Use the 'collapse_threads' field from user.json.

html.c

@@ -1459,6 +1459,9 @@ xs_html *html_entry(snac *user, xs_dict *msg, int read_only,
     if ((read_only || !user) && !is_msg_public(msg))
         return NULL;
 
+    if (user && level == 0 && xs_is_true(xs_dict_get(user->config, "collapse_threads")))
+        collapse_threads = 1;
+
     /* hidden? do nothing more for this conversation */
     if (user && is_hidden(user, id)) {
         xs *s1 = xs_fmt("%s_entry", md5);