Fix drag-out giving live drags to OLE: prove the pointer left REAPER

OffReaper leaves the surface vocabulary; OsHandoff now gates on a window-ownership
proof resolved in the shell, so no in-REAPER surface can reach DoDragDrop.

src/shell/actions/CLAUDE.md

@@ -41,8 +41,8 @@ is owned by other directories and only skinned here.
 
 - `shell/actions` (`action_registry` / `design_view_actions` / `bank_actions` / `prune_action`) — the bindable action families, all routed via the `command_id`/`gaccel`/`hookcommand` contract. `action_registry` owns the shared registration plumbing (interned channel-qualified id strings; register and mirror-unregister present the identical pointer) **and the Q-W6 registration TABLE**: `main.cpp`'s own family (capture scopes, panel toggle, insert, batch, realtime, recapture, version) is one `ActionTableRow` array — suffix, phrase, flat function-pointer handler — that registration, hookcommand dispatch, and the unload mirror-unregister all iterate, so adding an action touches the table only (OCP). Bank mutations flow through the promptless `shell/bank_ops` verbs (`bankOp*` + `persistBankOp`, taking `ReaSamplerSession&`), which the panel menus and `bank_actions` consume as thin UX skins. **Every bank index verb wraps its mutation in a batched REAPER undo point (`Undo_BeginBlock2`/`EndBlock2`, `UNDO_STATE_MISCCFG`) so one bank operation is one Ctrl-Z.** The prune action (`prune_action`, `BANK_PRUNE_FOLDER`) is **the ONLY file-deletion action in the system**; it opens no undo point (file deletion is not REAPER-undoable). `BANK_PRUNE_FOLDER` halts on `blockedByTracking` and prints each blocker that fired, with recovery instructions.
 - `package_export_action` — the "export bank as package" skin: survey and report first, confirm what is absent (and, separately, a destination being replaced), pick a destination, write. Every prompt in the flow lives here so `shell/package/export_bank` stays promptless. Read-only against the project — it holds the session by `const&`, so no ext-state write, generation bump or undo point is reachable. Registration rides `main.cpp`'s action table (`EXPORT_BANK_PACKAGE`); the panel's tab menu is the second skin over the same body.
-- `drag_out_win` — OS drag-out shell: Windows OLE `DoDragDrop`/`CF_HDROP`, copy-only (`DROPEFFECT_MOVE` not offered); macOS/Linux via `SWELL_InitiateDragDropOfFileList`.
-- `instrument_drop_win` — instrument-drop shell: `probeDropTarget` resolves a screen point to a track + a `ReaperSurface` (via the pure `wire::classifyReaperSurface`, whose token rules `core/wire/CLAUDE.md` owns), and the drop half adds a ReaSampler 9000 instance and applies the dragged capture's state via a transient `.vstpreset` + `TrackFX_SetPreset` (the former `TrackFX_SetNamedConfigParm` "vst_chunk" write was silently unappliable for VST3). Exposes `loadInstrumentOntoTrack` (inner half, no own undo block) and `performInstrumentDrop` (wraps in its own undo block). **Never captures, never writes the bank, never inserts a timeline item.**
+- `drag_out_win` — the host/OS boundary of drag-out: Windows OLE `DoDragDrop`/`CF_HDROP`, copy-only (`DROPEFFECT_MOVE` not offered); macOS/Linux via `SWELL_InitiateDragDropOfFileList`. Also owns `pointerOverHostWindow`, the window-ownership test behind `ui::DropContext::pointerOffHost` — process identity on Windows (`WindowFromPoint` + `GetWindowThreadProcessId`), non-null `WindowFromPoint` under SWELL, whose window list is already this-process-only.
+- `instrument_drop_win` — instrument-drop shell: `probeDropTarget` resolves a screen point to a track + a `ReaperSurface` (via the pure `wire::classifyReaperSurface`, whose token rules `core/wire/CLAUDE.md` owns) — it answers only what REAPER named, never whether the pointer is still in REAPER, which is `drag_out_win`'s — and the drop half adds a ReaSampler 9000 instance and applies the dragged capture's state via a transient `.vstpreset` + `TrackFX_SetPreset` (the former `TrackFX_SetNamedConfigParm` "vst_chunk" write was silently unappliable for VST3). Exposes `loadInstrumentOntoTrack` (inner half, no own undo block) and `performInstrumentDrop` (wraps in its own undo block). **Never captures, never writes the bank, never inserts a timeline item.**
 - `arrange_drop_win` — the drag-out gesture's arrange outcome: `arrangeTimeAtScreenX` (pointer column → time via `GetSet_ArrangeView2`'s one-pixel-span reading — inferred, not SDK-documented) and `performArrangeDrop` (snap the drop time, then one `InsertMedia` per capture on the pointer's track — assumed, not confirmed, to land end-to-end via REAPER's own cursor advance — in ONE undo block, counting only InsertMedia's reported successes, with the caller's track selection and edit cursor restored). The one timeline-placing shell here, per the invariant above; it never captures and never writes the bank.
 - `package_import_action` — the bindable / bank-menu / file-drop skin over `shell/package`'s `importBankPackage`. Owns the **ledger gate**, which runs BEFORE the file picker (a refusal must not cost the user a file choice) and is keyed on the session's `LedgerStatus` alone — never on `PruneReport::blockedByTracking`, whose undecodable-`rsusage_*` arm governs deletion-time protection and would refuse an import that only writes birth records. Builds and shows every message the import produces, but the ledger-refusal body itself is `core/package::ledgerRefusalMessage` — a pure fold this TU only supplies the channel-correct namespace to — so the wording is assertable without a DAW. `doImportBankPackage`/`doImportBankPackageFile` return the minted bank id on a landed import (empty otherwise) so a caller can focus it; the verb itself is promptless.
 - `ingest` — ingest-through-the-bank shell on the EXTENSION side: three surfaces — (1) arrange capture→bank→assign (bindable action), (2) Media-Explorer import→bank→instrument on the selected track, (3) file drop onto the bank panel→bank only. Only surface (1) writes the `assignment_request` ext-state wire. **ingest NEVER inserts a timeline item.** Surface (2)'s action is the one in this directory published into a NON-main action section (Media Explorer) as well as Main — two ids, one handler, two dispatch hooks; see root `CLAUDE.md` §"REAPER extension contract" for the mechanism.

src/shell/actions/drag_out_win.cpp

@@ -244,6 +244,23 @@ bool canInitiateDragOut(const std::vector<std::string>& absolutePaths) {
     return true;
 }
 
+bool pointerOverHostWindow(int screenX, int screenY) {
+    // Process identity, not window identity: REAPER's arrange, its floating FX and VST editor
+    // windows, its menus and its docker chrome are separate top-level HWNDs with no common
+    // ancestor, so no GetAncestor/GetParent walk reaches them all — but every one of them is
+    // created by the process this extension is loaded into.
+    // Mouse capture does not affect WindowFromPoint: it hit-tests the desktop window tree, not
+    // input routing. It does skip hidden and DISABLED windows, so a REAPER window disabled
+    // behind a modal dialog could fall through to whatever sits beneath — no such dialog can be
+    // up while our panel holds capture for a drag.
+    const POINT pt{screenX, screenY};
+    const HWND hwnd = WindowFromPoint(pt);
+    if (!hwnd) return false;
+    DWORD pid = 0;
+    GetWindowThreadProcessId(hwnd, &pid);
+    return pid == GetCurrentProcessId();
+}
+
 }  // namespace reasampler
 
 #else  // ---- macOS / Linux (SWELL) -----------------------------------------------------
@@ -277,6 +294,15 @@ bool canInitiateDragOut(const std::vector<std::string>& absolutePaths) {
     return !absolutePaths.empty();
 }
 
+// SWELL's WindowFromPoint walks only THIS process's window list (SWELL_topwindows on
+// generic/GDK, [NSApp orderedWindows] on macOS — swell-wnd-generic.cpp / swell-wnd.mm), so a
+// non-null return already carries the process-ownership meaning Win32 needs GetWindowThread-
+// ProcessId for, and a point over any other application returns null.
+bool pointerOverHostWindow(int screenX, int screenY) {
+    POINT pt{screenX, screenY};
+    return WindowFromPoint(pt) != nullptr;
+}
+
 }  // namespace reasampler
 
 #endif

src/shell/actions/drag_out_win.h

@@ -1,7 +1,8 @@
 #pragma once
-// drag_out_win — the OS/COM initiation half of native OS drag-out: hands a resolved
-// existing-file path list to the OS's drag-drop machinery so the user can drop bank
-// samples into Explorer / another app / another DAW. The pure gesture-boundary
+// drag_out_win — the host/OS boundary of native OS drag-out: whether the pointer has
+// crossed it, whether the OS is ready to take the drag, and the hand-off itself, which
+// gives a resolved existing-file path list to the OS's drag-drop machinery so the user can
+// drop bank samples into Explorer / another app / another DAW. The pure gesture-boundary
 // decision + path-list assembly live in drag_out.*.
 //
 // COPY-ONLY is STRUCTURAL on Windows: DoDragDrop's effect mask is DROPEFFECT_COPY
@@ -32,4 +33,12 @@ bool initiateDragOut(HWND__* panelHwnd, const std::vector<std::string>& absolute
 // probe HGLOBAL immediately; SWELL exposes no probe, so macOS/Linux reduces to the non-empty check.
 bool canInitiateDragOut(const std::vector<std::string>& absolutePaths);
 
+// True iff a window belonging to the host (REAPER) process sits under the screen point —
+// the POSITIVE proof ui::DropContext::pointerOffHost is the negation of. Every REAPER
+// surface qualifies whether or not GetThingFromPoint can name it: the arrange, a TCP, a
+// floating FX or VST editor window, the transport, the toolbar, a menu, the docker chrome
+// and our own panel are all windows of this process, because the extension runs inside it.
+// Side-effect-free; safe on every mouse-move.
+bool pointerOverHostWindow(int screenX, int screenY);
+
 } // namespace reasampler

src/shell/actions/instrument_drop_win.cpp

@@ -83,7 +83,7 @@ DropProbe probeDropTarget(int screenX, int screenY) {
     // doc-comment says so), so the track and the surface are two independent facts and both
     // are reported. The pure classifier owns every token rule.
     out.track = GetThingFromPoint(screenX, screenY, info, sizeof(info));
-    out.surface = classifyReaperSurface(info, out.track != nullptr);
+    out.surface = classifyReaperSurface(info);
     return out;
 }
 

src/shell/actions/instrument_drop_win.h

@@ -29,12 +29,14 @@ namespace reasampler {
 // (ui::decideDropClass) turns this plus the payload size into an outcome.
 struct DropProbe {
     MediaTrack* track = nullptr;  // the track under the pointer (null if none / not a track)
-    ui::ReaperSurface surface = ui::ReaperSurface::OffReaper;
+    ui::ReaperSurface surface = ui::ReaperSurface::Other;
 };
 
-// Wraps GetThingFromPoint and hands its (info string, track) pair to the pure
+// Wraps GetThingFromPoint: its track comes back as-is, its info string goes to the pure
 // wire::classifyReaperSurface. Cheap enough to run on every mouse-move, but the panel
 // evaluates it only OUTSIDE its own client rect — the internal drag never pays for it.
+// It reports only what REAPER named; whether the pointer is still inside REAPER at all is
+// drag_out_win::pointerOverHostWindow's, and no surface reported here implies an exit.
 DropProbe probeDropTarget(int screenX, int screenY);
 
 // Adds a fresh ReaSampler 9000 instance to `track` and applies `presetBytes` as its