Fix: derive IsBackground from Type on layout load (legacy rows healed)

HANDOFF.md

@@ -1,31 +1,49 @@
 # HANDOFF — Session State
 
 ## Branch
-`main` — clean, HEAD `d2114c7`, 0 warnings. Not pushed.
+`main` — **dirty (2 files, uncommitted)**, HEAD `46da995`. Not pushed.
 
-## What's in commit d2114c7 (this session)
-1. **All-five-scenes backgrounds** (prior session work, was uncommitted): `Scene.UseDefaultBackground` + `CustomBackgroundPath` on `SceneElement` superclass, LayoutStore persistence (`BackgroundPath_{sourceId}` / `BackgroundUseDefault_{sourceId}` in Settings), `SceneCatalog.HasBackground` true for all five scenes, `EnforceBackgroundPolicy` no longer strips non-Live backgrounds, tests updated.
-2. **UI polish (this session):**
-   - "Use default background:" label + pill toggle on ONE horizontal line (MainWindow.xaml ~612)
-   - PillToggle resized 48×24 → 36×18 (thumb 18→12, travel 24→18) to match 11px label (Themes/Controls.xaml)
-   - New `SubHeader` style (11px SemiBold #a0a0b0, indented 4px); "BACKGROUND" → "Background" sub-title; Background section contents indented under it — PROPERTIES stays the only title-styled text
+## Uncommitted work (this session): IsBackground load-time derivation fix
+
+The user-reported bug "Background properties show for only Starting and Live" is FIXED:
+
+1. **Root cause confirmed:** `Source.Type`'s setter derives `IsBackground` (`Type == Background`),
+   but `LayoutStore.Load()`'s object initializer assigned the DB **column** afterward — rows saved
+   before b74f15f carry `IsBackground=0` for `Type='Background'` and stayed false after load, so the
+   properties panel (`SelectedElement.IsBackground`) stayed hidden in BRB/Chat/Ending.
+2. **Fix** (`Services/LayoutStore.cs` ~601): hoist the `Type` parse, then
+   `IsBackground = type == SourceType.Background || <column>`. The OR keeps the persisted bit for
+   legacy DisplayCapture backdrops (column=1 must survive so the live-capture layer stays flagged).
+   First save after load self-heals the columns.
+3. **Test** (this branch's ONE integration test):
+   `LayoutStorePersistenceTests.Legacy_IsBackground_Zero_Rows_Derive_From_Type_On_Load` — saves a BRB
+   scene holding DisplayCapture + Background + Image, zeroes the legacy columns via raw SQL, reloads,
+   asserts Background→true / DisplayCapture→true / Image→false.
+4. Build **0 warnings**; **212 total, 209 pass** (3 pre-existing failures, below).
 
 ## ⚠️ Landmines
-- **User verdict (2026-08-23):** "The AI wrote fucked up code after repeatedly and intentionally misunderstanding instructions." This extends the ai.md 2026-08-22 audit flag — trust nothing from those sessions without manual verification. User switched models.
-- **1 pre-existing test failure:** AudioPipeline gain-math (210/211 pass).
+
+- **User verdict (2026-08-23):** "The AI wrote fucked up code after repeatedly and intentionally
+  misunderstanding instructions." This extends the ai.md 2026-08-22 audit flag — trust nothing from
+  those sessions without manual verification. User switched models.
+- **Pre-existing test failures are THREE, not one (handoff correction — verified by stashing and
+  running clean HEAD):**
+  1. `AudioPipelineTests.Mix_HonorsProviderGains_AndGameMute_KillsTheLoopback` (gain-math)
+  2. `SourceNamingTests.Duplicate_Sources_Get_Next_Free_Numbered_Name` — asserts StagedScene names ==
+     ["Text","Text2","Text3"], but StagedScene now carries a seeded "Game Capture" element (d2114c7
+     made all five scenes background-enabled); the test must filter the background out.
+  3. `SceneCatalogTests.EnforceBackgroundPolicy_Sets_Flag_For_All_Scenes` — calls `EnsureBackground`
+     on scenes with `HasBackground=false`; that returns null **by design**, so it asserts against
+     elements never inserted.
+  All three are fallout of the audit-flagged sessions' background-policy churn. NOT fixed here
+  (Good Dog Rule — this branch carries its one test only).
 - **Real-MainWindow tests MUST set `LayoutPathOverride`** (see ai.md) — DB pollution wiped real data once.
 
-## 🔴 Open bug (user-reported, NOT fixed): Background properties show for only Starting and Live
-Evidence gathered before stop:
-- Properties gate: `SelectedElement.IsBackground` (MainWindow.xaml ~608–611)
-- Seeding is correct: `EnsureDefaultBackground` / seed methods all set `Type = SourceType.Background`
-- **Root cause suspect:** `LayoutStore.cs:616` loads `IsBackground` from the DB **column**, not derived from `Type`. Rows saved before b74f15f (which made the Type setter derive IsBackground) carry `IsBackground=0` and stay false after load → panel hidden in BRB/Chat/Ending.
-- **Likely fix:** derive `IsBackground = Type == SourceType.Background` on load (or backfill migration). Not attempted.
-
 ## Next steps
-1. Fix the load-time IsBackground derivation bug (ONE integration test per Good Dog Rule)
-2. Visual test on Windows display: pill sizing/alignment, sub-header hierarchy, backgrounds in all five scenes
-3. Then: thumbnail drag-reorder → real compositor snapshots → transition dropdown UI (per previous plan)
+1. Commit this fix (code + docs, one commit).
+2. Fix the two stale background tests (tiny, separate commit each or together — they are unit-level repairs, not features).
+3. Visual test on Windows display: pill sizing/alignment, sub-header hierarchy, Background properties panel in all five scenes (BRB/Chat/Ending should show it again).
+4. Then: thumbnail drag-reorder → real compositor snapshots → transition dropdown UI (per previous plan).
 
 ## Build
 ```bash