Mesh Studio: Raylib Preview + Git Graph UX

name: Mesh Studio Raylib Git overview: Fix black Raylib Preview by starting the embedded host when entering Preview mode, and upgrade the History panel to a readable git-style graph with branch-colored lanes and a prominent HEAD "you are here" dot. todos:

• id: raylib-host-lifecycle

content: Call SetHostActive in ViewportModeCoordinator + auto-start on RaylibHostControl attach; publish Novolis.Avalonia.Raylib status: completed

• id: git-graph-model

content: Extend GitGraphTimelineRow + GitGraphPalette (branch/kind colors, HEAD marker) status: completed

• id: git-graph-ui

content: Redesign row template with colored dot, branch lanes, fix GitHistoryPanel layout + node fallback status: completed

• id: verify-mesh-studio

content: Manual test Preview/Quality toggle + Save/Branch graph; build MeshBench status: completed isProject: false

Diagnosis

Raylib Preview is black (Quality works)

Path trace uses `ViewportSurface` and works. Preview uses `RaylibHostControl` via `ViewportModeCoordinator`.

sequenceDiagram
  participant MW as MainWindow
  participant Coord as ViewportModeCoordinator
  participant Ray as RaylibHostControl

  MW->>Coord: EnterFast / StartInFastMode
  Coord->>Ray: AttachRaylibHost (re-add to Grid)
  Note over Ray: OnAttached starts present timer only
  Note over Ray: StartHost never called
  Ray-->>MW: Black viewport (_session is null)

`RaylibHostControl.OnAttachedToVisualTree` only starts the present timer; the render loop starts in StartHost(), which is only reached via `SetHostActive(true)`. The coordinator never calls that API (grep shows zero usage in MeshBench).

After Quality mode, DetachRaylibHost triggers OnDetachedFromVisualTree → SetHostActive(false) → host stopped. Returning to Preview re-attaches the control but does not restart the host.

Git graph panel looks empty / unusable

Current stack: `GitHistoryPanel` → `GitGraphTimelineBuilder` → `GitGraphTimelineList`.

Gaps vs your request:

Part 1 — Fix Raylib Preview

1.1 Wire host lifecycle in coordinator

In `ViewportModeCoordinator.cs`:

• `EnterFast` / `StartInFastMode`: after AttachRaylibHost(), call _raylibHost.SetHostActive(true).
• `EnterQuality`: call _raylibHost.SetHostActive(false) before DetachRaylibHost() (belt-and-suspenders with OnDetached).
• `EnsureViewportSized` path (via `MainWindow`): keep setting FrameWidth / FrameHeight from _viewportHost.Bounds so restarts pick up size (already done).

1.2 Safety net in `RaylibHostControl` (novolis-avalonia)

In `RaylibHostControl.cs`:

• OnAttachedToVisualTree: call SetHostActive(true) when attached (so first launch works even if coordinator forgets).
• Keep OnDetachedFromVisualTree → SetHostActive(false) (GLFW single-host rule from `RaylibGlfwProcessSync`).

1.3 GPR package

MeshBench consumes Novolis.Avalonia.Raylib via GPR (`MeshBench.csproj`). After avalonia changes, publish Novolis.Avalonia.Raylib so SetHostActive is available to dogfooding (per nuget-only policy).

1.4 Verify

• Open app → Preview shows meshes immediately (Raylib grid + objects).
• Switch Quality → path trace (already works).
• Switch back Preview → Raylib returns (not black).

Part 2 — Git graph with branch colors + HEAD dot

2.1 Enrich row model

Extend `GitGraphTimelineRow`:

• BranchName (string)
• SnapshotKind (from node.Presentation.Kind)
• BranchColor / KindColor (Avalonia Color or ARGB int)
• IsHere (maps to node.IsHead — workspace HEAD / "you are here")
• Marker (● for HEAD, ○ for normal, ◉ optional for branch-point)

Add small palettes in new GitGraphPalette.cs:

• Branches: stable hash of BranchName → 6–8 distinct hues (main always one fixed color).
• Snapshot kinds: manual = green tint, safety = amber, autosave = gray, quick = cyan, etc. (from SnapshotKinds constants).

2.2 Improve graph builder

In GitGraphTimelineBuilder:

• Pass BranchName, Kind, IsHead into each row.
• Colorize graph prefix characters (│, ├, └) conceptually via row metadata (UI applies brush).
• Fallback: if TimelineTreeView.Roots is empty but GetNodesAsync() has nodes, build a simple linear git log --oneline list (newest first) so saves always appear even if tree projection edge case fails.

2.3 Row template redesign

In `GitGraphTimelineList.cs` (or new GitGraphRowControl.cs):

[ colored ● ]  │─┬─*   Subject label          branch refs
   12px dot    graph   (kind badge optional)

• HEAD / you are here: large filled dot (10–12px), white ring or glow, ToolTip: "You are here (HEAD)".
• Other commits: smaller dot filled with branch color.
• Graph column: monospace lanes tinted with branch color (lower opacity).
• Subject: white; optional small pill for snapshot kind (e.g. manual) using kind color.
• Refs column: branch name only (drop redundant HEAD text when dot conveys it).

2.4 Fix History panel layout

In `GitHistoryPanel.cs`:

• Replace overlapping Grid with DockPanel: header area N/A (header stays in MainWindow), ScrollViewer fills center, empty hint only when rows.Count == 0 (no overlapping black ListBox).
• Ensure MinHeight and visible border so panel never looks like a void.

2.5 Session refresh

In `MeshBenchSession.RefreshTimelineAsync`: pass head into builder so IsHead is accurate after save/restore/branch.

After Save in MainWindow.OnSavePoint, RefreshUi() already runs — graph should populate immediately.

2.6 Optional polish

• Auto-select HEAD row on refresh.
• Legend line under "History (git graph)": colored swatches for main + active branches (only if ≥2 branches).

Files to touch

Verification

1. Preview: meshes visible on open; survives Preview ↔ Quality toggles.
2. Ctrl+S: History shows ≥1 row with colored branch dot; HEAD row has prominent ●.
3. Branch: create branch, save — second branch color differs from main.
4. dotnet build MeshBench; verify-nuget-only.ps1 after GPR publish.