Ψ-W1-T2 review remediation: solo restore drops on visible-in-target, not parked; N-mode segments read dead when unroutable

Fixes a hidden-parent solo replay that could silence the mix. Also closes the N-mode segment silent no-op, amends the invariant comment, trims view.cpp under 600 lines, hedges two SDK inferences, drops a dead null-check.

src/shell/view/view.cpp

@@ -60,15 +60,6 @@ constexpr int kFreeModeFixedLanes = 2;
 // deliberately excluded, nothing is moving there.
 constexpr int kTransportMoving = 1 | 4;
 
-// GUIDs the plan parks in the mode being entered — the set a solo restore skips.
-std::set<std::string> parkedGuidsOf(const TogglePlan& plan) {
-    std::set<std::string> parked;
-    for (const TrackPlan& tp : plan.park) {
-        if (!tp.flags.empty()) parked.insert(tp.flags.front().guid);
-    }
-    return parked;
-}
-
 // C_LANESCOLLAPSED=2: render a tool-split track like a normal single-lane
 // track showing only the playing lane (SDK: 1=collapsed, 2=hidden-lanes-exist
 // but displays as non-fixed-lane).
@@ -394,7 +385,6 @@ bool applyMintPlan(ViewModeModel& model, const LaneMintPlan& plan,
 } // namespace
 
 bool transportBlocksModeSwitch(ReaProject* proj) {
-    if (!GetPlayStateEx) return false;  // fail-open: never gate on a missing API pointer
     return (GetPlayStateEx(proj) & kTransportMoving) != 0;
 }
 
@@ -439,11 +429,7 @@ bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject
     // ride the existing undo block — one mode toggle stays one Ctrl-Z.
     if (realSwitch) {
         model.soloCache().store(outgoingModeId, outgoingSolo);
-        std::vector<view::SoloOp> clearOps;
-        clearOps.reserve(outgoingSolo.size());
-        for (const auto& entry : outgoingSolo)
-            clearOps.push_back(view::SoloOp{entry.first, 0});
-        applySoloOps(handleByGuid, clearOps);
+        clearTrackSolos(handleByGuid, outgoingSolo);
     }
 
     // PARK: snapshot before mutating, store into the model, then apply.
@@ -502,11 +488,13 @@ bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject
 
     model.setActiveMode(targetModeId);
 
-    // Replay + consume, before the single relayout below picks the change up.
+    // Replay + consume, before the single relayout below picks the change up. Dropped
+    // against `visible` (computed above for parent visibility), not the park plan: a
+    // folder parent can be hidden without being parked, and a hidden track must not
+    // receive a replayed solo it carries no visible control to undo.
     if (realSwitch) {
         if (const std::map<std::string, int>* cached = model.soloCache().query(targetModeId)) {
-            applySoloOps(handleByGuid,
-                         view::planSoloRestore(*cached, liveGuids, parkedGuidsOf(plan)));
+            restoreTrackSolos(handleByGuid, *cached, liveGuids, visible);
             model.soloCache().clear(targetModeId);
         }
     }