feat(ludic.lab): the visual lab as a package - a scene on a plate, never a world

A scene is an entry in the open registry LabScenes, shown on a plate: a
flat lit disc, the package's own small sky with the sun at one hour, and
a frame clock. Headless each camera (lab_shot, lab_shot_at) settles and
is written as build/lab/<scene>/<shot>.png (a stored PNG, written here);
in a window N and P step through them. tools/lab/run.sh and sheet.py
make the contact sheet; tools/lab/plate_build.py makes plate/.
ludic.render3d gains r3d_plate_mode (no terrain, grass or water is made)
and r3d_sky_path. quit() in a program with no frame loop links. The
example takes ~120 MB resident, 417 MiB peak footprint. Reseed.

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

selfhost/backend/emit_call.ludic

@@ -582,7 +582,7 @@ function emit_call(e: Node) -> Val {
     emit("  call void @L_world_load(ptr ");  emit(b.code);  emit(", i32 ");  emit(l.code);  emit(")\n")
     return val("0", "void")
   }
-  if (name == "quit") { emit("  store i32 0, ptr @L_running\n");  return val("0", "void") }
+  if (name == "quit") { g_uses_quit = true;  emit("  store i32 0, ptr @L_running\n");  return val("0", "void") }
   # NETWORKING (NETWORKING-DESIGN §5) — the low-level freedom layer, callable from
   # Ludic. serialize/apply/sync_size lower to the @Sync by-kind dispatchers (N2);
   # owner/set_owner/is_owner to the @Owned storage (N3); is_server/local_id read

selfhost/backend/emit_core.ludic

@@ -46,6 +46,7 @@ var g_fprintf_declared: bool = false  # @fprintf is declared once, by whoever ne
 var g_bounds: bool = true        # check every slice index (--no-bounds turns it off)
 var g_uses_result: bool = false  # ok()/err()/try was emitted -> define the %Result value type (issue #46)
 var g_uses_option: bool = false  # some()/none() was emitted -> define the %Option value type (issue #53)
+var g_uses_quit: bool = false    # quit() was lowered: a program with no frame loop still needs @L_running
 var g_tests: []Node              # test "name" { ... } blocks collected by the parser
 var g_src_name: pointer = "?"    # base name of the source file, for panic/expect file:line messages
 var g_uses_longstr: bool = false  # string(long) / interpolating a long was emitted -> emit fn_long_str

selfhost/backend/emit_decl.ludic

@@ -273,6 +273,7 @@ function emit_program() -> void {
   g_fprintf_declared = false
   g_uses_result = false
   g_uses_option = false
+  g_uses_quit = false
   g_uses_world_despawn = false                   # #84: set when a world_despawn call is emitted (below)
   g_cov_lines = new []int
   g_cov_active = true
@@ -312,6 +313,8 @@ function emit_program() -> void {
     i = 0
     while i < len(prog) { if prog[i].kind == N_MAIN { emit_main(prog[i]) };  i += 1 }
   } } }
+  # quit() in a program with no frame loop (a package's code in a test program): the flag it sets
+  if g_uses_quit and not has_ecs() { emith("@L_running = internal global i32 1\n") }
   if g_uses_world_despawn { emit_world_despawn_fn() }   # #84: @fn_world_despawn, after all World.despawn / esys_bounds-kill uses are seen
   if g_uses_loopback { emit_loopback() }         # built-in transport, after all net_send/net_poll uses are seen
   if g_uses_str { emit_str_prelude() }          # @lp_str_eq / @lp_str_concat, after all uses are seen