capture: refuse the multi-track ranged item render, silence the track's children and receives for it, and gate every exact-bounds capture on its frame count

src/shell/capture/render_selection.cpp

@@ -18,9 +18,11 @@ namespace reasampler::capture {
 
 namespace {
 
-// Deselect every track in GetTrack's index space (which excludes the master, SDK
-// ~2634), then select exactly `tracks` — so the resulting selection is the set,
-// not the set unioned with whatever was already selected.
+// Deselect every track in GetTrack's index space, then select exactly `tracks` — so
+// the resulting selection is the set, not the set unioned with whatever was already
+// selected. That index space holds no master track (the master is reached only via
+// GetMasterTrack); the header states this nowhere, so treat it as behavior rather
+// than a documented guarantee.
 void selectOnly(const std::vector<MediaTrack*>& tracks)
 {
     const int total = CountTracks(nullptr);