fn main() {
    // RFC 019 §7 test canary (agreed Q3): compiled without stack-clash
    // protection so its 96 KiB local is a genuine one-displacement guard
    // jumper; distro-hardened compilers would otherwise probe it page-wise
    // and defeat the test's purpose.
    cc::Build::new()
        .file("canary/canary.c")
        .flag_if_supported("-fno-stack-clash-protection")
        .compile("smarm_canary");
    println!("cargo:rerun-if-changed=canary/canary.c");

    // RFC 010 c6d — build_hash inputs. The compile-time facts a peer must
    // share for a mesh link: the exact toolchain and the declared (enabled)
    // feature set. Emitted as a plain string; the hashing (FNV-1a folded
    // with PROTO_VERSION) happens in src/cluster.rs where the protocol
    // version actually lives — parsing it out of a source file here would
    // be a second, fragile copy. Always emitted, even for non-cluster
    // builds: one env var costs the default build nothing.
    let rustc = std::env::var("RUSTC").unwrap_or_else(|_| "rustc".to_string());
    let version = std::process::Command::new(&rustc)
        .arg("-V")
        .output()
        .ok()
        .map(|o| String::from_utf8_lossy(&o.stdout).trim().to_string())
        .filter(|v| !v.is_empty())
        .unwrap_or_else(|| "rustc-unknown".to_string());
    let mut feats: Vec<String> = std::env::vars()
        .filter_map(|(k, _)| k.strip_prefix("CARGO_FEATURE_").map(str::to_string))
        .collect();
    feats.sort();
    println!(
        "cargo:rustc-env=SMARM_BUILD_HASH_INPUTS={version};features={}",
        feats.join(",")
    );
    println!("cargo:rerun-if-env-changed=RUSTC");
}