warning when another browser tab holds the flag

copyparty/web/browser.css

@@ -1747,6 +1747,14 @@ html.light #bbox-overlay figcaption a {
 	box-shadow: none;
 	opacity: .2;
 }
+#u2flagblock {
+	display: none;
+	margin: 2em auto 4em auto;
+	padding: .5em;
+	max-width: 27em;
+	text-align: center;
+	border: .2em dashed rgba(128, 128, 128, 0.3);
+}
 #u2foot {
 	color: #fff;
 	font-style: italic;

copyparty/web/browser.js

@@ -127,6 +127,7 @@ ebi('op_up2k').innerHTML = (
 	'	<tbody></tbody>\n' +
 	'</table>\n' +
 
+	'<p id="u2flagblock"><b>the files were added to the queue</b><br />however there is a busy up2k in another browser tab,<br />so waiting for that to finish first</p>\n' +
 	'<p id="u2foot"></p>\n' +
 	'<p id="u2footfoot" data-perm="write">( you can use the <a href="#" id="u2nope">basic uploader</a> if you don\'t need lastmod timestamps, resumable uploads, or progress bars )</p>'
 );

copyparty/web/up2k.js

@@ -1081,6 +1081,7 @@ function up2k_init(subtle) {
                 if (flag) {
                     if (is_busy) {
                         flag.take(now);
+                        ebi('u2flagblock').style.display = flag.ours ? '' : 'block';
                         if (!flag.ours)
                             return defer();
                     }