feat(threads): up-arrow edits your last thread reply (+ fix cross-fire)

The thread composer reused RoomInput's hardcoded editableName="RoomInput", so
the main timeline's global up-arrow "edit last message" handler fired while
focused in a thread composer and targeted the MAIN timeline's last message
(wrong), and there was no up-arrow edit for the thread itself.

- Make editableName a RoomInput prop (default "RoomInput"); the thread composer
  passes "ThreadInput", so the two up-arrow handlers never cross-fire.
- Add an up-arrow-edit handler to ThreadTimeline (parity with RoomTimeline):
  empty thread composer + Up -> edit the latest editable reply in that thread,
  using thread.liveTimeline + canEditEvent + setEditId.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/room/thread/ThreadPanel.tsx

@@ -196,6 +196,7 @@ export function ThreadPanel({ room, threadId, requestClose }: ThreadPanelProps)
               roomId={room.roomId}
               threadRootId={threadId}
               editor={editor}
+              editableName="ThreadInput"
               fileDropContainerRef={fileDropContainerRef}
             />
           </Box>

src/app/features/room/thread/ThreadTimeline.tsx

@@ -32,11 +32,12 @@ import { useAtomValue, useSetAtom } from 'jotai';
 import { Badge, Box, Chip, Icon, Icons, Line, Scroll, Spinner, Text, color, config } from 'folds';
 import classNames from 'classnames';
 import { Opts as LinkifyOpts } from 'linkifyjs';
+import { isKeyHotkey } from 'is-hotkey';
 import { eventWithShortcode, factoryEventSentBy } from '../../../utils/matrix';
 import { useMatrixClient } from '../../../hooks/useMatrixClient';
 import { useVirtualPaginator, ItemRange } from '../../../hooks/useVirtualPaginator';
 import { useAlive } from '../../../hooks/useAlive';
-import { scrollToBottom } from '../../../utils/dom';
+import { editableActiveElement, scrollToBottom } from '../../../utils/dom';
 import {
   DefaultPlaceholder,
   MessageBase,
@@ -55,9 +56,11 @@ import {
   renderMatrixMention,
 } from '../../../plugins/react-custom-html-parser';
 import {
+  canEditEvent,
   decryptAllTimelineEvent,
   getEditedEvent,
   getEventReactions,
+  getLatestEditableEvt,
   getMemberName,
   getReactionContent,
   reactionOrEditEvent,
@@ -76,7 +79,8 @@ import {
   today,
   yesterday,
 } from '../../../utils/time';
-import { createMentionElement, moveCursor } from '../../../components/editor';
+import { createMentionElement, isEmptyEditor, moveCursor } from '../../../components/editor';
+import { useKeyDown } from '../../../hooks/useKeyDown';
 import { roomIdToReplyDraftAtomFamily } from '../../../state/room/roomInputDrafts';
 import { usePowerLevelsContext } from '../../../hooks/usePowerLevels';
 import { GetContentCallback, MessageEvent, StateEvent } from '../../../../types/matrix/room';
@@ -580,6 +584,32 @@ export function ThreadTimeline({ room, thread, editor }: ThreadTimelineProps) {
     [editor],
   );
 
+  // Up-arrow in the (empty) thread composer edits your last editable reply in
+  // this thread — parity with the main timeline. Gated on the thread composer's
+  // distinct editableName so it and the main handler never cross-fire.
+  useKeyDown(
+    window,
+    useCallback(
+      (evt) => {
+        if (
+          isKeyHotkey('arrowup', evt) &&
+          editableActiveElement() &&
+          document.activeElement?.getAttribute('data-editable-name') === 'ThreadInput' &&
+          isEmptyEditor(editor)
+        ) {
+          const editableEvt = getLatestEditableEvt(thread.liveTimeline, (mEvt) =>
+            canEditEvent(mx, mEvt),
+          );
+          const editableEvtId = editableEvt?.getId();
+          if (!editableEvtId) return;
+          setEditId(editableEvtId);
+          evt.preventDefault();
+        }
+      },
+      [mx, thread, editor],
+    ),
+  );
+
   const handleOpenReply: MouseEventHandler = useCallback(
     (evt) => {
       const targetId = evt.currentTarget.getAttribute('data-event-id');