McpServer forward reference fails at runtime with Pydantic 2.12+

[kaminoguo]

Problem

claude_code_sdk/types.py imports McpServer only under TYPE_CHECKING, but McpSdkServerConfig uses it as a type annotation. Pydantic 2.12+ requires this type at runtime.

Error

PydanticUserError: Settings is not fully defined; you should define McpServer, then call Settings.model_rebuild().

Location

types.py:11-12 and types.py:182:

if TYPE_CHECKING:
    from mcp.server import Server as McpServer  # line 11-12

class McpSdkServerConfig(TypedDict):
    instance: "McpServer"  # line 182 - fails at runtime

Fix

if TYPE_CHECKING:
    from mcp.server import Server as McpServer
else:
    McpServer = Any

Environment

• claude-code-sdk: 0.0.25
• pydantic: 2.12.5
• Python: 3.11