fix(view): snapshot-once park guard + correct per-mode undo label

Only capture a track's pre-park snapshot when none exists, so a re-park while
already parked no longer overwrites it with hidden-state zeros (leaves vanished
after toggling twice). Undo label now names the actual target mode.

src/view.cpp

@@ -158,7 +158,15 @@ bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject
         MediaTrack* tr = resolve(handleByGuid, guid);
         if (!tr) continue;  // stale GUID — prune
 
-        model.storeSnapshot(guid, snapshotTrack(tr));
+        // Snapshot ONCE, at the first park. If a snapshot already exists the track is
+        // still parked from a prior apply, and its live flags are the PARKED (hidden)
+        // values — recapturing here would overwrite the true pre-park state with zeros,
+        // so a later restore would restore the track to hidden and it would vanish for
+        // good. Re-applying the park flags to an already-parked track is idempotent and
+        // fine; only the snapshot must not be recaptured. Restore clears the snapshot,
+        // so the next genuine park recaptures fresh state.
+        if (model.snapshot(guid) == nullptr)
+            model.storeSnapshot(guid, snapshotTrack(tr));
         applyFlags(tr, tp.flags);
         parkFxOffline(tr);
     }
@@ -191,6 +199,15 @@ bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject
         SetMediaTrackInfo_Value(tr, "B_SHOWINMIXER", show);
     }
 
+    // Build the undo label from the ACTUAL target mode's display name, so activating
+    // Arrange doesn't leave an "activate Design view" undo point (and vice versa).
+    // The target is guaranteed registered (checked at entry), so query() is non-null;
+    // fall back to the id defensively if that ever changes.
+    const Mode* targetMode = model.modes().query(targetModeId);
+    const std::string undoLabel =
+        "ReaSampler: activate " +
+        (targetMode ? targetMode->displayName : targetModeId) + " view";
+
     model.setActiveMode(targetModeId);
 
     // Force REAPER to rebuild the TCP + MCP so visibility/park changes appear now,
@@ -201,7 +218,7 @@ bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject
     TrackList_AdjustWindows(false);
     UpdateArrange();
 
-    Undo_EndBlock2(proj, "ReaSampler: apply Design View mode", -1);
+    Undo_EndBlock2(proj, undoLabel.c_str(), -1);
     return true;
 }