Describe the escalation step vocabulary

Everything needed to build a valid escalation chain: the triggers, actions, channels and acknowledgement modes, what delay_minutes means, how a step names its target, the size limits, the account-wide default steps, a worked example ladder under examples, and the providers this company may actually use. The provider list depends on the plan and on which credentials are connected, which is why it cannot live in this specification — read it here rather than assuming. Each provider carries ack_capabilities per channel: an acknowledgement mode a provider cannot report will simply never acknowledge. configured: false means a step naming that provider will save and then deliver nothing — it is the same verdict GET /capabilities reports as a channel status other than ready, so the two can no longer contradict each other about Slack, Teams or email.