add dockerfile

crates/rsh-backend/build.rs

@@ -0,0 +1,25 @@
+use std::path::{Path, PathBuf};
+
+fn resolve_stub(env_var: &str, out_name: &str, out_dir: &Path) -> PathBuf {
+    println!("cargo:rerun-if-env-changed={env_var}");
+    let dest = out_dir.join(out_name);
+    if let Ok(src) = std::env::var(env_var) {
+        let src = PathBuf::from(&src);
+        if src.exists() {
+            println!("cargo:rerun-if-changed={}", src.display());
+            std::fs::copy(&src, &dest).expect("copy stub");
+            return dest;
+        }
+        println!("cargo:warning={env_var} set to {src:?} but file not found; serving 503 for this arch");
+    }
+    std::fs::write(&dest, []).expect("write placeholder");
+    dest
+}
+
+fn main() {
+    let out_dir = PathBuf::from(std::env::var("OUT_DIR").unwrap());
+    let x86 = resolve_stub("RSH_STUB_X86_64", "rsh-x86_64", &out_dir);
+    let arm = resolve_stub("RSH_STUB_AARCH64", "rsh-aarch64", &out_dir);
+    println!("cargo:rustc-env=STUB_X86_64_PATH={}", x86.display());
+    println!("cargo:rustc-env=STUB_AARCH64_PATH={}", arm.display());
+}