608 green, 0 warnings. Completes the layer half of TASK 65.
- **(+) → Replay Clip** adds an ordinary media layer with an app-owned path, one per scene, silent by
default (`MediaMuted`) and looping only outside Live — the compositor needs no special case.
- **F10 saves → the Live layer plays it once, then hides** (`SessionCompleted` → invisible, guard
cleared). Every other scene with a replay layer keeps looping the kept set, advancing on each clip's
completion, wrapping at the end.
- **The guard the creator asked for:** while that Live replay is playing, **F10 is inert** with a plain
explanation. That is what replaces the impossible "exclude the layer from its own clip" — with one
encoder and two muxes the clip *is* the program, so the fix is to not clip a clip.
`ReplayLayerTests` drives the real VM: one layer per scene, muted by default, once-through in Live,
looping in BRB, and a stray F10 with clips off writes nothing.
Slice 4. 607 green, 0 warnings. Clips remain **off by default** and, while off, the ring is never
constructed — so no reader thread and no encoder output exist until someone asks for the feature.
- **F10** (`HotkeyId.SaveClip`, default F10, remappable in the hotkey dialog) snapshots the ring, writes
the file, prunes to the retention count and toasts the name. Empty ring → "nothing to clip yet"
instead of a zero-byte file; clips off → says so and points at Settings.
- **Settings**: Enable, length (10 or 15, default 10), keep (3/4/5, default 3). Persisted in the layout
store and **coerced on load** — a bad stored value falls back to a legal one, so the ring can never be
sized for a length the UI cannot show.
- The ring is sized from length × tier bitrate × 1.25 and rebuilt if either changes; it is created at
session start and dropped at stop, so memory is only spent while a show is running.
- The drawer states the boundary in the creator's terms: "A capture, not an editor: for trimming,
captions or a library, use a video editor."
Still to come: the replay layer itself (play once then hide in Live, loop the kept clips elsewhere).