Removes a step from the draft sequence, closing the chain around it and keeping the delay above it. The start step cannot be deleted.

This writes the draft. Call Publish Sequence to make it live — at which point any lead sitting on the removed step completes.

Concurrent writes are safe — overlapping calls to one campaign serialize, and every change is kept. A sequence builder open in the browser saves its own copy of the whole graph, so an edit made through the API while that canvas is open is overwritten by the next canvas save.