fix(composer): recover silently from a composer render error; capture details

Reported on chat.lotusguild.org: picking a name from the @-mention list
showed "The message composer hit a snag." — clicking OK continued with the
draft intact. The composer's known failure mode is a transient render error
right after an autocomplete insert (slate-react's DOM selection sync racing
the model; 477df4ae fixed one such path). It did not reproduce locally in 60
attempts (click / Enter / Tab, fast and slow, display names with spaces and
emoji, Chromium and WebKit), so this makes it harmless and diagnosable:

- ComposerErrorBoundary: the first failure clears the selection and remounts
  the composer immediately, with no notice (the draft is intact). A second
  failure within 5 s shows the notice, now saying the draft is safe, with
  "Reload composer" and "Copy details" (time, error, stack, component stack,
  browser). Every failure is logged to the console as "[composer] render
  error".
- Used for the room composer and, newly, the thread panel composer (which had
  no boundary, so the same error took the whole panel down).

Verified with a temporary injected crash (not committed): one crash recovers
with the draft kept and no notice; two within 5 s show the notice, Copy
details copies the report, Reload composer restores the full draft.
Chromium e2e 19 passed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/room/RoomView.tsx

@@ -1,9 +1,8 @@
 import React, { useCallback, useMemo, useRef } from 'react';
 import { ErrorBoundary } from 'react-error-boundary';
-import { Box, Button, Text, config } from 'folds';
+import { Box, Text, config } from 'folds';
 import { EventType } from 'matrix-js-sdk';
 import { ReactEditor } from 'slate-react';
-import { Transforms } from 'slate';
 import { isKeyHotkey } from 'is-hotkey';
 import { useStateEvent } from '../../hooks/useStateEvent';
 import { StateEvent } from '../../../types/matrix/room';
@@ -15,6 +14,7 @@ import { RoomTimeline } from './RoomTimeline';
 import { RoomViewTyping } from './RoomViewTyping';
 import { RoomTombstone } from './RoomTombstone';
 import { RoomInput } from './RoomInput';
+import { ComposerErrorBoundary } from './ComposerErrorBoundary';
 import { RoomViewFollowing, RoomViewFollowingPlaceholder } from './RoomViewFollowing';
 import { Page } from '../../components/page';
 import { useSetting } from '../../state/hooks/settings';
@@ -162,40 +162,7 @@ export function RoomView({ eventId }: { eventId?: string }) {
           ) : (
             <>
               {canMessage && (
-                <ErrorBoundary
-                  onReset={() => {
-                    // The composer crash is a transient bad-selection render
-                    // (e.g. after an autocomplete insert); the draft content is
-                    // intact. Clear the selection so the remounted composer can
-                    // render — the user clicks in to continue, no page refresh.
-                    try {
-                      Transforms.deselect(editor);
-                    } catch {
-                      /* editor already in a safe state */
-                    }
-                  }}
-                  fallbackRender={({ resetErrorBoundary }) => (
-                    <RoomInputPlaceholder
-                      role="alert"
-                      style={{ padding: config.space.S200 }}
-                      direction="Column"
-                      alignItems="Center"
-                      justifyContent="Center"
-                      gap="200"
-                    >
-                      <Text align="Center">The message composer hit a snag.</Text>
-                      <Button
-                        size="300"
-                        variant="Secondary"
-                        fill="Soft"
-                        radii="300"
-                        onClick={resetErrorBoundary}
-                      >
-                        <Text size="B300">Reload composer</Text>
-                      </Button>
-                    </RoomInputPlaceholder>
-                  )}
-                >
+                <ComposerErrorBoundary editor={editor}>
                   <RoomInput
                     room={room}
                     editor={editor}
@@ -203,7 +170,7 @@ export function RoomView({ eventId }: { eventId?: string }) {
                     fileDropContainerRef={roomViewRef}
                     ref={roomInputRef}
                   />
-                </ErrorBoundary>
+                </ComposerErrorBoundary>
               )}
               {!canMessage && (
                 <RoomInputPlaceholder