fix(gopher): bound cancel goroutine to Download lifetime

internal/protocol/gopher/gopher.go

@@ -83,10 +83,18 @@ func (p *Protocol) Download(ctx context.Context, req *core.DownloadRequest) (*co
 
 	// Close the connection when the context is cancelled so any
 	// blocking Read returns immediately instead of waiting for the
-	// 30-second deadline.
+	// dial deadline. The done channel bounds the goroutine to the
+	// lifetime of Download: the goroutine exits either when the
+	// context fires (we close the conn) or when Download returns
+	// successfully and defer close(done) signals shutdown.
+	done := make(chan struct{})
+	defer close(done)
 	go func() {
-		<-ctx.Done()
+		select {
-		conn.Close()
+		case <-ctx.Done():
+			conn.Close()
+		case <-done:
+		}
 	}()
 
 	// Send selector + CRLF