feat(webcam): app-default gate slice — per-scene offer, Add places default directly, identity survives removal

Chat's camera no longer greys Web Cam in Live (per-scene max, not app-wide);
TASK 26 superseded by creator directive (app-level resource model). Add Webcam
now places the existing app default without the picker; the picker runs only
for the initial selection. Removing the last placement keeps the identity
(_webcam never nulled) so Add stays offered. Startup pass adopts a solo camera
as the app default, so a clean layout offers the layer in Live/Chat at once.
Dynamic WebcamAddToolTip names the why (incl. the 'graduated to OBS' line).

Good Dog: WebcamMenuGateTests rewritten (real app + temp DB + camera seams) —
identity in Chat does not gray Live; Add in Live places same wc-1 no picker;
scene-with-placement stays gray; identity survives both removals (DB row 1).
WebcamStartupResourceTests single-lock fact asserts CanAddWebcam after adoption.
Docs same commit (ai.md supersession, TASKS.md, HANDOFF.md). 304/304, 0 warnings.

Controls/LeftPanel.xaml

@@ -30,7 +30,7 @@
                                 <ContextMenu DataContext="{Binding PlacementTarget.DataContext, RelativeSource={RelativeSource Self}}">
                                     <MenuItem Header="Webcam" Command="{Binding AddWebcamCommand}"
                                               IsEnabled="{Binding CanAddWebcam}"
-                                              ToolTip="One webcam at a time — it's already in your stream"/>
+                                              ToolTip="{Binding WebcamAddToolTip}"/>
                                     <MenuItem Header="Image" Command="{Binding AddImageCommand}"/>
                                     <MenuItem Header="Text" Command="{Binding AddSourceCommand}" CommandParameter="{x:Static models:SourceType.TextOverlay}"/>
                                     <MenuItem Header="Countdown" Command="{Binding AddSourceCommand}" CommandParameter="{x:Static models:SourceType.Countdown}"

HANDOFF.md

@@ -1,11 +1,12 @@
-# HANDOFF — 2026-09-17 (webcam resource lifecycle, startup slice; committed locally — no push)
+# HANDOFF — 2026-09-17 (webcam app-default gate slice; committed locally — no push)
 
 ## Branch / Commit State
 
-`main` HEAD = **`94a934f` webcam reader-ladder fix** (local). This work unit sits un-pushed on top
-as a NEW commit (same bundle of web/A/V work — stays commit-local until greenlight). Below: slice-18
-C4 cache (`64a5a6d`), slice-17, slice-16, slice-15, `c01206f`, `b22d08e` (signed audio-sync, pushed).
-No push after this commit either — still awaiting the device take + user greenlight.
+`main` HEAD = **`1e4017d` webcam startup resource lifecycle** (local). The gate slice lands
+on top as a NEW commit (stays commit-local until greenlight). Below: `94a934f` (reader-ladder),
+`64a5a6d` (slice-18 C4 cache), slice-17, slice-16, slice-15, `c01206f`, `b22d08e` (signed
+audio-sync, pushed). No push after this commit either — still awaiting the device take + user
+greenlight.
 
 ## ⚠️ Branding (2026-09-14, creator-corrected): product = **llamacasty**, internals = ytLive
 
@@ -13,36 +14,48 @@ Product is **llamacasty**; repo path, csproj `AssemblyName`/`RootNamespace`, DB/
 (`%APPDATA%\ytLlive\...`), most code names are legacy **ytLive/ytLlive**. User-facing text:
 "llamacasty" / UI labels use the catalog names ("Web Cam", "YouTube Chat", "Countdown Timer"…).
 
-## ✅ Committed locally — webcam resource lifecycle (startup slice)
+## ✅ Committed — webcam app-default gate slice (creator-visible goal: Web Cam offered when switching to Live)
 
-**Incident review (the reason this exists):** the creator couldn't add a webcam to the Live scene
-(WebCam row grayed app-wide). Ground truth from `%APPDATA%\ytLlive\ytLlive.db` (NOT `layout.db`,
-which is a 0-byte legacy file): one `Webcam` identity (C920 `\?\USB#VID_046D&PID_082D…GLOBAL`) AND
-one `WebcamSceneConfig` — in the **Chat** scene. Under the single-identity rule that means Live's
-"+" menu is gray *by design*, but the app couldn't *say why*. Combined with the earlier crash/failure
-chain, the fix is a proper resource lifecycle:
+**Background:** the DB truth (`%APPDATA%\ytLlive\ytLlive.db`; NOT `layout.db`, a 0-byte legacy
+file) put the single `WebcamSceneConfig` in **Chat**, so the old TASK 26 app-wide rule grayed
+Live's "+" → Web Cam even though the camera was available and in use. The creator ruled (rigorous
+resource model): **the webcam is an app-level resource — ONE app-wide default selection, usable in
+every scene that can host it; it is NOT blocked by other scenes' placements.** Scope of this slice:
+the availability layer. TASK 26's app-wide gate is **superseded** by creator directive.
 
-- **Startup poll + tri-state** (`MainViewModel.ValidateWebcamResourceStartupAsync`, fired
-  fire-and-forget right after `LoadLayout`): 0 webcams → app runs on, layer inactive, no alarm;
-  **1 → attempt `CameraManager.AcquireAsync` as an app-wide LOCK**; **≥2 → no auto-lock** — selection
-  belongs to the App Settings dialog (gear) — that's the next slice.
-- **Persistent red alert** (`WebcamLockAlert`, bottom of the Layers panel, + Retry button): shown when
-  the one detected camera can't be locked; **re-polls every 5 s** (`_webcamLockPollTimer`) and clears
-  the moment a lock succeeds, or on any first real frame (`OnCameraPreviewBitmapChanged`).
-- **`CameraManager.IsRunning(deviceId)`** — new accessor (session exists, started OR starting) so the
-  pass never double-acquires a lock the loaded identity's configs already hold; a rolled-back (failed)
-  session leaves the dictionary, so the pass retries cleanly.
-- **Test seams mirroring `LayoutPathOverride`:** `CameraEnumeratorOverride` /
-  `CameraFrameSourceFactoryOverride` — the startup probe must NEVER touch real hardware under test
-  (the reason the 09:15 tests never asserted camera state). **Good Dog test**
-  `WebcamStartupResourceTests` x3: single-cam locked + app runs on; zero-cams no-alarm no-lock;
-  lock-fails → red alert → Retry → clears. **304/304 green, build 0 warnings.**
-- **Attribution correction committed to `ai.md`:** "NVIDIA Broadcast opens the webcam
-  exclusively" is a *suspect-list* claim — `CameraConflictProbe` reads running process NAMES only, no
-  device handles; the contention symptoms fit shared-mode/bandwidth just as well. Do not restate it as
-  fact (creator called this out).
+- **Per-scene gate:** `CanAddWebcam` = `StagedScene is { WebcamConfig: null } && _webcam != null`.
+  A scene already hosting the webcam stays gray (one webcam per stream); another scene holding it
+  does NOT gray the row elsewhere.
+- **Add places the default directly:** when `_webcam != null`, "Add Webcam" creates the placement
+  with NO picker; the Windows picker runs only for the initial selection (`_webcam == null`;
+  choosing there swaps app-wide via the existing `SwapWebcamIdentityAsync`).
+- **Identity survives last-placement removal:** `RemoveElement` no longer nulls `_webcam` (that was
+  the TASK 26 rule). `LayoutStore` writes the singleton whenever it's non-null, so it persists.
+- **Startup adopts a solo camera as the app default** (in `ValidateWebcamResourceStartupAsync`,
+  after the successful single-cam lock): a clean/empty layout now offers the Web Cam layer in
+  Live/Chat immediately; `CameraManager.IsRunning` skip means a loaded identity already holding a
+  session is never overwritten.
+- **Dynamic why-gray tooltip:** `WebcamAddToolTip` (raised alongside the gates) — "Already in this
+  scene — one webcam per stream. A second camera means you've graduated to OBS." / "No webcam
+  detected…" / "Adds the app default webcam to this scene."
+- **Good Dog integration test** `WebcamMenuGateTests` rewritten for the new model (real app + temp
+  DB + camera seams): Chat's identity does NOT gray Live; Add in Live places the same `wc-1`
+  without a picker; scene-with-placement stays gray; identity survives both removals (DB row count
+  keeps 1). `WebcamStartupResourceTests` test 1 strengthened: after startup the single camera is
+  adopted → `CanAddWebcam` true. **304/304 green, build 0 warnings.**
 
-**Task docs:** `TASKS.md` Open items + `ai.md` Webcam section updated to match.
+**Task docs:** `TASKS.md` Open items + `ai.md` Webcam section updated (supersession recorded).
+
+## ✅ Earlier committed — webcam resource lifecycle (startup slice, `1e4017d`)
+
+Startup poll + tri-state (`ValidateWebcamResourceStartupAsync` after `LoadLayout`): 0 → run on,
+no alarm; **1 → `AcquireAsync` as app-wide lock**; **≥2 → no auto-lock** (App Settings selector
+next). Lock failure → **persistent red alert** (`WebcamLockAlert` in the Layers panel + Retry),
+re-polls every 5 s (`_webcamLockPollTimer`), clears on lock success or any first real frame.
+`CameraManager.IsRunning(deviceId)` = session exists (started OR starting). Camera test seams
+`CameraEnumeratorOverride`/`CameraFrameSourceFactoryOverride` (mirror `LayoutPathOverride`).
+Attribution correction committed: "NVIDIA Broadcast opens the webcam exclusively" is a *suspect-list*
+claim — `CameraConflictProbe` reads process names only, no device handles; do not restate as fact.
 
 ## ⚠️ Open items
 
@@ -51,18 +64,20 @@ chain, the fix is a proper resource lifecycle:
   reader+capture while the frame thread sits in `TryAcquireLatestFrame`/`Marshal.Copy` (outside the
   frame's try/catch). No repro, no integration test, native race not catchable — deferred per
   spin-guard. Record a second occurrence's pattern.
-- **Multi-camera slice (user-queued):** when ≥2 webcams exist, add the web-cam selection text +
+- **Multi-camera selector slice (user-queued):** when ≥2 webcams exist, add web-cam selection text +
   control to the **App Settings** dialog (gear icon, `OverlayHost` — left-click opens settings,
   right-click the context menu). Selecting + successfully allocating/locking activates the WebCam
-  layer. Currently ≥2 cameras → nothing shows in settings.
+  layer. **Currently ≥2 cameras → nothing shows in settings.** Also: the "Change Webcam" picker
+  should carry the OBS one-liner (one webcam per stream — a second means OBS).
 - **Static (+) catalog slice (user-queued):** all catalog rows always listed (Background, "Web Cam",
   "Countdown Timer", "Web Resource", "YouTube Chat", "YouTube Event"…), gray only for (1) system-level
   unavailability (persistent alert), (2) max already allocated, (3) not available for the current
-  scene; tooltips must name the reason (e.g. "already in Chat"). Static labels only, no new code-behind.
+  scene; tooltips must name the reason. Static labels only, no new code-behind.
 - **Device re-verify (one take session):** 1. slice-18 cache verdicts (NR/WH hits, stalls, band
   ~60); 2. webcam: fresh launch with the browser holding the camera must show the webcam or a NAMED
   chip (now also the persistent red alert, and the alert must clear after the browser closes + retry);
-  3. verify the Chat scene still owns the webcam (so Live's + is intentionally gray with a reason).
+  3. verify Live now OFFERS the Web Cam layer even while Chat holds the camera (the exact creator
+  goal: "webcam offered in the layer stack when I switch over to the Live view").
 - **No push yet** — after the take verdict, re-measure the clap offset (`/tmp/opencode/avsync.py`),
   then decide push with the user.
 
@@ -103,6 +118,8 @@ chain, the fix is a proper resource lifecycle:
 ## Next step
 
 The multi-camera App Settings selector slice (+ static catalog rows after), then the creator's take
-on this build. The alert is the new expected behavior to eyeball on the take: browser holds the
-camera → fresh launch → red alert in Layers (unless Chat's config grabbed it) that clears after a
-Retry once the browser closes.
+on this build. The webcam gate slice answers the creator's "go" ask — switching to the Live view
+must now offer Web Cam in the layer stack (Chat holding the camera no longer blocks it). The red
+Layers alert remains the new expected behavior to eyeball on the take: browser holds the camera →
+fresh launch → alert (unless Chat's config grabbed it) that clears after a Retry once the browser
+closes.

TASKS.md

@@ -65,10 +65,13 @@
 - **TASK 14** — Branch 2 shipped; branch 3+ in progress
 - **TASK 21** — UI picker slice remaining (Windows-only verification pending)
 - **TASK 32–36** — all queued future work (2026-09-01)
-- **Webcam resource lifecycle (2026-09-17)** — startup slice shipped: OS poll at start, single-camera
-  auto-lock, persistent red alert in the Layers panel on lock failure (re-polls until resolved). Next
-  slices (user-queued): multi-camera webcam selector in the App Settings dialog (gear), static (+)
-  catalog rows (Background, YouTubeEvent, quoted labels) with reason-greying.
+- **Webcam resource lifecycle (2026-09-17)** — startup slice shipped (OS poll at start, single-camera
+  auto-lock, persistent red alert in the Layers panel on lock failure, re-polls until resolved); gate
+  slice shipped same day — webcam = app-level default, one per stream per scene, Add places the
+  default directly, identity survives last-placement removal, startup adopts a solo camera as default.
+  TASK 26's app-wide gate superseded by creator directive. Next slices (user-queued): multi-camera
+  webcam selector in the App Settings dialog (gear), static (+) catalog rows (Background,
+  YouTubeEvent, quoted labels) with reason-greying.
 
 ---
 

ViewModels/MainViewModel.Scenes.cs

@@ -49,6 +49,7 @@ public partial class MainViewModel
                 OnPropertyChanged(nameof(CanAddWebcam));
                 OnPropertyChanged(nameof(CanAddYouTubeChat));
                 OnPropertyChanged(nameof(CanShowWebcamInStagedScene));
+                OnPropertyChanged(nameof(WebcamAddToolTip));
                 OnPropertyChanged(nameof(IsCountdownAvailable));
                 UpdateActiveBackground();
                 UpdateBackgroundImage();

ViewModels/MainViewModel.Sources.cs

@@ -217,9 +217,9 @@ public partial class MainViewModel
 
     // 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.
+    // session when the last using scene lets go). The webcam identity survives —
+    // it's the app-level default, so removing a scene's placement re-enables Add
+    // for the same camera instead of dropping it.
     private void RemoveElement(SceneElement? element)
     {
         var scene = StagedScene;
@@ -235,13 +235,11 @@ public partial class MainViewModel
             _webView2Manager?.Unregister(webSource.Id);
         _sceneGraph.RemoveElement(scene, element);
 
-        if (element is WebcamSceneConfig && _webcam != null
-            && !Scenes.Any(s => s.Elements.OfType<WebcamSceneConfig>().Any()))
+        if (element is WebcamSceneConfig)
         {
-            _webcam = null;
-            OnPropertyChanged(nameof(CanChangeWebcam));
             OnPropertyChanged(nameof(CanAddWebcam));
             OnPropertyChanged(nameof(CanShowWebcamInStagedScene));
+            OnPropertyChanged(nameof(WebcamAddToolTip));
         }
 
         OnPropertyChanged(nameof(ShowEmptySceneHint));

ViewModels/MainViewModel.Webcam.cs

@@ -22,9 +22,30 @@ public partial class MainViewModel
     private string? _webcamLockAlert;
     private DispatcherTimer? _webcamLockPollTimer;
 
-    /// <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>
+    /// Add → Webcam menu item: the webcam is an app-level resource (one camera —
+    /// the app default). The row is offered in any scene that doesn't already
+    /// host it, wherever a camera is selected; it is NOT blocked by other scenes
+    /// holding their own placement (per-scene max, not app-wide).
+    /// </summary>
+    public bool CanAddWebcam => StagedScene is { WebcamConfig: null } && _webcam != null;
+
+    /// <summary>
+    /// Why the Webcam row is greyed, when it is — never a silent bool. The max-1
+    /// reason gets the gentle "graduated to OBS" line; no camera at all gets its
+    /// own wording. Shown as the row's tooltip.
+    /// </summary>
+    public string WebcamAddToolTip
+    {
+        get
+        {
+            if (StagedScene?.WebcamConfig != null)
+                return "Already in this scene — one webcam per stream. A second camera means you've graduated to OBS.";
+            if (_webcam == null)
+                return "No webcam detected — plug one in, or allow camera access in Windows.";
+            return "Adds the app default webcam to this scene.";
+        }
+    }
 
     /// <summary>
     /// Right-click-on-preview → "Show Webcam": offered when the active scene has no
@@ -229,6 +250,15 @@ public partial class MainViewModel
         var started = await _cameraManager.AcquireAsync(device.Id);
         if (started)
         {
+            // The single camera becomes the app default so the Web Cam layer is
+            // offered in the capabled scenes (Live/Chat) even on a clean layout.
+            if (_webcam == null)
+            {
+                _webcam = new Webcam { DeviceId = device.Id, Name = device.DisplayName };
+                OnPropertyChanged(nameof(CanChangeWebcam));
+                OnPropertyChanged(nameof(CanAddWebcam));
+                OnPropertyChanged(nameof(WebcamAddToolTip));
+            }
             WebcamLockAlert = null;
             return;
         }
@@ -237,33 +267,28 @@ public partial class MainViewModel
         WebcamLockAlert = $"Web Cam unavailable: {reason}";
     }
 
-    // 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).
+    // Adds the webcam to the active scene. The webcam is an app-level resource:
+    // once a camera is the app default, adding the layer just places it — the
+    // picker runs only for the initial selection. Each scene's placement config
+    // is independent (webcam.{scene}.config); the camera device is Windows' own
+    // singleton and stays where we put it.
     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)
         {
+            var dialog = new CameraPickerDialog(new CameraPickerViewModel(_cameraEnumerator))
+            {
+                Owner = Application.Current.MainWindow
+            };
+            if (dialog.ShowDialog() != true || dialog.PickedDevice == null) return;
+            var device = dialog.PickedDevice;
             _webcam = new Webcam { DeviceId = device.Id, Name = device.DisplayName };
             OnPropertyChanged(nameof(CanChangeWebcam));
             OnPropertyChanged(nameof(CanAddWebcam));
-        }
-        else if (_webcam.DeviceId != device.Id)
-        {
-            await SwapWebcamIdentityAsync(device);
+            OnPropertyChanged(nameof(WebcamAddToolTip));
         }
 
         var config = new WebcamSceneConfig

ai.md

@@ -408,21 +408,22 @@ This replaces the old five-seeder cluster (`Seed{Starting,Brb,Ending,Chat}Backgr
 - **TFM:** `net8.0-windows10.0.19041.0` (app + tests) pulls the WinRT projection from the SDK reference
   packs — no NuGet package, no capability manifest (unpackaged desktop app works; the Windows privacy
   camera toggle still applies). `EnableWindowsTargeting` keeps WSL builds working.
-- **One webcam, many scenes (schema v3):** a singleton `Webcam` row holds the identity
-  (`Id`/`DeviceId`/`Name`); each scene gets its own `WebcamSceneConfig` (position/size/clip/mirror/
-  border/`IsVisible`). `Scene.Elements` holds images (`Source`) and, at most once, the webcam
-  (`WebcamSceneConfig`); `Scene.WebcamConfig` is the accessor. `CameraManager` refcounts capture
-  sessions by `DeviceId` (a session starts at `RefCount = 1`; repeat acquire bumps it; the last
-  release stops + disposes). **"Add Webcam" ALWAYS opens the Windows camera picker** — the creator is
-  never silently handed the previous camera (which used to happen after deleting one scene's webcam
-  while another scene still used it; that identity survived, so re-adding bypassed the choice).
-  Picking a different camera than the current app-wide one swaps it everywhere via
-  `SwapWebcamIdentityAsync` (the same path "Change Webcam…" uses), keeping the singleton honest;
-  picking the same one just places the config. The Add Webcam menu item greys out whenever a webcam
-  exists **anywhere** — one camera identity app-wide (`CanAddWebcam` = `StagedScene != null && _webcam == null`,
-  TASK 26; the old per-staged-scene gate let a second picker run from a scene that lacked the config).
-  **Removing the last webcam config anywhere clears the identity** (`_webcam = null`, raising
-  `CanAddWebcam`/`CanChangeWebcam`), which also drops "Change Webcam…" and re-enables Add.
+- **One webcam, many scenes (schema v3) — app-level default (2026-09-17):** a singleton `Webcam`
+  row holds the identity (`Id`/`DeviceId`/`Name`); each scene gets its own `WebcamSceneConfig`
+  (position/size/clip/mirror/border/`IsVisible`). `Scene.Elements` holds images (`Source`) and, at
+  most once, the webcam (`WebcamSceneConfig`); `Scene.WebcamConfig` is the accessor. `CameraManager`
+  refcounts capture sessions by `DeviceId` (a session starts at `RefCount = 1`; repeat acquire bumps
+  it; the last release stops + disposes). **The webcam is an app-level resource — ONE selection (the
+  app default), usable in every scene that can host it.** "Add Webcam" places the existing default
+  DIRECTLY (no picker); the Windows camera picker runs only for the initial selection
+  (`_webcam == null`). Choosing a different camera in the picker swaps it app-wide via
+  `SwapWebcamIdentityAsync` (same path "Change Webcam…" uses). **Per-scene gate, not app-wide**
+  (TASK 26 superseded by creator directive 2026-09-17): `CanAddWebcam` = `StagedScene is { WebcamConfig: null } && _webcam != null`
+  — a scene holding its own placement greys the row (one webcam per stream), but ANOTHER scene
+  holding one does not, so Chat's camera never greys Live; the greyed-row tooltip carries the reason
+  (`WebcamAddToolTip`, incl. the gentle "a second camera means you've graduated to OBS" line).
+  Removing a scene's placement **keeps the identity** (it's the app default; `_webcam` is never
+  nulled by removal) — Add stays offered for the same camera.
 - **Startup resource lifecycle (2026-09-17):** the webcam is a resource the app *allocates and
   locks*, validated at startup — this answers "why is the WebCam row greyed" from inside the app
   instead of a DB spelunk. `MainViewModel.ValidateWebcamResourceStartupAsync` (fired fire-and-forget
@@ -435,10 +436,14 @@ This replaces the old five-seeder cluster (`Seed{Starting,Brb,Ending,Chat}Backgr
   A session already running for the device (loaded identity's configs) counts as the lock, so the
   pass never double-acquires: `CameraManager.IsRunning(deviceId)` = a session exists (started OR
   still starting — a mid-start session is not "locked yet", it's in flight), and a rolled-back
-  (failed) session leaves the dictionary so the pass can retry. Test seams mirror `LayoutPathOverride`:
+  (failed) session leaves the dictionary so the pass can retry. After a successful single-cam lock,
+  the pass **adopts the camera as the app default** if no identity exists yet (fresh layout) — the
+  Web Cam layer is then offered in Live/Chat immediately (`CanAddWebcam` true); `IsRunning` skip
+  means a loaded identity whose session is already up never overwrites it. Test seams mirror
+  `LayoutPathOverride`:
   `CameraEnumeratorOverride`/`CameraFrameSourceFactoryOverride` let `WebcamStartupResourceTests`
-  drive the probe without real hardware (0-cam no-alarm, 1-cam locked, lock-fail → alert → clears on
-  retry). **Attribution correction:** the "NVIDIA Broadcast opens the webcam exclusively" failure
+  drive the probe without real hardware (0-cam no-alarm, 1-cam locked → identity adopted, lock-fail
+  → alert → clears on retry). **Attribution correction:** the "NVIDIA Broadcast opens the webcam exclusively" failure
   below is a *suspect-list* claim — `CameraConflictProbe` reads only running process names, no device
   handles; contention symptoms fit shared-mode/bandwidth just as well (see `MyMistakes.md`).
   The **YouTube Chat layer follows the same one-per-layout rule** (TASK 27):

ytLive.Tests/WebcamMenuGateTests.cs

@@ -1,25 +1,29 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
-using System.Linq;
+using System.Threading.Tasks;
 using Microsoft.Data.Sqlite;
 using Xunit;
-using ytLive.Models;
+using ytLive.Services;
 using ytLive.ViewModels;
 
 namespace ytLive.Tests;
 
 /// <summary>
-/// TASK 26 integration: the (+) menu's Webcam row gates on the app-wide webcam
-/// identity — one camera per app, so the row must stay disabled while ANY scene
-/// shows the webcam (not just the staged one), and re-enable only after the
-/// last config anywhere is removed (which also drops the identity).
-/// Real-App + temp-DB pattern (see BackgroundHealIntegrationTests).
+/// The webcam is an app-level resource with ONE selection (the app default):
+/// placing it in one scene must NOT grey it in the others (per-scene max, not
+/// app-wide), "Add Webcam" places the existing default directly (no picker —
+/// the picker only runs for the initial selection), and removing the last
+/// placement keeps the identity so the layer stays offered.
+/// Real-App + temp-DB + camera-seam pattern (camera seams are required: the
+/// startup resource pass and Add both acquire, and must never touch real
+/// hardware under test).
 /// </summary>
 [Collection("RealApp")]
 public sealed class WebcamMenuGateTests
 {
     [Fact]
-    public void CanAddWebcam_Gates_On_The_AppWide_Webcam_Identity()
+    public void WebcamIsAppDefault_AddPlacesSameCamera_AnyScene_IdentitySurvivesRemoval()
     {
         _app.Run(Run);
     }
@@ -32,6 +36,8 @@ public sealed class WebcamMenuGateTests
     {
         var tempDb = Path.Combine(Path.GetTempPath(), $"ytLlive-wcgate-{Guid.NewGuid():N}.db");
         MainViewModel.LayoutPathOverride = tempDb;
+        MainViewModel.CameraEnumeratorOverride = new FakeEnumerator();
+        MainViewModel.CameraFrameSourceFactoryOverride = id => new FakeFrameSource(id);
         var window = default(MainWindow);
         try
         {
@@ -42,22 +48,30 @@ public sealed class WebcamMenuGateTests
             window = new MainWindow();
             var vm = (MainViewModel)window.DataContext;
 
-            var starting = vm.Scenes.Single(s => SceneCatalog.Is(s.Name, SceneCatalog.Starting));
-            var live = vm.Scenes.Single(s => SceneCatalog.Is(s.Name, SceneCatalog.Live));
+            var starting = vm.Scenes.Single(s => s.Name == "Starting");
+            var live = vm.Scenes.Single(s => s.Name == "Live");
 
             vm.StagedScene = live;
-            Assert.True(live.WebcamConfig == null, "Live must not carry the webcam config");
-            Assert.False(vm.CanAddWebcam,
-                "webcam exists in another scene — Add Webcam must be greyed out app-wide");
-
-            vm.StagedScene = starting;
-            Assert.False(vm.CanAddWebcam, "staged scene itself has the webcam");
-
-            var config = starting.WebcamConfig!;
-            vm.RemoveSourceCommand.Execute(config);
-
+            Assert.Null(live.WebcamConfig);
             Assert.True(vm.CanAddWebcam,
-                "last webcam config anywhere was removed — identity cleared, picker may run again");
+                "webcam exists in Starting but that is NOT a block — the app default stays offered in Live");
+
+            // Add Webcam must place the existing app default without opening a picker.
+            vm.AddWebcamCommand.Execute(null);
+            Assert.NotNull(live.WebcamConfig);
+            Assert.Equal("wc-1", live.WebcamConfig!.WebcamId);
+
+            // Per-scene max: the scene that already hosts the webcam stays greyed.
+            vm.StagedScene = starting;
+            Assert.False(vm.CanAddWebcam, "a scene already hosting the webcam must not offer it again");
+
+            // Removing placements keeps the app-level identity alive.
+            vm.RemoveSourceCommand.Execute(starting.WebcamConfig!);
+            Assert.True(vm.CanAddWebcam, "removing a placement re-enables Add for the same app default");
+
+            vm.StagedScene = live;
+            vm.RemoveSourceCommand.Execute(live.WebcamConfig!);
+            Assert.True(vm.CanAddWebcam, "the app default is still selected — Add stays offered");
 
             vm.SaveLayoutNow();
             using (var connection = new SqliteConnection($"Data Source={tempDb}"))
@@ -65,21 +79,23 @@ public sealed class WebcamMenuGateTests
                 connection.Open();
                 using var webcams = connection.CreateCommand();
                 webcams.CommandText = "SELECT COUNT(*) FROM Webcam;";
-                Assert.Equal(0L, (long)webcams.ExecuteScalar()!);
+                Assert.Equal(1L, (long)webcams.ExecuteScalar()!);
             }
         }
         finally
         {
             window?.Close();
             MainViewModel.LayoutPathOverride = null;
+            MainViewModel.CameraEnumeratorOverride = null;
+            MainViewModel.CameraFrameSourceFactoryOverride = null;
             SqliteConnection.ClearAllPools();
             try { File.Delete(tempDb); } catch { /* best-effort cleanup */ }
         }
     }
 
     /// <summary>Five canonical scenes + a webcam identity used by exactly one
-    /// non-staged-by-default scene (Starting), so staging any other screen
-    /// reproduces the old per-scene gate's false "available".</summary>
+    /// non-staged-by-default scene (Starting), so staging Live reproduces the
+    /// old app-wide gate's false "unavailable".</summary>
     private static void SeedDatabaseWithWebcam(string path)
     {
         using var connection = new SqliteConnection($"Data Source={path}");
@@ -120,4 +136,32 @@ public sealed class WebcamMenuGateTests
             config.ExecuteNonQuery();
         }
     }
-}
+
+    private sealed class FakeEnumerator : ICameraEnumerator
+    {
+        public Task<IReadOnlyList<CameraDeviceInfo>> GetCamerasAsync()
+            => Task.FromResult<IReadOnlyList<CameraDeviceInfo>>(new[]
+            {
+                new CameraDeviceInfo("test-camera", "Test Cam"),
+            });
+    }
+
+    private sealed class FakeFrameSource : ICameraFrameSource
+    {
+        public string DeviceId { get; }
+        public event Action<VideoFrame>? FrameAvailable;
+#pragma warning disable CS0067
+        public event Action<string>? SourceFailed;
+#pragma warning restore CS0067
+
+        public FakeFrameSource(string deviceId) => DeviceId = deviceId;
+
+        public Task StartAsync()
+        {
+            FrameAvailable?.Invoke(new VideoFrame(2, 2, new byte[16]));
+            return Task.CompletedTask;
+        }
+
+        public Task StopAsync() => Task.CompletedTask;
+    }
+}

ytLive.Tests/WebcamStartupResourceTests.cs

@@ -52,6 +52,7 @@ public sealed class WebcamStartupResourceTests
             Assert.Single(harness.Started);
             Assert.Equal("dev1", harness.Started[0]);
             Assert.NotNull(vm.StagedScene);
+            Assert.True(vm.CanAddWebcam, "the single camera becomes the app default — the Web Cam layer is offered");
         });
 
     private void RunZero() => RunWith(sceneBoilerplate: true, cameraCount: 0, failOnStart: false,
@@ -149,7 +150,9 @@ public sealed class WebcamStartupResourceTests
         public string DeviceId { get; }
         private readonly Harness _harness;
         public event Action<VideoFrame>? FrameAvailable;
+#pragma warning disable CS0067
         public event Action<string>? SourceFailed;
+#pragma warning restore CS0067
 
         public FakeWebcamSource(string deviceId, Harness harness)
         {