[codex] fix nested MCP schema conversion

[117503445]

Summary

• Preserve nested MCP object schemas when converting through the LangChain adapter path.
• Thread the root JSON schema through _json_schema_to_pydantic / _json_type_to_python so deep anyOf / $ref wrappers can resolve $defs.
• Add regression coverage for nested optional object fields, direct anyOf + $ref schemas, and recursive $ref schemas that should not crash.

Root Cause

Optional nested object fields are represented by Pydantic as anyOf: [{"$ref": ...}, {"type": "null"}]. The second JSON Schema to Pydantic conversion in the LangChain adapter previously passed those nested field schemas into _json_type_to_python without the root schema, and _json_type_to_python defaulted schemas without a top-level type to string. That downgraded nested MCP objects into string | null.

The fix resolves wrapped schema fragments against the root schema and tracks active $ref entries while recursively constructing Pydantic models, so self-referential schemas degrade to dict at the recursive edge instead of raising RecursionError.

Validation

• .venv/bin/python -m pytest tests/unittests/integration/test_tool_utils.py::TestNestedObjectRoundTrip -q
• .venv/bin/python -m pytest tests/unittests/integration/test_tool_utils.py -q

[Copilot]

Pull request overview

This PR fixes JSON Schema → Pydantic conversion issues in the LangChain adapter path so that nested MCP object schemas (especially anyOf/$ref wrappers) remain objects after the second conversion, and recursive $ref graphs no longer crash during model construction.

Changes:

• Thread the root schema and add $ref-tracking/caching to _json_schema_to_pydantic / _json_type_to_python to correctly resolve deep $defs references and avoid exponential expansion.
• Add $ref-cycle protection so self-referential schemas degrade gracefully instead of raising recursion errors.
• Add regression tests covering nested optional objects, anyOf + $ref wrappers, recursive and shared $ref topologies, and reachable-ref caching.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
agentrun/integration/utils/tool.py	Threads root schema + adds ref-cycle guard and caching to preserve nested object typing across conversions.
tests/unittests/integration/test_tool_utils.py	Adds regression coverage for nested object round-trips and multiple $ref recursion/caching scenarios.

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