fix(compiler): the built-in ECS stops at its 1024th entity instead of writing past every store

L_alloc handed out a fresh slot without a bound, so the 1025th spawn wrote past the end of every
component array. It stops with a located message naming the store's size and where many things
belong (ludic.base's Table). Growable stores are plan 24.8: the save, rollback snapshot and mod
table write the stores whole at a compile-time size, so that is a file-format change. Reseeded;
ludic-dev test 305 passed, selfhost-test 33 passed.

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

changes/ecs-entity-overflow.md

@@ -0,0 +1,7 @@
+bump: patch
+type: fix
+**The 1,025th entity stops the program instead of corrupting it.** The built-in ECS keeps every
+component in a fixed array of 1024 slots, and `L_alloc` never checked: one entity more was written
+past the end of every component array at once. A spawn past the store now stops with `more than
+1024 entities: the built-in ECS holds 1024; keep many things in a ludic.base Table`. A game that
+keeps thousands of something keeps them as rows of `ludic.base`'s `Table<T>`, which grows.

selfhost/backend/game/emit_ecs.ludic

@@ -123,11 +123,15 @@ function emit_ecs_allocator() -> void {
   emit("  br label %done\n")
   emit("fresh:\n")
   emit("  %ec = load i32, ptr @L_entc\n")
+  emit(`  %full = icmp sge i32 %ec, {me}\n`)
+  emit("  br i1 %full, label %over, label %room\n")
+  emit_ecs_full(me)
+  emit("room:\n")
   emit("  %ec1 = add i32 %ec, 1\n")
   emit("  store i32 %ec1, ptr @L_entc\n")
   emit("  br label %done\n")
   emit("done:\n")
-  emit("  %e = phi i32 [ %re, %reuse ], [ %ec, %fresh ]\n")
+  emit("  %e = phi i32 [ %re, %reuse ], [ %ec, %room ]\n")
   emit("  call void @L_reset(i32 %e)\n")
   emit("  %ap = getelementptr inbounds [");  emit(me);  emit(" x i32], ptr @L_alive, i32 0, i32 %e\n")
   emit("  store i32 1, ptr %ap\n")
@@ -144,3 +148,15 @@ function emit_ecs_allocator() -> void {
   emit("  store i32 %fn1, ptr @L_freen\n")
   emit("  ret void\n}\n\n")
 }
+
+# the store is fixed at MAX_ENT: one more entity used to be written past the end of every component
+# array, silently. It stops the program instead, and says where many things belong.
+function emit_ecs_full(me: pointer) -> void {
+  g_uses_panic = true
+  emit("over:\n")
+  let prefix = emit_str_const(`{g_src_name}: panic: `)
+  let m = emit_str_const(`more than {me} entities: the built-in ECS holds {me}; keep many things in a ludic.base Table`)
+  let se = emit_bind(stdstream_rhs(2))
+  emit(`  call i32 (ptr, ptr, ...) @fprintf(ptr {se}, ptr @.fmt_panic, ptr {prefix}, ptr {m})\n`)
+  emit("  call void @exit(i32 1)\n  unreachable\n")
+}