fix(tracing): page legacy agent metadata with its spans

litellm-rust/crates/traces-cache/src/reader.rs

@@ -10,7 +10,7 @@ use crate::{
     spend::spend,
 };
 use litellm_traces::{
-    SpanDetail, SpanErrorPage, Trace, TracePage,
+    ObservationType, SpanDetail, SpanErrorPage, Trace, TracePage,
     query::named::{
         ListTracesParams, ReadAccessParams, SpanDetailParams, SpanErrorParams, TraceIdentityParams,
         TraceSpansParams,
@@ -329,6 +329,19 @@ fn page<E>(
             .iter()
             .filter_map(|span| span.actor_id.as_deref())
             .collect();
+        let legacy_agents: HashSet<&str> = page_spans
+            .iter()
+            .filter(|span| span.actor_id.is_none() && !span.actor_unassigned)
+            .filter_map(|span| {
+                if !span.agent.is_empty() {
+                    Some(span.agent.as_str())
+                } else if span.kind == ObservationType::Agent {
+                    Some(span.name.as_str())
+                } else {
+                    None
+                }
+            })
+            .collect();
         Trace {
             capture: snapshot.trace().capture.as_ref().map(|capture| {
                 litellm_traces::TraceCapture {
@@ -348,11 +361,9 @@ fn page<E>(
                 .trace()
                 .agents
                 .iter()
-                .filter(|agent| {
-                    agent
-                        .actor_id
-                        .as_deref()
-                        .is_none_or(|id| actors.contains(id))
+                .filter(|agent| match agent.actor_id.as_deref() {
+                    Some(id) => actors.contains(id),
+                    None => legacy_agents.contains(agent.name.as_str()),
                 })
                 .cloned()
                 .collect(),

litellm-rust/crates/traces-cache/tests/read.rs

@@ -561,6 +561,54 @@ async fn actor_metadata_pages_with_spans_without_losing_trace_totals(
     assert_eq!(store.calls(Operation::TraceSpans), 1);
 }
 
+#[rstest]
+#[case::explicit_names(4096, true)]
+#[case::span_name_fallback(4096, false)]
+#[case::larger_pages(8192, true)]
+#[tokio::test]
+async fn legacy_agent_metadata_fits_each_page_without_losing_agents(
+    #[case] response_bytes: usize,
+    #[case] explicit_names: bool,
+) {
+    let rows = (0..120)
+        .map(|index| TraceSpansRow {
+            kind: ObservationType::Agent,
+            name: format!("legacy-{index}"),
+            agent: if explicit_names {
+                format!("legacy-{index}")
+            } else {
+                String::new()
+            },
+            parent_span_id: String::new(),
+            ..span(index)
+        })
+        .collect();
+    let store = FakeStore::with_spans("ref", rows);
+    let reader = TraceReader::new(response_bytes);
+    let mut cursor = None;
+    let mut names = HashSet::new();
+    loop {
+        let page = reader
+            .get_trace_page(&store, &access(), "trace", "ref", cursor.as_deref(), 200)
+            .await
+            .unwrap()
+            .unwrap();
+        assert!(serde_json::to_vec(&page).unwrap().len() <= response_bytes);
+        assert_eq!(page.summary.agent_count, 120);
+        assert_eq!(page.agents.len(), page.spans.len());
+        for agent in page.agents {
+            assert!(page.spans.iter().any(|span| span.name == agent.name));
+            assert!(names.insert(agent.name));
+        }
+        cursor = page.next_cursor;
+        if cursor.is_none() {
+            break;
+        }
+    }
+    assert_eq!(names.len(), 120);
+    assert_eq!(store.calls(Operation::TraceSpans), 1);
+}
+
 #[rstest]
 #[tokio::test]
 async fn oversized_run_batch_falls_back_to_each_run_and_keeps_listed_summaries() {