Type alias NormalizedCallEvent

Normalized webhook event from any telephony provider.

Uses a discriminated union on the kind field so consumers can narrow with a switch (event.kind) and get full type safety for each variant's payload.

Provider-specific webhook formats (Twilio form-encoded, Telnyx JSON, Plivo URL-encoded/JSON) are all mapped into these canonical shapes by each provider's IVoiceCallProvider.parseWebhookEvent implementation.