capture: render a ranged item capture time-bounded — the selected-items source can't narrow a window, only a full-extent one uses it

sourceModeForScope now takes the item extent vs. the requested window. Full-extent item captures and the batch keep the old path unchanged.

src/shell/capture/render_selection.cpp

@@ -0,0 +1,54 @@
+// render_selection.cpp — see the header.
+//
+// Compiled into the reaper_reasampler module. Includes reaper_plugin_functions.h
+// WITHOUT REAPERAPI_IMPLEMENT — main.cpp is the one TU that defines the API
+// pointers; here they are extern.
+
+#include "shell/capture/render_selection.h"
+
+#define REAPERAPI_MINIMAL
+#define REAPERAPI_WANT_CountTracks
+#define REAPERAPI_WANT_GetTrack
+#define REAPERAPI_WANT_CountSelectedTracks
+#define REAPERAPI_WANT_GetSelectedTrack
+#define REAPERAPI_WANT_SetTrackSelected
+#include "reaper_plugin_functions.h"
+
+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.
+void selectOnly(const std::vector<MediaTrack*>& tracks)
+{
+    const int total = CountTracks(nullptr);
+    for (int i = 0; i < total; ++i)
+        if (MediaTrack* tr = GetTrack(nullptr, i))
+            SetTrackSelected(tr, false);
+    for (MediaTrack* tr : tracks)
+        if (tr) SetTrackSelected(tr, true);
+}
+
+}  // namespace
+
+RenderTrackSelection::RenderTrackSelection(const std::vector<MediaTrack*>& tracks)
+{
+    if (tracks.empty()) return;
+
+    const int n = CountSelectedTracks(nullptr);  // nullptr = active project
+    for (int i = 0; i < n; ++i)
+        if (MediaTrack* tr = GetSelectedTrack(nullptr, i))
+            original_.push_back(tr);
+
+    selectOnly(tracks);
+    applied_ = true;
+}
+
+RenderTrackSelection::~RenderTrackSelection()
+{
+    if (applied_) selectOnly(original_);
+}
+
+}  // namespace reasampler::capture