docs: rewrite HANDOFF — Phase 1 (MainViewModel split) complete

Session-end state: all 11 partials landed, core 1,890 -> 758 lines. Refactor
commits 6-11 + tags are local-only pending a milestone push; Phase 2
(MainWindow.xaml -> UserControls) queued. Grep-verified per-partial using lists
recorded so no future session re-derives them.

HANDOFF.md

@@ -2,62 +2,87 @@
 
 ## Branch / Commit State
 
-**`main`**, working tree is **CLEAN** — all changes committed and pushed.
+**`main`**, working tree is **CLEAN**.
 
-No feature branches pre-1.0: all work lands on `main` per work unit.
+Commits `46978b8` (AGENTS push policy), `fc33022` (HANDOFF), and refactor
+commits `0–5` through `e286719` are **pushed** (incl. `refactor-commit-0..5`).
+Refactor commits **6–11 are LOCAL ONLY** (policy 2026-08-30: no per-commit
+push; `git push --tags` only at a user-agreed milestone / "push it"):
 
-**Latest commit:** `e286719` — Commit 5/12 of the MainViewModel refactor (Webcam partial, tag `refactor-commit-5`).
+| Commit | Hash | Tag | Partial | Lines |
+|--------|------|-----|---------|-------|
+| 6 Audio | `c1126a5` | `refactor-commit-6` | `MainViewModel.Audio.cs` | 408 |
+| 7 Trax | `535a501` | `refactor-commit-7` | `MainViewModel.Trax.cs` | 132 |
+| 8 Socials | `c41ff7f` | `refactor-commit-8` | `MainViewModel.Socials.cs` | 161 |
+| 9 Streaming | `e1006a0` | `refactor-commit-9` | `MainViewModel.Streaming.cs` | 787 |
+| 10 Chat | `3b77a13` | `refactor-commit-10` | `MainViewModel.Chat.cs` | 194 |
+| 11 Overlays | `1efde5a` | `refactor-commit-11` | `MainViewModel.Overlays.cs` | 194 |
+
+Nightly summary: **Phase 1 complete.** The plan was 11 partials + scaffold;
+all live in `ViewModels/`. Core `MainViewModel.cs` shrank 1,890 → **758
+lines**. Every change: clean build (0 warnings), `scripts/verify.sh` (246
+passed + 2 known failures only), `scripts/scope-check.sh` with explicit file
+args, `ViewModels/index.md` updated in the SAME commit, tagged
+`refactor-commit-N`, no per-commit push.
 
 ## What's In Flight
 
-**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.
+Nothing code-in-flight — working tree clean, Phase 1 done.
 
-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.
+**Next (queued, not started): Phase 2 — split `MainWindow.xaml` (1,681 lines)
+into UserControls.** Same rules: one work unit per control, docs in the same
+commit, verify + scope-check, commit locally, `git push` only on user go.
 
-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;`.
+**Push pending:** refactor commits 6–11 + their tags are local. The Session-1
+push checkpoint was never reached because the user directive was to run the
+series to completion; Phase 1 completion is the natural milestone to push on
+explicit user confirmation.
 
 ## Landmines
 
-- **TextBox.Mode=OneWay** is required for `RecordFolderDisplay` binding (get-only computed property).
-- **Pre-existing test failures (do not chase):** `AudioPipelineTests.Mix_HonorsProviderGains…` +
-  `RoundClipInteractionTests.Round_Clip_Corner_Is_Grabbable…`.
+- **Pre-existing test failures (do not chase):**
+  `AudioPipelineTests.Mix_HonorsProviderGains_AndGameMute_KillsTheLoopback` +
+  `RoundClipInteractionTests.Round_Clip_Corner_Is_Grabbable_And_Shape_Is_Circle`.
+- **Tests occasionally abort early (236/237)** — known flake, accepted by `verify.sh`.
 - **App running locks `ytLive.exe`** → build fails MSB3027. Kill PID before building.
-- **Test suite hangs** when running full vstest (WPF `RealAppHost` dispatcher deadlock); individual
-  tests pass in isolation. Use `dotnet test` on individual test classes, not the full suite DLL.
-- **Pre-commit gate:** `./scripts/verify.sh` — clean build (0 warnings) + full tests + scope check.
+- **Implicit usings are SDK-default but partials must still carry their own
+  domain usings** (they do not inherit core's): `ICommand`/`ObservableCollection`/
+  `WriteableBitmap`/`DispatcherTimer` etc. are NOT implicit. Grep-verified usings:
+  - Audio: Input, Media, Threading, `NAudio.CoreAudioApi`, `ytLive`, Helpers, Models, Services, Services.Audio
+  - Trax: IO, Media, `Microsoft.Win32`, Helpers, Models, Services.Audio
+  - Socials: Windows, Input, Media, `ytLive`, Helpers, Models, Services, Services.Compositor
+  - Streaming: ObjectModel, IO, Windows, Input, Threading, `Microsoft.Win32`, Helpers, Models, Services, Services.Encoder
+  - Chat: ObjectModel, Media, Media.Imaging, Threading, Helpers, Models, Services
+  - Overlays: Diagnostics, IO, Input, Helpers
+- **Pre-commit gate:** `scripts/verify.sh` (0-warning build + full tests) and
+  `scripts/scope-check.sh "file1" …` — scope-check REQUIRES explicit file args.
+- Build from WSL with the Windows dotnet host only (see `AGENTS.md`).
 
 ## Todo state
 
-- TASK 3 (Capture Pipeline): 27/30 items done. Open: preview compositor (16), text source (17), alerts (20). Window capture absorbed into Screen picker (done). Background removal excluded from this build.
-- TASK 4 (RTMP Ingest): ✅ Shipped — all 7 items done (compositor, FFmpeg locator, encoder+RTMP, WASAPI audio, frame-pipeline, health stats, one-click go-live).
-- TASK 9 (Stream Management): items 1–3 shipped (reusable stream, health monitoring). Items 4–7 open: live chat, error handling, visibility picker, full broadcast form.
-- TASK 10 (Monetization): steps 1–7 shipped. Velopack auto-update pending.
-- TASK 18: shipped. Remaining = running-app verification (creator).
-- TASK 19/23 (Control Surface UX): ✅ Shipped — thumbnails, transitions (Cut/Fade/Move), edit mode, left panel two-state.
-- TASK 20 (Hotkeys): ✅ Shipped — F1-F5 scenes, F6-F9 actions, config UI, global hotkeys, conflict detection, persistence.
-- TASK 21 (Media source): Increment A shipped (model + persistence). Slices 4–12 open (decoder, FramePump wiring, compositor, loop/volume, UI, tests). Blocked on ffmpeg for integration test.
-- 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 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.
+- MainViewModel refactor: **Phase 1 complete (11/11 partials + scaffold).**
+  `ViewModels/index.md` has a per-partial table row (code↔commit map in the
+  tracker section). Core row now describes only what remains (ctor wiring,
+  lifecycle, source commands, WebView2 hosting, frame-pump seam,
+  `SelectedElement`, `BrandFlash*`, `BuildCompositorOptions`/`ResolveOutputFrame`).
+- TASK 3: 27/30 (preview compositor 16, text source 17, alerts 20 still open).
+- TASK 4: ✅ shipped. TASK 9: items 1–3 shipped; 4–7 open. TASK 10: steps 1–7; Velopack pending.
+- TASK 18: shipped, creator verification pending. TASK 19/23, 20, 21-A: shipped.
+- TASK 22 (audio sync offset): not started — required for v1.
+- Monitoring: cross-partial private access is the point of partial classes —
+  no moved member re-declared anywhere; moved setters reference other partials
+  purely by name.
 
 ## Session summary (2026-08-30)
 
-- 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.
+- Ran the MainViewModel split to completion under the standing directive
+  ("continue until you can continue no longer" — no interruption prompts).
+- Commits 9 (Streaming), 10 (Chat), 11 (Overlays) landed locally, each ~8:40
+  back-to-back: cut → 0-warning build → verify (246 pass + 2 known) →
+  scope-check → index.md in-commit → `git tag refactor-commit-N`. No push.
+- Streaming was the hardest cut (interleaved props, master-frame consts,
+  session timer, health pipeline, record rename-on-stop); Chat and Overlays
+  were clean contiguous cuts. One build fix each: Streaming needed
+  `ObjectModel`/`Input`, Chat needed `Media.Imaging` for `WriteableBitmap`.
+- Docs kept honest throughout: `index.md` rows for Streaming/Chat/Overlays,
+  About-hub row re-pointed to the Overlays partial, core row trimmed each time.