Model-turn telemetry

Bonus: model-turn telemetry

Time: 5 minutes

Checkpoint 6 uses built-in agent tracing and needs no application observer. In this experiment, add a focused runtime-event subscriber that exports model tokens, duration, failures, and the provider’s gatewayLogId to Workers Logs.

1. Add a model-turn observer

Update src/app.ts to register the observer before creating the route map. The diff starts from completed checkpoint 6; Complete file retains every route:

src/app.ts+21−0

Changes from Checkpoint 6 (guide) → Model-turn telemetry bonus

Changes

src/app.ts

===================================================================
--- a/src/app.ts  Checkpoint 6 (guide)
+++ b/src/app.ts  Model-turn telemetry bonus
@@ -1,8 +1,29 @@
 import { Hono } from 'hono';
 import { createAgentRouter } from '@flue/runtime/routing';
+import { observe } from '@flue/runtime';
 import { FieldTrip } from './agents/field-trip.ts';
 import chatUi from './ui/index.html?raw';

+observe((event) => {
+  if (event.type !== 'turn') return;
+  const usage = event.response.usage;
+  console.log({
+    event: 'flue_model_turn',
+    agent: event.agentName ?? null,
+    conversationId: event.conversationId ?? null,
+    submissionId: event.submissionId ?? null,
+    turnId: event.turnId,
+    model: event.request.requestedModel,
+    durationMs: event.durationMs,
+    inputTokens: usage?.input ?? null,
+    outputTokens: usage?.output ?? null,
+    totalTokens: usage?.totalTokens ?? null,
+    gatewayLogId: event.response.gatewayLogId ?? null,
+    isError: event.isError,
+    error: event.response.error?.message ?? null,
+  });
+});
+
 // src/app.ts is the Flue route map. Its default export owns every HTTP request
 // the Worker receives. Agents get mounted here with createAgentRouter(...)
 // starting in checkpoint 1.

Complete file

src/app.ts

import { Hono } from 'hono';
import { createAgentRouter } from '@flue/runtime/routing';
import { observe } from '@flue/runtime';
import { FieldTrip } from './agents/field-trip.ts';
import chatUi from './ui/index.html?raw';

observe((event) => {
  if (event.type !== 'turn') return;
  const usage = event.response.usage;
  console.log({
    event: 'flue_model_turn',
    agent: event.agentName ?? null,
    conversationId: event.conversationId ?? null,
    submissionId: event.submissionId ?? null,
    turnId: event.turnId,
    model: event.request.requestedModel,
    durationMs: event.durationMs,
    inputTokens: usage?.input ?? null,
    outputTokens: usage?.output ?? null,
    totalTokens: usage?.totalTokens ?? null,
    gatewayLogId: event.response.gatewayLogId ?? null,
    isError: event.isError,
    error: event.response.error?.message ?? null,
  });
});

// src/app.ts is the Flue route map. Its default export owns every HTTP request
// the Worker receives. Agents get mounted here with createAgentRouter(...)
// starting in checkpoint 1.
const app = new Hono();

// A small chat UI for trying the agent in a browser, locally and on workers.dev.
app.get('/', (c) => c.html(chatUi));
app.get('/api/ping', (c) => c.text('pong'));
app.route('/agents/field-trip', createAgentRouter(FieldTrip));

export default app;

2. Run one turn

Live deploy

npm run typecheck
npm run deploy
sleep 5
npm run smoke -- https://field-trip-agent.<subdomain>.workers.dev telemetry-live-1 "Describe what you do in one sentence."

Open Workers & Pages → field-trip-agent → Observability → Logs and filter event = flue_model_turn. Copy a non-null gatewayLogId, then locate that request in AI → AI Gateway → Logs. If the provider does not return this ID, the field remains null; it is not evidence of a failed model call.

Save your workers.dev subdomain to open this test ↗https://field-trip-agent.<subdomain>.workers.dev/?id=telemetry-live-1

This opens the same conversation as the smoke test. If you repeat this checkpoint, use a fresh test IDbefore copying its commands.

Local dev

Restart npm run dev in Terminal A, then run in Terminal B:

npm run typecheck
npm run smoke -- http://localhost:5173 telemetry-1 "Describe what you do in one sentence."

The dev terminal prints the flue_model_turn object.

Open local chat in your browser ↗http://localhost:5173/?id=telemetry-1

This opens the same conversation as the smoke test. If you repeat this checkpoint, use a fresh test IDbefore copying its commands.

Verification gate

Prove it works

• Workers Logs contains an object with event: ‘flue_model_turn’.
• The object identifies the Gemma model and reports token counts.
• gatewayLogId correlates the turn with its AI Gateway log when available.

Reset

Remove the observe import and callback, then redeploy (or restart Vite for Local dev). Checkpoint 6’s built-in agent tracing continues to work without this observer.

Reference: Flue observability.