Split placeholder TERMINAL_CWD resolution into three cases: local falls
back to MESSAGING_CWD/home; docker without workspace mount leaves cwd unset;
docker with mount enabled preserves an explicit host MESSAGING_CWD path for
terminal_tool's /workspace mapping. Stops leaking host Path.home() into
containers without breaking the mount contract.
Co-authored-by: Cursor <cursoragent@cursor.com>
