Allow setting entrypoint from CLI

tests/integration.rs

@@ -755,6 +755,40 @@ fn config_entrypoint_alone_without_command_or_passthrough() {
     );
 }
 
+#[test]
+fn cli_entrypoint_appends_passthrough_args() {
+    let output = sandbox(&["--entrypoint", "bash"])
+        .args(["--", "-c", "echo cli-entrypoint-works"])
+        .output()
+        .expect("failed to execute");
+
+    let stdout = String::from_utf8_lossy(&output.stdout).trim().to_string();
+    assert_eq!(
+        stdout, "cli-entrypoint-works",
+        "expected --entrypoint to receive trailing args, got: {stdout}"
+    );
+}
+
+#[test]
+fn cli_entrypoint_overrides_config_entrypoint() {
+    let cfg = ConfigFile::new(
+        r#"
+        entrypoint = ["/bin/false"]
+    "#,
+    );
+
+    let output = sandbox_withconfig(&["--config", &cfg, "--entrypoint", "bash"])
+        .args(["--", "-c", "echo override-works"])
+        .output()
+        .expect("failed to execute");
+
+    let stdout = String::from_utf8_lossy(&output.stdout).trim().to_string();
+    assert_eq!(
+        stdout, "override-works",
+        "expected CLI --entrypoint to override config entrypoint, got: {stdout}"
+    );
+}
+
 #[test]
 fn config_command_alone_without_passthrough() {
     let cfg = ConfigFile::new(