fix(studio): show spans while trace details arrive

web/packages/studio/src/components/IntakeDetail/SessionDetailView.tsx

@@ -180,6 +180,7 @@ export const SessionDetailView: FC<SessionDetailViewProps> = ({
             sessionId={sessionId}
             parentBreadcrumbs={traceParentBreadcrumbs}
             traceSummary={trajectories.find(({ trace }) => trace.id === traceId)?.trace}
+            isTraceSummaryLoading={explorer.isSpansFetching && !explorer.spansLoaded}
           >
             {(trace) => (
               <TraceSpanAccordions

web/packages/studio/src/components/IntakeDetail/TraceDetailView.tsx

@@ -4,7 +4,7 @@
 import { IntakeAccordion } from '@nemo/common/src/components/IntakeAccordion';
 import { useGetTrace } from '@nemo/sdk/generated/platform/api';
 import type { Trace } from '@nemo/sdk/generated/platform/schema';
-import { Stack, StatusMessage, Text } from '@nvidia/foundations-react-core';
+import { Banner, Stack, StatusMessage, Text } from '@nvidia/foundations-react-core';
 import { KeyValueRows } from '@studio/components/IntakeDetail/IntakeComponents/KeyValueRows';
 import { RawJsonDebug } from '@studio/components/IntakeDetail/IntakeComponents/RawJsonDebug';
 import {
@@ -29,6 +29,7 @@ interface TraceDetailViewProps {
   traceId: string;
   sessionId: string;
   traceSummary?: Trace;
+  isTraceSummaryLoading?: boolean;
   parentBreadcrumbs: BreadcrumbsItemProps[];
   children: (trace: Trace) => ReactNode;
 }
@@ -39,6 +40,7 @@ export const TraceDetailView: FC<TraceDetailViewProps> = ({
   traceId,
   sessionId,
   traceSummary,
+  isTraceSummaryLoading = false,
   parentBreadcrumbs,
   children,
 }) => {
@@ -53,6 +55,7 @@ export const TraceDetailView: FC<TraceDetailViewProps> = ({
   // The session already owns enough trace data to keep its explorer mounted
   // while the selected trace's full payload hydrates in the background.
   const resolvedTrace = trace ?? traceSummary;
+  const traceNotFound = error?.response?.status === 404;
 
   const { setBreadcrumbs } = useBreadcrumbs();
   const traceBreadcrumbLabel = resolvedTrace ? getTraceDisplayName(resolvedTrace) : traceId;
@@ -70,7 +73,11 @@ export const TraceDetailView: FC<TraceDetailViewProps> = ({
     setBreadcrumbs([...parentBreadcrumbs, { slotLabel: `Trace ${traceBreadcrumbLabel}` }]);
   }, [parentBreadcrumbs, setBreadcrumbs, traceBreadcrumbLabel]);
 
-  if (error?.response?.status === 404) {
+  if (!resolvedTrace && (isLoading || (traceNotFound && isTraceSummaryLoading))) {
+    return <Loading description="Loading trace..." />;
+  }
+
+  if (traceNotFound && !resolvedTrace) {
     return (
       <NotFound
         subheader="Trace Not Found"
@@ -79,10 +86,6 @@ export const TraceDetailView: FC<TraceDetailViewProps> = ({
     );
   }
 
-  if (isLoading && !resolvedTrace) {
-    return <Loading description="Loading trace..." />;
-  }
-
   if (error && !resolvedTrace) {
     return (
       <StatusMessage
@@ -110,6 +113,11 @@ export const TraceDetailView: FC<TraceDetailViewProps> = ({
 
   return (
     <>
+      {traceNotFound && (
+        <Banner kind="inline" status="info">
+          Trace details are still arriving. The activity received so far is shown below.
+        </Banner>
+      )}
       {children(resolvedTrace)}
       <IntakeAccordion
         variant="section"

web/packages/studio/src/components/IntakeDetail/useSessionTrajectories.ts

@@ -2,9 +2,13 @@
 // SPDX-License-Identifier: Apache-2.0
 
 import { useGetSession, useListSpans, useListTraces } from '@nemo/sdk/generated/platform/api';
-import type { Span } from '@nemo/sdk/generated/platform/schema';
+import { type Span, SpanStatus, type Trace } from '@nemo/sdk/generated/platform/schema';
 import { type SessionExplorerData } from '@studio/components/IntakeDetail/TraceSpanAccordions';
-import { buildSpanTree, type SessionTrajectory } from '@studio/util/intakeTelemetry';
+import {
+  buildSpanTree,
+  compareSpansByStartedAt,
+  type SessionTrajectory,
+} from '@studio/util/intakeTelemetry';
 import { useMemo } from 'react';
 
 const SESSION_TRACES_PAGE_SIZE = 1000;
@@ -57,11 +61,33 @@ export function useSessionTrajectories(workspace: string, sessionId: string) {
       traceSpans.push(span);
       groupedSpans.set(span.trace_id, traceSpans);
     }
-    return traces.map((trace) => {
+
+    const traceSummaries: Trace[] = [...traces];
+    const knownTraceIds = new Set(traces.map((trace) => trace.id));
+    for (const [traceId, spans] of groupedSpans) {
+      if (knownTraceIds.has(traceId)) continue;
+      const earliestSpan = spans.reduce((earliest, span) =>
+        compareSpansByStartedAt(span, earliest) < 0 ? span : earliest
+      );
+      traceSummaries.push({
+        id: traceId,
+        session_id: sessionId,
+        workspace,
+        started_at: earliestSpan.started_at,
+        status: SpanStatus.unknown,
+        span_count: spans.length,
+      });
+    }
+
+    traceSummaries.sort((a, b) => {
+      const startedAtDifference = Date.parse(a.started_at) - Date.parse(b.started_at);
+      return startedAtDifference || a.id.localeCompare(b.id);
+    });
+    return traceSummaries.map((trace) => {
       const spans = groupedSpans.get(trace.id) ?? [];
       return { trace, spans, spanTree: buildSpanTree(spans) };
     });
-  }, [sessionSpansResponse?.data, traces]);
+  }, [sessionId, sessionSpansResponse?.data, traces, workspace]);
 
   const explorer = useMemo<SessionExplorerData>(
     () => ({

web/packages/studio/src/routes/IntakeSessionDetailRoute/index.test.tsx

@@ -387,6 +387,96 @@ describe('IntakeSessionDetailRoute', () => {
     expect((await screen.findAllByText('Outside page span')).length).toBeGreaterThan(0);
   });
 
+  it('renders received spans while trace details are still arriving', async () => {
+    const traceId = 'trace-still-arriving';
+    const receivedSpan = {
+      ...mockSpanById('span-llm-001')!,
+      span_id: 'span-received-before-trace',
+      parent_span_id: 'span-root-not-received',
+      trace_id: traceId,
+      name: 'Generate response from received activity',
+    };
+
+    server.use(
+      http.get('*/apis/intake/v2/workspaces/:workspace/traces', () =>
+        HttpResponse.json({
+          ...mockTracesPage,
+          data: [],
+          pagination: {
+            ...mockTracesPage.pagination,
+            current_page_size: 0,
+            total_results: 0,
+          },
+        })
+      ),
+      http.get('*/apis/intake/v2/workspaces/:workspace/traces/:traceId', ({ params }) =>
+        params['traceId'] === traceId
+          ? new HttpResponse(null, { status: 404 })
+          : new HttpResponse(null, { status: 500 })
+      ),
+      http.get('*/apis/intake/v2/workspaces/:workspace/spans', () =>
+        HttpResponse.json({
+          ...mockSpansPage,
+          data: [receivedSpan],
+          pagination: {
+            ...mockSpansPage.pagination,
+            current_page_size: 1,
+            total_results: 1,
+          },
+        })
+      )
+    );
+
+    renderSessionDetail('session-agent-run-001', `?traceId=${traceId}`);
+
+    expect(
+      await screen.findByText(
+        'Trace details are still arriving. The activity received so far is shown below.'
+      )
+    ).toBeInTheDocument();
+    expect(screen.queryByText('Trace Not Found')).not.toBeInTheDocument();
+    expect(
+      (await screen.findAllByText('Generate response from received activity')).length
+    ).toBeGreaterThan(0);
+  });
+
+  it('shows not found when neither trace details nor matching spans exist', async () => {
+    const traceId = 'trace-never-received';
+    server.use(
+      http.get('*/apis/intake/v2/workspaces/:workspace/traces', () =>
+        HttpResponse.json({
+          ...mockTracesPage,
+          data: [],
+          pagination: {
+            ...mockTracesPage.pagination,
+            current_page_size: 0,
+            total_results: 0,
+          },
+        })
+      ),
+      http.get(
+        '*/apis/intake/v2/workspaces/:workspace/traces/:traceId',
+        () => new HttpResponse(null, { status: 404 })
+      ),
+      http.get('*/apis/intake/v2/workspaces/:workspace/spans', () =>
+        HttpResponse.json({
+          ...mockSpansPage,
+          data: [],
+          pagination: {
+            ...mockSpansPage.pagination,
+            current_page_size: 0,
+            total_results: 0,
+          },
+        })
+      )
+    );
+
+    renderSessionDetail('session-agent-run-001', `?traceId=${traceId}`);
+
+    expect(await screen.findByText('Trace Not Found')).toBeInTheDocument();
+    expect(screen.queryByText(/Trace details are still arriving/)).not.toBeInTheDocument();
+  });
+
   it('rejects a trace deep link that belongs to another session', async () => {
     renderSessionDetail('session-agent-run-001', '?traceId=trace-agent-run-002');