fn validate_system_catalog_query(sql: &str) -> Result<(), McpRequestError>Expand description
Validates that a query only references system catalog tables.
For SELECT statements, all table references must be in system schemas
(from SYSTEM_SCHEMAS, excluding mz_unsafe), and at least one system
table must be referenced (constant queries like SELECT 1 are rejected
to prevent misuse of the observatory endpoint for arbitrary computation).
SHOW and EXPLAIN statements are allowed without table references.