diff --git a/packages/iios-messaging-ui/src/components/composer.tsx b/packages/iios-messaging-ui/src/components/composer.tsx
new file mode 100644
index 0000000..56c50ec
--- /dev/null
+++ b/packages/iios-messaging-ui/src/components/composer.tsx
@@ -0,0 +1,147 @@
+import { useMemo, useRef, useState, type ChangeEvent, type FormEvent, type KeyboardEvent } from 'react';
+import {
+  SPECIAL_MENTIONS,
+  insertMention,
+  resolveMentions,
+  trailingMentionQuery,
+} from '../mentions';
+import type { Attachment, Person, SendOpts } from '../types';
+
+interface Suggestion {
+  key: string;
+  label: string;
+  insert: string;
+}
+
+/**
+ * The message input: draft, @mention autocomplete, and attachment staging. Shared by the main
+ * Thread and the ThreadPane (which passes a parentInteractionId so a reply lands in the thread).
+ */
+export function Composer({
+  members,
+  canUpload,
+  upload,
+  onSend,
+  onTyping,
+  parentInteractionId,
+  placeholder = 'Type a message… @ to mention',
+}: {
+  members: Person[];
+  canUpload: boolean;
+  upload: (file: File) => Promise<Attachment>;
+  onSend: (text: string, opts?: SendOpts) => Promise<void>;
+  onTyping?: () => void;
+  parentInteractionId?: string;
+  placeholder?: string;
+}) {
+  const [draft, setDraft] = useState('');
+  const [sending, setSending] = useState(false);
+  const [staged, setStaged] = useState<Attachment | null>(null);
+  const [uploading, setUploading] = useState(false);
+  const fileRef = useRef<HTMLInputElement>(null);
+
+  const query = trailingMentionQuery(draft);
+  const suggestions = useMemo<Suggestion[]>(() => {
+    if (query === null) return [];
+    const q = query.toLowerCase();
+    const specials = SPECIAL_MENTIONS.filter((s) => s.startsWith(q)).map((s) => ({ key: `@${s}`, label: `@${s}`, insert: s }));
+    const people = members.filter((m) => m.name.toLowerCase().includes(q)).map((m) => ({ key: m.id, label: m.name, insert: m.name }));
+    return [...specials, ...people].slice(0, 6);
+  }, [query, members]);
+  const showSuggest = query !== null && suggestions.length > 0;
+
+  function pick(insert: string): void {
+    setDraft((d) => insertMention(d, insert));
+  }
+
+  async function onPickFile(e: ChangeEvent<HTMLInputElement>): Promise<void> {
+    const file = e.target.files?.[0];
+    e.target.value = '';
+    if (!file) return;
+    setUploading(true);
+    try {
+      setStaged(await upload(file));
+    } catch {
+      /* host surfaces upload errors */
+    } finally {
+      setUploading(false);
+    }
+  }
+
+  async function submit(e?: FormEvent): Promise<void> {
+    e?.preventDefault();
+    const text = draft.trim();
+    if ((!text && !staged) || sending) return;
+    const mentions = resolveMentions(text, members);
+    const att = staged;
+    setDraft('');
+    setStaged(null);
+    setSending(true);
+    try {
+      await onSend(text, {
+        ...(mentions.length ? { mentions } : {}),
+        ...(att ? { attachment: att } : {}),
+        ...(parentInteractionId ? { parentInteractionId } : {}),
+      });
+    } catch {
+      setStaged(att);
+    } finally {
+      setSending(false);
+    }
+  }
+
+  function onKeyDown(e: KeyboardEvent<HTMLInputElement>): void {
+    if (showSuggest && e.key === 'Enter') {
+      e.preventDefault();
+      pick(suggestions[0]!.insert);
+    }
+  }
+
+  return (
+    <form className="miu-composer" onSubmit={submit}>
+      {showSuggest ? (
+        <ul className="miu-suggest" role="listbox" aria-label="Mention suggestions">
+          {suggestions.map((s) => (
+            <li key={s.key}>
+              <button type="button" role="option" aria-selected="false" className="miu-suggest-item" onClick={() => pick(s.insert)}>
+                {s.label}
+              </button>
+            </li>
+          ))}
+        </ul>
+      ) : null}
+      {staged ? (
+        <div className="miu-staged">
+          📎 {staged.name}
+          <button type="button" className="miu-staged-x" onClick={() => setStaged(null)} aria-label="Remove attachment">
+            ✕
+          </button>
+        </div>
+      ) : null}
+      <div className="miu-composer-row">
+        {canUpload ? (
+          <>
+            <input ref={fileRef} type="file" className="miu-file-input" onChange={onPickFile} aria-label="Attach a file" />
+            <button type="button" className="miu-attach-btn" title="Attach a file" disabled={uploading} onClick={() => fileRef.current?.click()}>
+              {uploading ? '…' : '📎'}
+            </button>
+          </>
+        ) : null}
+        <input
+          className="miu-input"
+          value={draft}
+          placeholder={placeholder}
+          aria-label="Message"
+          onChange={(e) => {
+            setDraft(e.target.value);
+            onTyping?.();
+          }}
+          onKeyDown={onKeyDown}
+        />
+        <button type="submit" className="miu-send" disabled={(!draft.trim() && !staged) || sending}>
+          Send
+        </button>
+      </div>
+    </form>
+  );
+}
diff --git a/packages/iios-messaging-ui/src/components/message-item.tsx b/packages/iios-messaging-ui/src/components/message-item.tsx
new file mode 100644
index 0000000..34c0f9f
--- /dev/null
+++ b/packages/iios-messaging-ui/src/components/message-item.tsx
@@ -0,0 +1,107 @@
+import { useState } from 'react';
+import { highlightMentions } from '../mentions';
+import type { Attachment } from '../types';
+import type { UiMessage } from '../hooks/use-messages';
+
+const REACTION_EMOJIS = ['👍', '❤️', '😂', '🎉', '👀'];
+
+const isImage = (mime: string): boolean => mime.startsWith('image/');
+
+function AttachmentView({ att }: { att: Attachment }) {
+  if (isImage(att.mime)) {
+    return (
+      <a href={att.url} target="_blank" rel="noreferrer" className="miu-att-img-link">
+        <img src={att.url} alt={att.name} className="miu-att-img" />
+      </a>
+    );
+  }
+  return (
+    <a href={att.url} target="_blank" rel="noreferrer" className="miu-att-file">
+      📎 {att.name}
+    </a>
+  );
+}
+
+/** One rendered message: bubble (with @mention highlighting), attachment, reactions, seen tick,
+ *  and — in the main thread only — a thread/reply affordance. */
+export function MessageItem({
+  message,
+  memberNames,
+  canReact,
+  onReact,
+  seen,
+  replyCount,
+  onOpenThread,
+}: {
+  message: UiMessage;
+  memberNames: string[];
+  canReact: boolean;
+  onReact: (messageId: string, emoji: string) => void;
+  seen: boolean;
+  /** Present only in the main thread (not inside the pane). undefined => no thread affordance. */
+  replyCount?: number;
+  onOpenThread?: (messageId: string) => void;
+}) {
+  const [pickerOpen, setPickerOpen] = useState(false);
+  const m = message;
+
+  return (
+    <div className={`miu-msg${message.mine ? ' is-mine' : ''}${message.pending ? ' is-pending' : ''}`}>
+      <div className="miu-bubble-row">
+        <div className="miu-bubble">
+          {m.text ? highlightMentions(m.text, memberNames) : null}
+          {m.attachment ? <AttachmentView att={m.attachment} /> : null}
+        </div>
+        <div className="miu-msg-actions">
+          {canReact ? (
+            <div className="miu-react-wrap">
+              <button type="button" className="miu-react-btn" title="React" onClick={() => setPickerOpen((p) => !p)}>
+                🙂
+              </button>
+              {pickerOpen ? (
+                <div className="miu-react-picker">
+                  {REACTION_EMOJIS.map((e) => (
+                    <button
+                      key={e}
+                      type="button"
+                      className="miu-react-emoji"
+                      onClick={() => {
+                        onReact(m.id, e);
+                        setPickerOpen(false);
+                      }}
+                    >
+                      {e}
+                    </button>
+                  ))}
+                </div>
+              ) : null}
+            </div>
+          ) : null}
+          {onOpenThread ? (
+            <button type="button" className="miu-react-btn" title="Reply in thread" onClick={() => onOpenThread(m.id)}>
+              💬
+            </button>
+          ) : null}
+        </div>
+      </div>
+
+      {m.reactions && m.reactions.length > 0 ? (
+        <div className="miu-reactions">
+          {m.reactions.map((r) => (
+            <button key={r.emoji} type="button" className={`miu-reaction${r.mine ? ' is-mine' : ''}`} onClick={() => canReact && onReact(m.id, r.emoji)}>
+              {r.emoji} {r.count}
+            </button>
+          ))}
+        </div>
+      ) : null}
+
+      {replyCount !== undefined && replyCount > 0 && onOpenThread ? (
+        <button type="button" className="miu-thread-link" onClick={() => onOpenThread(m.id)}>
+          💬 {replyCount} {replyCount === 1 ? 'reply' : 'replies'}
+        </button>
+      ) : null}
+
+      {message.mine && seen ? <span className="miu-seen">Seen</span> : null}
+    </div>
+  );
+}
diff --git a/packages/iios-messaging-ui/src/components/messenger.tsx b/packages/iios-messaging-ui/src/components/messenger.tsx
index 604df07..9a5b198 100644
--- a/packages/iios-messaging-ui/src/components/messenger.tsx
+++ b/packages/iios-messaging-ui/src/components/messenger.tsx
@@ -4,6 +4,7 @@ import { useAdapter } from '../provider';
 import { ConversationList } from './conversation-list';
 import { ChannelBrowser } from './channel-browser';
 import { Thread } from './thread';
+import { ThreadPane } from './thread-pane';
 
 /**
  * The drop-in messenger: sectioned conversation list (Channels / Direct messages) + open thread,
@@ -17,6 +18,7 @@ export function Messenger() {
 
   const [selected, setSelected] = useState<string | null>(null);
   const [browsing, setBrowsing] = useState(false);
+  const [activeRoot, setActiveRoot] = useState<string | null>(null); // open thread pane's root message
 
   useEffect(() => {
     if (browsing) return;
@@ -24,6 +26,9 @@ export function Messenger() {
     setSelected(conversations[0]?.threadId ?? null);
   }, [conversations, selected, browsing]);
 
+  // Switching conversations (or into browse) closes any open thread pane.
+  useEffect(() => setActiveRoot(null), [selected, browsing]);
+
   const channels = useMemo(() => conversations.filter((c) => c.membership === 'channel'), [conversations]);
   const dms = useMemo(() => conversations.filter((c) => c.membership !== 'channel'), [conversations]);
 
@@ -73,9 +78,13 @@ export function Messenger() {
             }}
           />
         ) : (
-          <Thread threadId={selected} />
+          <Thread threadId={selected} activeRootId={activeRoot} onOpenThread={setActiveRoot} />
         )}
       </section>
+
+      {!browsing && selected && activeRoot ? (
+        <ThreadPane threadId={selected} rootId={activeRoot} onClose={() => setActiveRoot(null)} />
+      ) : null}
     </div>
   );
 }
diff --git a/packages/iios-messaging-ui/src/components/thread-pane.test.tsx b/packages/iios-messaging-ui/src/components/thread-pane.test.tsx
new file mode 100644
index 0000000..6cea6d3
--- /dev/null
+++ b/packages/iios-messaging-ui/src/components/thread-pane.test.tsx
@@ -0,0 +1,36 @@
+import { describe, it, expect } from 'vitest';
+import { render, screen, fireEvent, waitFor } from '@testing-library/react';
+import { MessagingProvider } from '../provider';
+import { Messenger } from './messenger';
+import { MockAdapter } from '../adapters/mock';
+
+function mount() {
+  return render(
+    <MessagingProvider adapter={new MockAdapter()}>
+      <Messenger />
+    </MessagingProvider>,
+  );
+}
+
+describe('Slack-style thread pane', () => {
+  it('opens a thread on 💬, posts a reply into it, and shows the reply count on the parent', async () => {
+    mount();
+    // Wait for the auto-selected thread's message to render WITH its actions (not just the sidebar
+    // preview), then open the thread pane via the message's reply affordance (💬).
+    const replyButtons = await screen.findAllByTitle('Reply in thread');
+    fireEvent.click(replyButtons[0]!);
+    expect(await screen.findByText('Thread')).toBeTruthy(); // pane header
+
+    // The pane's composer (placeholder "Reply…") — send a threaded reply.
+    const replyInput = screen.getByPlaceholderText('Reply…') as HTMLInputElement;
+    fireEvent.change(replyInput, { target: { value: 'on it' } });
+    // The pane has its own Send; grab the last one (pane is rendered after the main composer).
+    const sends = screen.getAllByText('Send');
+    fireEvent.click(sends[sends.length - 1]!);
+
+    // The reply shows in the pane (replies are hidden from the main thread, so this is unique)...
+    await waitFor(() => expect(screen.getByText('on it')).toBeTruthy());
+    // ...and the parent now advertises the reply count as a thread-link button in the main thread.
+    await waitFor(() => expect(screen.getByRole('button', { name: /1 reply/ })).toBeTruthy());
+  });
+});
diff --git a/packages/iios-messaging-ui/src/components/thread-pane.tsx b/packages/iios-messaging-ui/src/components/thread-pane.tsx
new file mode 100644
index 0000000..7252dca
--- /dev/null
+++ b/packages/iios-messaging-ui/src/components/thread-pane.tsx
@@ -0,0 +1,60 @@
+import { useMemo } from 'react';
+import { useMessages } from '../hooks/use-messages';
+import { useMembers } from '../hooks/use-members';
+import { Composer } from './composer';
+import { MessageItem } from './message-item';
+
+/**
+ * The Slack-style thread side panel: the root message + its replies + a composer that posts back
+ * into the thread (parentInteractionId = root). Uses its own useMessages on the same thread; the
+ * shared adapter subscription keeps it and the main view in sync.
+ */
+export function ThreadPane({
+  threadId,
+  rootId,
+  onClose,
+}: {
+  threadId: string;
+  rootId: string;
+  onClose: () => void;
+}) {
+  const { messages, send, react, upload, seenIds, sendTyping, canReact, canUpload } = useMessages(threadId);
+  const members = useMembers(threadId);
+  const memberNames = useMemo(() => members.map((m) => m.name), [members]);
+
+  const root = useMemo(() => messages.find((m) => m.id === rootId), [messages, rootId]);
+  const replies = useMemo(() => messages.filter((m) => m.parentInteractionId === rootId), [messages, rootId]);
+
+  return (
+    <aside className="miu-pane">
+      <header className="miu-pane-head">
+        <span>Thread</span>
+        <button type="button" className="miu-pane-close" onClick={onClose} aria-label="Close thread">
+          ✕
+        </button>
+      </header>
+
+      <div className="miu-messages miu-pane-messages">
+        {root ? (
+          <MessageItem message={root} memberNames={memberNames} canReact={canReact} onReact={(id, e) => void react(id, e)} seen={seenIds.has(root.id)} />
+        ) : (
+          <div className="miu-empty">Message not found.</div>
+        )}
+        <div className="miu-pane-divider">{replies.length} {replies.length === 1 ? 'reply' : 'replies'}</div>
+        {replies.map((m) => (
+          <MessageItem key={m.id} message={m} memberNames={memberNames} canReact={canReact} onReact={(id, e) => void react(id, e)} seen={seenIds.has(m.id)} />
+        ))}
+      </div>
+
+      <Composer
+        members={members}
+        canUpload={canUpload}
+        upload={upload}
+        onSend={send}
+        onTyping={sendTyping}
+        parentInteractionId={rootId}
+        placeholder="Reply…"
+      />
+    </aside>
+  );
+}
diff --git a/packages/iios-messaging-ui/src/components/thread.tsx b/packages/iios-messaging-ui/src/components/thread.tsx
index fc94b17..0f21efa 100644
--- a/packages/iios-messaging-ui/src/components/thread.tsx
+++ b/packages/iios-messaging-ui/src/components/thread.tsx
@@ -1,214 +1,61 @@
-import { useMemo, useRef, useState, type ChangeEvent, type FormEvent, type KeyboardEvent } from 'react';
+import { useMemo } from 'react';
 import { useMessages } from '../hooks/use-messages';
 import { useMembers } from '../hooks/use-members';
-import {
-  SPECIAL_MENTIONS,
-  highlightMentions,
-  insertMention,
-  resolveMentions,
-  trailingMentionQuery,
-} from '../mentions';
-import type { Attachment } from '../types';
-
-const REACTION_EMOJIS = ['👍', '❤️', '😂', '🎉', '👀'];
-
-interface Suggestion {
-  key: string;
-  label: string;
-  insert: string;
-}
-
-const isImage = (mime: string): boolean => mime.startsWith('image/');
-
-function AttachmentView({ att }: { att: Attachment }) {
-  if (isImage(att.mime)) {
-    return (
-      <a href={att.url} target="_blank" rel="noreferrer" className="miu-att-img-link">
-        <img src={att.url} alt={att.name} className="miu-att-img" />
-      </a>
-    );
-  }
-  return (
-    <a href={att.url} target="_blank" rel="noreferrer" className="miu-att-file">
-      📎 {att.name}
-    </a>
-  );
-}
+import { Composer } from './composer';
+import { MessageItem } from './message-item';
 
 /**
- * One conversation: message list + composer, driven by useMessages. Includes @mention autocomplete,
- * emoji reactions, and attachments — each degrading if the adapter doesn't support it. Transport-agnostic.
+ * The main conversation view: top-level messages + composer. Replies (messages with a
+ * parentInteractionId) are hidden here and live in the ThreadPane — a message with replies shows a
+ * "N replies" link that opens it. @mentions, reactions, and attachments all work.
  */
-export function Thread({ threadId }: { threadId: string | null }) {
+export function Thread({
+  threadId,
+  activeRootId,
+  onOpenThread,
+}: {
+  threadId: string | null;
+  activeRootId?: string | null;
+  onOpenThread?: (rootId: string) => void;
+}) {
   const { messages, loading, error, send, react, upload, typingUserIds, seenIds, sendTyping, canReact, canUpload } = useMessages(threadId);
   const members = useMembers(threadId);
-  const [draft, setDraft] = useState('');
-  const [sending, setSending] = useState(false);
-  const [pickerFor, setPickerFor] = useState<string | null>(null);
-  const [staged, setStaged] = useState<Attachment | null>(null);
-  const [uploading, setUploading] = useState(false);
-  const fileRef = useRef<HTMLInputElement>(null);
-
   const memberNames = useMemo(() => members.map((m) => m.name), [members]);
-  const query = trailingMentionQuery(draft);
-  const suggestions = useMemo<Suggestion[]>(() => {
-    if (query === null) return [];
-    const q = query.toLowerCase();
-    const specials = SPECIAL_MENTIONS.filter((s) => s.startsWith(q)).map((s) => ({ key: `@${s}`, label: `@${s}`, insert: s }));
-    const people = members.filter((m) => m.name.toLowerCase().includes(q)).map((m) => ({ key: m.id, label: m.name, insert: m.name }));
-    return [...specials, ...people].slice(0, 6);
-  }, [query, members]);
-  const showSuggest = query !== null && suggestions.length > 0;
 
-  function pick(insert: string): void {
-    setDraft((d) => insertMention(d, insert));
-  }
-
-  async function onPickFile(e: ChangeEvent<HTMLInputElement>): Promise<void> {
-    const file = e.target.files?.[0];
-    e.target.value = '';
-    if (!file) return;
-    setUploading(true);
-    try {
-      setStaged(await upload(file));
-    } catch {
-      // swallow — a real host surfaces upload errors; keep the composer usable
-    } finally {
-      setUploading(false);
-    }
-  }
-
-  async function submit(e?: FormEvent): Promise<void> {
-    e?.preventDefault();
-    const text = draft.trim();
-    if ((!text && !staged) || sending) return;
-    const mentions = resolveMentions(text, members);
-    const att = staged;
-    setDraft('');
-    setStaged(null);
-    setSending(true);
-    try {
-      await send(text, {
-        ...(mentions.length ? { mentions } : {}),
-        ...(att ? { attachment: att } : {}),
-      });
-    } catch {
-      setStaged(att);
-    } finally {
-      setSending(false);
-    }
-  }
-
-  function onKeyDown(e: KeyboardEvent<HTMLInputElement>): void {
-    if (showSuggest && e.key === 'Enter') {
-      e.preventDefault();
-      pick(suggestions[0]!.insert);
-    }
-  }
+  const topLevel = useMemo(() => messages.filter((m) => !m.parentInteractionId), [messages]);
+  const replyCount = useMemo(() => {
+    const counts = new Map<string, number>();
+    for (const m of messages) if (m.parentInteractionId) counts.set(m.parentInteractionId, (counts.get(m.parentInteractionId) ?? 0) + 1);
+    return counts;
+  }, [messages]);
 
   if (!threadId) {
     return <div className="miu-empty miu-thread-empty">Select a conversation.</div>;
   }
 
   return (
-    <div className="miu-thread">
+    <div className={`miu-thread${activeRootId ? ' has-pane' : ''}`}>
       <div className="miu-messages">
         {loading && messages.length === 0 ? <div className="miu-empty">Loading…</div> : null}
         {error ? <div className="miu-empty miu-error">{error}</div> : null}
-        {messages.map((m) => (
-          <div key={m.id} className={`miu-msg${m.mine ? ' is-mine' : ''}${m.pending ? ' is-pending' : ''}`}>
-            <div className="miu-bubble-row">
-              <div className="miu-bubble">
-                {m.text ? highlightMentions(m.text, memberNames) : null}
-                {m.attachment ? <AttachmentView att={m.attachment} /> : null}
-              </div>
-              {canReact ? (
-                <div className="miu-react-wrap">
-                  <button type="button" className="miu-react-btn" title="React" onClick={() => setPickerFor((p) => (p === m.id ? null : m.id))}>
-                    🙂
-                  </button>
-                  {pickerFor === m.id ? (
-                    <div className="miu-react-picker">
-                      {REACTION_EMOJIS.map((e) => (
-                        <button
-                          key={e}
-                          type="button"
-                          className="miu-react-emoji"
-                          onClick={() => {
-                            void react(m.id, e);
-                            setPickerFor(null);
-                          }}
-                        >
-                          {e}
-                        </button>
-                      ))}
-                    </div>
-                  ) : null}
-                </div>
-              ) : null}
-            </div>
-            {m.reactions && m.reactions.length > 0 ? (
-              <div className="miu-reactions">
-                {m.reactions.map((r) => (
-                  <button key={r.emoji} type="button" className={`miu-reaction${r.mine ? ' is-mine' : ''}`} onClick={() => canReact && void react(m.id, r.emoji)}>
-                    {r.emoji} {r.count}
-                  </button>
-                ))}
-              </div>
-            ) : null}
-            {m.mine && seenIds.has(m.id) ? <span className="miu-seen">Seen</span> : null}
-          </div>
+        {topLevel.map((m) => (
+          <MessageItem
+            key={m.id}
+            message={m}
+            memberNames={memberNames}
+            canReact={canReact}
+            onReact={(id, emoji) => void react(id, emoji)}
+            seen={seenIds.has(m.id)}
+            replyCount={replyCount.get(m.id) ?? 0}
+            {...(onOpenThread ? { onOpenThread } : {})}
+          />
         ))}
         {typingUserIds.length > 0 ? (
           <div className="miu-typing">{typingUserIds.length === 1 ? 'typing…' : 'several people are typing…'}</div>
         ) : null}
       </div>
 
-      <form className="miu-composer" onSubmit={submit}>
-        {showSuggest ? (
-          <ul className="miu-suggest" role="listbox" aria-label="Mention suggestions">
-            {suggestions.map((s) => (
-              <li key={s.key}>
-                <button type="button" role="option" aria-selected="false" className="miu-suggest-item" onClick={() => pick(s.insert)}>
-                  {s.label}
-                </button>
-              </li>
-            ))}
-          </ul>
-        ) : null}
-        {staged ? (
-          <div className="miu-staged">
-            📎 {staged.name}
-            <button type="button" className="miu-staged-x" onClick={() => setStaged(null)} aria-label="Remove attachment">
-              ✕
-            </button>
-          </div>
-        ) : null}
-        <div className="miu-composer-row">
-          {canUpload ? (
-            <>
-              <input ref={fileRef} type="file" className="miu-file-input" onChange={onPickFile} aria-label="Attach a file" />
-              <button type="button" className="miu-attach-btn" title="Attach a file" disabled={uploading} onClick={() => fileRef.current?.click()}>
-                {uploading ? '…' : '📎'}
-              </button>
-            </>
-          ) : null}
-          <input
-            className="miu-input"
-            value={draft}
-            placeholder="Type a message… @ to mention"
-            aria-label="Message"
-            onChange={(e) => {
-              setDraft(e.target.value);
-              sendTyping();
-            }}
-            onKeyDown={onKeyDown}
-          />
-          <button type="submit" className="miu-send" disabled={(!draft.trim() && !staged) || sending}>
-            Send
-          </button>
-        </div>
-      </form>
+      <Composer members={members} canUpload={canUpload} upload={upload} onSend={send} onTyping={sendTyping} />
     </div>
   );
 }
diff --git a/packages/iios-messaging-ui/src/index.ts b/packages/iios-messaging-ui/src/index.ts
index 80aca86..1d160cd 100644
--- a/packages/iios-messaging-ui/src/index.ts
+++ b/packages/iios-messaging-ui/src/index.ts
@@ -15,6 +15,7 @@ export { Messenger } from './components/messenger';
 export { ConversationList } from './components/conversation-list';
 export { ChannelBrowser } from './components/channel-browser';
 export { Thread } from './components/thread';
+export { ThreadPane } from './components/thread-pane';
 
 export type { MessagingAdapter } from './adapter';
 export type { ConversationsState } from './hooks/use-conversations';
diff --git a/packages/iios-messaging-ui/src/styles.css b/packages/iios-messaging-ui/src/styles.css
index 2d0d0e5..97c58ac 100644
--- a/packages/iios-messaging-ui/src/styles.css
+++ b/packages/iios-messaging-ui/src/styles.css
@@ -157,6 +157,26 @@
 .miu-msg.is-mine .miu-bubble-row {
   flex-direction: row-reverse;
 }
+.miu-msg-actions {
+  display: flex;
+  gap: 2px;
+  flex-shrink: 0;
+}
+.miu-thread-link {
+  align-self: flex-start;
+  margin-top: 3px;
+  padding: 3px 9px;
+  border-radius: 999px;
+  border: 1px solid var(--miu-border);
+  background: var(--miu-panel);
+  color: var(--miu-accent);
+  font-size: 12px;
+  font-weight: 600;
+  cursor: pointer;
+}
+.miu-msg.is-mine .miu-thread-link {
+  align-self: flex-end;
+}
 .miu-react-wrap {
   position: relative;
   flex-shrink: 0;
@@ -490,6 +510,43 @@
   color: var(--miu-muted);
 }
 
+/* thread pane (Slack-style) */
+.miu-pane {
+  width: 340px;
+  flex-shrink: 0;
+  display: flex;
+  flex-direction: column;
+  min-height: 0;
+  border-left: 1px solid var(--miu-border);
+  background: var(--miu-panel);
+}
+.miu-pane-head {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 12px 16px;
+  border-bottom: 1px solid var(--miu-border);
+  font-weight: 700;
+}
+.miu-pane-close {
+  border: none;
+  background: none;
+  color: var(--miu-muted);
+  cursor: pointer;
+  font-size: 15px;
+}
+.miu-pane-messages {
+  background: var(--miu-bg);
+}
+.miu-pane-divider {
+  font-size: 11.5px;
+  color: var(--miu-muted);
+  text-align: center;
+  margin: 4px 0;
+  padding-bottom: 4px;
+  border-bottom: 1px solid var(--miu-border);
+}
+
 /* misc */
 .miu-empty {
   padding: 24px;