Merge FX-park snapshot guard: refuse to park when the pre-park truth is gone

A snapshot is never taken from a chain a park has touched, on either
half -- flags or per-FX offline. Stranded tracks are refused, named
once in the console, and left recoverable by hand.

src/app/CMakeLists.txt

@@ -65,9 +65,10 @@ target_include_directories(reaper_reasampler PRIVATE ${SDK_INC} ${WDL_INC})
 # The deferred FX-park queue's re-entrancy rule is pure (header-inline, no REAPER
 # types), so it is CTest-covered like a core/ module. Declared here rather than in a
 # src/shell/view/CMakeLists.txt because that directory deliberately has none — its
-# TUs are compiled into this target directly. view_mode_model is linked for
-# makeRestorePlan alone: the cancel path's round trip is a contract between the two,
-# and pinning it against hand-built ops would not catch a change to either half.
+# TUs are compiled into this target directly. view_mode_model is linked for the plan
+# builders the pure half is a contract WITH — makeRestorePlan's round trip through
+# the cancel path, and makeParkPlan's flag set behind the trust test; pinning either
+# against hand-built ops would not catch a change to the other half.
 reasampler_test(view_fx_park LINK fx_offline view_mode_model)
 
 # Bank-package import: the promptless verb plus its action skin. Kept as its own