setup usage_rules

.claude/skills/ash-framework/references/exist_expressions.md

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+# Exists Expressions
+
+Use `exists/2` to check for the existence of records, either through relationships or unrelated resources:
+
+### Related Exists
+
+```elixir
+# Check if user has any admin roles
+Ash.Query.filter(User, exists(roles, name == "admin"))
+
+# Check if post has comments with high scores
+Ash.Query.filter(Post, exists(comments, score > 50))
+```
+
+### Unrelated Exists
+
+```elixir
+# Check if any profile exists with the same name
+Ash.Query.filter(User, exists(Profile, name == parent(name)))
+
+# Check if user has any reports
+Ash.Query.filter(User, exists(Report, author_name == parent(name)))
+
+# Complex existence checks
+Ash.Query.filter(User, 
+  active == true and 
+  exists(Profile, active == true and name == parent(name))
+)
+```
+
+Unrelated exists expressions automatically apply authorization using the target resource's primary read action. Use `parent/1` to reference fields from the source resource.