Your Line Agent

A Line agent is your code deployed on Cartesia’s platform. When a Teams call arrives through this bridge, everything below reaches it through Cartesia’s normal Line surfaces - the start metadata and UserCustomSent events. This page is the contract to build against.

Detecting a Teams call

The bridge always sets from: "msteams" in the start metadata, so your agent code can branch on the transport:

{
  "from": "msteams",
  "callId": "19:meeting_...",
  "callerName": "Alice W",
  "tenantId": "72f9...",
  "direction": "inbound"
}

callerName, tenantId and direction are always present (defaulted to "caller" / "unknown-tenant" / "inbound" when Teams provides no identity - guest and anonymous callers exist).

Live context (custom events)

The bridge forwards call state as custom events with type: "call_context". Each carries a human-readable note (drop it straight into your context if you like) plus structured fields:

{ "type": "call_context", "note": "Call context snapshot at stream start.", "participantCount": 1, "recordingStatus": "unknown" }
{ "type": "call_context", "note": "There are 3 human participants on this call. Stay quiet unless directly addressed.", "participantCount": 3 }
{ "type": "call_context", "note": "The person now speaking is Sara.", "activeSpeaker": "Sara" }
{ "type": "call_context", "note": "Teams recording is now active.", "recordingStatus": "active" }

Notes on semantics:

• One snapshot at stream start (the first example) carries the participant count and recording state the call began with, so state that changed before the stream was ready is never lost.
• Active speaker is only sent in group calls, only when the speaker changes, and rate-limited (at most one update per 5 s) so VAD flapping cannot spam your agent.
• Recording state matters if your agent persists anything: Teams tenants often require recording to be active before content is stored. The bridge forwards the signal; the policy is yours to implement in agent code.

Governor goodbyes (goodbye_request)

When a call hits a time limit (StandIn tier cutoff or the bridge’s MAX_CALL_MINUTES cap) and no TTS goodbye is configured on the bridge, your agent code receives:

{ "type": "goodbye_request", "text": "I'm sorry, we've reached the time limit for this call. Goodbye!" }

Handle it by speaking the text; the bridge ends the call after the grace window either way, so an unhandled event means the caller hears silence before the drop. If the bridge has CARTESIA_TTS_MODEL + a voice configured, the goodbye is synthesized deterministically instead and your agent is muted while it plays - no event is sent.

DTMF

Keypad digits arrive as native Line dtmf events (0-9, *, #) - the bridge does not translate them into prompt text.

Hanging up

End the call from your agent code the way Line normally ends calls; when the stream closes, the bridge ends the Teams call with session.end(agent-disconnected).

Known limitation: transfer_call

If your agent yields a transfer, the bridge logs it and ignores it: there is no phone number to transfer a Teams call to, and the StandIn wire currently has no Teams-side transfer/escalation capability. Disable transfer paths for calls with metadata.from == "msteams".

Audio format

The stream is pinned to pcm_16000 (16 kHz, 16-bit, mono). Your agent’s audio comes back over the same stream config - see the note in Troubleshooting about the first-frame tripwire.