fix(audit): correctness wave — ghost sends, Escape coordination, panel exclusion

- ScheduledMessagesTray: cancel prunes local state ONLY on confirmed server
  cancel; failures keep the item + show an inline error (was: a failed cancel
  looked cancelled but still sent at the scheduled time).
- Escape semantics: the composer consumes Escape (preventDefault+stopPropagation)
  iff autocomplete is open or a reply draft is set; the thread panel and Room's
  markAsRead act only on unconsumed Escape, and markAsRead defers entirely while
  a thread panel is open (listener order made it fire before the panel closed).
- Room: thread panel / media gallery are mutually exclusive (most-recently-
  opened wins); on mobile at most one right panel renders (thread > gallery >
  members) instead of stacked fullscreen overlays.
- RemindMeDialog: busy-disabled presets (no more double-click duplicates),
  try/catch with inline error, close only on success.
- ThreadTimeline: "Jump to Latest" floating chip when scrolled up (RoomTimeline
  idiom).

From the 4-auditor deep-audit wave; reviewer-verified.

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

src/app/features/room/ScheduledMessagesTray.tsx

@@ -33,6 +33,7 @@ export function ScheduledMessagesTray({ roomId }: ScheduledMessagesTrayProps) {
   const [scheduledMessages, setScheduledMessages] = useAtom(scheduledMessagesAtom);
   const [expanded, setExpanded] = useState(false);
   const [cancelling, setCancelling] = useState<Set<string>>(new Set());
+  const [cancelErrors, setCancelErrors] = useState<Set<string>>(new Set());
 
   const messages = useMemo(() => scheduledMessages.get(roomId) ?? [], [scheduledMessages, roomId]);
 
@@ -68,12 +69,17 @@ export function ScheduledMessagesTray({ roomId }: ScheduledMessagesTrayProps) {
     async (msg: ScheduledMessage) => {
       if (cancelling.has(msg.delayId)) return;
       setCancelling((prev) => new Set(prev).add(msg.delayId));
+      setCancelErrors((prev) => {
+        if (!prev.has(msg.delayId)) return prev;
+        const next = new Set(prev);
+        next.delete(msg.delayId);
+        return next;
+      });
       try {
         await cancelScheduledMessage(mx, msg.delayId);
-      } catch {
-        // If cancellation fails on the server, still remove locally
-        // since the user intends to remove it
-      } finally {
+        // Only prune local state once the server confirms cancellation. If we
+        // removed it optimistically the still-live delayed event would fire and
+        // the "cancelled" message would send anyway.
         setScheduledMessages((prev) => {
           const next = new Map(prev);
           const current = next.get(roomId) ?? [];
@@ -85,6 +91,11 @@ export function ScheduledMessagesTray({ roomId }: ScheduledMessagesTrayProps) {
           }
           return next;
         });
+      } catch {
+        // Keep the item (still cancellable) and surface an inline error; the
+        // delayed event is still scheduled on the server.
+        setCancelErrors((prev) => new Set(prev).add(msg.delayId));
+      } finally {
         setCancelling((prev) => {
           const next = new Set(prev);
           next.delete(msg.delayId);
@@ -131,41 +142,52 @@ export function ScheduledMessagesTray({ roomId }: ScheduledMessagesTrayProps) {
           {messages.map((msg) => (
             <Box
               key={msg.delayId}
-              alignItems="Center"
-              gap="200"
+              direction="Column"
               style={{
                 padding: `${config.space.S100} ${config.space.S300}`,
                 borderTop: `${config.borderWidth.B300} solid ${color.SurfaceVariant.ContainerLine}`,
               }}
             >
-              <Text
-                size="T200"
-                priority="400"
-                style={{
-                  flex: 1,
-                  overflow: 'hidden',
-                  textOverflow: 'ellipsis',
-                  whiteSpace: 'nowrap',
-                }}
-              >
-                {typeof msg.content.body === 'string' ? (msg.content.body as string) : '(message)'}
-              </Text>
-              <Text size="T200" priority="300" style={{ whiteSpace: 'nowrap', flexShrink: 0 }}>
-                {formatSendAt(msg.sendAt)}
-              </Text>
-              <IconButton
-                size="300"
-                radii="300"
-                variant="SurfaceVariant"
-                aria-label="Cancel scheduled message"
-                disabled={cancelling.has(msg.delayId)}
-                onClick={(e) => {
-                  e.stopPropagation();
-                  handleCancel(msg);
-                }}
-              >
-                <Icon src={Icons.Cross} size="50" />
-              </IconButton>
+              <Box alignItems="Center" gap="200">
+                <Text
+                  size="T200"
+                  priority="400"
+                  style={{
+                    flex: 1,
+                    overflow: 'hidden',
+                    textOverflow: 'ellipsis',
+                    whiteSpace: 'nowrap',
+                  }}
+                >
+                  {typeof msg.content.body === 'string'
+                    ? (msg.content.body as string)
+                    : '(message)'}
+                </Text>
+                <Text size="T200" priority="300" style={{ whiteSpace: 'nowrap', flexShrink: 0 }}>
+                  {formatSendAt(msg.sendAt)}
+                </Text>
+                <IconButton
+                  size="300"
+                  radii="300"
+                  variant="SurfaceVariant"
+                  aria-label="Cancel scheduled message"
+                  disabled={cancelling.has(msg.delayId)}
+                  onClick={(e) => {
+                    e.stopPropagation();
+                    handleCancel(msg);
+                  }}
+                >
+                  <Icon src={Icons.Cross} size="50" />
+                </IconButton>
+              </Box>
+              {cancelErrors.has(msg.delayId) && (
+                <Text
+                  size="T200"
+                  style={{ color: color.Critical.Main, paddingTop: config.space.S100 }}
+                >
+                  Could not cancel this message. Try again.
+                </Text>
+              )}
             </Box>
           ))}
         </Box>