//! Compile-fail tests pinning structural invariants of the curated
//! `lean_rs::*` surface that the type markers alone cannot express:
//!
//! 1. `LeanModule::exported_unchecked` is `unsafe fn`—arbitrary dynamic-export
//! lookup cannot be validated from a symbol name plus caller-chosen
//! `Args`/`R`, so calling it requires an `unsafe` block.
//! 2. `LeanIo<T>` is an opaque type-level marker whose single field is private,
//! so downstream code cannot construct a value.
//!
//! Each negative case is a standalone `.rs` file with a matching `.stderr`
//! snapshot. The snapshots capture `rustc` diagnostics, whose exact wording
//! and whitespace drift across platforms and toolchain versions, so the suite
//! runs only when `RUN_TRYBUILD=1` is set—the pinned `compile-fail` CI job
//! sets it on a single OS + the repo's pinned stable toolchain. Locally,
//! regenerate after a refactor or toolchain bump with:
//!
//! ```sh
//! TRYBUILD=overwrite RUN_TRYBUILD=1 \
//! cargo test -p lean-rs --test compile_fail_surface
//! ```