claude
cbd8077d2c
serveConn dispatched under context.Background(), so a dispatch in flight during shutdown could not be told to stop and closeGrace could only abandon it. The server now carries a context, Close cancels it, and each conn derives its own so nothing outlives the connection. A zero-value Server built outside Listen falls back to Background; two wiring tests do that. Client.Close read c.conn with no lock while roundtrip re-dialed and dropped it, which -race caught on the new test. The conn field now has its own mutex, held only across a read or an assignment, so Close and the watchdog reach the connection without queueing behind the call they are interrupting.