Run the turns of an agent in a loop

A user message goes to the log when it comes and wakes the loop. A turn
waits until every build is done, so the view holds the summaries of the
messages before it. Its first request holds the prompt, the six tools,
and one user message with the view, the date and time of the turn, and
each new message whole. The view leaves out the leaf lines of the new
messages, but it keeps every other line, also the replies that came
after a message that waited.

The loop runs the tool calls of each response and sends their results
back until a response has no tool call. Each later request begins with
the whole previous input, then the output items with the encrypted
reasoning and without their ids, because the calls do not store them,
then the tool results. So each request of a turn begins with all of the
one before it. User messages that come during a turn join the next
request after the tool results, and a message that comes during the
final request starts a new turn. Replies, tool calls, and results go to
the log as they happen, and the reasoning never does.

An interrupt cancels the turn and kills a running tool. A failed call
ends the turn without a retry, and its messages stay in the log, so a
lasting failure does not repeat. Only a failed log write stops the loop.

The prompt gets a paragraph on persistent mode: a reply with no tool
call ends the turn, a question in the middle of a task does not end the
task, and "continue" resumes the latest unfinished task.

Issue: 5daf23e