feat(observability): focus PR 596 on Prometheus backend

src/agent/agent.rs

@@ -544,8 +544,8 @@ pub async fn run(
         .to_string();
 
     agent.observer.record_event(&ObserverEvent::AgentStart {
-        provider: provider_name,
-        model: model_name,
+        provider: provider_name.clone(),
+        model: model_name.clone(),
     });
 
     if let Some(msg) = message {
@@ -556,10 +556,11 @@ pub async fn run(
     }
 
     agent.observer.record_event(&ObserverEvent::AgentEnd {
-        provider: "cli".to_string(),
-        model: "unknown".to_string(),
+        provider: provider_name,
+        model: model_name,
         duration: start.elapsed(),
         tokens_used: None,
+        cost_usd: None,
     });
 
     Ok(())

src/agent/loop_.rs

@@ -1336,6 +1336,7 @@ pub async fn run(
         model: model_name.to_string(),
         duration,
         tokens_used: None,
+        cost_usd: None,
     });
 
     Ok(final_output)