chore(gopher): extract dial timeout constant

internal/protocol/gopher/gopher.go

@@ -34,6 +34,12 @@ const (
 	typeSearch      = '7' // index search
 )
 
+// dialTimeout caps the time spent establishing a TCP connection and
+// waiting for the first response byte. Generous enough for slow Gopher
+// servers, short enough that a stalled connection does not block the
+// caller indefinitely.
+const dialTimeout = 30 * time.Second
+
 // Protocol implements gopher:// downloads (RFC 1436).
 type Protocol struct {
 	*protocol.BaseProtocol
@@ -68,12 +74,12 @@ func (p *Protocol) Download(ctx context.Context, req *core.DownloadRequest) (*co
 	}
 
 	addr := net.JoinHostPort(host, port)
-	conn, err := net.DialTimeout("tcp", addr, 30*time.Second)
+	conn, err := net.DialTimeout("tcp", addr, dialTimeout)
 	if err != nil {
 		return nil, core.NewNetworkError("failed to connect to gopher server", err, core.SafeURL(req.URL))
 	}
 	defer conn.Close()
-	conn.SetDeadline(time.Now().Add(30 * time.Second))
+	conn.SetDeadline(time.Now().Add(dialTimeout))
 
 	// Close the connection when the context is cancelled so any
 	// blocking Read returns immediately instead of waiting for the