diff --git a/packages/stage-ui/package.json b/packages/stage-ui/package.json
index 37e2b07bc..1bc2d07ae 100644
--- a/packages/stage-ui/package.json
+++ b/packages/stage-ui/package.json
@@ -61,6 +61,9 @@
     "@formkit/auto-animate": "^0.9.0",
     "@huggingface/transformers": "^3.8.1",
     "@moeru/eventa": "catalog:",
+    "@opentelemetry/api": "^1.9.0",
+    "@opentelemetry/core": "^2.6.0",
+    "@opentelemetry/sdk-trace-base": "^2.6.0",
     "@proj-airi/audio": "workspace:^",
     "@proj-airi/ccc": "workspace:^",
     "@proj-airi/chromatic": "^1.0.2",
diff --git a/packages/stage-ui/src/composables/use-io-tracer.ts b/packages/stage-ui/src/composables/use-io-tracer.ts
new file mode 100644
index 000000000..972859000
--- /dev/null
+++ b/packages/stage-ui/src/composables/use-io-tracer.ts
@@ -0,0 +1,161 @@
+import type { Span, SpanContext, SpanStatusCode } from '@opentelemetry/api'
+import type { ReadableSpan, SpanExporter } from '@opentelemetry/sdk-trace-base'
+import type { TimedEvent } from '@opentelemetry/sdk-trace-base/build/esm/TimedEvent'
+
+import { context, trace } from '@opentelemetry/api'
+import { hrTimeToNanoseconds } from '@opentelemetry/core'
+import { BasicTracerProvider, SimpleSpanProcessor } from '@opentelemetry/sdk-trace-base'
+import { shallowRef } from 'vue'
+
+export type { ReadableSpan } from '@opentelemetry/sdk-trace-base'
+
+const TRACER_NAME = 'ai.moeru.airi.io-tracer'
+const BROADCAST_CHANNEL = 'io-tracer-channel' // TODO: Use simple BroadcastChannel for now
+
+export interface SerializedSpan {
+  traceId: string
+  spanId: string
+  parentSpanId: string
+  name: string
+  kind: number
+  startTimeNano: string
+  endTimeNano: string
+  attributes: Record<string, unknown>
+  events: { name: string, timeNano: string, attributes: Record<string, unknown> }[]
+  status: { code: number, message: string }
+  ended: boolean
+}
+
+function serializeSpan(span: ReadableSpan): SerializedSpan {
+  const ctx = span.spanContext()
+  const parentCtx = span.parentSpanContext
+  return {
+    traceId: ctx.traceId,
+    spanId: ctx.spanId,
+    parentSpanId: parentCtx?.spanId ?? '',
+    name: span.name,
+    kind: span.kind,
+    startTimeNano: String(hrTimeToNanoseconds(span.startTime)),
+    endTimeNano: span.ended ? String(hrTimeToNanoseconds(span.endTime)) : '0',
+    attributes: { ...span.attributes },
+    events: span.events.map((e: TimedEvent) => ({
+      name: e.name,
+      timeNano: String(hrTimeToNanoseconds(e.time)),
+      attributes: { ...e.attributes },
+    })),
+    status: { code: span.status.code, message: span.status.message ?? '' },
+    ended: span.ended,
+  }
+}
+
+export function deserializeSpan(s: SerializedSpan): ReadableSpan {
+  const nanoToHr = (nano: string): [number, number] => {
+    const n = Number(nano)
+    return [Math.floor(n / 1e9), n % 1e9]
+  }
+  const spanCtx: SpanContext = {
+    traceId: s.traceId,
+    spanId: s.spanId,
+    traceFlags: 1,
+    isRemote: false,
+  }
+  const parentCtx: SpanContext | undefined = s.parentSpanId
+    ? { traceId: s.traceId, spanId: s.parentSpanId, traceFlags: 1, isRemote: false }
+    : undefined
+
+  return {
+    name: s.name,
+    kind: s.kind,
+    spanContext: () => spanCtx,
+    parentSpanContext: parentCtx,
+    startTime: nanoToHr(s.startTimeNano),
+    endTime: nanoToHr(s.endTimeNano),
+    status: { code: s.status.code as SpanStatusCode, message: s.status.message },
+    attributes: s.attributes as Record<string, string | number | boolean>,
+    links: [],
+    events: s.events.map(e => ({
+      name: e.name,
+      time: nanoToHr(e.timeNano),
+      attributes: e.attributes as Record<string, string | number | boolean>,
+      droppedAttributesCount: 0,
+    })),
+    duration: nanoToHr(String(Number(s.endTimeNano) - Number(s.startTimeNano))),
+    ended: s.ended,
+    resource: { attributes: {}, merge: () => ({ attributes: {} }) } as any,
+    instrumentationScope: { name: TRACER_NAME },
+    droppedAttributesCount: 0,
+    droppedEventsCount: 0,
+    droppedLinksCount: 0,
+  }
+}
+
+type SpanCallback = (span: ReadableSpan) => void
+
+let provider: BasicTracerProvider | undefined
+let spanCallback: SpanCallback | undefined
+let broadcastChannel: BroadcastChannel | undefined
+
+export function createCallbackSpanExporter(): SpanExporter {
+  return {
+    export: (spans, resultCallback) => {
+      for (const span of spans) {
+        spanCallback?.(span)
+
+        broadcastChannel?.postMessage({
+          type: 'span',
+          span: serializeSpan(span),
+        })
+      }
+      resultCallback({ code: 0 /* SUCCESS */ })
+    },
+    shutdown: () => Promise.resolve(),
+    forceFlush: () => Promise.resolve(),
+  }
+}
+
+export function initIOTracer() {
+  if (!broadcastChannel)
+    broadcastChannel = new BroadcastChannel(BROADCAST_CHANNEL)
+
+  if (provider)
+    return
+
+  provider = new BasicTracerProvider({
+    spanProcessors: [new SimpleSpanProcessor(createCallbackSpanExporter())],
+  })
+  trace.setGlobalTracerProvider(provider)
+}
+
+export function getIOTracer() {
+  if (provider)
+    return provider.getTracer(TRACER_NAME)
+  return trace.getTracer(TRACER_NAME)
+}
+
+export function onIOSpan(cb: SpanCallback | undefined) {
+  spanCallback = cb
+}
+
+export function onRemoteIOSpan(cb: SpanCallback): () => void {
+  const channel = new BroadcastChannel(BROADCAST_CHANNEL)
+  const handler = (event: MessageEvent) => {
+    if (event.data?.type === 'span') {
+      cb(deserializeSpan(event.data.span))
+    }
+  }
+  channel.addEventListener('message', handler)
+  return () => {
+    channel.removeEventListener('message', handler)
+    channel.close()
+  }
+}
+
+export function startSpan(name: string, parent?: Span, attrs?: Record<string, string | number | boolean>): Span {
+  initIOTracer()
+
+  const tracer = getIOTracer()
+  const ctx = parent ? trace.setSpan(context.active(), parent) : undefined
+  return tracer.startSpan(name, { attributes: attrs }, ctx)
+}
+
+export const activeTurnSpan = shallowRef<Span | undefined>()
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 4454ba1ac..10a8722fa 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -2942,6 +2942,15 @@ importers:
       '@moeru/eventa':
         specifier: 'catalog:'
         version: 1.0.0-beta.3(electron@40.8.5)(h3@2.0.1-rc.20(crossws@0.4.4(patch_hash=4d79ec736d10d2a81a9e2a31b067d43f0b6665122267981e652ab9923d165958)(srvx@0.11.15)))
+      '@opentelemetry/api':
+        specifier: ^1.9.0
+        version: 1.9.1
+      '@opentelemetry/core':
+        specifier: ^2.6.0
+        version: 2.6.1(@opentelemetry/api@1.9.1)
+      '@opentelemetry/sdk-trace-base':
+        specifier: ^2.6.0
+        version: 2.6.1(@opentelemetry/api@1.9.1)
       '@proj-airi/audio':
         specifier: workspace:^
         version: link:../audio