204 while no entry carries the key, with the attribute's sets. 409 for a row a connector owns or has bound, and 409 once an entry carries the key: an attribute an entry carries is DEACTIVATED and never deleted, so a released line keeps meaning what it said. A matter that still names one of the deleted sets keeps naming it, and an id that names nothing is ignored when the entry's options are worked out.

Operator mount: an operator acting for the firm named in the path, as its oldest active admin, else its oldest active billing member; X-Six-Minute-Acting-As names them. 404 for no such firm, 409 urn:six-minute:problem:no-acting-member for one with neither.