Claude Agent SDK - New Session User-defined skills are not getting loaded

[kmarrrahul]

Bug: Claude Agent SDK Skills Not Persisting Correctly

This project integrates with multiple agent SDKs, including:

GitHub Copilot SDK: https://github.com/github/copilot-sdk
Google Antigravity SDK: https://github.com/google-antigravity/antigravity-sdk-python
Claude Agent SDK: https://code.claude.com/docs/en/agent-sdk/overview
Cursor SDK: https://cursor.com/docs/sdk/python

There is an issue with the Claude Agent SDK implementation of Agent Skills.

Expected

Both user-defined Agent Skills and Claude internal skills should be available throughout the session lifecycle.

Actual
New Session: User-defined skills are not loaded, but Claude internal skills are available.
Follow-up Prompt / Session Resume: User-defined skills become available, but Claude internal skills are lost.
Reproduction
Configure custom Agent Skills in the UI.
Start a new Claude session.
Check available skills.
Send a follow-up prompt in the same session.
Check available skills again.
Notes

This behavior is not seen with the GitHub Copilot SDK, Antigravity integration, where skills are loaded correctly and remain available across the entire session.

Please investigate the difference between session initialization and session resume logic in the Claude Agent SDK integration.