Realtime Agents SDK - failed to start pipeline error

### Example URL(s)

- https://developers.cloudflare.com/realtime/agents/getting-started/

### Actual Behavior

Hey! 👋 I'm following the Realtime Agents getting started guide and running into an issue.

Error: failed to start pipeline

What I've done:
✅ Deployed the Worker successfully
✅ Set all 4 secrets: ACCOUNT_ID, API_TOKEN (Realtime Admin scope), DEEPGRAM_API_KEY, ELEVENLABS_API_KEY
✅ Added nodejs_compat flag, AI binding, Durable Object + migrations in wrangler.jsonc
✅ Joined the meeting myself before calling /init
✅ Generated two separate authTokens (one for me, one for the agent)
✅ Tested Deepgram and ElevenLabs API keys directly — both return 200 OK
✅ ACCOUNT_ID is the Cloudflare Account ID
Curl command:
curl -X POST "https://.workers.dev/init?meetingId=" -H "Authorization: Bearer "

Log error:
{ "message": "failed to start pipeline", "exception": { "name": "Error", "message": "failed to start pipeline" } }

Is this a known issue with the experimental Realtime Agents SDK? Any idea what could be causing this? Thanks!

### Expected Behavior

Calling `this.initPipeline()` with valid credentials (Cloudflare Account ID,
Realtime Admin API Token, Deepgram API Key, ElevenLabs API Key, and a valid
RealtimeKit authToken) should successfully initialize the agent pipeline and
allow the agent to join the meeting via `RealtimeKitTransport`.

The agent should then:
1. Connect to the RealtimeKit meeting
2. Start transcribing audio using DeepgramSTT
3. Process transcripts via the TextComponent
4. Speak responses using ElevenLabsTTS
5. Return HTTP 200 from the /init endpoint

### Additional information

_No response_