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/check/check_call.ludic

@@ -95,6 +95,11 @@ function ck_walk_args(e: Node) -> void {
 }
 # the builtins whose type is their name, and push, whose element must fit the slice
 function ck_builtin(e: Node, name: pointer) -> pointer {
+  if (name == "keep") and len(e.kids) == 1 { return ck_expr(e.kids[0]) }       # 25.3: a copy on the heap, the same type
+  if (name == "intern") and len(e.kids) == 1 {                                   # 25.3: one heap string per distinct text
+    ck_walk_args(e)
+    return "string"
+  }
   if (name == "string") or (name == "int") or (name == "float") or (name == "fixed") or (name == "long") or (name == "double") {
     ck_walk_args(e)
     return name