Is it possible to add a lock feature to prevent task edits after assignment, as well as an audit trail to log all changes made to tasks?

Is it possible to add a lock feature to prevent task edits after assignment, as well as an audit trail to log all changes made to tasks?

Also I am unable to add pdf files as an attachment whereas jpg files and docx files can be uploaded.

Originally posted by @Nero-devbot in https://github.com/basecamp/fizzy/discussions/2931