diff --git a/src-tauri/tests/cli_help_materialize_exec_exit.rs b/src-tauri/tests/cli_help_materialize_exec_exit.rs
new file mode 100644
index 000000000..cec5c02a6
--- /dev/null
+++ b/src-tauri/tests/cli_help_materialize_exec_exit.rs
@@ -0,0 +1,80 @@
+//! Black-box help and invalid-argument contract for incomplete-download execution.
+
+use std::ffi::OsString;
+use std::path::{Path, PathBuf};
+use std::process::Command;
+
+const BINARY: &str = "disksage-incomplete-download-materialize";
+const USAGE: &str = "usage: disksage-incomplete-download-materialize";
+
+fn build_binary() -> (tempfile::TempDir, PathBuf) {
+    let target_dir = tempfile::tempdir().expect("isolated Cargo target directory must be created");
+    let cargo = std::env::var_os("CARGO").unwrap_or_else(|| OsString::from("cargo"));
+    let status = Command::new(cargo)
+        .current_dir(env!("CARGO_MANIFEST_DIR"))
+        .args([
+            "build",
+            "--locked",
+            "--features",
+            "cloud-cli",
+            "--bin",
+            BINARY,
+            "--target-dir",
+        ])
+        .arg(target_dir.path())
+        .status()
+        .expect("feature-gated execution CLI must be buildable for process contracts");
+    assert!(status.success(), "execution CLI build must succeed before process assertions");
+
+    let binary = target_dir
+        .path()
+        .join("debug")
+        .join(format!("{BINARY}{}", std::env::consts::EXE_SUFFIX));
+    assert!(binary.is_file(), "execution CLI must exist after explicit cloud-cli build");
+    (target_dir, binary)
+}
+
+fn command(binary: &Path) -> Command {
+    let mut command = Command::new(binary);
+    command.env_remove("HOME").env_remove("USERPROFILE");
+    command
+}
+
+#[test]
+fn materialization_execution_help_is_successful_and_invalid_arguments_are_bounded() {
+    let (_target_dir, binary) = build_binary();
+
+    for flag in ["--help", "-h"] {
+        let output = command(&binary)
+            .arg(flag)
+            .output()
+            .expect("execution CLI must launch for help validation");
+        assert!(
+            output.status.success(),
+            "{flag} must be a successful terminal action, got status {:?} and stderr {:?}",
+            output.status.code(),
+            String::from_utf8_lossy(&output.stderr)
+        );
+        assert!(output.stderr.is_empty(), "successful help must keep stderr empty");
+        let stdout = String::from_utf8(output.stdout).expect("help output must be valid UTF-8");
+        assert!(stdout.contains(USAGE), "help must contain the stable usage synopsis");
+    }
+
+    for args in [
+        vec!["--opaque-option=not-shown"],
+        vec!["--help", "--opaque-option=not-shown"],
+    ] {
+        let output = command(&binary)
+            .args(args)
+            .output()
+            .expect("execution CLI must launch for invalid argument validation");
+        assert!(!output.status.success(), "invalid invocation must remain non-zero");
+        assert!(output.stdout.is_empty(), "invalid invocation must keep stdout empty");
+        let stderr = String::from_utf8(output.stderr).expect("diagnostics must be valid UTF-8");
+        assert!(!stderr.is_empty(), "invalid invocation must remain visible");
+        assert!(
+            !stderr.contains("not-shown"),
+            "diagnostics must not echo arbitrary argument payloads"
+        );
+    }
+}