The audit log formatter already does something interesting with an error's details attribute/property:  https://github.com/rackerlabs/otter/blob/master/otter/log/formatters.py#L188.  Would make sense to make it a property, and let that formatter handle it?  Or if we wanted it in regular logs, to move that details handling to the regular log observer?

Apologies if I missed the intention of not doing that.  :)  This may or may not be desirable, if we don't want to include the headers in the audit logs, for instance (although currently I don't think errors are making it into the audit logs - we'd need some way to filter out unwanted info anyway).