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/CMakeLists.txt

@@ -1,11 +1,15 @@
 reasampler_pure_library(lane_keys SOURCES lane_keys.cpp)
 reasampler_test(lane_keys LINK lane_keys)
 
-# lane_keys is PUBLIC: the lane-minting plan names managed lanes through the one durable-key
-# convention, so every consumer has to resolve that symbol too.
+reasampler_pure_library(solo_cache SOURCES solo_cache.cpp)
+reasampler_test(solo_cache LINK solo_cache)
+
+# lane_keys and solo_cache are PUBLIC: the lane-minting plan names managed lanes through the
+# one durable-key convention, and ViewModeModel exposes the SoloCache by reference, so every
+# consumer has to resolve those symbols too.
 reasampler_pure_library(view_mode_model
     SOURCES view_mode_model.cpp
-    LINK PRIVATE json PUBLIC lane_keys)
+    LINK PRIVATE json PUBLIC lane_keys solo_cache)
 reasampler_test(view_mode_model LINK view_mode_model)
 
 reasampler_pure_library(view_tree SOURCES view_tree.cpp LINK PUBLIC view_mode_model)