With no since the pages are the whole list. The last page carries an ETag, the position the read ended at: send it as since to read only what changed since then, and also as If-None-Match, so that a read finding nothing changed is a 304 with no body. Send each next_cursor as since to continue; a null next_cursor means the last page. A since the API cannot continue (from another sign-in) is a 400: read from the start. Where a practice system shows each person their own matters (capabilities.matter_visibility is member), the page holds the clients the firm made itself and the clients of the matters THE CALLER is served by GET /v1/matters, and no others: a client that system named is served only while one of its matters is the caller's to see, with an updated_at that is the later of its own and the instant such a matter came into the caller's sight, so it arrives on an incremental pull. Every other firm's answer is unchanged.

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.