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/core/view/CLAUDE.md

@@ -92,7 +92,7 @@ settled 2026-07-23):
 ## Modules
 
 - `view_mode_model` — Design View mode system: mode registry, GUID-keyed membership, folder-tree-aware visibility derivation, snapshot-based park/restore planner, the per-mode `SoloCache` it owns, JSON round-trip.
-- `solo_cache` — the per-mode solo surface: `SoloCache` (mode id → GUID → raw `I_SOLO`), the soloed-subset filter, and `planSoloRestore`, whose two drop rules (dead GUID, track parked in the incoming mode) and their reasoning live in its header.
+- `solo_cache` — the per-mode solo surface: `SoloCache` (mode id → GUID → raw `I_SOLO`), the soloed-subset filter, and `planSoloRestore`, whose two drop rules (dead GUID, not visible in the incoming mode) and their reasoning live in its header.
 - `view_tree` — pure `I_FOLDERDEPTH`→FolderTree helper for the Design View shell.
 - `mode_switch` — REAPER-free segment layout + hit-test for the bank_panel's Design View mode switch.
 - `guid_diff` — the pure, REAPER-free core of the D2 Wave-2 new-content detection: `newGuids(previous, current)` computes the GUIDs present in `current` but absent from `previous` (empty GUIDs ignored); `GuidBaseline` tracks the live GUID set across polls for one project, implementing the first-poll-after-open guard (the first `observe()` after construction/`reset()` records a baseline and reports nothing new, so pre-existing content is never mass-tagged) and re-arms via `reset()` on a detected project switch so detection never diffs across two unrelated projects.

src/core/view/solo_cache.cpp

@@ -53,11 +53,11 @@ std::size_t SoloCache::reconcile(const std::set<std::string>& liveGuids) {
 
 std::vector<SoloOp> planSoloRestore(const std::map<std::string, int>& cached,
                                     const std::set<std::string>& liveGuids,
-                                    const std::set<std::string>& parkedGuids) {
+                                    const std::set<std::string>& visibleGuids) {
     std::vector<SoloOp> ops;
     for (const auto& [guid, value] : cached) {
         if (liveGuids.count(guid) == 0) continue;
-        if (parkedGuids.count(guid) != 0) continue;
+        if (visibleGuids.count(guid) == 0) continue;
         ops.push_back(SoloOp{guid, value});
     }
     return ops;

src/core/view/solo_cache.h

@@ -73,14 +73,18 @@ private:
 // The incoming mode's restore writes, in GUID order. Two kinds of entry are dropped
 // rather than written:
 //   * a GUID absent from `liveGuids` — the track is gone (same prune rule as above);
-//   * a GUID parked in the incoming mode — a parked track is hidden and carries
-//     B_MAINSEND=0, so soloing it would silence the whole mix while contributing
-//     nothing audible, and the user would have no visible control to undo it.
+//   * a GUID absent from `visibleGuids` — not visible in the incoming mode, whether
+//     because the leaf is parked or because it is a folder parent that is itself
+//     derived-invisible there. Either way the track is hidden and (for a parked
+//     leaf) carries B_MAINSEND=0, so soloing it would silence the whole mix while
+//     contributing nothing audible, and the user would have no visible control to
+//     undo it. A show-both leaf is a member of every mode's visible set, so it is
+//     never dropped by this rule.
 // The caller consumes the whole mode entry regardless (clear-on-restore), so a
 // dropped entry does not linger as zombie state waiting on a track that may never
-// come back unparked.
+// become visible again.
 std::vector<SoloOp> planSoloRestore(const std::map<std::string, int>& cached,
                                     const std::set<std::string>& liveGuids,
-                                    const std::set<std::string>& parkedGuids);
+                                    const std::set<std::string>& visibleGuids);
 
 } // namespace reasampler::view