refactor: split MainViewModel core under 500 lines — 500-limit Phase 3, Commit A

Core MainViewModel.cs 758 -> 495 lines. Moved the source add/remove/image
block (AddSource, NextSourceName, AddImage, BuildImageCandidates,
PickImageBytes, AddAsset, AddImageSource, AddReusedImage, RemoveElement) into a
new MainViewModel.Sources.cs partial, and WebView2 source hosting
(RegisterLoadedWebSources, InitWebView2, OnWebView2PreviewBitmapChanged) into a
new MainViewModel.Web.cs partial. Pruned now-dead usings from core.

Zero behavior change; build 0 warnings; 246 pass, only the 2 known failures.
Docs: ViewModels/index.md Phase 3 tracker updated in same commit.

Controls/index.md

@@ -0,0 +1,58 @@
+# Controls — index
+
+The phase-2 carved pieces of what used to be one monolithic `MainWindow.xaml`
+(1,681 lines → a 123-line shell). Each is a `UserControl` in the `ytLive.Controls`
+namespace, extracted one roll-back commit at a time (refactor-commit-12..18).
+See [`schema.md`](../schema.md) for the memory-map conventions.
+
+| File | Purpose |
+|------|---------|
+| `BottomBar.xaml(.cs)` | Footer (Row 3): gear menu (stop/mic/game-mute/quality dropdown), stream stats (bitrate/fps/dropped/duration/health), resolution dropdown |
+| `HealthBanner.xaml(.cs)` | Row 1 status banner + the 7 value→visibility converters live in the app theme, not here |
+| `TopBar.xaml(.cs)` | Row 0 stream controls: REC/ON-AIR pills+signs, elapsed timer, start/stop, account avatar/name (`RefreshAvatar()`) |
+| `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) |
+| `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 |
+| `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 |
+
+## Window ↔ control contract
+
+The shell (`MainWindow.xaml(.cs)`) wires up each control and routes the few
+cross-cutting calls through it:
+
+- Ctor finds each control by `x:Name` (`TopBar`, `PreviewPane`, `LeftPanel`)
+  AFTER `InitializeComponent`, **before** any method touches it (null-ref guard).
+- `_previewPane.IsClickInsidePreview/Drawer` + `_leftPanel.IsClickInside` →
+  deselection guard in `Window_PreviewMouseLeftButtonDown`.
+- `_previewPane.UpdateSelectionOverlay(bool)` + `_leftPanel.OnSelectionChanged(vm)`
+  → selection/edit-mode routing from the VM's `SelectedElement` change.
+- `_topBar.RefreshAvatar()` on `IsConnected`/`AccountAvatarUrl` change.
+- Handlers in moved controls cast `(DataContext as MainViewModel)` — controls
+  inherit the window's DataContext; never pass the VM through a property.
+
+## Gotchas learned the hard way
+
+- **A UserControl cannot see `Window.Resources`** (StaticResource resolves by
+  element lookup, so it stops at the control boundary). The 7 converters
+  (`BoolToVis`, `InverseBoolToVis`, `NotNullToVis`, `NullToVis`, `HiddenBoolToVis`,
+  `EnumToBool`, `AllTrueToVis`) were promoted from `MainWindow.Resources` into
+  `Themes/Controls.xaml` (see [`Themes/index.md`](../Themes/index.md)).
+- **Moved XAML can lose its namespace**: a block cut from MainWindow carries no
+  root xmlns, so any `models:`/`Helpers:` ref in it breaks the build with
+  `MC2000: Value cannot be null (key)`. Declare `xmlns:models` / `xmlns:Helpers`
+  on each control's root (LeftPanel hit this).
+- **Name-looked-up host stubs must stay in the window**, not a control:
+  `WebViewHostPanel` (ctor `InitWebView2(WebViewHostPanel)`) and `ToastArea`
+  (`NotificationService.InArea("ToastArea")`) are resolved by name from the
+  window root — so `OverlayHost` deliberately leaves them as thin window-root
+  children (Commit 18).
+- When cutting visual wrappers, don't drop the outer `Border`'s
+  background/glow/margin — Commit 15 initially lost the preview's outer border
+  and had to restore it same-commit.
+
+Related: [`ViewModels/index.md`](../ViewModels/index.md) (MainViewModel the
+controls bind to), [`Themes/index.md`](../Themes/index.md) (styles/converters),
+[`Helpers/index.md`](../Helpers/index.md) (ViewModelBase, converters), the
+`MainWindow.xaml` shell at repo root that hosts these.

HANDOFF.md

@@ -4,39 +4,43 @@
 
 **`main`**, working tree is **CLEAN**.
 
-Commits `46978b8` (AGENTS push policy), `fc33022` (HANDOFF), and refactor
-commits `0–5` through `e286719` are **pushed** (incl. `refactor-commit-0..5`).
-Refactor commits **6–11 are LOCAL ONLY** (policy 2026-08-30: no per-commit
-push; `git push --tags` only at a user-agreed milestone / "push it"):
+Both split phases are now complete. Phase 1 (view-model partials) is pushed;
+Phase 2 (MainWindow.xaml → UserControls) is complete but **local-only**.
 
-| Commit | Hash | Tag | Partial | Lines |
-|--------|------|-----|---------|-------|
-| 6 Audio | `c1126a5` | `refactor-commit-6` | `MainViewModel.Audio.cs` | 408 |
-| 7 Trax | `535a501` | `refactor-commit-7` | `MainViewModel.Trax.cs` | 132 |
-| 8 Socials | `c41ff7f` | `refactor-commit-8` | `MainViewModel.Socials.cs` | 161 |
-| 9 Streaming | `e1006a0` | `refactor-commit-9` | `MainViewModel.Streaming.cs` | 787 |
-| 10 Chat | `3b77a13` | `refactor-commit-10` | `MainViewModel.Chat.cs` | 194 |
-| 11 Overlays | `1efde5a` | `refactor-commit-11` | `MainViewModel.Overlays.cs` | 194 |
+**Pushed** (reached `origin/main` == `14d3ed4`, incl. tags): Phase 1 commit `0`
+and refactor commits `1..11` (`refactor-commit-0..11`), plus policy/HANDOFF.
 
-Nightly summary: **Phase 1 complete.** The plan was 11 partials + scaffold;
-all live in `ViewModels/`. Core `MainViewModel.cs` shrank 1,890 → **758
-lines**. Every change: clean build (0 warnings), `scripts/verify.sh` (246
-passed + 2 known failures only), `scripts/scope-check.sh` with explicit file
-args, `ViewModels/index.md` updated in the SAME commit, tagged
-`refactor-commit-N`, no per-commit push.
+**LOCAL ONLY (Phase 2 — 12, 13, 14, 15, 16, 17, 18)** — policy 2026-08-30: no
+per-commit push; `git push` only at a user-agreed milestone / "push it".
+**Push pending on explicit user approval:**
+
+| Commit | Hash | Tag | Control | From Loc |
+|--------|------|-----|---------|----------|
+| 12 | `bc23b64` | `refactor-commit-12` | `Controls/BottomBar` | footer |
+| 13 | `6914252` | `refactor-commit-13` | `Controls/HealthBanner` | row 1 banner |
+| 14 | `90f5ad5` | `refactor-commit-14` | `Controls/TopBar` | row 0 top bar |
+| 15 | `c5e3466` | `refactor-commit-15` | `Controls/PreviewPane` | center preview |
+| 16 | `73397cf` | `refactor-commit-16` | `Controls/SceneThumbnailStrip` | row 0 strip |
+| 17 | `c9fd1bd` | `refactor-commit-17` | `Controls/LeftPanel` | row 1 col 0 |
+| 18 | `544208e` | `refactor-commit-18` | `Controls/OverlayHost` | overlay dialogs |
 
 ## What's In Flight
 
-Nothing code-in-flight — working tree clean, Phase 1 done.
+Nothing code-in-flight — working tree clean, **Phase 2 complete**.
 
-**Next (queued, not started): Phase 2 — split `MainWindow.xaml` (1,681 lines)
-into UserControls.** Same rules: one work unit per control, docs in the same
-commit, verify + scope-check, commit locally, `git push` only on user go.
+**Phase 2 result:** `MainWindow.xaml` carved 1,681 → **123 lines** (a shell over
+6 UserControls under `Controls/`, namespace `ytLive.Controls`). Every change:
+0-warning build, `scripts/verify.sh` (246 pass + 2 known only), explicit-file
+`scripts/scope-check.sh`, `ViewModels/index.md` in the SAME commit, tagged
+`refactor-commit-N`, no per-commit push.
 
-**Push pending:** refactor commits 6–11 + their tags are local. The Session-1
-push checkpoint was never reached because the user directive was to run the
-series to completion; Phase 1 completion is the natural milestone to push on
-explicit user confirmation.
+**Next:** 
+- If user says "push": `git push origin main && git push --tags` (7 commits 12-18
+  + their tags).
+- Then optional Phase 3 if queued. Nothing is queued beyond Phase 2.
+
+**Pending bus:** `ViewModels/index.md` Phase 2 tracker has rows 12–18 (closed);
+Phase 1 tracker closed. `Controls/` has `index.md`-style facts only if needed.
 
 ## Landmines
 
@@ -45,44 +49,51 @@ explicit user confirmation.
   `RoundClipInteractionTests.Round_Clip_Corner_Is_Grabbable_And_Shape_Is_Circle`.
 - **Tests occasionally abort early (236/237)** — known flake, accepted by `verify.sh`.
 - **App running locks `ytLive.exe`** → build fails MSB3027. Kill PID before building.
-- **Implicit usings are SDK-default but partials must still carry their own
-  domain usings** (they do not inherit core's): `ICommand`/`ObservableCollection`/
-  `WriteableBitmap`/`DispatcherTimer` etc. are NOT implicit. Grep-verified usings:
-  - Audio: Input, Media, Threading, `NAudio.CoreAudioApi`, `ytLive`, Helpers, Models, Services, Services.Audio
-  - Trax: IO, Media, `Microsoft.Win32`, Helpers, Models, Services.Audio
-  - Socials: Windows, Input, Media, `ytLive`, Helpers, Models, Services, Services.Compositor
-  - Streaming: ObjectModel, IO, Windows, Input, Threading, `Microsoft.Win32`, Helpers, Models, Services, Services.Encoder
-  - Chat: ObjectModel, Media, Media.Imaging, Threading, Helpers, Models, Services
-  - Overlays: Diagnostics, IO, Input, Helpers
+- **WinForm crash from `Window_PreviewMouseLeftButtonDown`** — handled in-side the
+  preview/left panel; don't add handlers that deref `OriginalSource` unguarded.
+- **Controls cannot see `Window.Resources`** (converter rule, Commit 13): any
+  StaticResource the window once supplied must live at app level in
+  `Themes/Controls.xaml`. The 7 converters were promoted there.
+- **Some control XAML needs its own `xmlns:models` / `xmlns:Helpers`** — a moved
+  block lost its namespace when it left MainWindow's root (LeftPanel hit this,
+  MC2000 "key null"). Always add the model/helper xmlns on each control root.
+- **Name-looked-up host stubs must stay in the window:** `WebViewHostPanel`
+  (ctor `InitWebView2(WebViewHostPanel)`) and `ToastArea`
+  (`NotificationService.InArea("ToastArea")`) are resolved by name from the
+  window — keep them as window-root children, don't bury them in a control.
+  OverlayHost deliberately left them in place (Commit 18) for this reason.
 - **Pre-commit gate:** `scripts/verify.sh` (0-warning build + full tests) and
   `scripts/scope-check.sh "file1" …` — scope-check REQUIRES explicit file args.
 - Build from WSL with the Windows dotnet host only (see `AGENTS.md`).
 
 ## Todo state
 
-- MainViewModel refactor: **Phase 1 complete (11/11 partials + scaffold).**
-  `ViewModels/index.md` has a per-partial table row (code↔commit map in the
-  tracker section). Core row now describes only what remains (ctor wiring,
-  lifecycle, source commands, WebView2 hosting, frame-pump seam,
-  `SelectedElement`, `BrandFlash*`, `BuildCompositorOptions`/`ResolveOutputFrame`).
+- MainViewModel refactor: **Phase 1 complete (11/11 partials)**, pushed.
+- MainWindow.xaml refactor: **Phase 2 complete (6/6 controls)**, local-only.
 - TASK 3: 27/30 (preview compositor 16, text source 17, alerts 20 still open).
 - TASK 4: ✅ shipped. TASK 9: items 1–3 shipped; 4–7 open. TASK 10: steps 1–7; Velopack pending.
 - TASK 18: shipped, creator verification pending. TASK 19/23, 20, 21-A: shipped.
 - TASK 22 (audio sync offset): not started — required for v1.
-- Monitoring: cross-partial private access is the point of partial classes —
-  no moved member re-declared anywhere; moved setters reference other partials
-  purely by name.
 
 ## Session summary (2026-08-30)
 
-- Ran the MainViewModel split to completion under the standing directive
-  ("continue until you can continue no longer" — no interruption prompts).
-- Commits 9 (Streaming), 10 (Chat), 11 (Overlays) landed locally, each ~8:40
-  back-to-back: cut → 0-warning build → verify (246 pass + 2 known) →
-  scope-check → index.md in-commit → `git tag refactor-commit-N`. No push.
-- Streaming was the hardest cut (interleaved props, master-frame consts,
-  session timer, health pipeline, record rename-on-stop); Chat and Overlays
-  were clean contiguous cuts. One build fix each: Streaming needed
-  `ObjectModel`/`Input`, Chat needed `Media.Imaging` for `WriteableBitmap`.
-- Docs kept honest throughout: `index.md` rows for Streaming/Chat/Overlays,
-  About-hub row re-pointed to the Overlays partial, core row trimmed each time.
+- Ran the **MainWindow.xaml split to completion** under the standing "continue
+  without stopping" directive — no interruption prompts, no `question` tool.
+- Commits 12–18 landed locally, each: cut → 0-warning build → verify (246 pass +
+  2 known) → scope-check → index.md in-commit → `git tag refactor-commit-N`. No push.
+- **Commit 15 (PreviewPane** the hardest: 1920×1080 canvas + drag/select/resize/
+  hit-test, webcam menu handlers, social glow, audio meters. A dropped outer
+  `Border` (background/glow/margin) was caught and restored same-commit.
+- **Commit 17 (LeftPanel)** the biggest: property editors + chat autoscroll
+  (moved to self-subscribe on `Loaded`), drag-to-reorder, snapshot revert/accept
+  family; window routes via `_leftPanel.IsClickInside` and
+  `_leftPanel.OnSelectionChanged(vm)`.
+- **Commit 18 (OverlayHost)** the scope-decision: moved only the three dialogs;
+  kept `WebViewHostPanel` + `ToastArea` as window-root stubs because their
+  name-based lookups (WebView2 init, toast `InArea`) would break if buried in a
+  control — a spin-guard decision, not a guess.
+- Two XAML extraction gotchas recorded: (a) a moved block losing its `xmlns`
+  → MC2000 "key null" (Line n col m), fixed by adding `xmlns:models` on the
+  control root; (b) re-deriving line numbers after each edit before `sed`/awk
+  deletion ranges (the edit tool shifts numbers).
+- Push checkpoint reached; awaiting explicit "push" for commits 12–18 + tags.

ViewModels/MainViewModel.Sources.cs

@@ -0,0 +1,251 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Linq;
+using System.Windows;
+using Microsoft.Win32;
+using ytLive.Helpers;
+using ytLive.Models;
+using ytLive.Services;
+using ytLive.ViewModels;
+
+namespace ytLive.ViewModels;
+
+public partial class MainViewModel
+{
+    private void AddSource(object? parameter)
+    {
+        var scene = StagedScene;
+        if (scene == null) return;
+
+        var sourceType = parameter is SourceType typed
+            ? typed
+            : Enum.TryParse<SourceType>(parameter?.ToString(), true, out var parsed) ? parsed : SourceType.Image;
+        var baseName = sourceType switch
+        {
+            SourceType.Image => "Image",
+            SourceType.TextOverlay => "Text",
+            SourceType.Countdown => "Countdown",
+            SourceType.WebSource => "Web Resource",
+            SourceType.ChatBox => "YouTube Chat",
+            _ => "Layer",
+        };
+
+        // The (+) menu only adds regular layers. The Background is a locked
+        // per-screen layer managed by EnsureBackground/NormalizeBackgrounds —
+        // never user-created, never deleted. YouTube Chat is one-per-layout.
+        if (sourceType is SourceType.DisplayCapture or SourceType.WindowCapture or SourceType.Background)
+            return;
+        if (sourceType == SourceType.ChatBox && !CanAddYouTubeChat)
+            return;
+
+        // Web resources use "Web Resource-N" naming (0-indexed per scene)
+        var webCount = scene.Elements.OfType<Source>().Count(s => s.Type == SourceType.WebSource);
+        var source = new Source
+        {
+            Name = sourceType == SourceType.WebSource
+                ? $"{baseName}-{webCount}"
+                : NextSourceName(scene, baseName),
+            Type = sourceType,
+            X = sourceType == SourceType.ChatBox ? 1400 : 0,
+            Y = sourceType == SourceType.ChatBox ? 20 : 0,
+            Width = sourceType == SourceType.WebSource ? 640 : sourceType == SourceType.ChatBox ? 500 : 0,
+            Height = sourceType == SourceType.WebSource ? 480 : sourceType == SourceType.ChatBox ? 648 : 0,
+        };
+        scene.Elements.Add(source);
+
+        if (sourceType == SourceType.WebSource)
+        {
+            _webView2Manager?.Register(source);
+            source.PropertyChanged += (_, e) =>
+            {
+                if (e.PropertyName == nameof(Source.WebUri))
+                    _webView2Manager?.OnWebUriChanged(source);
+            };
+        }
+
+        if (sourceType == SourceType.ChatBox)
+        {
+            source.PropertyChanged += (_, e) =>
+            {
+                if (e.PropertyName is nameof(Source.ChatFontSize) or nameof(Source.ChatFontColor)
+                    or nameof(Source.ChatBackgroundColor) or nameof(Source.ChatBackgroundOpacity)
+                    or nameof(Source.ChatMaxMessages) or nameof(Source.ChatShowTimestamps)
+                    or nameof(Source.ChatShowBadges) or nameof(Source.ChatMemberColor)
+                    or nameof(Source.ChatSuperChatColor) or nameof(Source.ChatFontFamily)
+                    or nameof(Source.ChatFadeSeconds) or nameof(Source.Width) or nameof(Source.Height))
+                    UpdateChatBoxPreview(source);
+            };
+            UpdateChatBoxPreview(source);
+        }
+
+        OnPropertyChanged(nameof(ShowEmptySceneHint));
+        OnPropertyChanged(nameof(ShowSourcesEmptyHint));
+        UpdateActiveBackground();
+    }
+
+    // Duplicate resource names get an incrementing suffix with no space: Image,
+    // Image2, Image3… The next free number is derived from the names actually in
+    // the scene, so deleting a middle resource never collides with a survivor.
+    private static string NextSourceName(Scene scene, string baseName)
+    {
+        var taken = scene.Elements.OfType<Source>()
+            .Select(s => s.Name)
+            .Where(n => string.Equals(n, baseName, StringComparison.OrdinalIgnoreCase)
+                || (n.Length > baseName.Length
+                    && n.StartsWith(baseName, StringComparison.OrdinalIgnoreCase)
+                    && int.TryParse(n.Substring(baseName.Length), out _)))
+            .ToHashSet(StringComparer.OrdinalIgnoreCase);
+        if (!taken.Contains(baseName)) return baseName;
+        for (var i = 2; ; i++)
+            if (!taken.Contains($"{baseName}{i}"))
+                return $"{baseName}{i}";
+    }
+
+    private void AddImage()
+    {
+        var scene = StagedScene;
+        if (scene == null) return;
+
+        var candidates = BuildImageCandidates();
+        if (candidates.Count == 0)
+        {
+            var bytes = PickImageBytes("Choose an image");
+            if (bytes != null) AddImageSource(bytes);
+            return;
+        }
+
+        var dialog = new ReuseImageDialog(new ReuseImageViewModel(candidates))
+        {
+            Owner = Application.Current.MainWindow
+        };
+        if (dialog.ShowDialog() != true) return;
+
+        if (dialog.WantsNew)
+        {
+            var bytes = PickImageBytes("Choose an image");
+            if (bytes != null) AddImageSource(bytes);
+        }
+        else
+        {
+            AddReusedImage(dialog.PickedAssetId!);
+        }
+    }
+
+    private List<ReuseImageCandidate> BuildImageCandidates()
+    {
+        var candidates = new List<ReuseImageCandidate>();
+        foreach (var scene in Scenes)
+        foreach (var source in scene.Elements.OfType<Source>().Where(s => s.Type == SourceType.Image && !string.IsNullOrWhiteSpace(s.AssetId)))
+        {
+            candidates.Add(new ReuseImageCandidate
+            {
+                SceneName = scene.Name,
+                SourceName = source.Name,
+                AssetId = source.AssetId!
+            });
+        }
+        return candidates;
+    }
+
+    private byte[]? PickImageBytes(string title)
+    {
+        var dialog = new OpenFileDialog
+        {
+            Title = title,
+            Filter = "Image files (*.png;*.jpg;*.jpeg;*.bmp;*.gif;*.webp)|*.png;*.jpg;*.jpeg;*.bmp;*.gif;*.webp|All files (*.*)|*.*"
+        };
+        if (dialog.ShowDialog() != true) return null;
+        try
+        {
+            return File.ReadAllBytes(dialog.FileName);
+        }
+        catch (Exception ex)
+        {
+            _notifications.Warning("Couldn't read that image", ex.Message);
+            return null;
+        }
+    }
+
+    private string? AddAsset(byte[] bytes)
+    {
+        try
+        {
+            var image = ImageCache.FromBytes(bytes);
+            var id = _layoutStore.UpsertAsset(bytes, image?.PixelWidth ?? 0, image?.PixelHeight ?? 0);
+            if (id != null && image != null) ImageCache.Put(id, image);
+            return id;
+        }
+        catch (Exception ex)
+        {
+            Debug.WriteLine($"Asset store failed: {ex.Message}");
+            return null;
+        }
+    }
+
+    private void AddImageSource(byte[] bytes)
+    {
+        if (bytes.Length == 0) return;
+        var assetId = AddAsset(bytes);
+        if (assetId != null) AddReusedImage(assetId);
+    }
+
+    private void AddReusedImage(string assetId)
+    {
+        var scene = StagedScene;
+        if (scene == null || string.IsNullOrWhiteSpace(assetId)) return;
+
+        var source = new Source { Name = NextSourceName(scene, "Image"), Type = SourceType.Image, AssetId = assetId };
+
+        var image = ImageCache.Get(assetId);
+        if (image != null)
+        {
+            var scale = Math.Min(640.0 / image.PixelWidth, 480.0 / image.PixelHeight);
+            source.Width = image.PixelWidth * scale;
+            source.Height = image.PixelHeight * scale;
+            source.X = (1920 - source.Width) / 2;
+            source.Y = (1080 - source.Height) / 2;
+        }
+
+        scene.Elements.Add(source);
+        SelectedElement = source;
+        OnPropertyChanged(nameof(ShowEmptySceneHint));
+        OnPropertyChanged(nameof(ShowSourcesEmptyHint));
+        UpdateActiveBackground();
+    }
+
+    // Removes an element from the active scene. For a webcam config this drops the
+    // scene's usage and releases one camera reference (CameraManager stops the
+    // session when the last using scene lets go). When the last config anywhere is
+    // removed, the webcam identity is cleared too — re-adding opens the picker
+    // again instead of silently resurrecting the old camera.
+    private void RemoveElement(SceneElement? element)
+    {
+        var scene = StagedScene;
+        if (scene == null || element == null) return;
+        if (element is Source { IsBackground: true }) return;
+        if (element is WebcamSceneConfig && _webcam != null)
+        {
+            if (SelectedElement == element)
+                SelectedElement = null;
+            _ = _cameraManager.ReleaseAsync(_webcam.DeviceId);
+        }
+        if (element is Source { Type: SourceType.WebSource } webSource)
+            _webView2Manager?.Unregister(webSource.Id);
+        scene.Elements.Remove(element);
+
+        if (element is WebcamSceneConfig && _webcam != null
+            && !Scenes.Any(s => s.Elements.OfType<WebcamSceneConfig>().Any()))
+        {
+            _webcam = null;
+            OnPropertyChanged(nameof(CanChangeWebcam));
+            OnPropertyChanged(nameof(CanAddWebcam));
+            OnPropertyChanged(nameof(CanShowWebcamInStagedScene));
+        }
+
+        OnPropertyChanged(nameof(ShowEmptySceneHint));
+        OnPropertyChanged(nameof(ShowSourcesEmptyHint));
+        UpdateActiveBackground();
+    }
+}

ViewModels/MainViewModel.Web.cs

@@ -0,0 +1,41 @@
+using System.Linq;
+using System.Windows.Controls;
+using System.Windows.Media.Imaging;
+using ytLive.Models;
+using ytLive.Services;
+using ytLive.ViewModels;
+
+namespace ytLive.ViewModels;
+
+public partial class MainViewModel
+{
+    private void RegisterLoadedWebSources()
+    {
+        if (_webView2Manager == null) return;
+
+        foreach (var source in Scenes.SelectMany(s => s.Elements).OfType<Source>()
+                     .Where(s => s.Type == SourceType.WebSource))
+        {
+            _webView2Manager.Register(source);
+            source.PropertyChanged += (_, e) =>
+            {
+                if (e.PropertyName == nameof(Source.WebUri))
+                    _webView2Manager.OnWebUriChanged(source);
+            };
+        }
+    }
+
+    public void InitWebView2(Panel hostPanel)
+    {
+        _webView2Manager = new WebView2Manager(hostPanel, System.Windows.Application.Current.Dispatcher);
+        _webView2Manager.PreviewBitmapChanged += OnWebView2PreviewBitmapChanged;
+        RegisterLoadedWebSources();
+    }
+
+    private void OnWebView2PreviewBitmapChanged(string sourceId, WriteableBitmap bitmap)
+    {
+        foreach (var scene in Scenes)
+            foreach (var el in scene.Elements.OfType<Source>().Where(s => s.Id == sourceId))
+                el.VideoImageSource = bitmap;
+    }
+}

ViewModels/MainViewModel.cs

@@ -1,5 +1,3 @@
-using System.Collections.ObjectModel;
-using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Diagnostics;
 using System.IO;
@@ -8,10 +6,7 @@ using System.Windows.Controls;
 using System.Windows.Input;
 using System.Windows.Interop;
 using System.Windows.Media;
-using System.Windows.Media.Imaging;
 using System.Windows.Threading;
-using Microsoft.Win32;
-using NAudio.CoreAudioApi;
 using ytLive.Helpers;
 using ytLive.Models;
 using ytLive.Services;
@@ -383,35 +378,6 @@ public partial class MainViewModel : ViewModelBase
         AppLog.Write("LoadLayout end");
     }
 
-    private void RegisterLoadedWebSources()
-    {
-        if (_webView2Manager == null) return;
-
-        foreach (var source in Scenes.SelectMany(s => s.Elements).OfType<Source>()
-                     .Where(s => s.Type == SourceType.WebSource))
-        {
-            _webView2Manager.Register(source);
-            source.PropertyChanged += (_, e) =>
-            {
-                if (e.PropertyName == nameof(Source.WebUri))
-                    _webView2Manager.OnWebUriChanged(source);
-            };
-        }
-    }
-
-    public void InitWebView2(Panel hostPanel)
-    {
-        _webView2Manager = new WebView2Manager(hostPanel, System.Windows.Application.Current.Dispatcher);
-        _webView2Manager.PreviewBitmapChanged += OnWebView2PreviewBitmapChanged;
-        RegisterLoadedWebSources();
-    }
-
-    private void OnWebView2PreviewBitmapChanged(string sourceId, WriteableBitmap bitmap)
-    {
-        foreach (var scene in Scenes)
-            foreach (var el in scene.Elements.OfType<Source>().Where(s => s.Id == sourceId))
-                el.VideoImageSource = bitmap;
-    }
 
     public void Shutdown()
     {
@@ -463,240 +429,6 @@ public partial class MainViewModel : ViewModelBase
             OnPropertyChanged(nameof(BackgroundVisible));
     }
 
-    private void AddSource(object? parameter)
-    {
-        var scene = StagedScene;
-        if (scene == null) return;
-
-        var sourceType = parameter is SourceType typed
-            ? typed
-            : Enum.TryParse<SourceType>(parameter?.ToString(), true, out var parsed) ? parsed : SourceType.Image;
-        var baseName = sourceType switch
-        {
-            SourceType.Image => "Image",
-            SourceType.TextOverlay => "Text",
-            SourceType.Countdown => "Countdown",
-            SourceType.WebSource => "Web Resource",
-            SourceType.ChatBox => "YouTube Chat",
-            _ => "Layer",
-        };
-
-        // The (+) menu only adds regular layers. The Background is a locked
-        // per-screen layer managed by EnsureBackground/NormalizeBackgrounds —
-        // never user-created, never deleted. YouTube Chat is one-per-layout.
-        if (sourceType is SourceType.DisplayCapture or SourceType.WindowCapture or SourceType.Background)
-            return;
-        if (sourceType == SourceType.ChatBox && !CanAddYouTubeChat)
-            return;
-
-        // Web resources use "Web Resource-N" naming (0-indexed per scene)
-        var webCount = scene.Elements.OfType<Source>().Count(s => s.Type == SourceType.WebSource);
-        var source = new Source
-        {
-            Name = sourceType == SourceType.WebSource
-                ? $"{baseName}-{webCount}"
-                : NextSourceName(scene, baseName),
-            Type = sourceType,
-            X = sourceType == SourceType.ChatBox ? 1400 : 0,
-            Y = sourceType == SourceType.ChatBox ? 20 : 0,
-            Width = sourceType == SourceType.WebSource ? 640 : sourceType == SourceType.ChatBox ? 500 : 0,
-            Height = sourceType == SourceType.WebSource ? 480 : sourceType == SourceType.ChatBox ? 648 : 0,
-        };
-        scene.Elements.Add(source);
-
-        if (sourceType == SourceType.WebSource)
-        {
-            _webView2Manager?.Register(source);
-            source.PropertyChanged += (_, e) =>
-            {
-                if (e.PropertyName == nameof(Source.WebUri))
-                    _webView2Manager?.OnWebUriChanged(source);
-            };
-        }
-
-        if (sourceType == SourceType.ChatBox)
-        {
-            source.PropertyChanged += (_, e) =>
-            {
-                if (e.PropertyName is nameof(Source.ChatFontSize) or nameof(Source.ChatFontColor)
-                    or nameof(Source.ChatBackgroundColor) or nameof(Source.ChatBackgroundOpacity)
-                    or nameof(Source.ChatMaxMessages) or nameof(Source.ChatShowTimestamps)
-                    or nameof(Source.ChatShowBadges) or nameof(Source.ChatMemberColor)
-                    or nameof(Source.ChatSuperChatColor) or nameof(Source.ChatFontFamily)
-                    or nameof(Source.ChatFadeSeconds) or nameof(Source.Width) or nameof(Source.Height))
-                    UpdateChatBoxPreview(source);
-            };
-            UpdateChatBoxPreview(source);
-        }
-
-        OnPropertyChanged(nameof(ShowEmptySceneHint));
-        OnPropertyChanged(nameof(ShowSourcesEmptyHint));
-        UpdateActiveBackground();
-    }
-
-    // Duplicate resource names get an incrementing suffix with no space: Image,
-    // Image2, Image3… The next free number is derived from the names actually in
-    // the scene, so deleting a middle resource never collides with a survivor.
-    private static string NextSourceName(Scene scene, string baseName)
-    {
-        var taken = scene.Elements.OfType<Source>()
-            .Select(s => s.Name)
-            .Where(n => string.Equals(n, baseName, StringComparison.OrdinalIgnoreCase)
-                || (n.Length > baseName.Length
-                    && n.StartsWith(baseName, StringComparison.OrdinalIgnoreCase)
-                    && int.TryParse(n.Substring(baseName.Length), out _)))
-            .ToHashSet(StringComparer.OrdinalIgnoreCase);
-        if (!taken.Contains(baseName)) return baseName;
-        for (var i = 2; ; i++)
-            if (!taken.Contains($"{baseName}{i}"))
-                return $"{baseName}{i}";
-    }
-
-    private void AddImage()
-    {
-        var scene = StagedScene;
-        if (scene == null) return;
-
-        var candidates = BuildImageCandidates();
-        if (candidates.Count == 0)
-        {
-            var bytes = PickImageBytes("Choose an image");
-            if (bytes != null) AddImageSource(bytes);
-            return;
-        }
-
-        var dialog = new ReuseImageDialog(new ReuseImageViewModel(candidates))
-        {
-            Owner = Application.Current.MainWindow
-        };
-        if (dialog.ShowDialog() != true) return;
-
-        if (dialog.WantsNew)
-        {
-            var bytes = PickImageBytes("Choose an image");
-            if (bytes != null) AddImageSource(bytes);
-        }
-        else
-        {
-            AddReusedImage(dialog.PickedAssetId!);
-        }
-    }
-
-    private List<ReuseImageCandidate> BuildImageCandidates()
-    {
-        var candidates = new List<ReuseImageCandidate>();
-        foreach (var scene in Scenes)
-        foreach (var source in scene.Elements.OfType<Source>().Where(s => s.Type == SourceType.Image && !string.IsNullOrWhiteSpace(s.AssetId)))
-        {
-            candidates.Add(new ReuseImageCandidate
-            {
-                SceneName = scene.Name,
-                SourceName = source.Name,
-                AssetId = source.AssetId!
-            });
-        }
-        return candidates;
-    }
-
-    private byte[]? PickImageBytes(string title)
-    {
-        var dialog = new OpenFileDialog
-        {
-            Title = title,
-            Filter = "Image files (*.png;*.jpg;*.jpeg;*.bmp;*.gif;*.webp)|*.png;*.jpg;*.jpeg;*.bmp;*.gif;*.webp|All files (*.*)|*.*"
-        };
-        if (dialog.ShowDialog() != true) return null;
-        try
-        {
-            return File.ReadAllBytes(dialog.FileName);
-        }
-        catch (Exception ex)
-        {
-            _notifications.Warning("Couldn't read that image", ex.Message);
-            return null;
-        }
-    }
-
-    private string? AddAsset(byte[] bytes)
-    {
-        try
-        {
-            var image = ImageCache.FromBytes(bytes);
-            var id = _layoutStore.UpsertAsset(bytes, image?.PixelWidth ?? 0, image?.PixelHeight ?? 0);
-            if (id != null && image != null) ImageCache.Put(id, image);
-            return id;
-        }
-        catch (Exception ex)
-        {
-            Debug.WriteLine($"Asset store failed: {ex.Message}");
-            return null;
-        }
-    }
-
-    private void AddImageSource(byte[] bytes)
-    {
-        if (bytes.Length == 0) return;
-        var assetId = AddAsset(bytes);
-        if (assetId != null) AddReusedImage(assetId);
-    }
-
-    private void AddReusedImage(string assetId)
-    {
-        var scene = StagedScene;
-        if (scene == null || string.IsNullOrWhiteSpace(assetId)) return;
-
-        var source = new Source { Name = NextSourceName(scene, "Image"), Type = SourceType.Image, AssetId = assetId };
-
-        var image = ImageCache.Get(assetId);
-        if (image != null)
-        {
-            var scale = Math.Min(640.0 / image.PixelWidth, 480.0 / image.PixelHeight);
-            source.Width = image.PixelWidth * scale;
-            source.Height = image.PixelHeight * scale;
-            source.X = (1920 - source.Width) / 2;
-            source.Y = (1080 - source.Height) / 2;
-        }
-
-        scene.Elements.Add(source);
-        SelectedElement = source;
-        OnPropertyChanged(nameof(ShowEmptySceneHint));
-        OnPropertyChanged(nameof(ShowSourcesEmptyHint));
-        UpdateActiveBackground();
-    }
-
-    // Removes an element from the active scene. For a webcam config this drops the
-    // scene's usage and releases one camera reference (CameraManager stops the
-    // session when the last using scene lets go). When the last config anywhere is
-    // removed, the webcam identity is cleared too — re-adding opens the picker
-    // again instead of silently resurrecting the old camera.
-    private void RemoveElement(SceneElement? element)
-    {
-        var scene = StagedScene;
-        if (scene == null || element == null) return;
-        if (element is Source { IsBackground: true }) return;
-        if (element is WebcamSceneConfig && _webcam != null)
-        {
-            if (SelectedElement == element)
-                SelectedElement = null;
-            _ = _cameraManager.ReleaseAsync(_webcam.DeviceId);
-        }
-        if (element is Source { Type: SourceType.WebSource } webSource)
-            _webView2Manager?.Unregister(webSource.Id);
-        scene.Elements.Remove(element);
-
-        if (element is WebcamSceneConfig && _webcam != null
-            && !Scenes.Any(s => s.Elements.OfType<WebcamSceneConfig>().Any()))
-        {
-            _webcam = null;
-            OnPropertyChanged(nameof(CanChangeWebcam));
-            OnPropertyChanged(nameof(CanAddWebcam));
-            OnPropertyChanged(nameof(CanShowWebcamInStagedScene));
-        }
-
-        OnPropertyChanged(nameof(ShowEmptySceneHint));
-        OnPropertyChanged(nameof(ShowSourcesEmptyHint));
-        UpdateActiveBackground();
-    }
 
     // Scene-element → latest frame, for the live compositor. The map mirrors the
     // preview: webcam by DeviceId, live captures (the background) by CaptureKey,

ViewModels/index.md

@@ -62,5 +62,10 @@ Progress (Commit N/12 · tag):
 - [x] **Commit 17 · `refactor-commit-17`** — **LeftPanel** → `Controls/LeftPanel.xaml(.cs)` (Row 1 Col 0 left panel: layers/properties edit UI + live chat list). Moved ALL property-editor and chat handlers: `SourceNameBox_*`/`CommitSourceEdit`, `AddSourceButton_Click`, `OnChatMessagesChanged` (now self-subscribed on Loaded), `MirrorButton_Click`, `ShapeButton_Click`, `SourceMenu_Remove`, `BackgroundMenu_*`, `OpacitySlider_ValueChanged`, list drag-to-reorder (`_dragStartPoint`+`List_Preview*`+`EndListDrag`+`FindItemContainerAt`), and the snapshot family (`TakeSnapshot`, `WebcamBorder*`, `Countdown*`, `Web*`). Window exposes via `_leftPanel.IsClickInside(original)` (deselect guard) and `_leftPanel.OnSelectionChanged(vm)` (opacity label + snapshot). Pending: overlay host region.
 - [x] **Commit 18 · `refactor-commit-18`** — **OverlayHost** → `Controls/OverlayHost.xaml(.cs)` (settings/bug/feature/about dialogs). `BackToAbout_Click` moved with it (uses inherited `DataContext`). Window keeps the thin `WebViewHostPanel` + `ToastArea` root stubs so name lookups are untouched (WebView2 ctor init, `NotificationService.InArea("ToastArea")`) — toast/WebView2 behavior unchanged. **Phase 2 COMPLETE** — MainWindow.xaml carved down to a 123-line shell over 6 controls (TopBar, HealthBanner, BottomBar, SceneThumbnailStrip, LeftPanel, PreviewPane, OverlayHost). Pending: session wrap-up (HANDOFF.md) + push on approval.
 
+**Phase 3 — 500-line compliance (production `.cs` only).** Bring all production
+source files under 500 lines. One roll-back commit per file; same drill
+(0-warning build, `verify.sh` 246+2, explicit-file scope-check, tracker in same
+commit, tag `refactor-commit-N`, no per-commit push).
+- [x] **Commit A · `refactor-commit-A`** — **core** → `MainViewModel.cs` 758 → **495**. Moved source add/remove/image block to new **`MainViewModel.Sources.cs`** (234 lines: `AddSource`, `NextSourceName`, `AddImage`, `BuildImageCandidates`, `PickImageBytes`, `AddAsset`, `AddImageSource`, `AddReusedImage`, `RemoveElement`) and WebView2 hosting (`RegisterLoadedWebSources`, `InitWebView2`, `OnWebView2PreviewBitmapChanged`) to new **`MainViewModel.Web.cs`**. Pruned now-dead usings (`Microsoft.Win32`, `NAudio.CoreAudioApi`, `System.Windows.Media.Imaging`, `Collections.ObjectModel/Specialized`). Pending: Streaming, Background, SocialsDialogViewModel, LayoutStore.
 The partial `.cs` files land next to `MainViewModel.cs` in this folder as the split
 proceeds; each partial carries its own `using`s and re-declares nothing from core.