feat(observability): propagate optional cost_usd on agent end

src/agent/agent.rs

@@ -557,6 +557,7 @@ pub async fn run(
     agent.observer.record_event(&ObserverEvent::AgentEnd {
         duration: start.elapsed(),
         tokens_used: None,
+        cost_usd: None,
     });
 
     Ok(())

src/agent/loop_.rs

@@ -1048,6 +1048,7 @@ pub async fn run(
     observer.record_event(&ObserverEvent::AgentEnd {
         duration,
         tokens_used: None,
+        cost_usd: None,
     });
 
     Ok(final_output)

src/observability/log.rs

@@ -48,9 +48,10 @@ impl Observer for LogObserver {
             ObserverEvent::AgentEnd {
                 duration,
                 tokens_used,
+                cost_usd,
             } => {
                 let ms = u64::try_from(duration.as_millis()).unwrap_or(u64::MAX);
-                info!(duration_ms = ms, tokens = ?tokens_used, "agent.end");
+                info!(duration_ms = ms, tokens = ?tokens_used, cost_usd = ?cost_usd, "agent.end");
             }
             ObserverEvent::ToolCallStart { tool } => {
                 info!(tool = %tool, "tool.start");
@@ -133,10 +134,12 @@ mod tests {
         obs.record_event(&ObserverEvent::AgentEnd {
             duration: Duration::from_millis(500),
             tokens_used: Some(100),
+            cost_usd: Some(0.0015),
         });
         obs.record_event(&ObserverEvent::AgentEnd {
             duration: Duration::ZERO,
             tokens_used: None,
+            cost_usd: None,
         });
         obs.record_event(&ObserverEvent::ToolCallStart {
             tool: "shell".into(),

src/observability/noop.rs

@@ -48,10 +48,12 @@ mod tests {
         obs.record_event(&ObserverEvent::AgentEnd {
             duration: Duration::from_millis(100),
             tokens_used: Some(42),
+            cost_usd: Some(0.001),
         });
         obs.record_event(&ObserverEvent::AgentEnd {
             duration: Duration::ZERO,
             tokens_used: None,
+            cost_usd: None,
         });
         obs.record_event(&ObserverEvent::ToolCallStart {
             tool: "shell".into(),

src/observability/otel.rs

@@ -227,6 +227,7 @@ impl Observer for OtelObserver {
             ObserverEvent::AgentEnd {
                 duration,
                 tokens_used,
+                cost_usd,
             } => {
                 let secs = duration.as_secs_f64();
                 let start_time = SystemTime::now()
@@ -243,6 +244,9 @@ impl Observer for OtelObserver {
                 if let Some(t) = tokens_used {
                     span.set_attribute(KeyValue::new("tokens_used", *t as i64));
                 }
+                if let Some(c) = cost_usd {
+                    span.set_attribute(KeyValue::new("cost_usd", *c));
+                }
                 span.end();
 
                 self.agent_duration.record(secs, &[]);
@@ -394,10 +398,12 @@ mod tests {
         obs.record_event(&ObserverEvent::AgentEnd {
             duration: Duration::from_millis(500),
             tokens_used: Some(100),
+            cost_usd: Some(0.0015),
         });
         obs.record_event(&ObserverEvent::AgentEnd {
             duration: Duration::ZERO,
             tokens_used: None,
+            cost_usd: None,
         });
         obs.record_event(&ObserverEvent::ToolCallStart {
             tool: "shell".into(),

src/observability/traits.rs

@@ -27,6 +27,7 @@ pub enum ObserverEvent {
     AgentEnd {
         duration: Duration,
         tokens_used: Option<u64>,
+        cost_usd: Option<f64>,
     },
     /// A tool call is about to be executed.
     ToolCallStart {