Atomically applies an array of CompositionOps. All ops succeed or none do (trans...
https://api.cueframe.ai/v1/projects/:id/composition/applyOverview
Atomically applies an array of CompositionOps. All ops succeed or none do (transactional). A write must carry `if_match`, the composition ETag it observed (409 stale_etag on mismatch), or the stronger `concurrency` admission; with neither it is refused with 428 precondition_required. Pass `dry_run: true` to validate the batch — runs the same apply + projection accept/reject guards WITHOUT persisting, returning `{ valid, errors }` with `locator.op_index` on the first failing op.