region rule (25.3c): keep() and intern(), frame_keeps, and --arena-strict

keep(x) copies a string, a slice (header and elements) or a record (shallow) onto the heap; intern(s)
hands back one heap string per distinct text from a fixed table in the runtime (FNV-1a, 65536 slots,
copied the first time; past 49152 only copied). Both are how frame code keeps what it made on purpose:
the escape analysis takes the copy as the heap's and leaves the argument LOCAL.

The analysis now records why a class escapes (the store, the event, the global it reached) and
ludic deps lists every allocation frame code makes and keeps - fkeep lines, 'ludic deps --keeps',
the frame_keeps number --check ratchets - leaving out what is under @alloc_ok and a push's growth
(25.5's capacities). --arena-strict (or 'arena strict') makes each an error naming the store, before
anything is emitted. A test: a template stored into a state is the one error; keep and intern of the
next two, an @alloc_ok push and a scratch temporary are not; 195 frames of arena resets under
R3D_ARENA_CHECK=1 later the kept and interned texts read as made, and intern gives the same string.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

selfhost/main.ludic

@@ -232,6 +232,11 @@ entry {
   check_program()                                 # L4: the types agree before anything is emitted
   if g_es_report { escape_report() }              # 25.3: which allocations never outlive their frame
   else if g_arena { escape_analyse() }             # 25.3: and they allocate from the frame's scratch
+  if g_arena_strict and (getenv_or("LUDIC_DEPS", "") == "") {   # 25.3: the region rule, before anything is emitted
+    let sink = file_open("/dev/null", "wb")
+    deps_reach(sink)
+    file_close(sink)
+  }
   if g_migrate { mg_finish() }
   # --check: every check a build makes - the emitter refuses things too (a bind to a function that is
   # gone, an unknown name) - and nothing written