fix: default mechanism_id to 0 and handle Invalid Transaction 1010

- ChallengeConfig default mechanism_id was 1 but should be 0 (main mechanism).
  The old code masked this by always using mechanism_configs.keys().next()=0.
- Handle 'Invalid Transaction (1010)' same as Priority too low: mark epoch
  as submitted to prevent infinite retry loops.

Author: echobt

bins/validator-node/src/main.rs

@@ -3929,10 +3929,10 @@ async fn handle_block_event(
                         }
                         Err(e) => {
                             let err_str = format!("{}", e);
-                            if err_str.contains("Priority is too low") {
+                            if err_str.contains("Priority is too low") || err_str.contains("1010") {
                                 warn!(
-                                    "Mechanism {}: transaction already in mempool (Priority too low) - treating as submitted",
-                                    mechanism_id
+                                    "Mechanism {}: transaction rejected ({}) - marking epoch as submitted to avoid retry loop",
+                                    mechanism_id, err_str
                                 );
                                 *last_weight_submission_epoch = epoch;
                             } else {

crates/core/src/challenge.rs

@@ -118,7 +118,7 @@ pub struct ChallengeConfig {
 impl Default for ChallengeConfig {
     fn default() -> Self {
         Self {
-            mechanism_id: 1, // Default to mechanism 1
+            mechanism_id: 0, // Default to mechanism 0 (main mechanism)
             timeout_secs: 300,
             max_memory_mb: 512,
             max_cpu_secs: 60,
@@ -381,7 +381,7 @@ mod tests {
     #[test]
     fn test_challenge_config_default() {
         let config = ChallengeConfig::default();
-        assert_eq!(config.mechanism_id, 1);
+        assert_eq!(config.mechanism_id, 0);
         assert_eq!(config.timeout_secs, 300);
         assert_eq!(config.max_memory_mb, 512);
         assert_eq!(config.max_cpu_secs, 60);