Place a sequence in the dispatch chain, or take it out. The chain is every ranked sequence of the tenant, active or not, ordered by rank, then by creation time; automatic dispatch tries its active sequences in that order. position is the 1-based place the sequence takes: from 1 to the chain's length when the sequence is ranked, to one more when it is not (to append it). position: null takes it out of the chain, so it runs only when started by hand. Every sequence of the chain is then renumbered 1, 2, 3, … in one write, and each one whose rank changes advances its version; a move that changes no rank writes nothing. The sequence is not checked against the rules of POST /sequences, so a broken one can be taken out. A chain of more than 100 sequences cannot be renumbered in one write and answers 400; take sequences out first (PATCH /sequences/{sequenceId} with rank: null). When another request changed a sequence of the chain meanwhile, the answer is 409 CONCURRENT_UPDATE and nothing is written: list the sequences again and decide anew. The response is the moved sequence as stored, with its summary.