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/Room.tsx

@@ -1,4 +1,4 @@
-import React, { useCallback } from 'react';
+import React, { useCallback, useEffect, useRef } from 'react';
 import { Box, Line } from 'folds';
 import { useParams } from 'react-router-dom';
 import { isKeyHotkey } from 'is-hotkey';
@@ -49,15 +49,46 @@ export function Room() {
     useCallback(
       (evt) => {
         if (isKeyHotkey('escape', evt)) {
+          // Skip when a composer already consumed Escape (it preventDefaults).
+          if (evt.defaultPrevented) return;
+          // Skip while a thread panel is open: listener registration order
+          // means this can run BEFORE the panel's own Escape handler, and the
+          // user's intent there is "close the panel", not "mark room read".
+          if (activeThreadId) return;
           markAsRead(mx, room.roomId, hideActivity);
         }
       },
-      [mx, room.roomId, hideActivity],
+      [mx, room.roomId, hideActivity, activeThreadId],
     ),
   );
 
   const callView = callEmbed?.roomId === room.roomId || room.isCallRoom() || callMembers.length > 0;
 
+  // Thread panel and media gallery are mutually exclusive on every screen size:
+  // opening one closes the other. Detect the just-opened transition so whichever
+  // was opened most recently wins.
+  const prevThreadRef = useRef(activeThreadId);
+  const prevGalleryRef = useRef(galleryOpen);
+  useEffect(() => {
+    const threadJustOpened = Boolean(activeThreadId) && !prevThreadRef.current;
+    const galleryJustOpened = galleryOpen && !prevGalleryRef.current;
+    if (threadJustOpened && galleryOpen) {
+      setGalleryOpen(false);
+    } else if (galleryJustOpened && activeThreadId) {
+      setActiveThreadId(null);
+    }
+    prevThreadRef.current = activeThreadId;
+    prevGalleryRef.current = galleryOpen;
+  }, [activeThreadId, galleryOpen, setGalleryOpen, setActiveThreadId]);
+
+  // On non-desktop screens at most one right-side panel may show, priority
+  // thread > gallery > members. On desktop thread + members may coexist while
+  // thread + gallery stay mutually exclusive (via the effect above).
+  const isDesktop = screenSize === ScreenSize.Desktop;
+  const showThreadPanel = !callView && Boolean(activeThreadId);
+  const showGallery = !callView && galleryOpen && (isDesktop || !activeThreadId);
+  const showMembers = !callView && isDrawer && (isDesktop || (!activeThreadId && !galleryOpen));
+
   return (
     <PowerLevelsContextProvider value={powerLevels}>
       <Box grow="Yes">
@@ -86,7 +117,7 @@ export function Room() {
             <CallChatView />
           </>
         )}
-        {!callView && galleryOpen && (
+        {showGallery && (
           <>
             {screenSize === ScreenSize.Desktop && (
               <Line variant="Background" direction="Vertical" size="300" />
@@ -94,7 +125,7 @@ export function Room() {
             <MediaGallery key={room.roomId} room={room} onClose={() => setGalleryOpen(false)} />
           </>
         )}
-        {!callView && activeThreadId && (
+        {showThreadPanel && activeThreadId && (
           <>
             {screenSize === ScreenSize.Desktop && (
               <Line variant="Background" direction="Vertical" size="300" />
@@ -107,7 +138,7 @@ export function Room() {
             />
           </>
         )}
-        {!callView && isDrawer && (
+        {showMembers && (
           <>
             {screenSize === ScreenSize.Desktop && (
               <Line variant="Background" direction="Vertical" size="300" />