Fix stuck drag after OS hand-off withdrawal, split panel_drag_os, doc fixes

Re-checks the physical button before resuming an internal drag and treats a button-up move mid-drag as a release, closing a stale-payload/silent-drop bug; splits the OS hand-off seam into its own TU for the line ceiling; corrects two docs and skips a redundant module-path lookup.

src/app/CMakeLists.txt

@@ -27,6 +27,7 @@ add_library(reaper_reasampler MODULE
     ${REASAMPLER_SRC_DIR}/shell/panel/panel_audition.cpp
     ${REASAMPLER_SRC_DIR}/shell/panel/panel_bank_ops.cpp
     ${REASAMPLER_SRC_DIR}/shell/panel/panel_drag.cpp
+    ${REASAMPLER_SRC_DIR}/shell/panel/panel_drag_os.cpp
     ${REASAMPLER_SRC_DIR}/shell/panel/footer_input.cpp
     ${REASAMPLER_SRC_DIR}/shell/panel/panel_input.cpp
     ${REASAMPLER_SRC_DIR}/shell/panel/panel_layout.cpp

src/shell/actions/CLAUDE.md

@@ -57,7 +57,7 @@ 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; `src/shell/bank_ops/CLAUDE.md` owns the one-op-one-Ctrl-Z rule those verbs enforce. 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` — the host/OS boundary of drag-out: Windows OLE `DoDragDrop`/`CF_HDROP`, copy-only (`DROPEFFECT_MOVE` not offered); macOS/Linux via `SWELL_InitiateDragDropOfFileList`. Owns the two window tests behind `ui::DropContext`'s hand-off proofs (`core/ui/CLAUDE.md` owns the rule they feed). `pointerOverHostWindow` is process identity on Windows (`WindowFromPoint` + `GetWindowThreadProcessId`), non-null `WindowFromPoint` under SWELL, whose window list is already this-process-only; its shipped exception: a plugin bridged into `reaper_host*.exe` reports off-host though the pointer never left REAPER. `pointerOverPluginEditor` walks from the hit window to its root reading each window's owning process and the module of its CLASS procedure (`GetClassLongPtr(GCLP_WNDPROC)` → `GetModuleHandleEx(FROM_ADDRESS)`), and lets `ui::window_origin` decide; its failure modes are listed at the declaration, and it is always false under SWELL. The OLE drop source re-asks the gesture law on every `QueryContinueDrag` (a function pointer the panel supplies) and withdraws the drag per `ui::decideOsDragTurn`, reporting it as `OsDragEnd::Withdrawn*` so the panel resumes its own gesture. A drop into a plugin writes nothing to the bank and inserts no timeline item — the plugin receives a copy-only path list, exactly as from Explorer.
+- `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`. Owns the two window tests behind `ui::DropContext`'s hand-off proofs (`core/ui/CLAUDE.md` owns the rule they feed). `pointerOverHostWindow` is process identity on Windows (`WindowFromPoint` + `GetWindowThreadProcessId`), non-null `WindowFromPoint` under SWELL, whose window list is already this-process-only; its shipped exception: a plugin bridged into `reaper_host*.exe` reports off-host though the pointer never left REAPER. `pointerOverPluginEditor` walks from the hit window to its root reading each window's owning process and the module of its CLASS procedure (`GetClassLongPtr(GCLP_WNDPROC)` → `GetModuleHandleEx(FROM_ADDRESS)`), and lets `ui::window_origin` decide; its failure modes are listed at the declaration, and it is always false under SWELL. The OLE drop source re-asks the gesture law on every `QueryContinueDrag` (a function pointer the panel supplies) and withdraws the drag per `ui::decideOsDragTurn`, reporting it as `OsDragEnd::Withdrawn*` so the panel resumes its own gesture. A drop into a plugin means the extension writes nothing to the bank and inserts no timeline item — the plugin receives a copy-only path list, exactly as from Explorer (the plugin's own reaction to that path list is outside the extension's control).
 - `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 or over a plugin's own editor (so an FX surface reaches the instrument drop only as its chrome; a plugin's editor inside it hands off to the OS) — 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.**
 - `insert_fx_action` — the "Insert as FX" verb: a second ENTRY POINT to `instrument_drop_win`'s drop body (the bank panel's Placement button and a bindable action), loading the panel's focused capture onto the first selected track. Owns no insert logic of its own — it resolves the selection, folds `core/ui/insert_fx_enable`, and calls `performInstrumentDrop` (which keeps the one undo block). Refuses visibly on every failing precondition; the panel button additionally paints dead for the two panel-local ones.
 - `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.

src/shell/actions/drag_out_win.cpp

@@ -356,7 +356,9 @@ ui::WindowFacts windowFacts(HWND hwnd) {
     }
     f.procResolved = true;
     f.hostModule = mod == GetModuleHandleW(nullptr);
-    f.modulePath = moduleFileName(mod);
+    // classifyWindowCode returns Host on hostModule before ever reading modulePath — skip the
+    // (string-building) lookup in that case.
+    if (!f.hostModule) f.modulePath = moduleFileName(mod);
     return f;
 }
 

src/shell/actions/drag_out_win.h

@@ -64,9 +64,21 @@ bool pointerOverHostWindow(int screenX, int screenY);
 //   - a plugin that draws straight into the parent REAPER hands it, creating no window of its
 //     own, leaves nothing of its code in the chain;
 //   - a plugin binary installed beneath the Windows directory reads as an OS module;
-//   - a class procedure that resolves to no module (a charset-mismatch handle) is no evidence.
+//   - a class procedure that resolves to no module (a charset-mismatch handle) is no evidence;
+//   - an all-#32770 dialog-based editor (the generic Windows dialog class) resolves to no
+//     recognizable plugin module — falls to REAPER's outcome;
+//   - a .NET/WPF editor's class procedure is a CLR-thunked address with no resolvable module —
+//     also falls to REAPER's outcome.
+// The opposite direction is unguarded: a third-party hook that replaces REAPER's own chrome
+// class procedure via SetClassLongPtr(GCLP_WNDPROC) would make REAPER's own window read as
+// Plugin — toward OLE instead of away from it.
 // [verify — DAW] that REAPER's GetThingFromPoint names an fx_* token over the plugin's own child
 // window — the law requires it, so an unnamed editor would refuse rather than hand off.
+// [verify — DAW] that OLE never walks up to an ancestor drop target (e.g. REAPER's own file
+// import) when the plugin editor's window registers no IDropTarget of its own.
+// [verify — DAW] that GetThingFromPoint cannot name a REAPER region (e.g. an fx_* token) when a
+// foreign window overlaps it at the same screen point — this fn trusts WindowFromPoint's hit
+// over whatever GetThingFromPoint separately reports.
 // SWELL: always false (no plugin-editor hand-off off Windows). Side-effect-free.
 bool pointerOverPluginEditor(int screenX, int screenY);
 

src/shell/panel/panel_drag.cpp

@@ -148,11 +148,13 @@ void applyDragCursor(CardGesture g) {
     SetCursor(LoadCursor(nullptr, idc));
 }
 
+}  // namespace
+
 // The out-of-client half of the same thin lookup: pure class -> pure cue -> stock cursor. The
 // cue is set on EVERY move, so "will this work" is visible before the button comes up, and a
 // refusal is a cursor the user can see rather than a release that does nothing. Cursor-only by
 // design — the docked panel is usually not under the pointer during an out-of-client drag, so
-// panel status text would be invisible exactly when it is needed.
+// panel status text would be invisible exactly when it is needed. Shared with panel_drag_os.cpp.
 void applyDropCue(DropCue cue) {
     const char* idc = nullptr;
     switch (cue) {
@@ -169,15 +171,7 @@ void applyDropCue(DropCue cue) {
     SetCursor(LoadCursor(nullptr, idc));
 }
 
-// One independent evaluation of the drag's target: the resolved class plus the live facts its
-// outcome needs. Nothing is remembered between calls (core/ui/CLAUDE.md: "the drag-out law is
-// per-move and stateless").
-struct LiveDrop {
-    DropClass cls = DropClass::None;
-    MediaTrack* track = nullptr;
-    int screenX = 0;  // the evaluated point in screen coords; meaningful only outside the client
-};
-
+// Shared with panel_drag_os.cpp (lawHandsOffAtCursor).
 LiveDrop resolveLiveDrop(int x, int y) {
     RECT cr{};
     GetClientRect(g_panel.hwnd, &cr);
@@ -220,80 +214,7 @@ LiveDrop resolveLiveDrop(int x, int y) {
     return out;
 }
 
-// Re-asked by the OS drag loop on every turn. The payload fields the law reads survive
-// resetDragState, so it still sees the drag the hand-off wound down. With the panel gone
-// mid-loop there is no gesture left to give back, so the OS keeps the drag.
-bool lawHandsOffAtCursor() {
-    if (!g_panel.hwnd) return true;
-    POINT p{};
-    GetCursorPos(&p);
-    ScreenToClient(g_panel.hwnd, &p);
-    return resolveLiveDrop(p.x, p.y).cls == DropClass::OsHandoff;
-}
-
-// The OS loop gave the gesture back (ui::OsDragTurn::Withdraw*): restore exactly the fields
-// resetDragState cleared that the drag still needs, then either keep dragging under our own
-// capture or — the release was consumed by the OS loop, so no WM_LBUTTONUP will follow — commit
-// at the release point now. No move is replayed here: the next WM_MOUSEMOVE re-resolves the cue,
-// and replaying one could re-enter handOffToOs from inside itself.
-void resumeInternalDrag(const std::string& primaryId, bool released) {
-    if (!g_panel.hwnd) return;
-    g_panel.dragArmed = true;
-    g_panel.dragging = true;
-    g_panel.dragPrimaryId = primaryId;
-
-    POINT p{};
-    GetCursorPos(&p);
-    ScreenToClient(g_panel.hwnd, &p);
-    if (released) {
-        onLBtnUp(p.x, p.y);
-        return;
-    }
-    // [verify — DAW] that SetCapture re-takes the mouse mid-press after DoDragDrop released it.
-    SetCapture(g_panel.hwnd);
-    invalidatePanel();
-}
-
-// The hand-off: DoDragDrop takes mouse capture and runs its own modal loop, so the internal drag
-// must be fully wound down first, and only once the payload is known to be hand-off-able. This
-// runs on every qualifying move — do not memoize a failed attempt. The OS loop may hand the
-// gesture back (ui::OsDragTurn owns why); a side effect worth keeping is that, on Windows, a
-// return trip can no longer drop a CF_HDROP on REAPER's file import or on this panel's own
-// WM_DROPFILES ingest — the release there is withdrawn, not dropped.
-void handOffToOs() {
-    // Resolve BEFORE tearing anything down (the resolver reads the live drag payload), then let
-    // the pure rule couple the two side effects: an unresolvable payload leaves the internal
-    // drag intact rather than winding it down for a hand-off that never runs — a half-torn-down
-    // drag reads as "the drag did nothing, try again". canInitiateDragOut extends the same
-    // coupling to the OS-readiness failures the pure decision cannot see.
-    const std::vector<std::string> paths = resolveDragPathsForOs();
-    if (!ui::decideOsHandoff(paths).handOffToOs || !canInitiateDragOut(paths)) {
-        applyDropCue(DropCue::Refuse);
-        invalidatePanel();
-        return;
-    }
-
-    const std::string primaryId = g_panel.dragPrimaryId;  // resetDragState clears it
-    if (GetCapture() == g_panel.hwnd) ReleaseCapture();
-    resetDragState();
-    invalidatePanel();
-
-    // COPY-ONLY; blocking on Windows.
-    switch (initiateDragOut(g_panel.hwnd, paths, &lawHandsOffAtCursor)) {
-        case OsDragEnd::Withdrawn:
-            resumeInternalDrag(primaryId, /*released=*/false);
-            return;
-        case OsDragEnd::WithdrawnAtRelease:
-            resumeInternalDrag(primaryId, /*released=*/true);
-            return;
-        case OsDragEnd::Concluded:
-            break;
-    }
-
-    // The drag state was reset above, so the WM_LBUTTONUP that ends the modal loop takes
-    // onLBtnUp's not-dragging branch and never restores the arrow — do it here instead.
-    SetCursor(LoadCursor(nullptr, IDC_ARROW));
-}
+namespace {
 
 // Resolves the topmost INTERACTIVE element under client (x, y) for hover feedback,
 // mirroring handleClick's precedence exactly (so the element that lights on hover is
@@ -381,7 +302,15 @@ void maybeShowTooltip() {
     }
 }
 
-void onMouseMove(int x, int y) {
+void onMouseMove(int x, int y, WPARAM wParam) {
+    // A move with the button already up while still dragging means the release was missed (the
+    // OS hand-off's own modal loop can eat a WM_LBUTTONUP, and coalescing can lose one too) —
+    // treat it as the release now rather than leaving dragging stuck for the next plain click.
+    if (g_panel.dragging && !(wParam & MK_LBUTTON)) {
+        onLBtnUp(x, y);
+        return;
+    }
+
     // Hover feedback: resolve + repaint-on-change, but NOT during a drag (the drag owns
     // the visual feedback then — a drop-target highlight, not a hover).
     if (!g_panel.dragging && !g_panel.dragArmed) updateHover(x, y);

src/shell/panel/panel_drag_os.cpp

@@ -0,0 +1,113 @@
+// panel_drag_os.cpp — the OS hand-off / resume seam split out of panel_drag.cpp (the ~600-line
+// file ceiling): the live re-ask the OS drag loop uses to decide whether to keep the drag, the
+// hand-off itself, and resuming the internal drag when the OS loop gives the gesture back.
+//
+// Compiled into the reaper_reasampler MODULE. No REAPER API functions are called directly here;
+// REAPER SDK types arrive via panel_state.h.
+
+#include <string>
+#include <vector>
+
+#include "shell/panel/panel_state.h"
+
+#include "shell/actions/drag_out_win.h"  // OLE / SWELL drag-out initiation seam
+
+namespace reasampler::panel {
+
+namespace {
+
+// The physical left button, honouring a swapped primary button (SM_SWAPBUTTON) — distinct from
+// dragging/dragArmed, which only say what OUR state machine last believed. Read fresh rather than
+// trusted, because DoDragDrop's own modal loop can consume the WM_LBUTTONUP that would otherwise
+// have told us the button came up.
+bool leftButtonPhysicallyDown() {
+    const int vk = GetSystemMetrics(SM_SWAPBUTTON) ? VK_RBUTTON : VK_LBUTTON;
+    return (GetAsyncKeyState(vk) & 0x8000) != 0;
+}
+
+// Re-asked by the OS drag loop on every turn. The payload fields the law reads survive
+// resetDragState, so it still sees the drag the hand-off wound down. With the panel gone
+// mid-loop there is no gesture left to give back, so the OS keeps the drag.
+bool lawHandsOffAtCursor() {
+    if (!g_panel.hwnd) return true;
+    POINT p{};
+    GetCursorPos(&p);
+    ScreenToClient(g_panel.hwnd, &p);
+    return resolveLiveDrop(p.x, p.y).cls == DropClass::OsHandoff;
+}
+
+// The OS loop gave the gesture back (ui::OsDragTurn::Withdraw*): restore exactly the fields
+// resetDragState cleared that the drag still needs, then either keep dragging under our own
+// capture or — the release was consumed by the OS loop, so no WM_LBUTTONUP will follow — commit
+// at the release point now. No move is replayed here: the next WM_MOUSEMOVE re-resolves the cue,
+// and replaying one could re-enter handOffToOs from inside itself.
+void resumeInternalDrag(const std::string& primaryId, bool released) {
+    if (!g_panel.hwnd) return;
+    g_panel.dragArmed = true;
+    g_panel.dragging = true;
+    g_panel.dragPrimaryId = primaryId;
+
+    POINT p{};
+    GetCursorPos(&p);
+    ScreenToClient(g_panel.hwnd, &p);
+    if (released) {
+        onLBtnUp(p.x, p.y);
+        return;
+    }
+    // [verify — DAW] that SetCapture re-takes the mouse mid-press after DoDragDrop released it.
+    SetCapture(g_panel.hwnd);
+    // The button can have come up between DoDragDrop's own release and this re-capture (the
+    // Withdrawn turn only promises the button was down AT the last OS-loop turn, not at this
+    // instant) — without this check dragging stays armed with a stale payload, and the very next
+    // plain click commits a reorder/replace nobody asked for.
+    if (!leftButtonPhysicallyDown()) {
+        onLBtnUp(p.x, p.y);
+        return;
+    }
+    invalidatePanel();
+}
+
+}  // namespace
+
+// The hand-off: DoDragDrop takes mouse capture and runs its own modal loop, so the internal drag
+// must be fully wound down first, and only once the payload is known to be hand-off-able. This
+// runs on every qualifying move — do not memoize a failed attempt. The OS loop may hand the
+// gesture back (ui::OsDragTurn owns why); a side effect worth keeping is that, on Windows, a
+// return trip can no longer drop a CF_HDROP on REAPER's file import or on this panel's own
+// WM_DROPFILES ingest — the release there is withdrawn, not dropped.
+void handOffToOs() {
+    // Resolve BEFORE tearing anything down (the resolver reads the live drag payload), then let
+    // the pure rule couple the two side effects: an unresolvable payload leaves the internal
+    // drag intact rather than winding it down for a hand-off that never runs — a half-torn-down
+    // drag reads as "the drag did nothing, try again". canInitiateDragOut extends the same
+    // coupling to the OS-readiness failures the pure decision cannot see.
+    const std::vector<std::string> paths = resolveDragPathsForOs();
+    if (!ui::decideOsHandoff(paths).handOffToOs || !canInitiateDragOut(paths)) {
+        applyDropCue(DropCue::Refuse);
+        invalidatePanel();
+        return;
+    }
+
+    const std::string primaryId = g_panel.dragPrimaryId;  // resetDragState clears it
+    if (GetCapture() == g_panel.hwnd) ReleaseCapture();
+    resetDragState();
+    invalidatePanel();
+
+    // COPY-ONLY; blocking on Windows.
+    switch (initiateDragOut(g_panel.hwnd, paths, &lawHandsOffAtCursor)) {
+        case OsDragEnd::Withdrawn:
+            resumeInternalDrag(primaryId, /*released=*/false);
+            return;
+        case OsDragEnd::WithdrawnAtRelease:
+            resumeInternalDrag(primaryId, /*released=*/true);
+            return;
+        case OsDragEnd::Concluded:
+            break;
+    }
+
+    // The drag state was reset above, so the WM_LBUTTONUP that ends the modal loop takes
+    // onLBtnUp's not-dragging branch and never restores the arrow — do it here instead.
+    SetCursor(LoadCursor(nullptr, IDC_ARROW));
+}
+
+}  // namespace reasampler::panel

src/shell/panel/panel_state.h

@@ -536,11 +536,28 @@ void registerAccel();
 void unregisterAccel();
 
 // panel_drag.cpp — the card-drag/hover state machine (pure mirror: core/ui/card_drag).
-// Per-mouse-move work stays plain free-function calls.
-void onMouseMove(int x, int y);
+// Per-mouse-move work stays plain free-function calls. wParam carries WM_MOUSEMOVE's own
+// button-state flags (MK_LBUTTON etc) so a move with the button already up can be told apart
+// from GetAsyncKeyState's live-polled state.
+void onMouseMove(int x, int y, WPARAM wParam);
 void onLBtnUp(int x, int y);
 void handleRightClick(int x, int y);
 void resetDragState();
 void maybeShowTooltip();
 
+// One independent evaluation of the drag's target: the resolved class plus the live facts its
+// outcome needs. Nothing is remembered between calls (core/ui/CLAUDE.md: "the drag-out law is
+// per-move and stateless"). Shared with panel_drag_os.cpp.
+struct LiveDrop {
+    DropClass cls = DropClass::None;
+    MediaTrack* track = nullptr;
+    int screenX = 0;  // the evaluated point in screen coords; meaningful only outside the client
+};
+LiveDrop resolveLiveDrop(int x, int y);
+void applyDropCue(DropCue cue);
+
+// panel_drag_os.cpp — the OS hand-off / resume seam split out of panel_drag.cpp (the ~600-line
+// file ceiling).
+void handOffToOs();
+
 }  // namespace reasampler::panel

src/shell/panel/panel_window.cpp

@@ -152,7 +152,7 @@ WDL_DLGRET dlgProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {
             return 0;
         }
         case WM_MOUSEMOVE:
-            onMouseMove(GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam));
+            onMouseMove(GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam), wParam);
             return 0;
         case WM_LBUTTONUP:
             onLBtnUp(GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam));