bug: schema validation does not detect circular $ref — can infinite loop

[nfvelten]

Migrated from nfvelten/arbitus#124

Summary

JSON Schema allows $ref to reference other schema definitions. If an upstream MCP server returns a schema with a circular $ref (A → B → A), the schema validation middleware could loop infinitely while resolving the reference chain.

Location

src/middleware/schema_validation.rs

Fix

Track visited $ref paths during schema resolution. Return an error (and block the request) if a cycle is detected.

References

• PROPOSAL.md §4.4