Strip FX writes from the Design View mode switch; split view.cpp into park/lanes/reconcile/tracks and add the record-scoped undo repair pass

src/shell/view/view_lanes.h

@@ -0,0 +1,43 @@
+#pragma once
+// Managed fixed lanes, REAPER side: minting one lane per mode on a track whose own
+// content spans modes, driving the active mode's lane audible and every other
+// managed lane silent+hidden, and recovering ownership from the durable P_LANENAME
+// on project open. Manual lanes are never minted, driven, renamed or reassigned.
+
+#include <vector>
+
+#include "core/view/view_mode_model.h"
+#include "shell/view/view_tracks.h"
+
+// Forward-declared to keep this header SDK-free; the .cpp includes the real SDK header.
+class ReaProject;
+
+namespace reasampler {
+
+// `freeMode` alone decides whether UpdateTimeline is owed (SDK: required after an
+// I_FREEMODE change); `wrote` is any project write at all, which is what the apply's
+// undo-point decision reads.
+struct LaneApplyResult {
+    bool freeMode = false;
+    bool wrote    = false;
+};
+
+// Reconciles each op's durable laneKey to the track's current ordinal (a
+// stale/renamed/deleted key is pruned, never mis-driven) and drives C_LANEPLAYS.
+LaneApplyResult applyLaneOps(const TrackByGuid& handleByGuid,
+                             const std::vector<LanePlayOp>& lanes);
+
+// Splits any track visible in more than one mode while carrying its own media into
+// fixed lanes (one managed lane per involved mode), assigns items, and records
+// ownership in `model`. Wraps the mutation in one Undo block when non-empty. Returns
+// true if any lane was minted (repaint hint). `proj` == nullptr means the current
+// project.
+bool mintManagedLanes(ViewModeModel& model, ReaProject* proj);
+
+// Recovers managed-lane ownership from durable P_LANENAME on project open —
+// self-healing, without minting/reassigning anything and without touching
+// membership. A lane without the managed prefix is left untouched (manual).
+// `proj` == nullptr means the current project.
+void reconcileManagedLanes(ViewModeModel& model, ReaProject* proj);
+
+}  // namespace reasampler