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This PR adds a regression test covering the JSON Schema `$ref` pattern found in MCP-style schemas, where a `$ref` points into a list-based structure such as: #/properties/body/anyOf/1/properties/Message/properties/bccRecipients/items This pattern historically failed due to incorrect handling of numeric list components in `_retrieve_ref`. The underlying bug has since been fixed, and this test ensures coverage so we don't regress on list-index `$ref` resolution. The new test (`test_dereference_refs_list_index_items_ref_mcp_like`) verifies: - correct traversal into `anyOf[1]` - proper dereferencing of `items.$ref` - no errors thrown - `ccRecipients.items` is identical to the resolved schema of `bccRecipients.items` No code changes are included, just the one test — this PR adds coverage to preserve the expected behavior and documents support for this real-world MCP schema pattern. Related to #32012. --------- Co-authored-by: Mason Daugherty <mason@langchain.dev>