BEAM process crashes when enumerating keys of a nested empty map proxy

[andr-ec]

Accessing a nested empty map from JavaScript via Object.keys or for...in crashes the entire BEAM process with a C assertion failure.

Reproduction

{:ok, rt} = QuickBEAM.start()
QuickBEAM.load_module(rt, "t", "globalThis.t = function(obj) { return Object.keys(obj.x).length; };")
QuickBEAM.call(rt, "t", [%{x: %{}}])  # crashes BEAM

beam.smp: quickjs.c:1626: void *js_malloc_rt(JSRuntime *, size_t): Assertion `size != 0' failed.
Aborted (core dumped)

Note: top-level empty maps work fine (QuickBEAM.call(rt, "t", [%{}])). The crash only occurs when the empty map is accessed as a nested property of another BEAM proxy object.

Root cause

beam_proxy.get_own_property_names in beam_proxy.zig:103-105 computes byte_size = total * @sizeOf(JSPropertyEnum) where total = map_size + override_count. For an empty map with no overrides, byte_size = 0, and js_malloc(ctx, 0) hits assert(size != 0) in QuickJS.

Top-level empty maps don't crash because QuickJS's JS_GetOwnPropertyNamesInternal uses max_int(atom_count, 1) before allocating. But when the BEAM proxy's exotic get_own_property_names handler is invoked through a nested property access path, it bypasses that guard.

Impact

This crashes any application using QuickBEAM for Vue SSR (via live_vue) when components receive empty maps as props — a common case (e.g. empty unread counts, empty reactions).

Environment

• QuickBEAM 0.10.3
• OTP 28.3.2
• Elixir 1.19.5