diff --git a/src/lembas/web/static/css/app.css b/src/lembas/web/static/css/app.css
index 98580e7..ca59b6b 100644
--- a/src/lembas/web/static/css/app.css
+++ b/src/lembas/web/static/css/app.css
@@ -626,7 +626,9 @@ button, input, textarea, select {
     z-index: 40;
     box-shadow: var(--shadow-lg);
   }
-  .sidebar[data-collapsed="true"] { display: none; }
+  /* Hiding it is the `hidden` attribute, forced to win at the top of this
+     file. There used to be a `[data-collapsed="true"]` rule here that nothing
+     ever set. */
 }
 
 /* --- Toasts ----------------------------------------------------------------
diff --git a/src/lembas/web/templates/chat/_thread.html b/src/lembas/web/templates/chat/_thread.html
index f6fc28d..c3c1afa 100644
--- a/src/lembas/web/templates/chat/_thread.html
+++ b/src/lembas/web/templates/chat/_thread.html
@@ -1,7 +1,11 @@
 {#
   The whole thread. Returned after a rewind, which changes an arbitrary number
   of messages at once -- replacing the lot is simpler and less error-prone than
-  working out which individual bubbles to remove.
+  working out which individual bubbles to remove. Also included by
+  chat/index.html, so the conversation is described in exactly one place.
+
+  Deliberately has no root element: it is swapped with innerHTML into #thread,
+  and an outerHTML swap would take the container with it.
 #}
 {% for message in messages %}
   {% with body_html = bodies.get(message.id, "") %}
diff --git a/src/lembas/web/templates/chat/index.html b/src/lembas/web/templates/chat/index.html
index c4dc057..0b8809c 100644
--- a/src/lembas/web/templates/chat/index.html
+++ b/src/lembas/web/templates/chat/index.html
@@ -16,7 +16,7 @@
   <main class="main">
     <header class="topbar">
       <button class="btn btn--icon" type="button" aria-label="Toggle sidebar"
-              onclick="document.getElementById('sidebar').toggleAttribute('hidden')">
+              aria-expanded="true" data-toggle="#sidebar">
         {{ icon("sidebar") }}
       </button>
 
@@ -161,13 +161,10 @@
           </div>
           {% endif %}
 
-          {% for message in messages %}
-            {# Markdown was rendered server-side in pages.py, keyed by message
-               id, so this loop stays a lookup rather than a render. #}
-            {% with body_html = bodies.get(message.id, "") %}
-              {% include "chat/_message.html" %}
-            {% endwith %}
-          {% endfor %}
+          {# The same include the rewind response returns, so the conversation
+             is described in one place. Markdown was rendered server-side in
+             pages.py, keyed by message id. #}
+          {% include "chat/_thread.html" %}
         </div>
       </div>