Collapse the FX-park drain's writes into one undo point instead of one per TrackFX_SetOffline

tests/test_view_fx_park.cpp

@@ -4,8 +4,9 @@
 // The properties under test: a mode switch leaves its per-FX offline work here,
 // so a second switch arriving before the first drained must leave every track in
 // the state the SECOND switch specifies — never the first's, never both replayed;
-// a cancel must not strand the pre-park FX state it was the last record of; and
-// a pre-park snapshot is never taken from a chain a park has already touched.
+// a cancel must not strand the pre-park FX state it was the last record of; a
+// pre-park snapshot is never taken from a chain a park has already touched; and
+// one drain closes as at most ONE undo point, in the FX domain only.
 
 #include "../src/shell/view/view_fx_park.h"
 
@@ -406,6 +407,30 @@ static void testAReEntrantParkCancelsOnlyWhatIsStillPending() {
     CHECK(intentFor(q, "{A}") && intentFor(q, "{A}")->park);
 }
 
+// -- the drain's undo point --------------------------------------------------
+
+static void testADrainThatWroteFxClosesItsBlockAsOneNamedFxPoint() {
+    const FxParkUndoClose close = fxParkUndoClose(true);
+
+    // 2 is UNDO_STATE_FX (reaper_plugin.h:1542), pinned as a literal here and
+    // static_asserted against the macro in view_fx_park.cpp. The drain writes
+    // per-FX offline and nothing else, so any wider mask would make it marshal
+    // track config or items it never touched.
+    CHECK(close.mask == 2);
+    CHECK(close.label != nullptr && std::string(close.label) ==
+                                        "ReaSampler: Design View FX park");
+}
+
+static void testADrainThatWroteNothingClosesItsBlockAsADiscard() {
+    // The project-load reapply: a park is planned for every inactive leaf, and a
+    // project saved parked already holds every one of those FX offline. Nothing is
+    // written, so the block must leave no undo point behind at all.
+    const FxParkUndoClose close = fxParkUndoClose(false);
+
+    CHECK(close.mask == 0);
+    CHECK(close.label != nullptr && std::string(close.label).empty());
+}
+
 int main() {
     testParkEnqueuesOneIntentCarryingNoOps();
     testParkReportsNothingCancelledWhenNoIntentWasPending();
@@ -442,6 +467,9 @@ int main() {
     testIntentsArrivingDuringADrainSurviveIt();
     testAReEntrantParkCancelsOnlyWhatIsStillPending();
 
+    testADrainThatWroteFxClosesItsBlockAsOneNamedFxPoint();
+    testADrainThatWroteNothingClosesItsBlockAsADiscard();
+
     if (g_fail == 0) std::printf("All tests passed.\n");
     return g_fail ? 1 : 0;
 }