The local retries variable in MCPServerTask.run() accumulated across
transient disconnections — each transport exception incremented it, but
only clean transport returns (auth recovery / manual refresh) or
park-wake reset it. Five transient blips over a long-uptime gateway
would permanently park the MCP server.
Promote retries to instance attribute _reconnect_retries and reset it
at all 4 session-establishment sites in _run_stdio / _run_http, so only
consecutive failures without successful reconnection count toward the
parking budget.
Fixes#57604
