arena (25.3b): LOCAL sites allocate from the frame's scratch; dispatch is not an allocation; @frame by property

Behind ludicc --arena (or 'arena on' in the program's package.ludic): the escape analysis runs and a
LOCAL site's allocation raises @lp_want for that one call, so it comes from the frame's arena. Two
halves in one mmap reservation (R3D_ARENA_MB each, 256 by default), bump-allocated with a 16-byte
size header, flipped at each frame mark: a frame's scratch is good through the next frame, then its
half is started again (R3D_ARENA_CHECK=1 fills it with 0xDD first). The heap takes over when no frame
is running, off the main thread, or past the half's end; lp_free ignores an arena block and
lp_realloc copies one out. R3D_ARENA=0 turns it off at run time; the census reports each half's
high-water mark. A program that builds text, a list and a record per frame: 29998 heap blocks made
and 18002 freed without it, 8 and 8 with it and 544 bytes of scratch a frame, the same output.

A dispatch's 'new' fills the queue's kept record (E_NEW.b), so 25.2 no longer counts it and 25.3
treats its fields as kept. '@frame' is keyed by property and field: a 'run' field is a root only in
a property that marks it, and 'tick' stays a System's.

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

selfhost/backend/emit_intrin.ludic

@@ -17,7 +17,13 @@ function is_intrinsic(name: pointer) -> bool {
   return false
 }
 # emit "  <r> = <rest>\n" and return r
-function emit_bind(rest: pointer) -> pointer { fence_bind(rest);  let r = nreg();  emit("  ");  emit(r);  emit(" = ");  emit(rest);  emit("\n");  return r }
+function emit_bind(rest: pointer) -> pointer {
+  let want = fence_bind(rest)                     # 25.3: a LOCAL site's allocation asks for the frame's scratch
+  let r = nreg()
+  emit("  ");  emit(r);  emit(" = ");  emit(rest);  emit("\n")
+  if want { emit("  store i8 0, ptr @lp_want\n") }
+  return r
+}
 
 function arg_code(e: Node, i: int) -> pointer { let v = emit_expr(e.kids[i]);  return v.code }
 # a buffer handed to the platform layer: a slice's elements, never its header (as an extern's are)