test(ffi): assert cdylib exists and is readable before ELF inspection

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: yannham

libdd-otel-thread-ctx-ffi/tests/elf_properties.rs

@@ -18,15 +18,27 @@ use std::process::Command;
 const SYMBOL: &str = "otel_thread_ctx_v1";
 
 fn cdylib_path() -> PathBuf {
-    PathBuf::from(env!("CDYLIB_PROFILE_DIR")).join("liblibdd_otel_thread_ctx_ffi.so")
+    let path = PathBuf::from(env!("CDYLIB_PROFILE_DIR")).join("liblibdd_otel_thread_ctx_ffi.so");
+    assert!(
+        path.exists(),
+        "cdylib not found at {}: \
+         ensure `cargo build -p libdd-otel-thread-ctx-ffi` has been run for this profile",
+        path.display()
+    );
+    assert!(
+        std::fs::File::open(&path).is_ok(),
+        "cdylib exists at {} but could not be opened for reading",
+        path.display()
+    );
+    path
 }
 
 fn readelf(args: &[&str], path: &PathBuf) -> String {
     let out = Command::new("readelf")
         .args(args)
         .arg(path)
         .output()
-        .expect("failed to run readelf — is binutils installed?");
+        .expect("failed to run readelf. Is binutils installed?");
     String::from_utf8_lossy(&out.stdout).into_owned()
 }