fix(client): respect server capabilities before querying components in ClientSessionGroup

[gauravSsinha]

Summary

ClientSessionGroup unconditionally calls list_tools(), list_prompts(), and list_resources() on every connect, regardless of whether the server advertised those capabilities. This violates the MCP lifecycle spec.

Problem

From the MCP spec (Capability Negotiation / Operation):

Both parties MUST: ... Only use capabilities that were successfully negotiated.

When a server doesn't implement tools/prompts/resources, the calls return Method not found errors that are caught and logged as warnings — but the calls should never be made in the first place.

Fix

Check session.initialize_result.capabilities before each list call:

caps = session.initialize_result.capabilities if session.initialize_result else None
if caps and caps.prompts is not None:
    prompts = (await session.list_prompts()).prompts

Only queries capabilities the server explicitly advertised.

Impact

• Eliminates spurious WARNING: Could not fetch prompts/resources/tools logs
• Brings the client into spec compliance
• Reduces unnecessary network round-trips to servers that don't support all capabilities

Fixes #2689