WIP - Add Telnyx voice provider

[whoiskatrin]

Summary

Adds first-class Telnyx support for the Cloudflare voice pipeline, addressing #1367.

This PR introduces a new @cloudflare/voice-telnyx provider package under voice-providers/telnyx and a phone/PSTN-focused examples/telnyx-voice-agent app that demonstrates the browser-side Telnyx WebRTC bridge model.

What changed

@cloudflare/voice-telnyx

• Adds a Telnyx provider package following the existing voice-providers/* conventions.
• Supports subpath imports so users can import only what they need:
  • @cloudflare/voice-telnyx
  • @cloudflare/voice-telnyx/stt
  • @cloudflare/voice-telnyx/tts
  • @cloudflare/voice-telnyx/telephony
• Ports Telnyx STT support implementing Transcriber / TranscriberSession:
  • Workers fetch-upgrade WebSocket connection
  • 16 kHz mono PCM16 streaming
  • WAV header emission for Telnyx's streaming API
  • interim and final transcript callbacks
• Ports Telnyx TTS support implementing TTSProvider and StreamingTTSProvider:
  • REST backend by default
  • Workers-only WebSocket streaming backend
• Adds Telnyx telephony helpers:
  • TelnyxCallBridge
  • TelnyxPhoneTransport
  • TelnyxPhoneClient
  • TelnyxJWTEndpoint
  • createTelnyxVoiceConfig
• Keeps STT/TTS subpaths independent from telephony imports.
• Adds README docs covering environment variables, subpath imports, browser voice usage, and PSTN/telephony setup.

Example app

• Adds examples/telnyx-voice-agent, focused on the phone/PSTN path:
  • phone call → Telnyx WebRTC bridge in the browser
  • browser bridge → Cloudflare Agent WebSocket
  • Telnyx STT → Workers AI LLM → Telnyx TTS
  • response audio injected back into the same phone call
• Uses createTelnyxVoiceConfig and TelnyxPhoneClient from @cloudflare/voice-telnyx/telephony.
• Uses the browser as a control panel/WebRTC bridge, not as a microphone/speaker voice demo.
• Includes .env.example with:
  • TELNYX_API_KEY
  • TELNYX_CREDENTIAL_CONNECTION_ID
• Documents the local-demo JWT endpoint and calls out replacing allowUnauthenticated: true with an authorize() callback in production.

Attribution / dependency metadata

• Adds @telnyx/webrtc for telephony support.
• Updates NOTICE to document that parts of this provider are adapted from Telnyx's @telnyx/voice-cloudflare package, whose npm metadata declares MIT licensing.

Validation

Passed:

npm run build -w @cloudflare/voice-telnyx
npm run build -w @cloudflare/agents-telnyx-voice-agent
npm run check

npm run check reports existing sherif warnings for unrelated workspace paths without package.json, then completes successfully: export checks, formatting, oxlint, and all 82 TypeScript projects pass.

Notes for reviewers

• The example now intentionally demonstrates the provider's distinctive phone/PSTN bridge value instead of a browser microphone/speaker STT/TTS flow.
• The phone example leaves the voice agent's default declared audio format in place because TelnyxTTS currently returns MP3 by default and TelnyxPhoneClient can decode non-PCM server audio before playing into the phone bridge.
• For production, the JWT endpoint should use an authorize() callback instead of allowUnauthenticated: true.

Refs #1367

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Latest commit: 69870fb

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commit: 69870fb

[Oliver-Zimmerman]

Nice port overall — I think you’ve preserved the core architecture well, especially the split between STT/TTS/telephony and the browser-side PSTN bridge model. My main ask would be to swap the example for one that better shows the real value of the provider: the current example reads mostly like a browser STT/TTS demo, while the distinctive bit here is the phone/PSTN path. I’d suggest porting one of the original phone/hybrid examples instead, e.g. examples/phone-voice-agent: https://github.com/team-telnyx/voice-cloudflare/tree/main/examples/phone-voice-agent”

[Oliver-Zimmerman]

Hey @whoiskatrin any update on this?

[cjol]

@Oliver-Zimmerman I've picked this up and ported over the tests for future maintenance. At first glance the new example works but I wasn't able to verify the phone call working -- possibly because I've only got a freemium account. Could you validate from your side?

[Oliver-Zimmerman]

@cjol I just tested, it is working as expected. I was able to call the genCred and have a conversation, the transcript was present.