The chat client's context no longer follows the bot's, so a stop no
longer sends it SIGTERM while the API is still finishing its requests.
The deferred stop in Run, which runs after the API's, stops it instead,
so a request in progress at a stop gets its answer rather than a 500.
The README says so.
The new test runs the whole bot with the test binary itself standing in
for simplex-chat on PATH. The stand-in holds its answer to the contacts
request until the test has told the bot to stop.
Model: opus-5-5
