Initiate Attended Transfer

Park the inbound caller in a Twilio conference room with hold music, then kick off the screener-ask outbound call. Replaces the built-in Vapi transferCall used in Phase 0; eliminates the dial-tone gap because the caller's leg is moved into the conference directly via the live Twilio CallSid (no second outbound call to a parking number).

The screener-accept bridge step joins the same conference_name we pin here, so accept flow auto-bridges. Decline reconnect (Phase 3) reads the same row and reroutes the caller's leg.

Vapi custom tool. Expects arguments:

• caller_name: str (required)
• call_reason: str (required for unknown callers; optional for known contacts)
• special_caller: bool (optional, default False)

Known-contact status is determined server-side via a strict E.164 phone-number lookup (see ScreeningService.lookup_known_contact); it is NOT a tool argument. Any is_known_contact arg the agent sends is ignored.