TASK 59: the properties panel is a hierarchy, and the shape is a choice

The creator's ruling on the webcam's properties: a "Shape" title above the
Mirror/Rect row; the drag hint indented under that row "to show parentage";
the same for Geometry, Border Color, Border Thickness; Remove and Blur indented
under Background; Strength indented under Blur.

One rule covers it: a title owns its content and the content is indented one
level (10px) under it - two levels where a title is itself nested (Strength
under Blur under Background). The titles are SemiBold 11px #a0a0b0 like the
ones already there.

The shape also stops being a toggle button that shows the NEXT action ("Round"
when the camera was a rectangle) and becomes a CHOICE: two segment options,
Rect | Circle, with Rect selected by default - which is what the creator asked
for ("Rect should be selected as a default if none exists"). The old
ShapeButtonText is gone.

The mutual exclusion lives in the MODEL: IsRectShape/IsRoundShape on
SceneElement, each setter flipping the shape through ToggleClipShape() (so the
pre-round rect is still stored/restored) and always re-raising, so a refused
write - the vertical Chat layout is rect-only (TASK 57) - makes the UI snap
back instead of sticking. Deliberately NOT a WPF RadioButton group: a group
unchecks its siblings by setting IsChecked in code, which makes WPF drop the
binding (stackoverflow 7376373; the same trap measured in 50980687/57275046).

The Circle option stays hidden where CanToggleClipShape is false, so the circle
is still not offered in the vertical Chat layout.

Guard: ytLive.Tests/PropertiesHierarchyTests.cs - the model half (Rect by
default, pick circle, pick rect, the locked Chat layout refuses the circle) and
the panel half (the Shape title owns both options, the circle is the gated one,
the hint is indented and follows the row, every titled block's content is at
10px, Strength at 20px). 432/432 green, 0 warnings.

Controls/index.md

@@ -12,7 +12,7 @@ See [`schema.md`](../schema.md) for the memory-map conventions.
 | `TopBar.xaml(.cs)` | Row 0 session surface (2026-09-22 redesign): brand + gear menu (left), one segmented REC|ON-AIR mode switch + world actions (Record: Start Recording · Stream: Go Live + Test) + reality line while running (dot/word/elapsed) + End (center), account zone — Sign In or avatar w/ Change Account/Logout context menu (right). `RefreshAvatar()`, `GearButton_Click` |
 | `PreviewPane.xaml(.cs)` | Row 1 Col 1 center: the 1920×1080 `OverlayCanvas`/`SelectionOverlay`/`BrandFlashLayer`/`SocialBarElement`, text pull-out drawer, and the live-controls row (TRAX / game / mic meters + sliders + speakers + socials). **TASK 57:** dragging a webcam under the vertical tier routes through `MainViewModel.MoveWebcamInVerticalTier` (the six-spot snap inside the cropped band) instead of free-floating over the master, and a resize re-snaps the tile onto its spot (TASK 57 Unit 2: the resize routes through `MainViewModel.ResizeWebcamInVerticalTier` — the Chat camera's two sizes, then the snap) |
 | `SceneThumbnailStrip.xaml(.cs)` | Row 0 scene-picker strip (`ItemsControl` over `Scenes`), staged-red / live-green border highlight |
-| `LeftPanel.xaml(.cs)` | Row 1 Col 0 left panel: edit mode → layers+properties; live → YouTube chat. Source add/edit/remove, list drag-to-reorder, snapshot revert-accept. **TASK 51:** the webcam properties carry the Background section — `RemoveBackgroundPill` / `BlurBackgroundPill` (`PillToggle`, radio-exclusive via `WebcamSceneConfig.RemoveBackground`/`BlurBackground`) + `BackgroundStrengthSlider` (0..1, 5% snaps, shown only while an effect is on). **TASK 57:** the webcam properties carry a Geometry section (X/Y/W/H) — manual placement of the camera, bound to the **live** placement (the one the current tier shows), gated on `IsWebcamSelected` (not `SelectedElement.IsWebcam` — the TASK 51 test finds that panel by binding text and would match twice); the Shape button's `Visibility` is bound to `CanToggleClipShape`, so the circle option is NOT OFFERED in the vertical Chat layout. **TASK 58:** every drop-down, check box and field in the properties panel carries the theme's style (`YtComboBox`/`YtCheckBox`/`YtTextBoxCompact`) and paints no colour of its own — the guard is `ytLive.Tests/PropertiesStyleTests.cs` |
+| `LeftPanel.xaml(.cs)` | Row 1 Col 0 left panel: edit mode → layers+properties; live → YouTube chat. Source add/edit/remove, list drag-to-reorder, snapshot revert-accept. **TASK 51:** the webcam properties carry the Background section — `RemoveBackgroundPill` / `BlurBackgroundPill` (`PillToggle`, radio-exclusive via `WebcamSceneConfig.RemoveBackground`/`BlurBackground`) + `BackgroundStrengthSlider` (0..1, 5% snaps, shown only while an effect is on). **TASK 57:** the webcam properties carry a Geometry section (X/Y/W/H) — manual placement of the camera, bound to the **live** placement (the one the current tier shows), gated on `IsWebcamSelected` (not `SelectedElement.IsWebcam` — the TASK 51 test finds that panel by binding text and would match twice); the Shape button's `Visibility` is bound to `CanToggleClipShape`, so the circle option is NOT OFFERED in the vertical Chat layout. **TASK 58:** every drop-down, check box and field in the properties panel carries the theme's style (`YtComboBox`/`YtCheckBox`/`YtTextBoxCompact`) and paints no colour of its own — the guard is `ytLive.Tests/PropertiesStyleTests.cs`. **TASK 59:** the webcam's properties are a HIERARCHY — a `Shape` title owns the mirror switch and the shape choice (`Rect` | `Circle` as two `SegmentToggle` options, Rect selected by default, the circle option hidden where `CanToggleClipShape` is false), and every titled block (Geometry, Border Color, Border Thickness, Background) owns its content one indent deeper (Strength sits under Blur) |
 | `OverlayHost.xaml(.cs)` | Root-grid overlay dialogs: Settings / Report Bug / Feature Request / About (+ licenses + license-key entry). `BackToAbout_Click` lives here |
 | `SceneThumbnailStrip.xaml.cs` | Code-behind for the strip above |
 | `LeftPanel.xaml.cs` | Code-behind for the panel above |