Ψ-W1-T2: disjoint per-mode solo surfaces and a playback-gated mode switch

Solo is cached, cleared and replayed per mode on a real switch only; the switch is refused visibly while the transport runs. The footer segment now routes through the activate actions, so a panel switch finally persists.

src/core/view/CLAUDE.md

@@ -3,12 +3,13 @@
 ## Scope
 
 Pure, REAPER-free Design View model: mode/track membership, folder-derived
-visibility, snapshot-based park/restore planning, new-content (GUID) detection,
-and the managed/manual lane-identity convention that underlies per-item mode
-separation (fixed lanes). Does **not** include: the actual DAW-side flag
-application (hide, CPU-park, per-FX offline, restore via `B_SHOWINTCP` /
-`B_SHOWINMIXER` / `B_MAINSEND` / `I_FXEN`) or the never-touch-master/mute/solo
-enforcement — those live in `shell/view`.
+visibility, snapshot-based park/restore planning, the per-mode solo cache and its
+replay plan, new-content (GUID) detection, and the managed/manual lane-identity
+convention that underlies per-item mode separation (fixed lanes). Does **not**
+include: the actual DAW-side flag application (hide, CPU-park, per-FX offline,
+restore via `B_SHOWINTCP` / `B_SHOWINMIXER` / `B_MAINSEND` / `I_FXEN`, solo
+cache/clear/replay via `I_SOLO`) or the never-touch-master/mute enforcement —
+those live in `shell/view`.
 
 ## Invariants
 
@@ -33,6 +34,12 @@ settled 2026-07-23):
   from the snapshot, never to a hardcoded default. Round-trip (snapshot → park →
   restore) returns every driven flag to its captured value — this is the
   phase's trust anchor, the analog of the capture null test.
+- **Disjoint solo surfaces, cached not destroyed.** Solo is per mode: a real
+  switch banks the outgoing mode's raw `I_SOLO` values, clears them, and replays
+  the incoming mode's verbatim. Same snapshot sense of non-destructive as the
+  bullet above — the tool never *loses* the user's solo, it parks it with the mode
+  it belongs to. `B_MUTE` and the master track stay untouched absolutely. A
+  reapply touches solo not at all.
 - **GUID-keyed, reorder-safe.** Membership keys on track GUID (`GetTrackGUID`),
   never track index; tolerates unknown/stale GUIDs (pruned on reconcile via
   `ViewModeModel::reconcile(liveGuids)`).
@@ -84,7 +91,8 @@ 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, JSON round-trip.
+- `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.
 - `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.