The longest I can find on my real-world, full operating system is also a build directory. However it's 349 characters:

    /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_lang_v8/v8/work/v8-3.21.3/out/x64.release/.deps/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_lang_v8/v8/work/v8-3.21.3/out/x64.release/obj.target/v8_base.x64/src/extensions/externalize-string-extension.o.d