Flow rule matcher for external storage mount

How to use GitHub

• Please use the 👍 reaction to show that you are interested into the same feature.
• Please don't comment if you have no relevant information to add. It's just extra noise for everyone subscribed to this issue.
• Subscribe to receive notifications on status change and new comments.

Is your feature request related to a problem? Please describe.

When creating flow rules it should be possible to let rules only trigger when a file is part of a specific external storage mount. While this works with external storages with shared credentials using system tags, in cases where the user credentials are used each mount for each user has a own file id and therefore applying the system tag as an admin doesn't work.

Describe the solution you'd like
Add a flow check to see if the file in question is part or not of a external storage mount (identified by the id for example)

Describe alternatives you've considered
Having a systemtag on the folder, but that cannot be set by the admin

No files, tests, or entry points are named. Start by tracing how flow rules inspect files and how external storage mounts are identified, then determine how a mount-specific condition should represent per-user file IDs; done means a flow rule can reliably match files from the selected external storage mount.