diff --git a/src/connection/types.ts b/src/connection/types.ts
index d6b0c414..6cead751 100644
--- a/src/connection/types.ts
+++ b/src/connection/types.ts
@@ -235,6 +235,10 @@ export interface ThreadSummary {
   locked?: boolean;
   /** Tag ids from the channel's palette. */
   tags?: string[];
+  /** Up to three who replied last, newest first. Absent from an older server. */
+  recent_repliers?: string[];
+  /** The reply that solved a topic, or null. Absent from an older server. */
+  answer_message_id?: string | null;
 }
 
 /**
diff --git a/src/shell/ChannelScreen.tsx b/src/shell/ChannelScreen.tsx
index 0482ca5a..14e694eb 100644
--- a/src/shell/ChannelScreen.tsx
+++ b/src/shell/ChannelScreen.tsx
@@ -1738,6 +1738,7 @@ export function MessageRow({
   row,
   firstUnread,
   flashed,
+  answer,
   host,
   mentionable,
   layout,
@@ -1761,6 +1762,8 @@ export function MessageRow({
   firstUnread?: boolean;
   /** Just jumped to, so drawn lit for a moment. */
   flashed?: boolean;
+  /** The reply that solved its topic (C22): a label over it and a green tint. */
+  answer?: boolean;
   /** Where the attachments live. */
   host: string;
   /** Nicknames on this server, so `@somebody` lights up. */
@@ -1912,6 +1915,12 @@ export function MessageRow({
 
   const body = (
     <>
+      {answer ? (
+        <View style={{ flexDirection: "row", alignItems: "center", gap: 4, marginBottom: 2 }}>
+          <CheckIcon size={12} color={theme.color.success} weight="bold" />
+          <Text style={{ color: theme.color.success, fontSize: 12, fontWeight: "700" }}>The answer</Text>
+        </View>
+      ) : null}
       {answering ? (
         <ReplyStub
           author={answering.author}
@@ -2156,7 +2165,8 @@ export function MessageRow({
           paddingHorizontal: theme.space(4),
           paddingTop: showHeader ? theme.space(compact ? 3 : 2) : 0,
           paddingBottom: 2,
-          backgroundColor: flashed ? tint(theme.color.accent, theme.color.surfaceHover) : "transparent",
+          backgroundColor: answerOrFlash(answer, flashed, theme),
+          ...(answer ? { marginHorizontal: theme.space(2), paddingHorizontal: theme.space(2), paddingBottom: theme.space(2), borderRadius: 16 } : null),
           // Greyed while the server has not confirmed it. The message is
           // readable either way — this says "not yet", not "unimportant".
           opacity: message.pending ? 0.5 : 1,
@@ -3069,6 +3079,11 @@ function useKeyboardVisible(): boolean {
 }
 
 /** The accent at a fifth of its strength, for your own bubbles. A non-hex accent falls back to the surface. */
+function answerOrFlash(answer: boolean | undefined, flashed: boolean | undefined, theme: ReturnType<typeof useTheme>): string {
+  if (answer) return /^#[0-9a-f]{6}$/i.test(theme.color.success) ? `${theme.color.success}1f` : theme.color.surfaceHover;
+  return flashed ? tint(theme.color.accent, theme.color.surfaceHover) : "transparent";
+}
+
 function tint(accent: string, fallback: string): string {
   return /^#[0-9a-f]{6}$/i.test(accent) ? `${accent}33` : fallback;
 }
diff --git a/src/threads/RepliesLine.tsx b/src/threads/RepliesLine.tsx
index 65ec43a5..5b9abcc2 100644
--- a/src/threads/RepliesLine.tsx
+++ b/src/threads/RepliesLine.tsx
@@ -6,7 +6,9 @@ import { ChatsTeardropIcon } from "phosphor-react-native/src/icons/ChatsTeardrop
 import type { ThreadMentionsByHost } from "../connection/mentions";
 import type { LocalMessage } from "../connection/outbox";
 import type { ThreadSummary } from "../connection/types";
+import { Faces } from "../shell/Faces";
 import { UnreadPill } from "../shell/UnreadPill";
+import { useMembers } from "../connection/MembersProvider";
 import type { ActionSheetOptions } from "../ui/actionSheet";
 import { openThread } from "./openThread";
 import { repliesLabel } from "./threads";
@@ -18,6 +20,8 @@ import type { ThreadUnreadCounts } from "./threadUnread";
  */
 export function RepliesLine({ thread, mentions, unread }: { thread: ThreadSummary; mentions: number; unread: number }) {
   const theme = useTheme();
+  const { byId } = useMembers();
+  const faces = (thread.recent_repliers ?? []).flatMap((id) => byId.get(id) ?? []);
   const color = mentions > 0 || unread > 0 ? theme.color.accent : theme.color.text;
   const label = repliesLabel(thread.reply_count);
   const last = new Date(thread.last_message_at).toLocaleTimeString(undefined, { hour: "2-digit", minute: "2-digit" });
@@ -45,7 +49,11 @@ export function RepliesLine({ thread, mentions, unread }: { thread: ThreadSummar
         backgroundColor: pressed ? theme.color.surfaceHover : theme.color.surface,
       })}
     >
-      <ChatsTeardropIcon size={15} color={color} weight="fill" />
+      {faces.length > 0 ? (
+        <Faces members={faces} size={20} limit={3} ground={theme.color.surface} />
+      ) : (
+        <ChatsTeardropIcon size={15} color={color} weight="fill" />
+      )}
       <Text style={{ color, fontSize: 13, fontWeight: "600" }}>{label}</Text>
       {Number.isNaN(Date.parse(thread.last_message_at)) ? null : (
         <Text style={{ color: theme.color.muted, fontSize: 13 }}>· {last}</Text>
diff --git a/src/threads/ThreadScreen.tsx b/src/threads/ThreadScreen.tsx
index 76bd4bf4..87e5a55e 100644
--- a/src/threads/ThreadScreen.tsx
+++ b/src/threads/ThreadScreen.tsx
@@ -139,10 +139,10 @@ export function ThreadScreen() {
   const rootRow = useMemo(() => (root ? groupMessages([root])[0] : null), [root]);
 
   const setStatus = useCallback(
-    async (status: Status) => {
+    async (status: Status, answerMessageId?: string) => {
       const accessToken = await getAccessToken();
       if (!socket || !accessToken || !channelId || !id) return;
-      socket.emit("thread:status:set", { conversationId: channelId, threadId: id, status, accessToken });
+      socket.emit("thread:status:set", { conversationId: channelId, threadId: id, status, answerMessageId, accessToken });
     },
     [socket, getAccessToken, channelId, id],
   );
@@ -161,14 +161,21 @@ export function ThreadScreen() {
   const mayModerateThread = !!thread && maySetStatus(thread, me?.serverUserId ?? null, mayHere("manage_messages"));
   const forumTags = channel?.forumTags ?? [];
   const open = thread ? takesReplies(thread) : true;
+  // C21: the newest reply from someone else, offered as the answer while the topic is open.
+  const offered =
+    channel?.layout === "forum" && mayModerateThread && thread?.status === "open"
+      ? messages.findLast((m) => m.sender_server_id !== me?.serverUserId && m.message_id !== root?.message_id)
+      : undefined;
 
-  const row = (item: (typeof rows)[number]) => (
+  const row = (item: (typeof rows)[number], inCard = false) => (
     <MessageRow
       row={item}
       host={host}
       mentionable={mentionable}
-      layout={messageLayout}
-              ownSide={ownMessageSide}
+      // The opening post in its card reads as the topic, not as a bubble of yours on the right.
+      layout={inCard && messageLayout === "bubbles" ? "cozy" : messageLayout}
+      ownSide={inCard ? "left" : ownMessageSide}
+      answer={!!thread?.answer_message_id && item.message.message_id === thread.answer_message_id}
       me={me?.serverUserId ?? null}
       parent={item.message.reply_to_message_id ? byId.get(item.message.reply_to_message_id) : undefined}
       getAccessToken={getAccessToken}
@@ -255,7 +262,7 @@ export function ThreadScreen() {
                 }}
               >
                 {!!rootRow && (
-                  row({ ...rootRow, dayLabel: null })
+                  row({ ...rootRow, dayLabel: null }, true)
                 )}
                 {!rootRow && !!thread && (
                   // Deleting the root takes the thread, but a blocked sender's is only hidden.
@@ -271,10 +278,36 @@ export function ThreadScreen() {
               ) : null}
             </View>
           }
-          contentContainerStyle={{ paddingVertical: theme.space(3) }}
+          contentContainerStyle={{ paddingVertical: theme.space(3), flexGrow: 1, justifyContent: "flex-end" }}
         />
       )}
 
+      {!gone && offered ? (
+        <View
+          style={{
+            flexDirection: "row",
+            alignItems: "center",
+            gap: theme.space(3),
+            marginHorizontal: theme.space(4),
+            marginBottom: theme.space(2),
+            paddingVertical: theme.space(2.5),
+            paddingLeft: theme.space(4),
+            paddingRight: theme.space(2.5),
+            borderRadius: 18,
+            borderWidth: 1,
+            borderColor: theme.color.border,
+            backgroundColor: theme.color.surfaceRaised,
+          }}
+        >
+          <Text numberOfLines={2} style={{ flex: 1, color: theme.color.text, fontSize: 14, lineHeight: 19 }}>
+            {offered.sender_nickname ? `Did ${offered.sender_nickname}’s reply answer it?` : "Did the last reply answer it?"}
+          </Text>
+          <Button size="small" onPress={() => void setStatus("solved", offered.message_id)} startIcon={<CheckIcon size={14} color={theme.color.onAccent} weight="bold" />}>
+            Mark solved
+          </Button>
+        </View>
+      ) : null}
+
       {!gone && !!open && (
         <>
           <TypingLine typers={typing.typers} />
@@ -392,13 +425,17 @@ function ThreadHeader({
   const open = thread ? takesReplies(thread) : true;
 
   const more = () => {
-    void present({
-      title,
-      message: "Nothing is deleted, and you can open it again.",
-      options: ["Close topic", "Cancel"],
-      cancelButtonIndex: 1,
-    }).then((index) => {
-      if (index === 0) onSetStatus?.("closed");
+    if (!thread) return;
+    const options = [
+      ...(thread.status === "open" ? ["Mark solved"] : ["Reopen"]),
+      ...(thread.status !== "closed" ? ["Close topic"] : []),
+      "Cancel",
+    ];
+    void present({ title, message: "Nothing is deleted, and you can open it again.", options, cancelButtonIndex: options.length - 1 }).then((index) => {
+      const picked = options[index];
+      if (picked === "Mark solved") onSetStatus?.("solved");
+      else if (picked === "Reopen") onSetStatus?.("open");
+      else if (picked === "Close topic") onSetStatus?.("closed");
     });
   };
 
@@ -440,30 +477,14 @@ function ThreadHeader({
             {!forum && channelName ? `Thread in #${channelName}` : null}
             {channelName ? null : repliesLabel(thread.reply_count)}
             {thread.status === "solved" ? (
-              <Text style={{ color: theme.color.accent, fontSize: 12 }}>{" · Solved"}</Text>
+              <Text style={{ color: theme.color.success, fontSize: 12, fontWeight: "600" }}>{" · Solved"}</Text>
             ) : null}
             {!open ? " · Closed" : null}
           </Text>
         ) : null}
       </View>
 
-      {!!onSetStatus && !!thread && (
-        thread.status !== "open" ? (
-          <Button size="small" tone="neutral" onPress={() => onSetStatus("open")} accessibilityLabel="Reopen this topic">
-            Reopen
-          </Button>
-        ) : (
-          <Button
-            size="small"
-            onPress={() => onSetStatus("solved")}
-            startIcon={<CheckIcon size={14} color={theme.color.onAccent} weight="bold" />}
-            accessibilityLabel="Mark this topic solved"
-          >
-            Mark solved
-          </Button>
-        )
-      )}
-      {onSetStatus && thread && thread.status !== "closed" ? (
+      {onSetStatus && thread ? (
         <RoundButton label="More for this topic" onPress={more}>
           <DotsThreeVerticalIcon size={20} color={theme.color.text} weight="bold" />
         </RoundButton>