fix: Stack overflow during validation of schemas with circular $ref chains

Signed-off-by: Dmitry Dygalo <dmitry@dygalo.dev>

Author: Stranger6667

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Fixed
 
+- Stack overflow during validation of schemas with circular `$ref` chains (e.g., `a` → `b` → `a`).
 - Local `$ref` resolution within fragment-extracted external resources. [#892](https://github.com/Stranger6667/jsonschema/issues/892)
 
 ### Removed

crates/jsonschema-py/CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Fixed
 
+- Stack overflow during validation of schemas with circular `$ref` chains (e.g., `a` → `b` → `a`).
 - Local `$ref` resolution within fragment-extracted external resources. [#892](https://github.com/Stranger6667/jsonschema/issues/892)
 
 ## [0.37.3] - 2025-11-28

crates/jsonschema/src/keywords/additional_items.rs

@@ -5,7 +5,7 @@ use crate::{
     node::SchemaNode,
     paths::{LazyLocation, Location},
     types::{JsonType, JsonTypeSet},
-    validator::Validate,
+    validator::{Validate, ValidationContext},
 };
 use serde_json::{Map, Value};
 
@@ -67,6 +67,48 @@ impl Validate for AdditionalItemsObjectValidator {
         }
         Ok(())
     }
+
+    fn is_valid_ctx(&self, instance: &Value, ctx: &mut ValidationContext) -> bool {
+        if let Value::Array(items) = instance {
+            items
+                .iter()
+                .skip(self.items_count)
+                .all(|item| self.node.is_valid_ctx(item, ctx))
+        } else {
+            true
+        }
+    }
+
+    fn validate_ctx<'i>(
+        &self,
+        instance: &'i Value,
+        location: &LazyLocation,
+        ctx: &mut ValidationContext,
+    ) -> Result<(), ValidationError<'i>> {
+        if let Value::Array(items) = instance {
+            for (idx, item) in items.iter().enumerate().skip(self.items_count) {
+                self.node.validate_ctx(item, &location.push(idx), ctx)?;
+            }
+        }
+        Ok(())
+    }
+
+    fn iter_errors_ctx<'i>(
+        &self,
+        instance: &'i Value,
+        location: &LazyLocation,
+        ctx: &mut ValidationContext,
+    ) -> ErrorIterator<'i> {
+        if let Value::Array(items) = instance {
+            let mut errors = Vec::new();
+            for (idx, item) in items.iter().enumerate().skip(self.items_count) {
+                errors.extend(self.node.iter_errors_ctx(item, &location.push(idx), ctx));
+            }
+            ErrorIterator::from_iterator(errors.into_iter())
+        } else {
+            no_error()
+        }
+    }
 }
 
 pub(crate) struct AdditionalItemsBooleanValidator {