feat: add custom_context field to research context

[igorvolk1961]

Summary

Adds an optional custom_context field to the ResearchContext class to enable projects extending sgr_deep_research to store project-specific data without modifying the core codebase.

Changes

• Added custom_context: dict | BaseModel | None field to ResearchContext class in core/models.py
• Field is optional with default=None for full backward compatibility
• Field description: "Custom context for project-specific data"

Motivation

This change allows downstream projects to extend ResearchContext with custom data structures (e.g., Pydantic models) stored in custom_context, enabling project-specific functionality while keeping the core codebase clean and minimal.

Backward Compatibility

✅ Fully backward compatible - the field is optional with default=None, so existing code will continue to work without any changes. No breaking changes.

Use Case Example

from pydantic import BaseModel

class MyProjectContext(BaseModel):
custom_field: str

context = ResearchContext()
context.custom_context = MyProjectContext(custom_field="value")

Testing

• ✅ No linter errors
• ✅ Existing functionality remains unchanged
• ✅ Field can be set to None, dict, or any BaseModel instance

[virrius]

Thanks!

Im uncertain whether the Context should be initialized inside the agent or passed in during initialization like DI style.

@EvilFreelancer