The slash-command worker is spawned as `-m tui_gateway.slash_worker` and
inherits the user's CWD. A local package in that CWD (e.g. a project shipping
its own `utils/`, `proxy/`, or `ui/`) shadows the installed hermes module, so
`import cli` crashes the worker with:
ImportError: cannot import name 'atomic_replace' from 'utils'
The child then exits 1 in a crash loop. #15989 added this sys.path guard to the
sibling entrypoint tui_gateway/entry.py but not to this worker, which is spawned
as a separate process and so starts with CWD back on sys.path.
Apply the same guard (insert HERMES_PYTHON_SRC_ROOT, strip ''/'.') before the
first non-stdlib import. Add a regression test that imports the worker from a
CWD containing colliding packages.
Fixes#51286
8dcbc910bf