Collapse a Design View mode switch and its background FX parking to ONE undo point

applyMode now returns with its undo block open; the reclaimer closes it when the drain
settles. A transport deferral or a tab switch ends it early -- two points, never a leak.

src/shell/view/view.h

@@ -32,9 +32,6 @@ bool transportBlocksModeSwitch(ReaProject* proj);
 //
 // A real switch mints regardless, fail-safe: it is an explicitly fired action and has
 // to stay undoable even in the degenerate case where the plan found nothing to write.
-// Note what applyMode CANNOT see when it decides — the `view_state` ext-state write
-// lands in persistViewState, after this block has closed (src/shell/view/CLAUDE.md's
-// Gotchas).
 inline bool applyMintsUndoPoint(bool realSwitch, bool wroteAnything) {
     return realSwitch || wroteAnything;
 }
@@ -54,6 +51,10 @@ bool modeApplyInProgress();
 // path: TrackFX_SetOffline was 1897ms of a measured 1942ms switch, against 0.02ms for
 // all the flag work below. Do not reintroduce a synchronous FX write.
 //
+// A REAL switch therefore RETURNS WITH ITS UNDO BLOCK STILL OPEN (fx_reclaim's
+// UndoSpan): the reclaimer closes it once the parking has drained, which is what keeps
+// the switch and its FX writes ONE point rather than two. A reapply closes its own.
+//
 // Returns false (no mutation) if `targetModeId` isn't registered, if this is a real
 // switch (target != active) while the transport is running, if it is re-entered
 // (modeApplyInProgress), or if the project does not validate. A reapply (target ==