fix(xatu): count bindings in empty let expressions

AGENTS.md

@@ -96,6 +96,8 @@
 - `rules_rust` `rust_test` targets cannot set both `crate` and `srcs`.
   Use one input style per test target.
 - Rust tests in this monorepo live in separate `*_test.rs` files, not inline `#[cfg(test)]` modules.
+- `rnix::ast::HasEntry::entries()` includes assignments and `inherit` statements.
+  Use `attrpath_values()` when code needs only assignment entries.
 - Ariadne Rust tests are declared in Bazel `BUILD` files; do not add `[[test]]` entries to
   `src/ariadne/Cargo.toml` unless explicitly requested.
 - In this monorepo, "dotfiles" refers to the dotfiles/NixOS configuration under `src/dotfiles/` and `configs/nixos/`.