SpiceDB is an open source, Google Zanzibar-inspired, database system for creating and managing security-critical application permissions.

SpiceDB

and a question of my own: does spicedb gracefully handle circularly defined permissions? I'm imagining something that looks like this:
```
definition user {}

definition one_thing {
  relation user: user
  relation another_thing: another_thing

  permission read: user + another_thing->read
}

definition another_thing {
  relation user: user
  relation one_thing: one_thing

  permission read: user + one_thing->read
}
```

answered my own question here - you'll just get recursion depth exceeded. turns out my model didn't actually demand this and i misread the requirements, so it's not a problem, but it's good to know.

only if you walk back to the same resource + permission

so long as it is actually not circular, you're fine moving back and forth