Os.heap_bytes: the heap without the renderer; string_temps reads it

Vk.heap_bytes pulled the Vk module - and on lang/uifree the GL window path - into a plain program,
which then failed to link (_cgl_offscreen, lgl_GetError). Os.heap_bytes is malloc_zone_statistics
through a weak reference (0 where there is none, and on Windows). Reseeded. Docs for it and for
Json.free / Json.free_all.

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

selfhost/backend/emit_core.ludic

@@ -37,6 +37,7 @@ var g_uses_noisert: bool = false  # Noise.* was emitted -> emit the fixed-point
 var g_uses_logrt: bool = false  # Log.* was emitted -> emit the log level register + console sink
 var g_uses_osrt: bool = false  # Os.* (prelude-backed methods) was emitted -> emit the Os runtime
 var g_uses_pid: bool = false   # Os.pid() was emitted -> declare libc getpid
+var g_uses_heap: bool = false  # Os.heap_bytes() was emitted -> @lp_os_heap_bytes
 var g_uses_unicodert: bool = false  # Unicode.* was emitted -> emit the UTF-8 runtime
 var g_uses_fsrt: bool = false  # Fs.*/Path.*/Mime.* was emitted -> emit the filesystem runtime
 var g_uses_pak: bool = false   # file_open was emitted -> emit the asset-pack runtime (implies fsrt)

selfhost/backend/emit_decl.ludic

@@ -350,6 +350,7 @@ function emit_program() -> void {
   if g_uses_logrt { emit_log_prelude() }         # @L_log_level + @lp_log_emit (levelled stderr sink)
   if g_uses_osrt { emit_os_prelude() }           # @lp_os_args/platform/arch/save_dir/... (libc env + uname)
   if g_uses_pid and (not g_target_win) { emith("declare i32 @getpid()\n") }
+  if g_uses_heap { emit_os_heap() }
   if g_uses_unicodert { emit_unicode_prelude() }  # @lp_uni_len/valid/decode/case/truncate/grapheme (UTF-8)
   if g_uses_fsrt { emit_fs_prelude() }           # @fn_fs_*/fn_path_*/fn_mime_* (libc + string ops)
   if g_uses_pak { emit_pak_prelude() }           # @lp_pak_* asset packs + the pre-main mount ctor

selfhost/backend/stdlib/emit_os.ludic

@@ -22,6 +22,8 @@
 #   Os.config_dir(app)     -> string     per-user config directory for `app`
 #   Os.cache_dir(app)      -> string     per-user cache directory for `app`
 #   Os.temp_dir()          -> string     the system temporary directory
+#   Os.heap_bytes()        -> long       malloc's live bytes (macOS; 0 elsewhere): a test that a
+#                                        path allocates nothing, with no renderer linked in
 #
 # Determinism: args/env/platform are non-deterministic host input — read them at
 # startup to configure the game, but keep them out of the replayable simulation.
@@ -39,6 +41,7 @@ function is_os_ns(meth: pointer) -> bool {
   if (meth == "exit") or (meth == "pid") or (meth == "platform") or (meth == "arch") { return true }
   if (meth == "stdout_write") or (meth == "stderr_write") { return true }
   if (meth == "save_dir") or (meth == "config_dir") or (meth == "cache_dir") or (meth == "temp_dir") { return true }
+  if (meth == "heap_bytes") { return true }
   return false
 }
 
@@ -53,6 +56,11 @@ function emit_os_ns(meth: pointer, e: Node) -> Val {
     return val(emit_bind(`load ptr, ptr {q}`), "string")
   }
   if (meth == "pid") { g_uses_pid = true;  return val(emit_bind("call i32 @getpid()"), "int") }
+  if (meth == "heap_bytes") {
+    if g_target_win { return val("0", "long") }
+    g_uses_heap = true
+    return val(emit_bind("call i64 @lp_os_heap_bytes()"), "long")
+  }
   if (meth == "exit") {
     let n = emit_expr(e.kids[0])
     emit(`  call void @exit(i32 {n.code})\n`)
@@ -243,3 +251,14 @@ function emit_os_prelude() -> void {
   emith("entry:\n  %buf = call ptr @malloc(i64 8192)\n  call i32 @uname(ptr %buf)\n")
   emith("  %m = getelementptr i8, ptr %buf, i64 1024\n  ret ptr %m\n}\n")
 }
+
+# Os.heap_bytes: malloc_zone_statistics' in-use bytes, all zones. The symbol is weak, so a libc
+# without it links and reads 0.
+function emit_os_heap() -> void {
+  emith("declare extern_weak void @malloc_zone_statistics(ptr, ptr)\n")
+  emith("define i64 @lp_os_heap_bytes() {\n")
+  emith("entry:\n  %has = icmp ne ptr @malloc_zone_statistics, null\n  br i1 %has, label %read, label %none\n")
+  emith("none:\n  ret i64 0\n")
+  emith("read:\n  %st = alloca [4 x i64], align 8\n  call void @malloc_zone_statistics(ptr null, ptr %st)\n")
+  emith("  %p = getelementptr [4 x i64], ptr %st, i32 0, i32 1\n  %n = load i64, ptr %p\n  ret i64 %n\n}\n")
+}