Retrieve an event stream

Creates an event stream that delivers the account's public events over Server-Sent Events (SSE), with the same payloads and ordering as the events collection. Optional filters restrict the stream to specific event types and resource types. Use `start` to choose whether the stream also delivers retained events published before it was created (`earliest`, the default) or only events published afterwards (`now`). Requires an `Idempotency-Key` header. The credential must also have the `events.read` permission; otherwise the request fails with `permission_denied`. The number of active event streams is limited per credential and per account. Creating a stream beyond these limits returns `429` with the `too_many_streams` error code in the standard error envelope, without the rate-limit fields.