Ψ-W1-T4: resolve drop targets per move, not once — every surface gets a defined outcome, a cue, and no silent no-op

src/shell/actions/arrange_drop_win.cpp

@@ -0,0 +1,105 @@
+// arrange_drop_win.cpp — see arrange_drop_win.h. main.cpp owns the API pointers; this TU gets
+// them extern via the WANT list.
+//
+// Runtime assumptions, all DAW-verifiable and none confirmed by the SDK header:
+//   A. InsertMedia base mode 0 targets the sole selected track and inserts at the edit cursor;
+//      SetOnlyTrackSelected isolates that track first (the same pair insert.cpp relies on).
+//   B. InsertMedia advances the edit cursor past the media it added. That advance IS the
+//      multi-file layout: the cursor is deliberately not reset between files, so N captures
+//      land end to end. If REAPER does not advance it, they stack at one position instead —
+//      visible and one Ctrl-Z away, never silent.
+//   C. SnapToGrid honors the project's snap-enabled toggle. The header documents no
+//      snap-enabled query for the arrange, so a drop taken with snapping OFF is the test that
+//      settles it.
+
+#include "shell/actions/arrange_drop_win.h"
+
+#include <string>
+#include <vector>
+
+#include "core/capture/insert_plan.h"  // computeInsertMode — the ONE InsertMedia bitfield owner
+
+#include "reaper_plugin.h"
+
+#define REAPERAPI_MINIMAL
+#define REAPERAPI_WANT_CountSelectedTracks
+#define REAPERAPI_WANT_GetCursorPosition
+#define REAPERAPI_WANT_GetSelectedTrack
+#define REAPERAPI_WANT_GetSet_ArrangeView2
+#define REAPERAPI_WANT_InsertMedia
+#define REAPERAPI_WANT_SetEditCurPos
+#define REAPERAPI_WANT_SetOnlyTrackSelected
+#define REAPERAPI_WANT_SetTrackSelected
+#define REAPERAPI_WANT_SnapToGrid
+#define REAPERAPI_WANT_Undo_BeginBlock2
+#define REAPERAPI_WANT_Undo_EndBlock2
+#include "reaper_plugin_functions.h"
+
+namespace reasampler {
+
+using capture::computeInsertMode;
+using capture::InsertOptions;
+
+namespace {
+
+// Selection snapshot/restore, so a drop leaves the user's track selection exactly as it found
+// it. Mirrors insert.cpp's pair; that TU belongs to the capture pillar and this one to the drag
+// chain, so they are kept separate rather than sharing a helper across the seam.
+std::vector<MediaTrack*> snapshotSelectedTracks() {
+    const int n = CountSelectedTracks(nullptr);  // nullptr = active project
+    std::vector<MediaTrack*> tracks;
+    tracks.reserve(static_cast<std::size_t>(n));
+    for (int i = 0; i < n; ++i) tracks.push_back(GetSelectedTrack(nullptr, i));
+    return tracks;
+}
+
+void restoreSelectedTracks(const std::vector<MediaTrack*>& tracks) {
+    if (tracks.empty()) return;  // nothing was selected; leave whatever the drop selected
+    SetOnlyTrackSelected(tracks[0]);
+    for (std::size_t i = 1; i < tracks.size(); ++i) SetTrackSelected(tracks[i], true);
+}
+
+}  // namespace
+
+double arrangeTimeAtScreenX(int screenX) {
+    double start = 0.0, end = 0.0;
+    // isSet=false reads the arrange times spanned by [screen_x_start, screen_x_end); a
+    // one-pixel span therefore reads the time at that column. (The all-zero span is the SDK's
+    // documented "whole view" form, which is why the span here must not be empty.)
+    GetSet_ArrangeView2(nullptr, false, screenX, screenX + 1, &start, &end);
+    return start < 0.0 ? 0.0 : start;
+}
+
+int performArrangeDrop(MediaTrack* track, double time,
+                       const std::vector<std::string>& absolutePaths) {
+    if (!track || absolutePaths.empty()) return 0;
+
+    const std::vector<MediaTrack*> priorSelection = snapshotSelectedTracks();
+    const double priorCursor = GetCursorPosition();
+    const int mode = computeInsertMode(InsertOptions{});  // current track, native length, no stretch
+
+    // One undo block around the whole drop (every item plus the selection/cursor restore) so a
+    // single Ctrl-Z returns the project to exactly its pre-drop state.
+    Undo_BeginBlock2(nullptr);
+
+    SetOnlyTrackSelected(track);
+    SetEditCurPos(SnapToGrid(nullptr, time), /*moveview=*/false, /*seekplay=*/false);
+
+    int inserted = 0;
+    for (const std::string& path : absolutePaths) {
+        // No cursor reset between files — see assumption B in the file header.
+        InsertMedia(path.c_str(), mode);
+        ++inserted;
+    }
+
+    restoreSelectedTracks(priorSelection);
+    SetEditCurPos(priorCursor, /*moveview=*/false, /*seekplay=*/false);
+
+    // extraflags -1 = UNDO_STATE_ALL, matching the insert action's own block.
+    const std::string label = "ReaSampler: drop " + std::to_string(inserted) +
+                              (inserted == 1 ? " capture" : " captures") + " onto arrange";
+    Undo_EndBlock2(nullptr, label.c_str(), -1);
+    return inserted;
+}
+
+}  // namespace reasampler