feat: LLM TTFT + heap/event telemetry

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ECe2qZWextwVCycC9EveFe

Author: Junyi-99

webapp/_webapp/src/libs/telemetry.ts

@@ -52,7 +52,21 @@ onLCP((m) => vitalsMs.record(m.value, { vital: "LCP" }));
 onINP((m) => vitalsMs.record(m.value, { vital: "INP" }));
 onCLS((m) => vitalsCls.record(m.value));
 
-// Error capture — also exported for manual use
+// Memory — JS heap size sampled every export interval
+const heapGauge = meter.createObservableGauge("js_heap_bytes", { unit: "By" });
+heapGauge.addCallback((result) => {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  const mem = (performance as any).memory;
+  if (mem) result.observe(mem.usedJSHeapSize);
+});
+
+// LLM metrics
+const llmTTFT = meter.createHistogram("llm_ttft_ms", { unit: "ms", description: "Time to first token" });
+export function recordLLMTTFT(ms: number, model: string) {
+  llmTTFT.record(ms, { model });
+}
+
+// Error capture
 export function captureError(error: unknown, attrs?: Record<string, string>) {
   const err = error instanceof Error ? error : new Error(String(error));
   logger.emit({
@@ -67,6 +81,15 @@ export function captureError(error: unknown, attrs?: Record<string, string>) {
   });
 }
 
+// Event capture
+export function captureEvent(name: string, attrs?: Record<string, string>) {
+  logger.emit({
+    severityText: "INFO",
+    body: name,
+    attributes: attrs,
+  });
+}
+
 window.addEventListener("error", (e) => captureError(e.error ?? e.message));
 window.addEventListener("unhandledrejection", (e) => captureError(e.reason));
 

webapp/_webapp/src/query/api.ts

@@ -1,4 +1,5 @@
 import apiclient, { apiclientV2 } from "../libs/apiclient";
+import { recordLLMTTFT } from "../libs/telemetry";
 import {
   LoginByGoogleRequest,
   LoginByGoogleResponseSchema,
@@ -126,8 +127,16 @@ export const createConversationMessageStream = async (
   data: PlainMessage<CreateConversationMessageStreamRequest>,
   onMessage: (chunk: CreateConversationMessageStreamResponse) => void,
 ) => {
+  const start = performance.now();
+  let ttftRecorded = false;
   const stream = await apiclientV2.postStream(`/chats/conversations/messages/stream`, data);
-  await processStream(stream, CreateConversationMessageStreamResponseSchema, onMessage);
+  await processStream(stream, CreateConversationMessageStreamResponseSchema, (chunk: CreateConversationMessageStreamResponse) => {
+    if (!ttftRecorded) {
+      recordLLMTTFT(performance.now() - start, data.modelSlug);
+      ttftRecorded = true;
+    }
+    onMessage(chunk);
+  });
 };
 
 export const deleteConversation = async (data: PlainMessage<DeleteConversationRequest>) => {

webapp/_webapp/vite.config.ts

@@ -27,7 +27,6 @@ function generateConfig(
           VERSION: process.env.VERSION,
           MONOREPO_REVISION: process.env.MONOREPO_REVISION,
           SAFARI_BUILD: process.env.SAFARI_BUILD || "false",
-          OTEL_AUTH_TOKEN: process.env.OTEL_AUTH_TOKEN || "ff4b3c7c2a66c5c9252696cf6cb111f79ff983d68700ff1051455cfe4ecf55ef",
         },
       },
       build: {