Previously shared one McpServer instance across all sessions/transports,
which caused Protocol._transport to be overwritten when new sessions
connected. This broke message routing for requests on previous transports
after long-running SSE streams.
Now creates a new McpServer instance per session, following the stateful
session pattern from the MCP SDK documentation. Each session gets its own
server+transport pair, preventing transport reference conflicts.
Fixes issue where get_agent_status would fail after wait_for_agent completed.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
