Transcripts and run logs page back with cursors, and get_run_log checks its cursors

What

A cursor is a bookmark a tool returns so the next request can carry on where the last one stopped.

• When older transcript events do not fit in a result, the result now tells Claude to pass next_cursor as cursor to read them, and it returns an olderCursor. Before, those events were only reported as not shown, with no way to read them.
• The routines tool text for list_runs and get_run_log now says to pass the page's next_cursor back as cursor, instead of "pass cursor for more". It adds that get_run_log pages only from the newest events to older ones, and that a cursor from elsewhere is refused.
• The RemoteTrigger tool's get_run_log now hands out cursors of the form prefix.hash.cursor, tied to the session_id. It rejects any cursor not in that form, including cursors from older versions, typed numbers, another run's cursor and edited cursors. The error is "cursor is not in the form that get_run_log hands out for this session_id, so nothing was read." Before, the cursor was passed straight through.
• The cursor field's description now says it is not an offset, a count or an event number.

Why

Claude can now page back through long transcripts and run logs. A get_run_log cursor that was stored earlier or built by hand now gives an error, and reading has to start again from the newest events.