigation errors / invalid URIs (TASK 17 ×9).
+1. AWAIT creator's verdict on the container==content auto-fit — reload a widget; the selection frame
+   must equal the widget exactly (no dead space, including during resize). Follow-ups only if asked:
+   crop hysteresis for animated widgets, ticker/percent-display widgets.
+2. Graceful handling of navigation errors / invalid URIs (TASK 17 ×9) — only if the creator asks.
 3. Continue queue: TASK 18 local recording, TASK 21 media source, TASK 22 audio sync offset.

MainWindow.xaml.cs

@@ -572,6 +572,7 @@ public partial class MainWindow : Window
         {
             _isResizing = true;
             _resizeAspect = sel.ClipShape == ClipShape.Round ? 1 : sel.Width / Math.Max(1, sel.Height);
+            _viewModel.IsPreviewDragging = true;
             grid.CaptureMouse();
             e.Handled = true;
             return;
@@ -583,6 +584,7 @@ public partial class MainWindow : Window
             _viewModel.SelectedElement = hit;
             _isDraggingOverlay = true;
             _grabOffset = new Point(p.X - hit.X, p.Y - hit.Y);
+            _viewModel.IsPreviewDragging = true;
             grid.CaptureMouse();
             e.Handled = true;
             return;
@@ -643,6 +645,7 @@ public partial class MainWindow : Window
             grid.ReleaseMouseCapture();
         _isDraggingOverlay = false;
         _isResizing = false;
+        _viewModel.IsPreviewDragging = false;
     }
 
     private bool HitHandle(Point mouseScreen, SceneElement element)

MyMistakes.md

@@ -31,17 +31,15 @@ Stream widget bounding box: hug the widget on all four sides, pinned to canvas (
    extents regardless. Lesson: verify declared mechanics actually execute; assume nothing ran.
 
 ## Current iteration (web bounding box — UNCOMMITTED, verification pending)
-ALPHA-BBOX CROP: `FindContentBounds` scans the captured Bgra32 frame and returns the bounding box
-of non-transparent pixels (the background is injected transparent, so alpha = the widget's extent).
-Capture is cropped to that rect and `Stretch="Fill"` maps it flush under the box. No DOM query, no
-layout timing — the crop rect IS the rendered widget by construction, so it can NEVER truncate
-visible content. Worst case (widget fills the canvas) = full frame = the confirmed-good render.
-Canvas-size viewport + Fill untouched. `QueryContentBoundsAsync` + the JS script are DELETED.
+CONTAINER == CONTENT. The element grid and the selection box now SIZE to the cropped frame:
+`WebView2Manager.ContentCanvasSize` maps the alpha-crop pixel rect to MASTER CANVAS units
+(1920/pixW per axis, DPI-correct) and the preview event carries it; `MainViewModel` sets the
+Source.Width/Height (the grid + SelectionOverlay bindings) to that size. No Fill-stretching of a
+cropped bitmap into a larger frame — the box IS the widget. Auto-fit is suppressed while the
+drag/resize gesture is active (`IsPreviewDragging`, set by MainWindow code-behind).
 
-## Iteration that just failed (`a5b9952` — wrapper-excluded DOM-union crop + image alignment)
-Broke the image rendering — creator could not evaluate the box because the image was gone/ruined.
-Why: the visible-element-union rect is measured ONCE on NavigationCompleted; widget layout isn't
-settled then (async fonts/images, load animations, iframes), so the crop rect comes out tiny/wrong
-and the Fill-stretched frame renders a broken/zoomed sliver. This was against the creator's explicit
-"don't break the rendering" instruction. Lesson: measure actual RENDERED PIXELS (alpha), never
-transient DOM state; and never ship a crop blind.
+## Iteration that just failed (`bccdb48` — alpha crop, but container stayed at Source.Width/Height)
+Crop trimmed the bitmap but the element grid/box still rendered at the UNcropped user-set size, so
+Fill stretched the tight widget across a larger frame and dead space floated between content bounds
+and the selection border. Lesson: fixing the BITMAP is not fixing the BOX — the layout container
+must match the cropped dimensions or the gap persists by construction.

Services/WebView2Manager.cs

@@ -20,7 +20,7 @@ public sealed class WebView2Manager : IDisposable
     private readonly Dispatcher _dispatcher;
     private readonly Dictionary<string, WebSourceSession> _sessions = new();
 
-    public event Action<string, WriteableBitmap>? PreviewBitmapChanged;
+    public event Action<string, WriteableBitmap, double, double>? PreviewBitmapChanged;
 
     private sealed class WebSourceSession
     {
@@ -182,6 +182,14 @@ public sealed class WebView2Manager : IDisposable
         return (minX, minY, maxX - minX + 1, maxY - minY + 1);
     }
 
+    // The cropped pixel extent, expressed in MASTER CANVAS units (the WebView2 is
+    // 1920×1080 DIPs and captures at its physical size, so 1920/pixW maps capture
+    // pixels back to canvas units). The element grid + selection box are sized to
+    // this, so the container matches the content exactly instead of Fill-stretching
+    // a cropped bitmap into a larger frame.
+    internal static (double W, double H) ContentCanvasSize(int cropW, int cropH, int pixW, int pixH)
+        => (cropW * (1920.0 / pixW), cropH * (1080.0 / pixH));
+
     private async Task CaptureFrame(string sourceId)
     {
         if (!_sessions.TryGetValue(sourceId, out var session) || session.Disposed) return;
@@ -232,11 +240,12 @@ public sealed class WebView2Manager : IDisposable
             wb.WritePixels(new Int32Rect(0, 0, cropW, cropH), outPixels, cropW * 4, 0);
             wb.Freeze();
 
+            var (canvasW, canvasH) = ContentCanvasSize(cropW, cropH, pixW, pixH);
             session.LatestFrame = new VideoFrame(cropW, cropH, outPixels);
 
             _ = _dispatcher.BeginInvoke(() =>
             {
-                PreviewBitmapChanged?.Invoke(sourceId, wb);
+                PreviewBitmapChanged?.Invoke(sourceId, wb, canvasW, canvasH);
             });
         }
         catch (ObjectDisposedException) { }

TASKS.md

@@ -917,16 +917,19 @@ capturing the primary display (which causes the infinity mirror effect).
 8. ✅ Preview shows live web content (not just a blank rectangle)
 9. ☐ Handle navigation errors, invalid URIs, timeout gracefully
 
-**Rendering model (2026-08-28, canvas-size viewport + ALPHA-BBOX crop):**
+**Rendering model (2026-08-28, canvas-size viewport + alpha crop + CONTAINER==CONTENT):**
 the page renders at the MASTER CANVAS size (1920×1080), stable, never tracked (no reflow/truncation;
 scrollbars suppressed via `overflow:hidden`). `FindContentBounds` scans the Bgra32 capture and crops
 to the bounding box of non-transparent pixels — the widget's true rendered extent, measured from the
-frame itself (NO DOM query, immune to layout timing; can never truncate content; full-canvas widgets
-fall through to the full frame = prior verified-good image). `Stretch="Fill"` maps the cropped frame
-flush under the selection box → box hugs the widget on all four sides. `QueryContentBoundsAsync` +
-the JS content-bounds script are DELETED. ⚠️ Lesson bank: never return `JSON.stringify` from
-`ExecuteScriptAsync` (double-encodes); never measure DOM stuff on NavigationCompleted (unsettled
-layout broke the image — `a5b9952`); measure rendered pixels instead.
+frame itself (NO DOM query, immune to layout timing, can never truncate content; full-canvas widgets
+fall through to the full frame). `ContentCanvasSize` maps the cropped pixel rect to canvas units
+(DPI-correct); `MainViewModel.OnWebView2PreviewBitmapChanged` sizes the element's Width/Height to it —
+so the element grid AND the SelectionOverlay (both bound to the element's Width/Height) equal the
+widget exactly. Auto-fit suppressed while dragging (`IsPreviewDragging`). `Stretch="Fill"` is now
+~1:1; no cropped bitmap is stretched into a larger frame.
+⚠️ Lesson bank: never return `JSON.stringify` from `ExecuteScriptAsync` (double-encodes); never
+measure DOM on NavigationCompleted (unsettled layout broke the image — `a5b9952`); fixing the
+bitmap crop without sizing the container leaves the gap (— `bccdb48`).
 
 **Properties panel (2026-08-28):** web URI ✓/✕ icon buttons are `IsTabStop="False"` so Tab flows
 X→Y→W→H→URI; the ✕ button now clears the URI textbox (was reverting to the pre-accept snapshot).

ViewModels/MainViewModel.cs

@@ -2290,6 +2290,11 @@ public class MainViewModel : ViewModelBase
         _ = RedesignateBackgroundAsync($"{MonitorKeyPrefix}{display.Index}");
     }
 
+    // True while the user is dragging/resizing an element on the preview canvas
+    // (set by MainWindow code-behind). Suppresses the web source's auto-fit so it
+    // doesn't fight the gesture mid-drag.
+    public bool IsPreviewDragging { get; set; }
+
     public void InitWebView2(Panel hostPanel)
     {
         _webView2Manager = new WebView2Manager(hostPanel, System.Windows.Application.Current.Dispatcher);
@@ -2297,11 +2302,26 @@ public class MainViewModel : ViewModelBase
         RegisterLoadedWebSources();
     }
 
-    private void OnWebView2PreviewBitmapChanged(string sourceId, WriteableBitmap bitmap)
+    private void OnWebView2PreviewBitmapChanged(string sourceId, WriteableBitmap bitmap, double canvasW, double canvasH)
     {
         foreach (var scene in Scenes)
             foreach (var el in scene.Elements.OfType<Source>().Where(s => s.Id == sourceId))
+            {
                 el.VideoImageSource = bitmap;
+
+                // The container must equal the content: size the element grid
+                // (and therefore the selection box) to the cropped frame's canvas
+                // extent. Skipped while the user is dragging/resizing the element
+                // so the gesture isn't fought mid-drag.
+                if (IsPreviewDragging || canvasW < 1 || canvasH < 1) continue;
+                var w = Math.Clamp(Math.Round(canvasW), 1, 1920);
+                var h = Math.Clamp(Math.Round(canvasH), 1, 1080);
+                if (Math.Abs(el.Width - w) > 1 || Math.Abs(el.Height - h) > 1)
+                {
+                    el.Width = w;
+                    el.Height = h;
+                }
+            }
     }
 
     public void Shutdown()

ytLive.Tests/WebView2ManagerTests.cs

@@ -154,4 +154,25 @@ public sealed class WebView2ManagerTests
 
         Assert.Equal((0, 0, w, h), (x, y, bw, bh));
     }
+
+    [Fact]
+    public void ContentCanvasSize_Full_Frame_Maps_To_Canvas()
+    {
+        var (cw, ch) = WebView2Manager.ContentCanvasSize(1920, 1080, 1920, 1080);
+        Assert.Equal((1920.0, 1080.0), (cw, ch));
+    }
+
+    [Fact]
+    public void ContentCanvasSize_Half_Widget_Is_Half_Canvas()
+    {
+        var (cw, ch) = WebView2Manager.ContentCanvasSize(960, 540, 1920, 1080);
+        Assert.Equal((960.0, 540.0), (cw, ch));
+    }
+
+    [Fact]
+    public void ContentCanvasSize_Corrects_For_Dpi_Scale()
+    {
+        var (cw, ch) = WebView2Manager.ContentCanvasSize(1200, 675, 2400, 1350);
+        Assert.Equal((960.0, 540.0), (cw, ch));
+    }
 }