feat: forbid running mixnode + entry on the same node

nym-node/src/cli/commands/run/mod.rs

@@ -78,6 +78,7 @@ pub(crate) async fn execute(mut args: Args) -> Result<(), NymNodeError> {
         }
         config
     };
+    config.validate()?;
 
     if !config.modes.any_enabled() {
         warn!("this node is going to run without mixnode or gateway support! consider providing `mode` value");

nym-node/src/config/mod.rs

@@ -426,6 +426,13 @@ impl Config {
     pub fn validate(&self) -> Result<(), NymNodeError> {
         self.mixnet.validate()?;
 
+        // it's not allowed to run mixnode mode alongside entry mode
+        if self.modes.mixnode && self.modes.entry {
+            return Err(NymNodeError::config_validation_failure(
+                "illegal modes configuration - node cannot run as a mixnode and an entry gateway",
+            ));
+        }
+
         Ok(())
     }
 }