File sync stops with a clear reason when a git setting changes attribute rules

What

Git can be told to treat certain files specially through attribute rules, for example in a .gitattributes file. A setting on your machine can change which of those rules git applies. File sync, which keeps your local folder and a cloud copy in step, cannot follow that.

• A new failure cause, attribute_source, is raised when the repository's attribute settings come from a source such as attributes_file.
• The failure detail now explains that "a git setting on the user's machine can change which attribute rules git applies, in a way file sync cannot follow". The text used to point to FILE_SYNC_STOPPED.md instead.
• Teleport, which carries a session over to another machine, reports attribute_source_unread when uploading its bundle hits this case.
• A check that decides whether a sync is eligible now also excludes the attribute_source cause, alongside other, host_config and legacy_tree.

Why

Sync now stops and names the reason instead of carrying on and possibly applying the attribute rules wrongly. If you see this message, a git setting on your machine is the thing to look at.