Fix AttributeError: use sources_count instead of source_count

[crugalde]

Problem

Calling list_notebooks via the MCP tool raises:

AttributeError: 'Notebook' object has no attribute 'source_count'

Root cause

The Notebook object returned by notebooklm-py exposes the attribute as sources_count (plural), not source_count. Confirmed via runtime introspection:

>>> nb.model_dump()
{'id': '...', 'title': '...', 'created_at': ..., 'sources_count': 0, 'is_owner': True}

Fix

One-line change in server.py to use the correct attribute name in the list_notebooks tool's response.

Verification

• Reproduced the original error end-to-end via Claude Desktop → MCP server → list_notebooks (returned isError: true with the AttributeError).
• Applied the fix; restarted the MCP server.
• Re-invoked from Claude Desktop chat; tool now returns isError: false with the full notebook list (verified with 36 notebooks).

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Created via Warp: https://app.warp.dev/conversation/886ab47d-482a-482c-9c85-3b22f15c10ad

Co-Authored-By: Oz oz-agent@warp.dev