From 8371f412f8f87cad7f2a71a515ce3613cb1e0c71 Mon Sep 17 00:00:00 2001
From: Chummy <chumyin0912@gmail.com>
Date: Tue, 17 Feb 2026 17:57:34 +0800
Subject: [PATCH] feat(observability): propagate optional cost_usd on agent end

---
 src/agent/agent.rs          | 1 +
 src/agent/loop_.rs          | 1 +
 src/observability/log.rs    | 5 ++++-
 src/observability/noop.rs   | 2 ++
 src/observability/otel.rs   | 6 ++++++
 src/observability/traits.rs | 1 +
 6 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/agent/agent.rs b/src/agent/agent.rs
index 05a9837..23c0cbf 100644
--- a/src/agent/agent.rs
+++ b/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(())
diff --git a/src/agent/loop_.rs b/src/agent/loop_.rs
index 47d02a6..8356d33 100644
--- a/src/agent/loop_.rs
+++ b/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)
diff --git a/src/observability/log.rs b/src/observability/log.rs
index 9e3d062..b932fe0 100644
--- a/src/observability/log.rs
+++ b/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(),
diff --git a/src/observability/noop.rs b/src/observability/noop.rs
index 1189490..004af21 100644
--- a/src/observability/noop.rs
+++ b/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(),
diff --git a/src/observability/otel.rs b/src/observability/otel.rs
index 5e0c37e..ae4932d 100644
--- a/src/observability/otel.rs
+++ b/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(),
diff --git a/src/observability/traits.rs b/src/observability/traits.rs
index a1eb10f..6fb114f 100644
--- a/src/observability/traits.rs
+++ b/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 {