Enforce a single daemon per geth home

crates/geth-node/src/lib.rs

@@ -195,6 +195,8 @@ pub enum NodeError {
     OverlayRuntime(String),
     #[error("unsupported platform: {0}")]
     UnsupportedPlatform(String),
+    #[error("geth daemon is already running for home: {0}")]
+    DaemonAlreadyRunning(PathBuf),
 }
 
 #[derive(Clone, Debug)]
@@ -11141,6 +11143,12 @@ mod tests {
             local_control::node_error_code(&NodeError::IrohEndpointUnavailable),
             "iroh_endpoint_unavailable"
         );
+        assert_eq!(
+            local_control::node_error_code(&NodeError::DaemonAlreadyRunning(PathBuf::from(
+                "/tmp/geth"
+            ))),
+            "daemon_already_running"
+        );
     }
 
     #[derive(Debug, PartialEq, Eq)]