Bulk create or patch items in a project (subject to change)

Items to create or patch, all in the same project. The request is all-or-nothing: if any item is invalid the whole request is rejected and nothing is written. Item order does not matter — intra-batch relations resolve regardless of order. Each item's id or sourceId must be unique within the request. Max 250 items per request.

Per-item result, in request order; correlate by id/sourceId. The request is all-or-nothing, so on success (HTTP 200) every item has success: true. Any failure is signaled by the HTTP status code — 400 for an invalid payload (each offending item reported in the issues array: position, message, and params.warningType/sourceId; INVALID_STATE_TRANSITION when a status change breaks the transition rules of the project), 409 for a write conflict, 500 for an unexpected error — and nothing is written.