Split an Operator After an Escaped Backslash the Way Bash Does #2313

Problem

The guard's tokenizer in host-setup/agent-safety/claude/gh-write-guard.py reads an escaped backslash followed by an operator as one word, so a shell wrapper glued to that operator is never seen as a command. Constructed example, allowed although bash runs the loop with no bound:

timeout 900 true \;bash -c 'while true; do sleep 1; done'

Bash reads \\ as a literal backslash argument to true and the ; as a real separator, so bash -c runs on its own. The tokenizer yields a single ;bash token instead, and the wait-loop check never reaches the wrapper. It may share a cause with #1959, which covers shlex pairing quotes differently from bash, but this shape holds no quote.

Done looks like

The tokenizer splits an unescaped operator after an escaped backslash the way bash does, or the check reads such a token as no bound, with a self-test row for the shape above.

Found by a local strict review pass on #2117. It predates that pull request.