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.

ai.md

@@ -277,6 +277,7 @@ C# / WPF (.NET 8) following MVVM:
 - **Element z-order is a unified space, not per-table (2026-09-20):** `Source` and `WebcamSceneConfig` live in different tables, and a webcam can be interleaved between sources in a scene. Both tables' `SortOrder` is stamped from the SAME counter — the element's index within `scene.Elements` — and `Load` merges the two tables' rows per scene by that shared z (tie-break sources-first, so legacy per-table rows read back stacked the way they were saved). Never re-introduce per-type sort counters + "append all Sources then all configs", or a webcam slotted mid-stack reverts on reload (creator-reproduced bug).
 - **Five-scene catalog (`Models/SceneCatalog.cs`):** the product is exactly Starting/Live/BRB/Chat/Ending — work with less, never more (the escape hatch for "more" is OBS). Scenes are matched **by name** (`SceneCatalog.Is`, case-insensitive trim). Empty DBs seed all five; the scenes-header "+" (`ShowAddScene`/`MissingScenes` on `MainViewModel`) only appears while ≥1 canonical scene is missing and its menu lists only the missing ones, re-adding them by name (`AddSceneCommand`). Renaming a canonical scene makes it missing again; `AddScene` rejects non-canonical names.
 - Theming: all custom styles live in `Themes/Controls.xaml`, merged in `App.xaml` — never duplicate styles per-window (dialog duplicates were consolidated into this dictionary). **Every control in the app carries a theme style (TASK 58, 2026-10-21):** an unstyled `ComboBox`/`CheckBox` falls back to the **light WPF system template** (grey border, system arrow, white popup list) and sticks out of the dark panels — the properties panel's drop-downs had been hand-painted with a `Background`/`Foreground` instead of a style (the chat Font drop-down was a copy of that), and every check box was default. The rule now: `ComboBox` → `YtComboBox`, `CheckBox` → `YtCheckBox`, the dense properties fields → `YtTextBoxCompact` (`BasedOn YtTextBox`: 11px, padding 4,2) — **no hand-painted `Background`/`BorderBrush` on a themed control**. `ytLive.Tests/PropertiesStyleTests.cs` is the guard: it fails if an unstyled drop-down, check box or properties field comes back
+- **The properties panel is a HIERARCHY (TASK 59, 2026-10-21):** a **title owns its content, and the content is indented one level (10px) under it** — the creator's ruling: *"the 'drag to move' help text needs to be indented under 'Mirror Rect' to show parentage … same with Geometry, Border Color, Border Thickness … Remove should be indented under Background as should Blur … Strength should be indented under Blur."* So the webcam's block reads `Shape` (the mirror switch + the shape choice) → `Geometry` → `Border Color` → `Border Thickness` → `Background` (Remove, Blur, and Strength one level deeper under Blur), each title SemiBold at 11px `#a0a0b0` like the existing ones. **The shape is a CHOICE, not a toggle button:** `IsRectShape`/`IsRoundShape` on `SceneElement` are two settable bools and the panel shows them as two `SegmentToggle` options (Rect | Circle) with **Rect selected by default** (an element that never picked a shape is a rect) — the old single button showed the *next* action ("Round"), which is why the creator could not tell what the camera was. The mutual exclusion lives in the MODEL (each setter flips through `ToggleClipShape()` and both props are re-raised), **not** in a WPF `RadioButton` group — a RadioButton group unchecks its siblings by setting `IsChecked` in code, which silently kills the binding (stackoverflow 7376373). Each setter always re-raises, so a refused write (the vertical Chat layout is rect-only) makes the UI snap back. Guard: `ytLive.Tests/PropertiesHierarchyTests.cs`
 - Resolution tiers: 1080p60@8 (default) → 1080p30@8 → 720p60@6 → 720p30@6 → **Vertical 1080p60@8 (9:16, 1080×1920)**. The composition master frame is **always 1920×1080** — a tier is an output rect + target resolution over that master, so source geometry is never rewritten (no rounding drift). 16:9 tiers use the full frame; the vertical tier uses a centered **607×1080** window and the preview dims the cropped side strips at 55% black with an accent outline (semi-crop — the cut area stays visible). A resolution badge in the preview corner shows the active tier. Bottom bar: gear icon far left, stream stats (bitrate/FPS/dropped/duration) centered under preview, resolution dropdown far right. A **tooltip** explains finding upload bandwidth — an in-app speed test was deliberately dropped (unreliable). The future encoder crops the master to the rect and scales to the tier's Width×Height
 - Crash diagnosis: `AppLog` writes startup checkpoints to `%APPDATA%\ytLlive\startup.log`; `App.xaml.cs` logs `DispatcherUnhandledException`/`AppDomain.UnhandledException`. When WPF won't run from WSL, this log is how you find the failure (it caught the `MenuItemRole.Separator` XAML crash and the ComboBox SelectionBoxItem bug)