refactor: split Audio out of MainViewModel — Commit 6/12

MainViewModel.Audio.cs: mic bar (AudioLevel/MeterFillWidth/MeterBrush,
MicVolume/MicMuted, ToggleMicMute, PickMicrophone), mic status dot
(MicStatus/MicStatusBrush/MicStatusToolTip), game bar
(GameAudioLevel/GameMeterFillWidth/GameMeterBrush, GameAudioVolume,
GameMuted, ToggleGameMute), PushSystemVolume, mixer event handlers
(OnMicLevelChanged/OnLoopbackLevelChanged/OnMicConnected/OnMicFailed),
StartMicCaptureAsync, command properties, 18 fields.

Kept in core: TraxIdleBrush, TRAX code block, ctor wiring
(mixer init + event hookup), timer construction.

Verify: 0 warnings, 246 passed, 2 known failures only.

AGENTS.md

@@ -20,6 +20,13 @@ work lands directly on `main`, committed and pushed per work unit. No
 `taskNN-*` branches, no PRs. The scope discipline above is about test focus,
 not git mechanics.
 
+**Commit / push policy (2026-08-30, user directive):** commit every work unit —
+committing is expected and never needs extra permission. Pushing is different:
+push ONLY at sub-milestones and milestones. During a multi-commit refactor,
+that means commits land locally every partial; `git push` happens at the
+session's agreed checkpoint(s), not per-commit. When a milestone warrants a
+push the user will say so (or say "push it").
+
 MUST read the architecture guide before planning or modifying the codebase:
 [`ai.md`](ai.md) (+ [`schema.md`](schema.md) for the memory-map conventions).
 

HANDOFF.md

@@ -6,11 +6,28 @@
 
 No feature branches pre-1.0: all work lands on `main` per work unit.
 
-**Latest commit:** `6031a56` — gear cleanup + Default Location for Recordings + single Start + socials hover glow.
+**Latest commit:** `e286719` — Commit 5/12 of the MainViewModel refactor (Webcam partial, tag `refactor-commit-5`).
 
 ## What's In Flight
 
-Nothing — clean tree, ready for next task.
+**MainViewModel partial split (Phase 1):** 5 of 12 refactor commits landed and pushed.
+Tags `refactor-commit-0…5` = scaffold, Account, License, Scenes, Background, Webcam.
+Latest head `e286719`. Working tree clean.
+
+Remaining partials in order: `Audio` (Commit 6), `Trax` (7), `Socials` (8), `Streaming` (9),
+`Chat` (10), `Overlays` (11). Each lands the same way: cut → build 0 warnings →
+`./scripts/verify.sh` + `./scripts/scope-check.sh "file1" …` → commit titled
+`refactor: split <Area> out of MainViewModel — Commit N/12 (tag refactor-commit-N)`
+with the `ViewModels/index.md` progress update in the SAME commit → `git tag refactor-commit-N`.
+**Do NOT push per commit (policy 2026-08-30):** commits land locally; `git push` only at
+a user-agreed sub-milestone/milestone ("push it"). Tags ride along on that push.
+
+Known partial-usings list (grep-verified):
+`Scenes` = ObjectModel+Specialized+ComponentModel+`ytLive`+Models+Services;
+`Background` = ObjectModel+IO+Windows+Input+Media+Media.Imaging+Helpers+Models+Services;
+`Webcam` = Windows+Input+Media.Imaging+`ytLive`+Models+Services.
+`INotificationService.Info/Warning/Error/Success` are default interface methods → any
+partial calling `_notifications.X` needs `using ytLive.Services;`.
 
 ## Landmines
 
@@ -35,11 +52,12 @@ Nothing — clean tree, ready for next task.
 - TASK 22 (Audio sync offset): not started — required for v1.
 - TASK 30: gear cleanup + record location + single Start + preview layout restructure — shipped across commits `6031a56` + `61b850f` + `455a409`.
 - Monetization: deferred (creator rethinking price/subscription model).
-- **File refactor (in progress — Commit 0 done):** MainViewModel.cs (3,900 lines) will be split into functional partials (Scenes, Background, Webcam, Audio, Trax, Socials, Streaming, Chat, Overlays, Account, License). `MainViewModel` is now `public partial class` (scaffold commit). Remaining: one commit per partial, each a roll-back point, `verify.sh` + `scope-check.sh` before each, docs in the same commit. MainWindow.xaml (1,681 lines) will be split into UserControls after Phase 1. Zero behavior change, tests stay green.
+- **File refactor (in progress — Commit 5/12 done):** MainViewModel.cs (3,900 lines) split into functional partials (Scenes, Background, Webcam ✔; Audio, Trax, Socials, Streaming, Chat, Overlays pending; Account, License ✔). One commit per partial, each a roll-back point (`refactor-commit-N` tags), `verify.sh` + `scope-check.sh` before each, docs in the same commit. MainWindow.xaml (1,681 lines) will be split into UserControls after Phase 1. Zero behavior change, tests stay green.
+- Monitoring: partials must re-declare their own `using`s — core file's usings do NOT carry across partial files. Field-initializer order across parts is compiler-ordered but no moved field has interdependent initializers.
 
-## Session summary (2026-08-29)
+## Session summary (2026-08-30)
 
-- Corrected task status tracking: TASK 4 → ✅ Done, TASK 3 item15 (Window capture) → ✅ absorbed into Screen picker, TASK 3 status updated to 27/30
-- ai.md updated: TASK 4 steps 5-7 added as shipped, stale "frame-pipeline wiring follows" removed
-- HANDOFF.md todo state expanded with full statuses for all active tasks
-- Discussed file organization: MainViewModel.cs (3,900 lines) is a god-object with 49 commands mixing scenes, camera, audio, streaming, socials, overlays, and auth. Next session: split into functional partials
+- Completed refactor Commits 3/12 (Scenes, `dcdfcb9`), 4/12 (Background, `db068ab`), 5/12 (Webcam, `e286719`) — each tagged `refactor-commit-N`, pushed with `--tags`, verified (0-warning clean build, only the 2 known test failures).
+- Background partial took the full bucket: background model, screen capture machinery, display picker, preview fns, capture commands. Webcam partial took identity + per-scene configs + capture callbacks + size safeguards.
+- Mea culpa: asked the user a bucket-boundary question that the rules already answered — won't repeat; buckets are fixed.
+- Test-suite note: full `vstest` run aborted early once (236/237) with only the 2 known failures — accepted by `verify.sh` as a known flake.

ViewModels/MainViewModel.Account.cs

@@ -0,0 +1,132 @@
+using ytLive.Helpers;
+using ytLive.Models;
+using ytLive.Services;
+
+namespace ytLive.ViewModels;
+
+public partial class MainViewModel
+{
+    private bool _isConnected;
+    private string _accountAvatarUrl = string.Empty;
+    private string _accountDisplayName = string.Empty;
+
+    public bool IsConnected
+    {
+        get => _isConnected;
+        set
+        {
+            if (SetProperty(ref _isConnected, value))
+            {
+                // ON-AIR requires a sign-in; dropping the session turns the pill
+                // off so the state can never offer a stream without an account.
+                if (!value) OnAirPillOn = false;
+                OnPropertyChanged(nameof(CanToggleOnAir));
+                OnPropertyChanged(nameof(ShowPrimaryStartButton));
+                OnPropertyChanged(nameof(AccountStatusLightToolTip));
+            }
+        }
+    }
+
+    /// <summary>The connected YouTube account's avatar + name — shown in the top
+    /// bar so the creator always sees WHICH account is about to go live.</summary>
+    public string AccountAvatarUrl
+    {
+        get => _accountAvatarUrl;
+        private set => SetProperty(ref _accountAvatarUrl, value);
+    }
+
+    public string AccountDisplayName
+    {
+        get => _accountDisplayName;
+        private set => SetProperty(ref _accountDisplayName, value);
+    }
+
+    /// <summary>Tooltip for the account status light explaining the color.</summary>
+    public string AccountStatusLightToolTip =>
+        IsLive ? "Live on YouTube — the top bar is red to show the stream is on the air."
+        : IsConnected ? "You're signed in to YouTube. The light is green; ON-AIR is available."
+        : "Signed out — the light is red and the ON-AIR pill is greyed out. You can still record locally.";
+
+    // Restores the DPAPI-saved OAuth session so sign-in survives restarts.
+    // Best-effort: refresh a near-expiry access token; a session that can no
+    // longer refresh is discarded and the user signs in again.
+    private async Task LoadSavedSessionAsync()
+    {
+        try
+        {
+            var saved = TokenStore.Load();
+            if (saved == null) return;
+
+            _youtubeAuth.SetSession(saved);
+            if (saved.TokenExpiry <= DateTime.UtcNow.AddMinutes(5))
+            {
+                var refreshed = await Task.Run(() => _youtubeAuth.RefreshToken());
+                if (!refreshed)
+                {
+                    TokenStore.Clear();
+                    AppLog.Write("Saved session could not be refreshed; signed out");
+                    _notifications.Info("Signed out of YouTube",
+                        "The saved session expired — sign in again when you next go live.");
+                    return;
+                }
+            }
+
+            IsConnected = true;
+            SyncConnectedAccount();
+        }
+        catch (Exception ex)
+        {
+            AppLog.Write($"LoadSavedSessionAsync failed: {ex}");
+        }
+    }
+
+    private void SyncConnectedAccount()
+    {
+        var channel = _youtubeAuth.CurrentChannel;
+        AccountAvatarUrl = channel?.ProfileImageUrl ?? string.Empty;
+        AccountDisplayName = channel?.DisplayName ?? string.Empty;
+    }
+
+    // Runs the OAuth flow (browser + loopback callback) on a background thread.
+    // The resulting channel is returned to the caller and persisted via the
+    // auth service's sessionChanged hook.
+    private async Task<YouTubeChannel?> SignInAsync()
+    {
+        try
+        {
+            var channel = await Task.Run(() => _youtubeAuth.AuthenticateAsync());
+            if (channel == null)
+            {
+                _notifications.Warning("Sign-in was unsuccessful", "Please try again.");
+                return null;
+            }
+
+            IsConnected = true;
+            SyncConnectedAccount();
+            return channel;
+        }
+        catch (Exception ex)
+        {
+            _notifications.Error("Sign-in failed", ex.Message);
+            return null;
+        }
+    }
+
+    /// <summary>Signs out of YouTube (the delete-the-YouTube-slot action in the dialog).</summary>
+    private async Task SignOutYouTubeAsync()
+    {
+        _youtubeAuth.ClearSession();
+        TokenStore.Clear();
+        IsConnected = false;
+        SyncConnectedAccount();
+        NotifySocialsChanged();
+        AppLog.Write("Socials: signed out of YouTube");
+        await Task.CompletedTask;
+    }
+
+    private async Task ChangeAccountAsync()
+    {
+        await SignOutYouTubeAsync();
+        await SignInAsync();
+    }
+}

ViewModels/MainViewModel.Audio.cs

@@ -0,0 +1,408 @@
+using System.Windows;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Threading;
+using NAudio.CoreAudioApi;
+using ytLive;
+using ytLive.Helpers;
+using ytLive.Models;
+using ytLive.Services;
+using ytLive.Services.Audio;
+
+namespace ytLive.ViewModels;
+
+public partial class MainViewModel
+{
+    private readonly DispatcherTimer _volumeFlashTimer;
+    private readonly DispatcherTimer _gameVolumeFlashTimer;
+    private double _audioLevel;
+    private bool _volumeAdjusting;
+    private bool _volumeFlash;
+    private double _micVolume = 0.8;
+    private bool _micMuted;
+    private double? _volumeBeforeMute;
+    private string? _micSourceName;
+    private MicStatus _micStatus = MicStatus.NotConnected;
+    private double _gameAudioLevel;
+    private bool _gameVolumeAdjusting;
+    private bool _gameVolumeFlash;
+    private double _gameVolume = 1.0;
+    private bool _gameMuted;
+    private double? _gameVolumeBeforeMute;
+    private AudioGainProvider? _gainProvider;
+    private readonly IMicrophoneEnumerator _microphoneEnumerator;
+    private readonly AudioMixer _audioMixer;
+
+    public ICommand ToggleMicMuteCommand { get; }
+    public ICommand ToggleGameMuteCommand { get; }
+    public ICommand OpenMicPickerCommand { get; }
+
+    // ─── Audio: the mic bar (meter + volume + mute + status dot) is always
+    // ─── visible; the game bar (meter + volume + mute) appears only while a
+    // ─── full-screen game is producing sound. Both meters preview live. ───
+
+    /// <summary>Live mic input level (0..1) — fed by the audio mixer once capture
+    /// lands; 0 with no input. Read by the meter, scaled by MicVolume.</summary>
+    public double AudioLevel
+    {
+        get => _audioLevel;
+        set
+        {
+            if (SetProperty(ref _audioLevel, Math.Clamp(value, 0, 1)))
+            {
+                OnPropertyChanged(nameof(MeterFillWidth));
+                OnPropertyChanged(nameof(MeterBrush));
+            }
+        }
+    }
+
+    /// <summary>Displayed meter level: 0 while muted; the volume position while
+    /// the slider is being dragged (or briefly after an unmute, so the restored
+    /// level flashes on the bar) so the creator sees where they're setting it;
+    /// otherwise the realtime live level scaled by volume (raising the volume
+    /// moves ambient noise up the bar). Read-only meter.</summary>
+    private double MeterLevel => MicMuted ? 0 : _volumeAdjusting || _volumeFlash ? MicVolume : Math.Min(1, AudioLevelMeter.ToDisplay((float)AudioLevel) * 1.2 * MicVolume);
+
+    public double MeterFillWidth => MeterLevel * 288;
+
+    public string MeterBrush => MeterLevel switch
+    {
+        < 0.6 => "#22c55e",
+        < 0.8 => "#eab308",
+        _ => "#ef4444",
+    };
+
+    /// <summary>Previewes the volume position while the slider is dragged; the
+    /// bar returns to the live level on release (empty when there is no input).
+    /// Starting a drag cancels any pending unmute flash.</summary>
+    public void SetVolumeAdjusting(bool adjusting)
+    {
+        if (adjusting)
+            CancelVolumeFlash();
+        if (SetProperty(ref _volumeAdjusting, adjusting))
+        {
+            OnPropertyChanged(nameof(MeterFillWidth));
+            OnPropertyChanged(nameof(MeterBrush));
+        }
+    }
+
+    private void BeginVolumeFlash()
+    {
+        _volumeFlash = true;
+        OnPropertyChanged(nameof(MeterFillWidth));
+        OnPropertyChanged(nameof(MeterBrush));
+        _volumeFlashTimer.Stop();
+        _volumeFlashTimer.Start();
+    }
+
+    private void EndVolumeFlash()
+    {
+        _volumeFlashTimer.Stop();
+        if (_volumeFlash)
+        {
+            _volumeFlash = false;
+            OnPropertyChanged(nameof(MeterFillWidth));
+            OnPropertyChanged(nameof(MeterBrush));
+        }
+    }
+
+    private void CancelVolumeFlash()
+    {
+        _volumeFlashTimer.Stop();
+        _volumeFlash = false;
+    }
+
+    /// <summary>Mic gain (0..1). Running to 0 mutes (the speaker flips to muted);
+    /// moving up from 0 unmutes (the mute indicator clears). The level being left
+    /// is remembered so the speaker button can restore it.</summary>
+    public double MicVolume
+    {
+        get => _micVolume;
+        set
+        {
+            var clamped = Math.Clamp(value, 0, 1);
+            if (clamped == 0 && !_micMuted)
+                _volumeBeforeMute ??= _micVolume;
+            if (SetProperty(ref _micVolume, clamped))
+            {
+                var muted = clamped == 0;
+                if (_micMuted != muted)
+                {
+                    _micMuted = muted;
+                    OnPropertyChanged(nameof(MicMuted));
+                    OnPropertyChanged(nameof(MicMuteText));
+                }
+                if (!muted)
+                    _volumeBeforeMute = null;
+                OnPropertyChanged(nameof(MeterFillWidth));
+                OnPropertyChanged(nameof(MeterBrush));
+            }
+        }
+    }
+
+    /// <summary>Read-only: true whenever the volume is 0. Only MicVolume may
+    /// change it, so the slider and the speaker can never disagree.</summary>
+    public bool MicMuted => _micMuted;
+
+    public string MicMuteText => MicMuted ? "Unmute" : "Mute";
+
+    /// <summary>Name of the picked voice source, shown left-justified INSIDE the meter
+    /// bar (FontSize 10, ellipsized to the bar) — ai.md is the authority here.</summary>
+    public string? MicSourceName
+    {
+        get => _micSourceName;
+        private set => SetProperty(ref _micSourceName, value);
+    }
+
+    private void ToggleMicMute()
+    {
+        if (MicMuted)
+        {
+            MicVolume = _volumeBeforeMute ?? 0.8;
+            BeginVolumeFlash();
+        }
+        else
+        {
+            _volumeBeforeMute = MicVolume;
+            MicVolume = 0;
+        }
+    }
+
+    private void PickMicrophone()
+    {
+        var dialog = new MicPickerDialog(new MicPickerViewModel(_microphoneEnumerator))
+        {
+            Owner = System.Windows.Application.Current?.MainWindow
+        };
+        if (dialog.ShowDialog() == true && dialog.PickedDevice != null)
+        {
+            MicSourceName = dialog.PickedDevice.DisplayName;
+            _layoutStore.SaveMicSourceName(MicSourceName); // persist across restarts
+            _audioMixer.RestartMic(); // swap the live device immediately
+        }
+    }
+
+    // ─── Mic status dot (the MIC button) ───
+
+    private static readonly SolidColorBrush MicProblemBrush = CreateBrush("#f1c40f");
+
+    /// <summary>Mic connection state, driven by the mixer's MicConnected/MicFailed
+    /// events and the startup device check (see StartMicCaptureAsync).</summary>
+    public MicStatus MicStatus
+    {
+        get => _micStatus;
+        private set
+        {
+            if (SetProperty(ref _micStatus, value))
+            {
+                OnPropertyChanged(nameof(MicStatusBrush));
+                OnPropertyChanged(nameof(MicStatusToolTip));
+            }
+        }
+    }
+
+    /// <summary>Status dot: green = connected, yellow = problem with the requested
+    /// connection, red = not connected (no device / not started).</summary>
+    public SolidColorBrush MicStatusBrush => MicStatus switch
+    {
+        MicStatus.Connected => BarOnBrush,
+        MicStatus.Problem => MicProblemBrush,
+        _ => BarOffBrush,
+    };
+
+    public string MicStatusToolTip => MicStatus switch
+    {
+        MicStatus.Connected => "Mic connected — click to change",
+        MicStatus.Problem => "Mic problem — the requested microphone is unavailable (in use or unplugged). Click to change",
+        _ => "No mic connected — click to choose a microphone",
+    };
+    // ─── Game audio bar (desktop/game): always visible — a mirror of the mic bar
+    // ─── (meter + mute + volume). Desktop/game audio is automatic (WASAPI loopback). ───
+    private static void PushSystemVolume(double volume)
+    {
+        try
+        {
+            using var enumerator = new MMDeviceEnumerator();
+            using var device = enumerator.GetDefaultAudioEndpoint(DataFlow.Render, Role.Multimedia);
+            device.AudioEndpointVolume.MasterVolumeLevelScalar = (float)volume;
+        }
+        catch { }
+    }
+
+    /// <summary>Live desktop/game input level (0..1), fed by the mixer's loopback
+    /// capture. Read by the game meter, scaled by GameAudioVolume.</summary>
+    public double GameAudioLevel
+    {
+        get => _gameAudioLevel;
+        set
+        {
+            if (SetProperty(ref _gameAudioLevel, Math.Clamp(value, 0, 1)))
+            {
+                OnPropertyChanged(nameof(GameMeterFillWidth));
+                OnPropertyChanged(nameof(GameMeterBrush));
+            }
+        }
+    }
+
+    /// <summary>Displayed game meter level: 0 while muted; the volume position
+    /// while the slider is dragged (or briefly after an unmute flash); otherwise
+    /// the realtime live level scaled by volume.</summary>
+    private double GameMeterLevel => GameMuted ? 0 : _gameVolumeAdjusting || _gameVolumeFlash ? GameAudioVolume : Math.Min(1, AudioLevelMeter.ToDisplay((float)GameAudioLevel));
+
+    public double GameMeterFillWidth => GameMeterLevel * 288;
+
+    public string GameMeterBrush => GameMeterLevel switch
+    {
+        < 0.6 => "#22c55e",
+        < 0.8 => "#eab308",
+        _ => "#ef4444",
+    };
+
+    public void SetGameVolumeAdjusting(bool adjusting)
+    {
+        if (adjusting)
+            CancelGameVolumeFlash();
+        if (SetProperty(ref _gameVolumeAdjusting, adjusting))
+        {
+            OnPropertyChanged(nameof(GameMeterFillWidth));
+            OnPropertyChanged(nameof(GameMeterBrush));
+        }
+    }
+
+    private void BeginGameVolumeFlash()
+    {
+        _gameVolumeFlash = true;
+        OnPropertyChanged(nameof(GameMeterFillWidth));
+        OnPropertyChanged(nameof(GameMeterBrush));
+        _gameVolumeFlashTimer.Stop();
+        _gameVolumeFlashTimer.Start();
+    }
+
+    private void EndGameVolumeFlash()
+    {
+        _gameVolumeFlashTimer.Stop();
+        if (_gameVolumeFlash)
+        {
+            _gameVolumeFlash = false;
+            OnPropertyChanged(nameof(GameMeterFillWidth));
+            OnPropertyChanged(nameof(GameMeterBrush));
+        }
+    }
+
+    private void CancelGameVolumeFlash()
+    {
+        _gameVolumeFlashTimer.Stop();
+        _gameVolumeFlash = false;
+    }
+
+    /// <summary>Game audio gain (0..1, unity default). Running to 0 mutes; the
+    /// prior level is remembered so the speaker button can restore it.</summary>
+    public double GameAudioVolume
+    {
+        get => _gameVolume;
+        set
+        {
+            var clamped = Math.Clamp(value, 0, 1);
+            if (clamped == 0 && !_gameMuted)
+                _gameVolumeBeforeMute ??= _gameVolume;
+            if (SetProperty(ref _gameVolume, clamped))
+            {
+                var muted = clamped == 0;
+                if (_gameMuted != muted)
+                {
+                    _gameMuted = muted;
+                    OnPropertyChanged(nameof(GameMuted));
+                    OnPropertyChanged(nameof(GameMuteText));
+                }
+                if (!muted)
+                    _gameVolumeBeforeMute = null;
+                OnPropertyChanged(nameof(GameMeterFillWidth));
+                OnPropertyChanged(nameof(GameMeterBrush));
+                UpdateTraxLocalGain();
+                PushSystemVolume(clamped);
+            }
+        }
+    }
+
+    /// <summary>Read-only: true whenever the volume is 0 (the slider and the
+    /// speaker can never disagree).</summary>
+    public bool GameMuted => _gameMuted;
+
+    public string GameMuteText => GameMuted ? "Unmute" : "Mute";
+
+    private void ToggleGameMute()
+    {
+        if (GameMuted)
+        {
+            GameAudioVolume = _gameVolumeBeforeMute ?? 1.0;
+            BeginGameVolumeFlash();
+        }
+        else
+        {
+            _gameVolumeBeforeMute = GameAudioVolume;
+            GameAudioVolume = 0;
+        }
+    }
+    private void OnMicLevelChanged(float level)
+    {
+        // NAudio raises on its capture thread; marshal to the UI thread so the
+        // meter binding updates safely.
+        var dispatcher = System.Windows.Application.Current?.Dispatcher;
+        if (dispatcher != null && !dispatcher.CheckAccess())
+            dispatcher.BeginInvoke(() => AudioLevel = level);
+        else
+            AudioLevel = level;
+    }
+
+    private void OnLoopbackLevelChanged(float level)
+    {
+        var dispatcher = System.Windows.Application.Current?.Dispatcher;
+        if (dispatcher != null && !dispatcher.CheckAccess())
+            dispatcher.BeginInvoke(() => GameAudioLevel = level);
+        else
+            GameAudioLevel = level;
+    }
+
+    private void OnMicConnected()
+    {
+        var dispatcher = System.Windows.Application.Current?.Dispatcher;
+        if (dispatcher != null && !dispatcher.CheckAccess())
+            dispatcher.BeginInvoke(() => MicStatus = MicStatus.Connected);
+        else
+            MicStatus = MicStatus.Connected;
+    }
+
+    private void OnMicFailed(Exception ex)
+    {
+        // The mixer logs the failure detail; here we only flip the dot to yellow.
+        var dispatcher = System.Windows.Application.Current?.Dispatcher;
+        if (dispatcher != null && !dispatcher.CheckAccess())
+            dispatcher.BeginInvoke(() => MicStatus = MicStatus.Problem);
+        else
+            MicStatus = MicStatus.Problem;
+    }
+
+    /// <summary>Starts capture once at startup: with no mic device present the
+    /// dot stays red and capture never starts; otherwise the mixer starts and
+    /// raises MicConnected (green) or MicFailed (yellow).</summary>
+    private async Task StartMicCaptureAsync()
+    {
+        try
+        {
+            var mics = await _microphoneEnumerator.GetMicrophonesAsync();
+            if (mics.Count == 0)
+            {
+                MicStatus = MicStatus.NotConnected;
+                AppLog.Write("Mic: no capture devices found — mic capture not started");
+                _notifications.Warning("No microphone found",
+                    "Mic capture wasn't started — plug one in and pick it from the mixer.");
+                return;
+            }
+            _audioMixer.Start();
+        }
+        catch (Exception ex)
+        {
+            AppLog.Write($"Mic: device check failed: {ex.Message}");
+        }
+    }
+}

ViewModels/MainViewModel.Background.cs

@@ -0,0 +1,568 @@
+using System.Collections.ObjectModel;
+using System.IO;
+using System.Windows;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using ytLive.Helpers;
+using ytLive.Models;
+using ytLive.Services;
+
+namespace ytLive.ViewModels;
+
+public partial class MainViewModel
+{
+    // Screen background: a permanent live capture (desktop/game) that every scene
+    // shows at the bottom layer. One shared capture session per key — the
+    // ScreenCaptureManager refcounts by key, mirroring CameraManager.
+    private readonly IFullScreenDetector _fullScreenDetector;
+    private readonly ScreenCaptureManager _screenCaptureManager;
+    private readonly ScreenCaptureSourceFactory _screenCaptureFactory;
+
+    private ImageSource? _activeBackgroundImage;
+    private ImageSource? _backgroundImage;
+    private bool _backgroundSizeMismatch;
+    private string _backgroundSizeMismatchText = "";
+    private HashSet<string> _liveCaptureKeys = new();
+
+    public ObservableCollection<DisplayInfo> Displays { get; } = new();
+
+    public ImageSource? ActiveBackgroundImage
+    {
+        get => _activeBackgroundImage;
+        private set => SetProperty(ref _activeBackgroundImage, value);
+    }
+
+    /// <summary>The active scene's live-capture background frame (rendered below the
+    /// static background). Set from the shared capture bitmap as it arrives.</summary>
+    public ImageSource? BackgroundImage
+    {
+        get => _backgroundImage;
+        private set
+        {
+            if (SetProperty(ref _backgroundImage, value))
+            {
+                OnPropertyChanged(nameof(ShowPreviewPlaceholder));
+                OnPropertyChanged(nameof(BackgroundVisible));
+            }
+        }
+    }
+
+    public bool BackgroundVisible => StagedScene?.Elements.OfType<Source>().FirstOrDefault(s => s.IsBackground)?.IsVisible == true;
+
+    public bool BackgroundSizeMismatch
+    {
+        get => _backgroundSizeMismatch;
+        private set => SetProperty(ref _backgroundSizeMismatch, value);
+    }
+
+    public string BackgroundSizeMismatchText
+    {
+        get => _backgroundSizeMismatchText;
+        private set => SetProperty(ref _backgroundSizeMismatchText, value);
+    }
+
+    public ICommand ChangeCaptureCommand { get; }
+    public ICommand RefreshCaptureCommand { get; }
+    public ICommand SetBackgroundDisplayCommand { get; }
+    public ICommand ToggleShowDesktopCommand { get; }
+    public ICommand BrowseBackgroundCommand { get; }
+
+    private void UpdateActiveBackground()
+    {
+        // Static-art rows only. Capture-flavored rows (Live) must NEVER feed
+        // ActiveBackgroundImage — it renders above BackgroundImage, so it would
+        // permanently cover the desktop/game capture. Live's canvas shows
+        // DisplaySource instead (capture, falling back to live-background.jpg).
+        var background = StagedScene?.Elements.OfType<Source>().FirstOrDefault(s => s.Type == SourceType.Background);
+        ActiveBackgroundImage = background != null && !string.IsNullOrWhiteSpace(background.AssetId)
+            ? ImageCache.Get(background.AssetId)
+            : null;
+        OnPropertyChanged(nameof(ShowPreviewPlaceholder));
+    }
+
+    private void UpdateBackgroundImage()
+    {
+        var scene = StagedScene;
+        var background = scene?.Elements.OfType<Source>().FirstOrDefault(s => s.IsBackground);
+        BackgroundImage = background?.DisplaySource;
+
+        if (background != null && !background.UseDefaultBackground
+            && !string.IsNullOrWhiteSpace(background.CustomBackgroundPath)
+            && System.IO.File.Exists(background.CustomBackgroundPath))
+        {
+            try
+            {
+                var bmi = new System.Windows.Media.Imaging.BitmapImage();
+                bmi.BeginInit();
+                bmi.UriSource = new System.Uri(background.CustomBackgroundPath);
+                bmi.CacheOption = System.Windows.Media.Imaging.BitmapCacheOption.OnLoad;
+                bmi.EndInit();
+                bmi.Freeze();
+
+                double expectedRatio = 1920.0 / 1080.0;
+                double imageRatio = (double)bmi.PixelWidth / bmi.PixelHeight;
+                double ratioDiff = Math.Abs(imageRatio - expectedRatio) / expectedRatio;
+
+                if (ratioDiff > 0.05)
+                {
+                    BackgroundSizeMismatch = true;
+                    BackgroundSizeMismatchText =
+                        $"Image is {bmi.PixelWidth}\u00d7{bmi.PixelHeight} \u2014 stream expects 1920\u00d71080 (16:9)";
+                }
+                else
+                {
+                    BackgroundSizeMismatch = false;
+                    BackgroundSizeMismatchText = "";
+                }
+            }
+            catch
+            {
+                BackgroundSizeMismatch = false;
+                BackgroundSizeMismatchText = "";
+            }
+        }
+        else
+        {
+            BackgroundSizeMismatch = false;
+            BackgroundSizeMismatchText = "";
+        }
+    }
+
+    private void RefreshSnapshotsAsync()
+    {
+        foreach (var scene in Scenes)
+        {
+            // Minis never render live captures. While the Live screen is staged
+            // (being previewed) its mini shows the green placeholder; unstaged,
+            // it shows the stored default art. Real-time surface = center only.
+            var stagedLive = ReferenceEquals(scene, StagedScene)
+                && SceneCatalog.Is(scene.Name, SceneCatalog.Live);
+            var img = stagedLive ? null : LoadBackgroundImage(scene);
+            if (img != null)
+                scene.Snapshot = img;
+            else if (scene.Snapshot == null || stagedLive)
+                scene.Snapshot = CreatePlaceholderSnapshot(scene.Name);
+        }
+    }
+
+    internal static System.Windows.Media.Imaging.BitmapSource? LoadBackgroundImage(Scene scene)
+    {
+        var bg = scene.Elements.OfType<Source>().FirstOrDefault(s => s.IsBackground);
+        if (bg != null && !bg.UseDefaultBackground
+            && !string.IsNullOrWhiteSpace(bg.CustomBackgroundPath)
+            && System.IO.File.Exists(bg.CustomBackgroundPath))
+        {
+            try
+            {
+                var bitmap = new System.Windows.Media.Imaging.BitmapImage();
+                bitmap.BeginInit();
+                bitmap.UriSource = new Uri(bg.CustomBackgroundPath);
+                bitmap.CacheOption = System.Windows.Media.Imaging.BitmapCacheOption.OnLoad;
+                bitmap.EndInit();
+                bitmap.Freeze();
+                return bitmap;
+            }
+            catch { /* fall through to AssetId */ }
+        }
+        if (bg != null && !string.IsNullOrWhiteSpace(bg.AssetId))
+            return ImageCache.Get(bg.AssetId);
+        return null;
+    }
+
+    private static BitmapSource CreatePlaceholderSnapshot(string sceneName)
+    {
+        var colors = new Dictionary<string, System.Windows.Media.Brush>(StringComparer.OrdinalIgnoreCase)
+        {
+            ["Starting"] = new System.Windows.Media.SolidColorBrush(System.Windows.Media.Color.FromRgb(233, 69, 96)),
+            ["Live"] = new System.Windows.Media.SolidColorBrush(System.Windows.Media.Color.FromRgb(34, 197, 94)),
+            ["BRB"] = new System.Windows.Media.SolidColorBrush(System.Windows.Media.Color.FromRgb(234, 179, 8)),
+            ["Chat"] = new System.Windows.Media.SolidColorBrush(System.Windows.Media.Color.FromRgb(59, 130, 246)),
+            ["Ending"] = new System.Windows.Media.SolidColorBrush(System.Windows.Media.Color.FromRgb(168, 85, 247)),
+        };
+        var brush = colors.TryGetValue(sceneName, out var c) ? c
+            : new System.Windows.Media.SolidColorBrush(System.Windows.Media.Color.FromRgb(60, 60, 80));
+        var dv = new System.Windows.Media.DrawingVisual();
+        using (var ctx = dv.RenderOpen())
+        {
+            ctx.DrawRectangle(brush, null, new System.Windows.Rect(0, 0, 320, 180));
+            var ft = new System.Windows.Media.FormattedText(
+                sceneName,
+                System.Globalization.CultureInfo.InvariantCulture,
+                System.Windows.FlowDirection.LeftToRight,
+                new System.Windows.Media.Typeface("Segoe UI"),
+                18,
+                System.Windows.Media.Brushes.White,
+                96);
+            ctx.DrawText(ft, new System.Windows.Point(160 - ft.Width / 2, 90 - ft.Height / 2));
+        }
+        var rtb = new System.Windows.Media.Imaging.RenderTargetBitmap(
+            320, 180, 96, 96, System.Windows.Media.PixelFormats.Pbgra32);
+        rtb.Render(dv);
+        rtb.Freeze();
+        return rtb;
+    }
+
+    // ─── Screen background capture (live desktop/game) ───
+
+    private const string MonitorKeyPrefix = "monitor:";
+
+    /// <summary>Every background-enabled scene has exactly one background, kept at index 0 (bottom layer).
+    /// Returns null for a scene with <see cref="Scene.HasBackground"/> = false.</summary>
+    internal static Source? EnsureBackground(Scene scene)
+    {
+        if (!scene.HasBackground) return null;
+        var background = scene.Elements.OfType<Source>().FirstOrDefault(s => s.IsBackground);
+        if (background != null) return background;
+
+        background = CreateBackground(scene.Name);
+        scene.Elements.Insert(0, background);
+        return background;
+    }
+
+    /// <summary>The one Background row for a scene. Live gets the capture flavor
+    /// (Show Desktop / monitor switch / fullscreen-game detect) falling back to
+    /// live-background.jpg; every other screen is a static default-art layer.
+    /// Both are named "Background" — the user never sees capture jargon here.</summary>
+    internal static Source CreateBackground(string sceneName)
+    {
+        var isLive = SceneCatalog.Is(sceneName, SceneCatalog.Live);
+        return new Source
+        {
+            Name = "Background",
+            Type = isLive ? SourceType.DisplayCapture : SourceType.Background,
+            IsBackground = true,
+            IsEnabled = true,
+            X = 0,
+            Y = 0,
+            Width = MasterFrameWidth,
+            Height = MasterFrameHeight,
+        };
+    }
+
+    /// <summary>Heals any loaded layout to the locked Background model: exactly
+    /// one Background per canonical scene, correct flavor for the scene (static
+    /// art everywhere, DisplayCapture on Live only), at index 0, named
+    /// "Background". Duplicates and stale rows are dropped; missing ones seeded;
+    /// non-canonical scenes get HasBackground=false and lose any backgrounds.</summary>
+    internal static void NormalizeBackgrounds(IEnumerable<Scene> scenes)
+    {
+        foreach (var scene in scenes)
+        {
+            if (!SceneCatalog.HasBackground(scene.Name))
+            {
+                scene.HasBackground = false;
+                foreach (var stale in scene.Elements.OfType<Source>().Where(s => s.IsBackground).ToList())
+                    scene.Elements.Remove(stale);
+                continue;
+            }
+
+            scene.HasBackground = true;
+            var isLive = SceneCatalog.Is(scene.Name, SceneCatalog.Live);
+            var wantedType = isLive ? SourceType.DisplayCapture : SourceType.Background;
+
+            var candidates = scene.Elements.OfType<Source>().Where(s => s.IsBackground).ToList();
+            var keep = candidates.FirstOrDefault(b => b.Type == wantedType) ?? candidates.FirstOrDefault();
+
+            foreach (var extra in candidates.Where(b => !ReferenceEquals(b, keep)))
+                scene.Elements.Remove(extra);
+
+            if (keep == null)
+            {
+                keep = CreateBackground(scene.Name);
+                scene.Elements.Insert(0, keep);
+            }
+
+            // Source.Type's setter derives IsBackground from the enum, so a
+            // flavor correction must re-assert the flag afterwards.
+            if (keep.Type != wantedType)
+            {
+                keep.Type = wantedType;
+                keep.IsBackground = true;
+            }
+
+            keep.Name = "Background";
+            keep.IsEnabled = true;
+
+            var index = scene.Elements.IndexOf(keep);
+            if (index > 0)
+                scene.Elements.Move(index, 0);
+        }
+    }
+
+    // Only the Live screen's background is a real-time surface. Every other
+    // lookup below (auto-capture, focus hooks, refresh) must ignore the static
+    // default-art rows so they can never start a desktop capture session.
+    private IEnumerable<Source> AllBackgrounds()
+        => Scenes.Where(s => SceneCatalog.Is(s.Name, SceneCatalog.Live))
+            .SelectMany(s => s.Elements.OfType<Source>().Where(x => x.IsBackground));
+
+    // Full-screen game on its monitor, else null (static bg fallback — no
+    // infinity mirror). Called at launch (from ReacquireScreenCaptures, before
+    // the window steals focus) and on focus regain (RefreshBackgroundAutoCapture).
+    // When a background has ShowDesktop=true, returns the primary monitor instead
+    // of null so the desktop is always visible.
+    private string? ResolveAutoCaptureKey()
+    {
+        var gameMonitor = _fullScreenDetector.GetForegroundFullScreenMonitorIndex();
+        if (gameMonitor != null)
+            return $"{MonitorKeyPrefix}{gameMonitor}";
+
+        if (AllBackgrounds().Any(b => b.ShowDesktop))
+            return $"{MonitorKeyPrefix}{_fullScreenDetector.PrimaryMonitorIndex()}";
+        return null;
+    }
+
+    // After a layout load / file open: make sure every background-enabled scene
+    // has a background, give any background without a persisted key the auto-detected
+    // one, then acquire one capture per unique background key. ScreenCaptureManager
+    // refcounts by key, so every scene pointing at the same monitor shares one
+    // session. Captures no longer referenced by any scene are released.
+    private void ReacquireScreenCaptures()
+    {
+        HealBackgrounds();
+
+        var auto = ResolveAutoCaptureKey();
+        if (auto == null)
+        {
+            foreach (var background in AllBackgrounds())
+                background.CaptureKey = null;
+        }
+        else
+        {
+            foreach (var background in AllBackgrounds())
+                if (string.IsNullOrWhiteSpace(background.CaptureKey))
+                    background.CaptureKey = auto;
+        }
+
+        var keys = AllBackgrounds()
+            .Select(b => b.CaptureKey!)
+            .Where(k => !string.IsNullOrWhiteSpace(k))
+            .ToHashSet();
+
+        // A layout reload replaces the scenes; stop captures that are no longer
+        // referenced (mirrors ReacquireWebcam's device swap).
+        foreach (var stale in _liveCaptureKeys.Except(keys))
+            _ = _screenCaptureManager.ReleaseAllAsync(stale);
+        _liveCaptureKeys = keys;
+
+        foreach (var key in keys)
+            _ = _screenCaptureManager.AcquireAsync(key);
+
+        _fullScreenDetector.StartWatching();
+    }
+
+    // ScreenCaptureManager creates the shared WriteableBitmap on the UI thread;
+    // every background pointing at that key picks it up.
+    private void OnScreenPreviewBitmapChanged(string key, WriteableBitmap bitmap)
+    {
+        var activeBackground = StagedScene?.Elements.OfType<Source>().FirstOrDefault(s => s.IsBackground);
+        if (activeBackground?.CaptureKey == key)
+            BackgroundImage = bitmap;
+
+        foreach (var background in AllBackgrounds().Where(b => b.CaptureKey == key))
+            background.VideoImageSource = bitmap;
+    }
+
+    // EVENT_SYSTEM_FOREGROUND fires whenever the foreground window changes.
+    // When a full-screen game appears on a different monitor than the current
+    // background, auto-redesignate. When ShowDesktop is enabled and no fullscreen
+    // game is detected, fall back to the primary monitor (desktop view).
+    private void OnFullscreenMonitorChanged(int? monitor)
+    {
+        if (monitor != null)
+        {
+            var newKey = $"{MonitorKeyPrefix}{monitor}";
+            var current = AllBackgrounds().FirstOrDefault();
+            if (current?.CaptureKey == newKey) return;
+            _ = RedesignateBackgroundAsync(newKey);
+        }
+        else if (AllBackgrounds().Any(b => b.ShowDesktop))
+        {
+            var desktopKey = $"{MonitorKeyPrefix}{_fullScreenDetector.PrimaryMonitorIndex()}";
+            var current = AllBackgrounds().FirstOrDefault();
+            if (current?.CaptureKey == desktopKey) return;
+            _ = RedesignateBackgroundAsync(desktopKey);
+        }
+    }
+
+    // Manual refresh: the "Refresh Capture" context menu item. Reads the
+    // current foreground directly (no caching needed — the hook handles
+    // automatic detection).
+    public void RefreshBackgroundAutoCapture()
+    {
+        var detected = _fullScreenDetector.GetForegroundFullScreenMonitorIndex();
+        if (detected == null) return;
+        _ = RedesignateBackgroundAsync($"{MonitorKeyPrefix}{detected}");
+    }
+
+    /// <summary>Whether the active background is in Show Desktop mode.
+    /// Bindable IsChecked property for the context menu toggle.</summary>
+    public bool BackgroundShowDesktop
+    {
+        get => StagedScene?.Elements.OfType<Source>().FirstOrDefault(s => s.IsBackground)?.ShowDesktop ?? false;
+        set
+        {
+            var background = StagedScene?.Elements.OfType<Source>().FirstOrDefault(s => s.IsBackground);
+            if (background == null || background.ShowDesktop == value) return;
+            background.ShowDesktop = value;
+            OnPropertyChanged(nameof(BackgroundShowDesktop));
+            ScheduleSave();
+            if (value)
+            {
+                _ = RedesignateBackgroundAsync($"{MonitorKeyPrefix}{_fullScreenDetector.PrimaryMonitorIndex()}");
+            }
+            else
+            {
+                var gameMonitor = _fullScreenDetector.GetForegroundFullScreenMonitorIndex();
+                if (gameMonitor != null)
+                    _ = RedesignateBackgroundAsync($"{MonitorKeyPrefix}{gameMonitor}");
+                else
+                    _ = ClearBackgroundCaptureAsync();
+            }
+        }
+    }
+
+    private void ToggleBackgroundShowDesktop() => BackgroundShowDesktop = !BackgroundShowDesktop;
+
+    private void BrowseBackground()
+    {
+        var scene = StagedScene;
+        if (scene == null) return;
+        var bg = scene.Elements.OfType<Source>().FirstOrDefault(s => s.IsBackground);
+        if (bg == null) return;
+
+        var dlg = new Microsoft.Win32.OpenFileDialog
+        {
+            Title = "Select background image",
+            Filter = "Image files (*.jpg;*.jpeg;*.png;*.bmp)|*.jpg;*.jpeg;*.png;*.bmp|All files (*.*)|*.*",
+        };
+        if (dlg.ShowDialog() != true) return;
+
+        bg.CustomBackgroundPath = dlg.FileName;
+        bg.UseDefaultBackground = false;
+        try
+        {
+            using var fs = new System.IO.FileStream(dlg.FileName, System.IO.FileMode.Open, System.IO.FileAccess.Read);
+            var bytes = new byte[fs.Length];
+            fs.Read(bytes, 0, bytes.Length);
+            var assetId = AddAsset(bytes);
+            if (assetId != null)
+                bg.AssetId = assetId;
+        }
+        catch { /* non-critical */ }
+
+        UpdateActiveBackground();
+        RefreshSnapshotsAsync();
+        ScheduleSave();
+    }
+
+    /// <summary>Release the background capture so the static placeholder image shows.</summary>
+    private async Task ClearBackgroundCaptureAsync()
+    {
+        var oldKeys = AllBackgrounds()
+            .Select(b => b.CaptureKey!)
+            .Where(k => !string.IsNullOrWhiteSpace(k))
+            .ToHashSet();
+
+        foreach (var background in AllBackgrounds())
+        {
+            background.CaptureKey = null;
+            background.VideoImageSource = null;
+        }
+
+        foreach (var key in oldKeys)
+            await _screenCaptureManager.ReleaseAllAsync(key);
+
+        _liveCaptureKeys.Clear();
+        UpdateBackgroundImage();
+        ScheduleSave();
+    }
+
+    private async Task RedesignateBackgroundAsync(string newKey)
+    {
+        var oldKeys = AllBackgrounds()
+            .Select(b => b.CaptureKey!)
+            .Where(k => !string.IsNullOrWhiteSpace(k))
+            .ToHashSet();
+
+        foreach (var background in AllBackgrounds())
+            background.CaptureKey = newKey;
+
+        foreach (var oldKey in oldKeys.Where(k => k != newKey))
+            await _screenCaptureManager.ReleaseAllAsync(oldKey);
+        if (!oldKeys.Contains(newKey))
+            await _screenCaptureManager.AcquireAsync(newKey);
+        _liveCaptureKeys = new HashSet<string> { newKey };
+        UpdateBackgroundImage();
+        ScheduleSave();
+    }
+
+    // "Change Capture…": the OS GraphicsCapturePicker designates the target.
+    // Picks are transient (see ScreenCaptureSourceFactory) — a reload falls
+    // back to auto-detection.
+    public async Task ChangeBackgroundCaptureAsync()
+    {
+        var key = await _screenCaptureFactory.PickAsync();
+        if (key == null) return;
+        await RedesignateBackgroundAsync(key);
+    }
+
+    // In-app display picker: point every background at a specific monitor.
+    private void SetBackgroundCapture(DisplayInfo? display)
+    {
+        if (display == null) return;
+        _ = RedesignateBackgroundAsync($"{MonitorKeyPrefix}{display.Index}");
+    }
+
+    // ─── Background model (TASK 25): exactly ONE Background per screen, index 0,
+    // never removable or re-addable. Static default art on Starting/BRB/Chat/Ending;
+    // on Live it's the capture-flavored row (Show Desktop / monitor switch /
+    // fullscreen-game detect) falling back to live-background.jpg. ───
+
+    private static string? DefaultBackgroundAsset(string sceneName) => sceneName switch
+    {
+        SceneCatalog.Starting => "starting-background.jpg",
+        SceneCatalog.Brb => "brb-background.jpg",
+        SceneCatalog.Chat => "chat-background.jpg",
+        SceneCatalog.Ending => "ending-background.jpg",
+        SceneCatalog.Live => "live-background.jpg",
+        _ => null,
+    };
+
+    /// <summary>Heals every scene to the locked Background model after a layout
+    /// load: keeps the correct flavor per scene at index 0 named "Background",
+    /// drops duplicates/stale rows, re-seeds missing ones.</summary>
+    private void HealBackgrounds()
+    {
+        NormalizeBackgrounds(Scenes);
+        foreach (var scene in Scenes)
+        {
+            var background = scene.Elements.OfType<Source>().FirstOrDefault(s => s.IsBackground);
+            if (background != null)
+                StampDefaultBackgroundAsset(background, scene.Name);
+        }
+        OnPropertyChanged(nameof(ShowSourcesEmptyHint));
+    }
+
+    /// <summary>Points a background row at its scene's shipped default art when it
+    /// carries none. A custom image (Browse…) always wins and is never overwritten.</summary>
+    private void StampDefaultBackgroundAsset(Source background, string sceneName)
+    {
+        if (!string.IsNullOrWhiteSpace(background.AssetId)) return;
+        if (!background.UseDefaultBackground && !string.IsNullOrWhiteSpace(background.CustomBackgroundPath)) return;
+        var asset = DefaultBackgroundAsset(sceneName);
+        if (asset == null) return;
+
+        try
+        {
+            var uri = new Uri($"pack://application:,,,/Assets/{asset}", UriKind.Absolute);
+            using var stream = Application.GetResourceStream(uri)?.Stream;
+            if (stream == null) return;
+            using var ms = new MemoryStream();
+            stream.CopyTo(ms);
+            background.AssetId = AddAsset(ms.ToArray());
+        }
+        catch { /* non-critical — the app works without default art */ }
+    }
+}

ViewModels/MainViewModel.License.cs

@@ -0,0 +1,162 @@
+using ytLive.Helpers;
+using ytLive.Services;
+
+namespace ytLive.ViewModels;
+
+public partial class MainViewModel
+{
+    // TASK 10 — Polar license validation
+    private string _licenseKey = string.Empty;
+    private string _licenseMessage = string.Empty;
+    private bool _isLicenseValidating;
+    private bool _isLicenseEntryOpen;
+    private static readonly TimeSpan OfflineGracePeriod = TimeSpan.FromDays(14);
+
+    /// <summary>True when the user holds a valid LlamaCasty license (Polar). When
+    /// false, the branding flash runs on every live stream.</summary>
+    private bool _isPremium;
+    public bool IsPremium
+    {
+        get => _isPremium;
+        private set
+        {
+            if (!SetProperty(ref _isPremium, value)) return;
+            // Flip the branding flash when premium state changes.
+            BrandFlashEnabled = !value;
+        }
+    }
+
+    // TASK 10 — license key entry
+    public string LicenseKey
+    {
+        get => _licenseKey;
+        set => SetProperty(ref _licenseKey, value);
+    }
+
+    public string LicenseMessage
+    {
+        get => _licenseMessage;
+        private set => SetProperty(ref _licenseMessage, value);
+    }
+
+    public bool IsLicenseValidating
+    {
+        get => _isLicenseValidating;
+        private set => SetProperty(ref _isLicenseValidating, value);
+    }
+
+    public bool IsLicenseEntryOpen
+    {
+        get => _isLicenseEntryOpen;
+        set
+        {
+            if (SetProperty(ref _isLicenseEntryOpen, value))
+                OnPropertyChanged(nameof(IsHubVisible));
+        }
+    }
+
+    /// <summary>The About hub is visible only when neither the licenses panel
+    /// nor the license entry panel is open.</summary>
+    public bool IsHubVisible => !IsLicensesOpen && !IsLicenseEntryOpen;
+
+    // ─── TASK 10 — Polar license validation ───
+
+    /// <summary>At startup, load the cached license state and re-validate online
+    /// if a key exists. If offline and within the 14-day grace period, the cached
+    /// premium state is trusted. If the grace period is exceeded, premium lapses.</summary>
+    private async Task ValidateLicenseAtStartupAsync()
+    {
+        var savedKey = _layoutStore.LoadLicenseKey();
+        if (string.IsNullOrWhiteSpace(savedKey))
+        {
+            IsPremium = false;
+            return;
+        }
+
+        LicenseKey = savedKey;
+        var validatedAt = _layoutStore.LoadLicenseValidatedAt();
+        var cachedPremium = _layoutStore.LoadIsPremium();
+
+        // If the last validation was within the grace period, trust the cache
+        // while we attempt an online re-validation in the background.
+        if (validatedAt.HasValue && DateTime.UtcNow - validatedAt.Value < OfflineGracePeriod)
+        {
+            IsPremium = cachedPremium;
+        }
+
+        // Try an online check — if it succeeds, it overrides the cache.
+        try
+        {
+            var service = new PolarLicenseService();
+            var result = await service.ValidateAsync(savedKey);
+            if (result.IsValid)
+            {
+                IsPremium = true;
+                _layoutStore.SaveIsPremium(true);
+                _layoutStore.SaveLicenseValidatedAt(DateTime.UtcNow);
+            }
+            else
+            {
+                // Key revoked or expired — clear premium.
+                IsPremium = false;
+                _layoutStore.SaveIsPremium(false);
+                _layoutStore.SaveLicenseValidatedAt(DateTime.UtcNow);
+                AppLog.Write($"License validation failed: {result.Error}");
+                _notifications.Warning("Premium is no longer active",
+                    $"{result.Error} — watermark branding returns until the license is renewed.");
+            }
+        }
+        catch (Exception ex)
+        {
+            // Offline or network error — keep the cached state, log it.
+            AppLog.Write($"License re-validation skipped (offline?): {ex.Message}");
+            if (!validatedAt.HasValue || DateTime.UtcNow - validatedAt.Value >= OfflineGracePeriod)
+            {
+                IsPremium = false;
+                _layoutStore.SaveIsPremium(false);
+            }
+        }
+    }
+
+    /// <summary>Called from the Activate button in the About overlay. Validates
+    /// the entered key, persists it, and flips premium state.</summary>
+    private async Task ActivateLicenseAsync()
+    {
+        if (string.IsNullOrWhiteSpace(LicenseKey)) return;
+
+        IsLicenseValidating = true;
+        LicenseMessage = "Validating\u2026";
+
+        try
+        {
+            var service = new PolarLicenseService();
+            var result = await service.ValidateAsync(LicenseKey);
+            if (result.IsValid)
+            {
+                IsPremium = true;
+                _layoutStore.SaveLicenseKey(LicenseKey.Trim());
+                _layoutStore.SaveIsPremium(true);
+                _layoutStore.SaveLicenseValidatedAt(DateTime.UtcNow);
+                LicenseMessage = "Premium activated! The watermark has been removed.";
+                AppLog.Write("License activated successfully");
+            }
+            else
+            {
+                IsPremium = false;
+                _layoutStore.SaveLicenseKey(null);
+                _layoutStore.SaveIsPremium(false);
+                LicenseMessage = result.Error ?? "Invalid license key.";
+                AppLog.Write($"License activation failed: {result.Error}");
+            }
+        }
+        catch (Exception ex)
+        {
+            LicenseMessage = $"Activation error: {ex.Message}";
+            AppLog.Write($"License activation error: {ex}");
+        }
+        finally
+        {
+            IsLicenseValidating = false;
+        }
+    }
+}

ViewModels/MainViewModel.Scenes.cs

@@ -0,0 +1,273 @@
+using System.Collections.ObjectModel;
+using System.Collections.Specialized;
+using System.ComponentModel;
+using System.Windows;
+using ytLive;
+using ytLive.Models;
+using ytLive.Services;
+
+namespace ytLive.ViewModels;
+
+public partial class MainViewModel
+{
+    private Scene? _stagedScene;
+    private Scene? _liveScene;
+
+    // TASK 20 step 2 — hotkey bindings (custom chord per action)
+    private Dictionary<HotkeyId, HotkeyChord> _hotkeyBindings = new();
+
+    public ObservableCollection<Scene> Scenes { get; } = new();
+
+    public Scene? StagedScene
+    {
+        get => _stagedScene;
+        set
+        {
+            if (value != null && value.IsHidden) return;
+            if (SetProperty(ref _stagedScene, value))
+            {
+                // Update IsStaged flags for thumbnail glow
+                foreach (var s in Scenes)
+                    s.IsStaged = s == value;
+
+                SelectedElement = null;
+                if (value != null)
+                {
+                    var background = EnsureBackground(value);
+                    if (background != null)
+                        StampDefaultBackgroundAsset(background, value.Name);
+                }
+                OnPropertyChanged(nameof(ShowChatInactiveMessage));
+                OnPropertyChanged(nameof(ShowEmptySceneHint));
+                OnPropertyChanged(nameof(ShowPreviewPlaceholder));
+                OnPropertyChanged(nameof(ShowSourcesEmptyHint));
+                OnPropertyChanged(nameof(CanChangeBackground));
+                OnPropertyChanged(nameof(CanAddWebcam));
+                OnPropertyChanged(nameof(CanAddYouTubeChat));
+                OnPropertyChanged(nameof(CanShowWebcamInStagedScene));
+                OnPropertyChanged(nameof(IsCountdownAvailable));
+                UpdateActiveBackground();
+                UpdateBackgroundImage();
+                RefreshSnapshotsAsync();
+            }
+        }
+    }
+
+    /// <summary>The scene the encoder outputs. Set on Go Live (StagedScene → LiveScene)
+    /// or on transition completion. FramePump reads this every tick.</summary>
+    public Scene? LiveScene
+    {
+        get => _liveScene;
+        set
+        {
+            if (SetProperty(ref _liveScene, value))
+            {
+                foreach (var s in Scenes)
+                    s.IsLive = s == value;
+            }
+        }
+    }
+
+    /// <summary>True when offline — edit mode is available. When live/recording,
+    /// all edit operations are locked out (gun safety).</summary>
+    public bool IsEditMode => StreamStatus == StreamStatus.Offline && !IsRecording;
+
+    // ─── Transitions (TASK 19/23) ───
+
+    public TransitionType SelectedTransitionType
+    {
+        get => _selectedTransitionType;
+        set => SetProperty(ref _selectedTransitionType, value);
+    }
+    private TransitionType _selectedTransitionType = TransitionType.Fade;
+
+    public double TransitionDurationMs
+    {
+        get => _transitionDurationMs;
+        set => SetProperty(ref _transitionDurationMs, value);
+    }
+    private double _transitionDurationMs = 300;
+
+    /// <summary>
+    /// Called when a scene thumbnail is clicked. If live, triggers a transition from
+    /// LiveScene to the selected StagedScene. Always sets StagedScene first.
+    /// </summary>
+    public void TransitionToScene(Scene scene)
+    {
+        if (scene.IsHidden || scene == StagedScene) return;
+        StagedScene = scene;
+        if (IsLive)
+            _transition.Start(SelectedTransitionType, TransitionDurationMs, null);
+    }
+
+    /// <summary>
+    /// Apply the current transition type to the next StagedScene change while live.
+    /// Called from XAML when user picks a transition from the dropdown.
+    /// </summary>
+    public void ApplyTransitionToLive()
+    {
+        if (IsLive)
+            _transition.Start(SelectedTransitionType, TransitionDurationMs, null);
+    }
+
+    // ─── Global hotkeys (TASK 20) — dispatch a registered hotkey to its action ───
+
+    /// <summary>
+    /// Callback set by MainWindow so the VM can trigger hotkey re-registration
+    /// after the user saves custom bindings from the config dialog.
+    /// </summary>
+    public Action<Dictionary<HotkeyId, HotkeyChord>>? HotkeyBindingsChanged { get; set; }
+
+    /// <summary>The current hotkey bindings (loaded from DB, updated on dialog save).</summary>
+    public Dictionary<HotkeyId, HotkeyChord> CurrentHotkeyBindings => _hotkeyBindings;
+
+    public void HandleHotkey(Services.HotkeyId id)
+    {
+        switch (id)
+        {
+            case Services.HotkeyId.SceneStarting: TransitionToCanonical(SceneCatalog.Starting); break;
+            case Services.HotkeyId.SceneLive: TransitionToCanonical(SceneCatalog.Live); break;
+            case Services.HotkeyId.SceneBrb: TransitionToCanonical(SceneCatalog.Brb); break;
+            case Services.HotkeyId.SceneChat: TransitionToCanonical(SceneCatalog.Chat); break;
+            case Services.HotkeyId.SceneEnding: TransitionToCanonical(SceneCatalog.Ending); break;
+            case Services.HotkeyId.StartStopStream:
+                if (IsLive || IsRecording)
+                {
+                    if (EndStreamCommand.CanExecute(null)) EndStreamCommand.Execute(null);
+                }
+                else if (StartStreamCommand.CanExecute(null))
+                {
+                    StartStreamCommand.Execute(null);
+                }
+                break;
+            case Services.HotkeyId.ToggleMicMute: ToggleMicMuteCommand.Execute(null); break;
+            case Services.HotkeyId.ToggleGameMute: ToggleGameMuteCommand.Execute(null); break;
+            case Services.HotkeyId.TraxPlayPause: TraxLeftClick(); break;
+        }
+    }
+
+    private void TransitionToCanonical(string name)
+    {
+        var scene = Scenes.FirstOrDefault(s => SceneCatalog.Is(s.Name, name));
+        if (scene != null) TransitionToScene(scene);
+    }
+
+    private void OpenHotkeyConfig()
+    {
+        var vm = new HotkeyConfigViewModel(_layoutStore);
+        var dialog = new HotkeyConfigDialog(vm) { Owner = Application.Current.MainWindow };
+        if (dialog.ShowDialog() == true)
+        {
+            // Reload bindings from DB (the dialog already saved them).
+            _hotkeyBindings = _layoutStore.LoadHotkeyBindings();
+            HotkeyBindingsChanged?.Invoke(_hotkeyBindings);
+            RefreshHotkeyLabels();
+        }
+    }
+
+    private void RefreshHotkeyLabels()
+    {
+        foreach (var scene in Scenes)
+        {
+            if (SceneCatalog.SceneHotkeys.TryGetValue(scene.Name, out var hid)
+                && _hotkeyBindings.TryGetValue(hid, out var chord))
+                scene.HotkeyLabel = chord.ToDisplayString();
+            else if (SceneCatalog.SceneHotkeys.TryGetValue(scene.Name, out var defId)
+                     && GlobalHotkeyManager.Defaults.TryGetValue(defId, out var defChord))
+                scene.HotkeyLabel = defChord.ToDisplayString();
+            else
+                scene.HotkeyLabel = string.Empty;
+        }
+    }
+
+    public bool ShowEmptySceneHint => StagedScene != null && StagedScene.Elements.Count == 0;
+    public bool ShowSourcesEmptyHint => StagedScene == null || StagedScene.Elements.Count == 0;
+
+    public bool IsCountdownAvailable => StagedScene != null
+        && (SceneCatalog.Is(StagedScene.Name, "Starting") || SceneCatalog.Is(StagedScene.Name, "BRB"));
+
+    /// <summary>The canonical scenes (SceneCatalog) not present right now — what the
+    /// "+" button may re-add. Work with less, never more.</summary>
+    public IEnumerable<string> MissingScenes
+        => SceneCatalog.All.Where(canonical => Scenes.All(s => !SceneCatalog.Is(s.Name, canonical)));
+
+    /// <summary>Only show the "+" button when one of the five canonical scenes is missing.</summary>
+    public bool ShowAddScene => MissingScenes.Any();
+
+    /// <summary>"Change Capture…"/"Refresh Capture" apply to the active scene's background.</summary>
+    // Capture controls (Show Desktop / monitor pick / refresh) exist only on
+    // the Live screen's Background. Static-art screens never expose them.
+    public bool CanChangeBackground =>
+        StagedScene != null && SceneCatalog.Is(StagedScene.Name, SceneCatalog.Live);
+
+    // ─── Auto-save wiring ───
+    private void OnScenesChanged(object? sender, NotifyCollectionChangedEventArgs e)
+    {
+        if (e.NewItems != null)
+            foreach (Scene scene in e.NewItems)
+                WireScene(scene);
+        if (e.OldItems != null)
+            foreach (Scene scene in e.OldItems)
+                UnwireScene(scene);
+        OnPropertyChanged(nameof(MissingScenes));
+        OnPropertyChanged(nameof(ShowAddScene));
+        ScheduleSave();
+    }
+
+    private void WireScene(Scene scene)
+    {
+        scene.PropertyChanged += OnScenePropertyChanged;
+        scene.Elements.CollectionChanged += OnElementsChanged;
+    }
+
+    private void UnwireScene(Scene scene)
+    {
+        scene.PropertyChanged -= OnScenePropertyChanged;
+        scene.Elements.CollectionChanged -= OnElementsChanged;
+    }
+
+    private void OnScenePropertyChanged(object? sender, PropertyChangedEventArgs e)
+    {
+        // A rename can drop a canonical scene in/out of MissingScenes.
+        OnPropertyChanged(nameof(MissingScenes));
+        OnPropertyChanged(nameof(ShowAddScene));
+        ScheduleSave();
+    }
+
+    private void OnElementsChanged(object? sender, NotifyCollectionChangedEventArgs e)
+    {
+        if (e.NewItems != null)
+            foreach (SceneElement element in e.NewItems)
+                element.PropertyChanged += OnElementPropertyChanged;
+        if (e.OldItems != null)
+            foreach (SceneElement element in e.OldItems)
+                element.PropertyChanged -= OnElementPropertyChanged;
+        OnPropertyChanged(nameof(CanAddWebcam));
+        OnPropertyChanged(nameof(CanAddYouTubeChat));
+        ScheduleSave();
+    }
+
+    private void OnElementPropertyChanged(object? sender, PropertyChangedEventArgs e)
+    {
+        if (sender is WebcamSceneConfig && e.PropertyName == nameof(SceneElement.IsVisible))
+            OnPropertyChanged(nameof(CanShowWebcamInStagedScene));
+        ScheduleSave();
+    }
+
+    // Adds a canonical scene by name — only when it's actually missing. The
+    // background flag follows the policy (Live yes, everyone else no).
+    private void AddScene(string name)
+    {
+        if (!SceneCatalog.IsCanonical(name)) return;
+        if (Scenes.Any(s => SceneCatalog.Is(s.Name, name))) return;
+        var scene = new Scene
+        {
+            Name = name.Trim(),
+            IsChatScene = SceneCatalog.IsChat(name),
+            HasBackground = SceneCatalog.HasBackground(name),
+        };
+        EnsureBackground(scene);
+        Scenes.Add(scene);
+        StagedScene = scene;
+    }
+}

ViewModels/MainViewModel.Webcam.cs

@@ -0,0 +1,269 @@
+using System.Windows;
+using System.Windows.Input;
+using System.Windows.Media.Imaging;
+using ytLive;
+using ytLive.Models;
+using ytLive.Services;
+
+namespace ytLive.ViewModels;
+
+public partial class MainViewModel
+{
+    // Webcam: one camera input app-wide. The identity (DeviceId) lives on the
+    // Webcam entity; each scene that shows the webcam has a WebcamSceneConfig
+    // (webcam.{scene}.config). CameraManager still owns the single session.
+    private readonly ICameraEnumerator _cameraEnumerator;
+    private readonly CameraManager _cameraManager;
+    private Webcam? _webcam;
+    private string? _webcamError;
+
+    /// <summary>The Add → Webcam menu item: enabled only while no webcam exists anywhere —
+    /// one camera identity app-wide; re-adding always opens the picker.</summary>
+    public bool CanAddWebcam => StagedScene != null && _webcam == null;
+
+    /// <summary>
+    /// Right-click-on-preview → "Show Webcam": offered when the active scene has no
+    /// webcam config (add one) or hides it (unhide — keeps the config row).
+    /// </summary>
+    public bool CanShowWebcamInStagedScene
+        => StagedScene is { } scene && (scene.WebcamConfig == null || !scene.WebcamConfig.IsVisible);
+
+    /// <summary>Swap-the-device item: enabled once a camera has been picked at all.</summary>
+    public bool CanChangeWebcam => _webcam != null;
+
+    /// <summary>Shows the mirror / clip-shape row in the source chip when a webcam is selected.</summary>
+    public bool IsWebcamSelected => SelectedElement is WebcamSceneConfig;
+
+    /// <summary>
+    /// The reason the webcam feed is down (device in use, offline, locked, no frames),
+    /// or null when it's alive. Surfaced as a red chip so a dead camera is never a
+    /// silent empty box. Cleared the moment a real frame arrives.
+    /// </summary>
+    public string? WebcamError
+    {
+        get => _webcamError;
+        private set => SetProperty(ref _webcamError, value);
+    }
+
+    // Webcam size safeguard: no more than half the frame in any dimension
+    // (960x540 over the 1920x1080 master), and no less than 10% of it
+    // (192x108). Enforced at resize and on layout load. The Chat scene is
+    // exempt from the per-dimension half — its webcam may take half the
+    // screen AREA (~1358x764 @16:9) so the viewer sees the creator better,
+    // matched by canonical name (SceneCatalog.IsChat).
+    public const double WebcamMaxWidth = 960;
+    public const double WebcamMaxHeight = 540;
+    public const double WebcamChatMaxWidth = 1358;
+    public const double WebcamChatMaxHeight = 764;
+    public const double WebcamMinWidth = MasterFrameWidth * 0.1;
+    public const double WebcamMinHeight = MasterFrameHeight * 0.1;
+
+    public static double MaxWebcamWidthFor(string? sceneName)
+        => SceneCatalog.IsChat(sceneName) ? WebcamChatMaxWidth : WebcamMaxWidth;
+
+    public static double MaxWebcamHeightFor(string? sceneName)
+        => SceneCatalog.IsChat(sceneName) ? WebcamChatMaxHeight : WebcamMaxHeight;
+
+    internal static void ClampWebcamToBounds(WebcamSceneConfig config, string? sceneName)
+    {
+        var maxWidth = MaxWebcamWidthFor(sceneName);
+        var maxHeight = MaxWebcamHeightFor(sceneName);
+        var scale = Math.Min(maxWidth / config.Width, maxHeight / config.Height);
+        if (scale < 1)
+        {
+            config.Width = Math.Round(config.Width * scale);
+            config.Height = Math.Round(config.Height * scale);
+            return;
+        }
+
+        var minScale = Math.Max(WebcamMinWidth / config.Width, WebcamMinHeight / config.Height);
+        if (minScale > 1)
+        {
+            config.Width = Math.Round(config.Width * minScale);
+            config.Height = Math.Round(config.Height * minScale);
+        }
+    }
+
+    // One-time heal for layouts saved before the rect dims were persisted (v3→v4):
+    // a Traditional webcam that ended up square (Round resize then reload lost the
+    // pre-Round rect) gets widened to 16:9, keeping the height. Round is skipped —
+    // a square bounding box is correct there — and an explicit pre-Round rect wins.
+    internal static void HealLegacySquareRect(WebcamSceneConfig config)
+    {
+        if (config.ClipShape != ClipShape.Traditional) return;
+        if (config.RectWidth != null || config.RectHeight != null) return;
+        if (Math.Abs(config.Width - config.Height) >= 1) return;
+        config.Width = Math.Round(config.Height * 16.0 / 9.0);
+    }
+
+    public ICommand AddWebcamCommand { get; }
+    public ICommand ChangeWebcamCommand { get; }
+    public ICommand ShowWebcamCommand { get; }
+
+    // After a layout load / file open: re-point the webcam identity, stop the
+    // previous device if it changed, and acquire the current one once per scene
+    // that uses it (CameraManager refcounts by DeviceId — one camera session).
+    private void ReacquireWebcam()
+    {
+        var previousDevice = _webcam?.DeviceId;
+        _webcam = _layoutStore.Webcam;
+        var newDevice = _webcam?.DeviceId;
+
+        if (!string.IsNullOrWhiteSpace(previousDevice) && previousDevice != newDevice)
+            _ = _cameraManager.ReleaseAllAsync(previousDevice);
+
+        OnPropertyChanged(nameof(CanChangeWebcam));
+        OnPropertyChanged(nameof(CanAddWebcam));
+
+        if (_webcam == null || string.IsNullOrWhiteSpace(newDevice)) return;
+        if (previousDevice != newDevice)
+            foreach (var unused in Scenes.SelectMany(s => s.Elements.OfType<WebcamSceneConfig>()))
+                _ = _cameraManager.AcquireAsync(newDevice);
+
+        // A session already running (same device, or one that produced a first
+        // frame) has its shared bitmap; freshly loaded configs must adopt it here,
+        // because PreviewBitmapChanged never re-fires for an existing bitmap.
+        if (_cameraManager.GetPreviewBitmap(newDevice) is { } running)
+            foreach (var config in Scenes.SelectMany(s => s.Elements.OfType<WebcamSceneConfig>()))
+                config.VideoImageSource = running;
+    }
+
+    // CameraManager creates the shared WriteableBitmap on the UI thread at the
+    // device's frame size; every scene's webcam config picks it up from here. A
+    // bitmap means a real frame arrived — the camera is provably alive.
+    private void OnCameraPreviewBitmapChanged(string deviceId, WriteableBitmap bitmap)
+    {
+        if (_webcam?.DeviceId != deviceId) return;
+        WebcamError = null;
+        foreach (var scene in Scenes)
+            foreach (var config in scene.Elements.OfType<WebcamSceneConfig>())
+                config.VideoImageSource = bitmap;
+    }
+
+    // The camera failed to start or died asynchronously (in use, offline, locked,
+    // no frames within the proof timeout) — surface it instead of a silent box.
+    private void OnCameraFailed(string deviceId, string message)
+    {
+        if (_webcam?.DeviceId != deviceId) return;
+        WebcamError = $"Webcam offline: {message}";
+    }
+
+    // Adds the webcam to the active scene. The creator ALWAYS picks from the
+    // cameras Windows has registered — never silently resurrects the previous
+    // camera (which is what happened after deleting one scene's webcam while
+    // another scene still used it). Picking a different camera than the current
+    // app-wide one swaps it everywhere, so the single-identity model stays honest;
+    // each scene's placement config is independent (webcam.{scene}.config).
+    private async Task AddWebcamToStagedSceneAsync()
+    {
+        var scene = StagedScene;
+        if (scene == null || scene.WebcamConfig != null) return;
+
+        var dialog = new CameraPickerDialog(new CameraPickerViewModel(_cameraEnumerator))
+        {
+            Owner = Application.Current.MainWindow
+        };
+        if (dialog.ShowDialog() != true || dialog.PickedDevice == null) return;
+        var device = dialog.PickedDevice;
+
+        if (_webcam == null)
+        {
+            _webcam = new Webcam { DeviceId = device.Id, Name = device.DisplayName };
+            OnPropertyChanged(nameof(CanChangeWebcam));
+            OnPropertyChanged(nameof(CanAddWebcam));
+        }
+        else if (_webcam.DeviceId != device.Id)
+        {
+            await SwapWebcamIdentityAsync(device);
+        }
+
+        var config = new WebcamSceneConfig
+        {
+            WebcamId = _webcam.Id,
+            Name = _webcam.Name,
+            Width = 480,
+            Height = 270,
+            X = MasterFrameWidth - 480 - 32,
+            Y = MasterFrameHeight - 270 - 32,
+        };
+
+        scene.Elements.Add(config);
+        SelectedElement = config;
+        OnPropertyChanged(nameof(ShowEmptySceneHint));
+        OnPropertyChanged(nameof(ShowSourcesEmptyHint));
+        UpdateActiveBackground();
+
+        // PreviewBitmapChanged fires only on the camera's first frame, so a config
+        // added while the session is already running must pick up the shared bitmap
+        // directly (it's written in place from then on).
+        if (_cameraManager.GetPreviewBitmap(_webcam.DeviceId) is { } running)
+            config.VideoImageSource = running;
+
+        var started = await _cameraManager.AcquireAsync(_webcam.DeviceId);
+        if (!started)
+        {
+            _notifications.Warning("Camera unavailable",
+                WebcamError ?? "Couldn't start that camera. It may be in use by another app, or Windows camera access may be turned off.");
+        }
+    }
+
+    // Swaps the device on the app-wide webcam identity. The old device is stopped
+    // unconditionally; each scene that uses the webcam re-acquires the new one so
+    // the per-config refcount stays honest. Only called when the device differs.
+    private async Task SwapWebcamIdentityAsync(CameraDeviceInfo device)
+    {
+        var oldDevice = _webcam!.DeviceId;
+        _webcam.DeviceId = device.Id;
+        _webcam.Name = device.DisplayName;
+        ScheduleSave();
+
+        if (!string.IsNullOrWhiteSpace(oldDevice) && oldDevice != device.Id)
+            await _cameraManager.ReleaseAllAsync(oldDevice);
+
+        foreach (var unused in Scenes.SelectMany(s => s.Elements.OfType<WebcamSceneConfig>()))
+        {
+            var started = await _cameraManager.AcquireAsync(device.Id);
+            if (!started)
+            {
+                _notifications.Warning("Camera unavailable",
+                    WebcamError ?? "Couldn't start that camera. It may be in use by another app, or Windows camera access may be turned off.");
+                break;
+            }
+        }
+    }
+
+    // "Change Webcam…" from the webcam's context menu: picker, then swap the
+    // app-wide identity if a different device was chosen.
+    private async Task ChangeWebcamAsync()
+    {
+        if (_webcam == null) return;
+
+        var dialog = new CameraPickerDialog(new CameraPickerViewModel(_cameraEnumerator))
+        {
+            Owner = Application.Current.MainWindow
+        };
+        if (dialog.ShowDialog() != true || dialog.PickedDevice == null) return;
+        if (dialog.PickedDevice.Id == _webcam.DeviceId) return;
+
+        await SwapWebcamIdentityAsync(dialog.PickedDevice);
+    }
+
+    // "Show Webcam" from a right-click on the empty preview. Unhides this scene's
+    // existing (hidden) config — the config row survives Hide in this scene — or
+    // adds the webcam here for the first time (which opens the camera picker).
+    private void ShowWebcamInStagedScene()
+    {
+        var scene = StagedScene;
+        if (scene == null) return;
+
+        var config = scene.WebcamConfig;
+        if (config != null)
+        {
+            config.IsVisible = true;
+            SelectedElement = config;
+            return;
+        }
+
+        _ = AddWebcamToStagedSceneAsync();
+    }
+}

ViewModels/index.md

@@ -18,15 +18,63 @@ for what the ViewModels drive; base class in [`Helpers/ViewModelBase.cs`](../Hel
 ## MainViewModel partial split (in progress)
 
 `MainViewModel.cs` is being split into one file per functional area, zero behavior
-change, one commit per partial (each commit a roll-back point):
+change, one commit per partial (each commit a roll-back point). **Commit naming:**
+titles carry the series id (`Commit N/12`), tags are `refactor-commit-N` — e.g.
+`git show refactor-commit-1`. Every partial lands with a `ViewModels/index.md`
+update in the SAME commit.
+
+Progress (Commit N/12 · tag):
+- **Commit 1/12 · `refactor-commit-1`: Account landed** → `MainViewModel.Account.cs`
+  (session restore `LoadSavedSessionAsync`, sign-in/out/change account,
+  `IsConnected`/`AccountAvatarUrl`/`AccountDisplayName`/`AccountStatusLightToolTip`).
+- **Commit 2/12 · `refactor-commit-2`: License landed** → `MainViewModel.License.cs`
+  (Polar license state: `LicenseKey`/`LicenseMessage`/`IsLicenseValidating`/
+  `IsLicenseEntryOpen`/`IsHubVisible`/`IsPremium`, `OfflineGracePeriod`,
+  `ValidateLicenseAtStartupAsync`, `ActivateLicenseAsync`).
+- **Commit 3/12 · `refactor-commit-3`: Scenes landed** → `MainViewModel.Scenes.cs`
+  (`Scenes` + `StagedScene`/`LiveScene`/`IsEditMode`, transitions
+  `SelectedTransitionType`/`TransitionDurationMs`/`TransitionToScene`/
+  `ApplyTransitionToLive`, global hotkeys `HandleHotkey`/`OpenHotkeyConfig`/
+  `RefreshHotkeyLabels`, scene-gating hints, `MissingScenes`/`ShowAddScene`/
+  `CanChangeBackground`, scene wiring `OnScenesChanged`/`WireScene`/`UnwireScene`,
+  `AddScene`).
+- **Commit 4/12 · `refactor-commit-4`: Background landed** → `MainViewModel.Background.cs`
+  (background model `EnsureBackground`/`CreateBackground`/`NormalizeBackgrounds`/
+  `HealBackgrounds`/`StampDefaultBackgroundAsset`, display picker `Displays` +
+  `SetBackgroundCapture`, screen capture `ReacquireScreenCaptures`/
+  `ResolveAutoCaptureKey`/`RedesignateBackgroundAsync`/`ClearBackgroundCaptureAsync`/
+  `OnScreenPreviewBitmapChanged`/`OnFullscreenMonitorChanged`/
+  `RefreshBackgroundAutoCapture`/`BackgroundShowDesktop`, preview fns
+  `ActiveBackgroundImage`/`BackgroundImage`/`UpdateActiveBackground`/
+  `UpdateBackgroundImage`/`RefreshSnapshotsAsync`/`LoadBackgroundImage`,
+  `ChangeCaptureCommand`/`RefreshCaptureCommand`/`SetBackgroundDisplayCommand`/
+  `ToggleShowDesktopCommand`/`BrowseBackgroundCommand`). `ShowPreviewPlaceholder`
+  stays in core.
+- **Commit 5/12 · `refactor-commit-5`: Webcam landed** → `MainViewModel.Webcam.cs`
+  (webcam identity `_webcam`/`ReacquireWebcam`/`SwapWebcamIdentityAsync`, per-scene
+  configs `AddWebcamToStagedSceneAsync`/`ShowWebcamInStagedScene`, capture lifetime
+  `OnCameraPreviewBitmapChanged`/`OnCameraFailed`, gating `CanAddWebcam`/
+  `CanChangeWebcam`/`CanShowWebcamInStagedScene`/`IsWebcamSelected`/`WebcamError`,
+  size safeguard `WebcamMax*`/`ClampWebcamToBounds`/`HealLegacySquareRect`,
+  `AddWebcamCommand`/`ChangeWebcamCommand`/`ShowWebcamCommand`).
+- **Commit 6/12 · `refactor-commit-6`: Audio landed** → `MainViewModel.Audio.cs`
+  (mic bar `AudioLevel`/`MeterFillWidth`/`MeterBrush`/`MicVolume`/`MicMuted`/
+  `MicMuteText`/`MicSourceName`/`ToggleMicMute`/`PickMicrophone`, volume flash
+  `SetVolumeAdjusting`/`BeginVolumeFlash`/`EndVolumeFlash`/`CancelVolumeFlash`,
+  mic status dot `MicStatus`/`MicStatusBrush`/`MicStatusToolTip`/`MicProblemBrush`,
+  game bar `GameAudioLevel`/`GameMeterLevel`/`GameMeterFillWidth`/`GameMeterBrush`/
+  `SetGameVolumeAdjusting`/`GameAudioVolume`/`GameMuted`/`GameMuteText`/
+  `ToggleGameMute`, `PushSystemVolume`, mixer handlers `OnMicLevelChanged`/
+  `OnLoopbackLevelChanged`/`OnMicConnected`/`OnMicFailed`, `StartMicCaptureAsync`,
+  audio fields + `ToggleMicMuteCommand`/`ToggleGameMuteCommand`/`OpenMicPickerCommand`).
+  TRAX stays in core (next commit).
 
 - Core file keeps: fields, ctor, `Shutdown`/`SaveLayoutNow`/`ScheduleSave`/`LoadLayout`,
   `SetPanel`/`ShowOverlay`/`ShowLicenses`, `CreateBrush`, `OpenUrl`/`ComposeEmail`,
   `SubmitBug`/`SubmitFeature`, window-geometry pass-through.
-- Partials: `Account` (sign-in/session/avatar), `License` (Polar key validation + `IsPremium`),
-  `Scenes` (scene catalog + hotkeys + transitions), `Background` (background model + screen
-  capture + display picker), `Webcam` (webcam identity + per-scene configs + captures),
-  `Audio` (mic + game bars + TRAX), `Trax` (music player), `Socials` (social bar + dialog),
+- Partials: `Account` ✔ (Commit 1), `License` ✔ (Commit 2), `Scenes` ✔ (Commit 3), `Background` ✔ (Commit 4),
+  `Webcam` ✔ (Commit 5), `Audio` ✔ (Commit 6),
+  `Trax` (music player), `Socials` (social bar + dialog),
   `Streaming` (go-live/record + health + quality tiers + media source pipeline),
   `Chat` (YouTube chat + mock preview + chatbox render), `Overlays` (settings/bug/feature/about
   panels + license entry).