TASK 4 ship step 5: live frame pipeline — FramePump paces the active scene's composite into the encoder, ScreenCaptureManager.GetLatestFrame, MainViewModel resolver/option-builder/pump wiring, FramePumpTests (7) + GetLatestFrame test — 147 tests passing, 0 warnings

TASKS.md

@@ -201,7 +201,7 @@ Preview shows the transition too (WYSIWYG). No wipes/slides/LUTs beyond the four
 2. ✅ **Ship step 2 — the FFmpeg locator SHIPPED** (2026-08-10)
 3. ✅ **Encoder + RTMP push SHIPPED** (2026-08-12) — the FFmpeg subprocess: raw BGRA frames via stdin, stderr health parsing, FLV mux + push to the ingestion URL (see the ship step 3 plan below)
 4. ✅ **WASAPI audio capture SHIPPED** (2026-08-12) — NAudio loopback (desktop/game) + the picked mic feeding `AudioLevel`, so the realtime meter comes alive (see the ship step 4 plan below)
-5. ☐ **Frame-pipeline wiring** — `CameraManager`/`ScreenCaptureManager` → compositor resolver → encoder
+5. ✅ **Frame-pipeline wiring SHIPPED** (2026-08-12) — `CameraManager`/`ScreenCaptureManager` → compositor resolver → encoder, driven by a paced `FramePump` (see the ship step 5 plan below)
 6. ☐ **Health stats** — bitrate, FPS, dropped frames reported live in the bottom bar (req 5)
 7. ☐ **One-click go live + private-only enforcement** — Go Live always creates/updates the broadcast with `privacyStatus = "private"` + PRIVATE badge (req 8, test-verifiable)
 
@@ -423,8 +423,57 @@ lifecycle/forwarding/failure against fakes, meter RMS/smoothing/reset, `WaveToFl
 extensible/truncation) — **139 passing**.
 
 **Deferred (later ship steps):** wiring the desktop-capture samples into the encoder's AAC mix (replaces
-the `-f lavfi -i anullsrc` placeholder; ship step 5 owns the encoder construction), WASAPI capture while
-not live, and any audio UI beyond the existing mic controls.
+the `-f lavfi -i anullsrc` placeholder; the encoder construction itself shipped in ship step 5), WASAPI
+capture while not live, and any audio UI beyond the existing mic controls.
+
+#### Ship step 5 — Frame-pipeline wiring (the encoder gets a frame source)
+
+**Goal:** the chain `CameraManager`/`ScreenCaptureManager` → compositor resolver → encoder, driven while
+live by a paced frame pump: snapshot the active scene → resolve each element to its latest frame →
+composite into the tier's output frame → pace into the encoder's stdin at the tier's FPS.
+
+**Decisions (locked via user Q&A, 2026-08-12):**
+1. **Video pipeline first** — the `-f lavfi -i anullsrc` silent track stays; mixing the loopback/mic
+   WASAPI samples into the encoder's AAC track is its own later step.
+2. **RTMP URL via a provider seam** — `MainViewModel._rtmpUrlProvider` is a `Func<string?>` returning
+   null today (the reusable stream's ingest URL lands with TASK 5); when it yields null the pump logs
+   and skips the encoder entirely, so go-live runs the existing visual flow without pushing.
+
+**Design:**
+1. `Services/Encoder/FramePump.cs` — the frame producer. All collaborators constructor-injected seams
+   (`Func<Scene?>`, `Func<SceneElement, VideoFrame?>` resolver, `Func<CompositorOptions>`,
+   `Func<EncoderOptions?>`, `Func<IFfmpegEncoder>`, `Action<string>` log, injectable pacing delay) so it
+   stays free of WPF and of the capture managers and is hermetic in tests. `StartAsync` never throws
+   (failures log + surface via `Failed` — the VM fires-and-forgets from the sync command handler);
+   loop = snapshot → render → `SubmitFrameAsync`, paced at `1/options.Fps` (default `Task.Delay`; tests
+   inject `Task.Yield`). `StopAsync` stops the encoder (closes stdin) BEFORE awaiting the loop — closing
+   stdin unblocks a write stuck on pipe backpressure, so stop can't deadlock on the pump. `ProcessFailed`
+   self-stops the pump. `HealthUpdated` forwards the encoder's stats (ship step 6 binds the bottom bar).
+2. `ScreenCaptureManager.GetLatestFrame(key)` — mirrors `CameraManager.GetLatestFrame(deviceId)`; the
+   backdrop's live frame for the compositor.
+3. `MainViewModel` — owns the resolver (`WebcamSceneConfig` → `GetLatestFrame(WebcamId)`;
+   `Source.IsLiveCapture` → `GetLatestFrame(CaptureKey)`; image/background → `StaticPixelCache.Get(AssetId)`),
+   builds `CompositorOptions` from the tier + `OutputRect*` (doubles rounded to ints — the vertical
+   607.5 half-pixel crop rounds to a perfectly-centered 608), builds `EncoderOptions` from the tier when
+   the URL provider returns one, constructs the real `FfmpegEncoder(new FfmpegLocator())`, starts the
+   pump on go-live, stops it on end-stream, disposes in `Shutdown`, and flips `StreamStatus.Error` when
+   the pump fails while live (minimal — detailed health surfacing is ship step 6).
+
+**Test plan (Good Dog Rule — ONE integration test):** `FramePumpTests.Start_CompositesScene_FeedsEncoder_StopsCleanly`
+drives the full lifecycle against fakes — real `SceneCompositor` + real `FramePump`, fake `IFfmpegEncoder`
+— asserting the composited red backdrop frame actually reaches the encoder at the tier size and that stop
+tears everything down. Units: no-URL start skips the encoder, re-entrant start/stop no-ops, encoder
+start-failure raises `Failed` + disposes, `ProcessFailed` self-stops the pump, `HealthUpdated` forwards.
+`ScreenCaptureManagerTests.GetLatestFrame_ReturnsLatestPump_UntilReleased` pins the new accessor.
+
+**Out of scope (later ship steps):** the loopback/mic → AAC mix (replaces `anullsrc`), health stats in the
+bottom bar (ship step 6), scene-switching transitions, and any flash-frame wiring.
+
+**Built (2026-08-12):** `FramePump` shipped in `Services/Encoder/`, `ScreenCaptureManager.GetLatestFrame`
+added, `MainViewModel` wired end-to-end (resolver + both option builders + pump lifecycle), `FramePumpTests`
+(7) + `GetLatestFrame` test (1) added — build **0 warnings**, **147 tests passing**. Known consideration:
+the pump reads the active scene on a background thread while the UI can still edit it; a concurrent-mutation
+exception is contained (logged + `Failed` + pump stops) rather than crashing.
 
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