Surface the path/repo/url tied to an AnonymousError when it gets
serialized for logging — previously logs only carried name, message,
and httpStatus, which made file_not_found entries impossible to trace
back to a specific file or repo. Extract the existing detail formatting
out of toString() into a public detail() method, harden it against
AnonymizedFile getters that can throw, and have serializeError include
the result as a "detail" field.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>