fix: handle pydantic generic models in JSON serializer

[zzstoatzz]

Summary

Fixes serialization failures when using parameterized Pydantic generic models (e.g., APIResult[str]) with the JSON serializer.

The Problem

When serializing a parameterized generic like APIResult[str], the JSON encoder was storing the class name with brackets:

{"__class__": "module.APIResult[str]", "data": {...}}

This causes deserialization to fail because Python's import system cannot import APIResult[str] - only APIResult.

The Fix

Extract the origin class from Pydantic's __pydantic_generic_metadata__ when encoding, so the serialized output uses the importable base class:

{"__class__": "module.APIResult", "data": {...}}

Test plan

• Added regression test test_pydantic_generic_model_roundtrip
• All existing serializer tests pass

🤖 Generated with Claude Code

[codspeed-hq]

CodSpeed Performance Report

Merging #19868 will not alter performance

_{Comparing fix/json-serializer-pydantic-generics (139b051) with main (080230e)}

Summary

✅ 2 untouched