Fix MCP tool call payload handling

[mariano]

Summary

• Update _tool_call_event_item in src/avalan/server/routers/mcp.py to handle EventType.TOOL_PROCESS payloads that provide calls as a list by extracting the first call so MCP tool-call notifications are emitted for streaming tool calls.
• Add test coverage in tests/server/mcp_router_test.py for the payload={'calls': [call]} variant to ensure the new code path is exercised.

Testing

• Ran make lint, which reformatted files but mypy failed due to a missing plugin error: pyproject.toml:1:1: error: Error importing plugin "pydantic.mypy": No module named 'pydantic'.
• Ran poetry run pytest --verbose -s and the test suite passed: 1566 passed, 11 skipped, 5 warnings.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Emit all tool call notifications for multi-call events

When a TOOL_PROCESS payload includes multiple calls (the tool parser can emit payload={"calls": [call1, call2, ...]} when a response contains several tool calls at once), this code only selects calls[0], so _tool_event_notifications emits a notification for the first call and silently drops the rest. That means MCP clients won’t receive tool-call notifications for subsequent calls in the same event, breaking multi-tool responses; this scenario is triggered whenever the model outputs multiple tool calls in a single chunk.

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