diff --git a/crates/colibri-daemon/src/socket.rs b/crates/colibri-daemon/src/socket.rs
index fd3d5db..850ec35 100644
--- a/crates/colibri-daemon/src/socket.rs
+++ b/crates/colibri-daemon/src/socket.rs
@@ -1360,4 +1360,39 @@ mod tests {
         assert!(path.exists(), "live socket must not be removed");
         let _ = std::fs::remove_dir_all(&dir);
     }
+
+    #[test]
+    fn default_agent_args_zot_gets_rpc() {
+        assert_eq!(super::default_agent_args("zot"), vec!["rpc"]);
+        assert_eq!(
+            super::default_agent_args("/usr/local/bin/zot"),
+            vec!["rpc"],
+            "basename extraction must work for path-prefixed zot"
+        );
+    }
+
+    #[test]
+    fn default_agent_args_pi_gets_mode_json() {
+        assert_eq!(super::default_agent_args("pi"), vec!["--mode", "json"]);
+        assert_eq!(
+            super::default_agent_args("/usr/local/bin/pi"),
+            vec!["--mode", "json"],
+            "basename extraction must work for path-prefixed pi"
+        );
+    }
+
+    #[test]
+    fn default_agent_args_unknown_gets_mode_json() {
+        // Any binary that isn't zot gets the self-driving JSON mode.
+        // This is the safe default — unknown harnesses are assumed to be
+        // pi-compatible (--mode json), not zot-compatible (rpc).
+        assert_eq!(
+            super::default_agent_args("sample-pi-agent.py"),
+            vec!["--mode", "json"]
+        );
+        assert_eq!(
+            super::default_agent_args("colibri-test-agent"),
+            vec!["--mode", "json"]
+        );
+    }
 }