Function validate_schema_against_database 

pub async fn validate_schema_against_database(
    schema: &CompiledSchema,
    introspector: &impl DatabaseIntrospector,
) -> Result<DatabaseValidationReport>

Validate a compiled schema against a live database.

Performs three levels of validation:

• L1: Checks that sql_source relations exist
• L2: Checks column existence and JSON column types
• L3: Checks JSONB key existence via sampling

All diagnostics are warnings — the report never causes compilation to fail.

Errors

Returns FraiseQLError if database introspection queries fail.