Reference: Inbound Voice Support Agent

Architectural notes

Reference architecture for a voice agent handling inbound support calls
with handoff to human on escalation.

Why these picks:
- Haiku 4.5 as default for sub-second turn latency; Sonnet escalation
  only when the call requires deeper reasoning.
- Vapi for end-to-end voice (STT + LLM + TTS + telephony) to avoid
  integration overhead.
- Cloudflare Workers + Durable Objects for low-cold-start session state.

Common gotchas:
- Turn-taking quality matters more to user satisfaction than model
  smarts on most calls.
- Mid-call model swaps add noticeable latency; design escalation as a
  handoff, not a swap.