v0.42.0

The owner watched the helper browser get opened, used and never closed. Measured
before touching anything, with the real model on a task that needs both
browsers: six runs out of six left `support` open at the end, and in the owner's
own sessions one conversation of 247 steps used it 29 times and never closed it.

Three origins, none of them the model:

- The server's instructions never reached it. They are the one place the
  two-browser contract is written - what `support` is for, and that whoever
  opens it closes it - and the loop sent the system prompt and the tool
  descriptions and nothing else. The link keeps what the server says at
  `initialize`, and one function builds the system message from this build's
  prompt plus those instructions, refreshed at the start of every run, so a
  restored transcript and a fresh one carry the same current text. It was
  assembled by hand in two places and had the instructions in neither.

- The end-of-turn sentence forbade the very call that closes the helper: "reply
  with the answer and do NOT call any more tools", at the exact moment the
  close should happen. The order is in the sentence now - close `support` if
  you opened it and nothing more needs it, then answer, then no more tools -
  without exception vocabulary, because an exception is what a model reaches
  for.

- The API cuts every tool description at 1024 characters, and `browser_open`
  was 1996: the model read it ending mid-word inside the paragraph about
  profiles, and the one sentence about closing was past the cut.
  `browser_click_at` was over too. Both fit now, the contract comes first, and
  what was cut moved into comments for a reader of the source.

Measured after, same bench, same task, same model, six runs: `support` closed
before the answer in six, left open at the end in none. Every sequence ends
with browser_close support.

Gates: every description under the limit and identical to what the loop sends,
executed against the real server; `browser_open` names `browser_close` in its
first half; the loop puts the instructions in the one system message and
replaces them run to run; the brain hands the link's instructions to the loop;
the end-of-turn sentence closes before it answers and carries no loophole.