bug: mcpServers field incorrectly required

[Smityz]

Current Behavior

# This fails with ValidationError
request = NewSessionRequest(cwd="/tmp")
# Error: Field required [type=missing]

Expected Behavior

# Should work per spec
request = NewSessionRequest(cwd="/tmp")
request = NewSessionRequest(cwd="/tmp", mcp_servers=[])

https://github.com/agentclientprotocol/python-sdk/blob/main/src/acp/schema.py#L1339-L1345
https://github.com/agentclientprotocol/python-sdk/blob/main/src/acp/schema.py#L1987-L1993

Set the default for these two to None.

Reproduction steps

easy to Reproduction

Expected result

keep the same behavior with spec

Actual result

mcpServers field incorrectly required

Versions / environment

0.7

Logs & screenshots

Open to submitting a fix?

• I’m willing to open a PR for this bug.