🪗 feat: Dock-Style Fisheye Nav Rail With Instant Hover Preview (#14021)

* ✨ feat: Dock-Fisheye Message Nav Rail with Instant Hover Preview

* 🎚️ refactor: Uniform resting ribs + clickable cursor for message nav

* 🧹 fix: One rib per message in nav rail (dedupe nested message-render)

* 🎯 fix: Accurate fisheye focus + click-anywhere-to-jump in message nav

- Measure rib centers relative to the column (getBoundingClientRect) instead
  of offsetTop, which was relative to the positioned <nav> and shifted the
  pointer->rib mapping by the chevron height (hovered line wasn't the peak,
  preview showed an earlier message).
- Column-level click jumps to the focused rib, so clicking anywhere the
  preview is showing works even when the pointer is off the thin line.
- Restore @librechat/client jest stub to keep the unit isolated.

* 💡 fix: Highlight only the hovered rib white in message nav

* 🫥 style: Transparent message nav (drop pill background)

* ♿ feat: Keyboard focus mirrors hover (magnify + highlight + preview) in message nav

Tabbing to / Shift+Alt+M focusing a rib now drives the same fisheye
pipeline as pointer hover via onFocus/onBlur on the column: the focused
rib magnifies, highlights white, and shows the shared preview. Also
addresses Codex finding on keyboard-focus previews.

* 🩹 fix: Live tooltip preview + legacy media-query fallback in message nav

- Derive the shared preview text from entryById at render time instead of
  snapshotting it into tip state, so a streaming/updating message refreshes
  the open tooltip without leaving and re-entering the rail.
- Feature-detect MediaQueryList.addEventListener and fall back to
  addListener/removeListener so the reduced-motion watcher no longer throws
  (and breaks the nav) on Safari/iOS < 14.

Addresses both Codex findings on review 4601236141.

client/src/components/Chat/Messages/MessageNav.tsx

@@ -1,7 +1,7 @@
 import { memo, useState, useEffect, useCallback, useRef, useMemo } from 'react';
+import { createPortal } from 'react-dom';
 import { ChevronUp, ChevronDown } from 'lucide-react';
 import { ContentTypes } from 'librechat-data-provider';
-import { HoverCard, HoverCardTrigger, HoverCardPortal, HoverCardContent } from '@librechat/client';
 import type { TMessage, TMessageContentParts } from 'librechat-data-provider';
 import { useMessagesConversation, useMessagesSubmission } from '~/Providers';
 import { useGetMessagesByConvoId } from '~/data-provider';
@@ -17,7 +17,7 @@ type MessageEntry = {
 
 const MESSAGES_END_ID = 'messages-end';
 
-function extractPreviewFromContent(content?: TMessageContentParts[]): string {
+export function extractPreviewFromContent(content?: TMessageContentParts[]): string {
   if (!content) {
     return '';
   }
@@ -36,7 +36,7 @@ function extractPreviewFromContent(content?: TMessageContentParts[]): string {
   return '';
 }
 
-function buildEntry(id: string, msg: TMessage): MessageEntry {
+export function buildEntry(id: string, msg: TMessage): MessageEntry {
   const raw = msg.text?.trim() ? msg.text : extractPreviewFromContent(msg.content);
   const trimmed = raw.trim();
   return {
@@ -48,7 +48,7 @@ function buildEntry(id: string, msg: TMessage): MessageEntry {
 
 const USER_TURN_SELECTOR = '.user-turn';
 
-function buildFallbackEntry(node: HTMLElement, id: string): MessageEntry {
+export function buildFallbackEntry(node: HTMLElement, id: string): MessageEntry {
   const isUser = node.querySelector(USER_TURN_SELECTOR) != null;
   const trimmed = (node.textContent ?? '').trim();
   return {
@@ -61,12 +61,14 @@ function buildFallbackEntry(node: HTMLElement, id: string): MessageEntry {
 function getMessageEntries(root: ParentNode, messagesById: Map<string, TMessage>): MessageEntry[] {
   const nodes = root.querySelectorAll<HTMLElement>('.message-render');
   const entries: MessageEntry[] = [];
+  const seen = new Set<string>();
   for (let i = 0; i < nodes.length; i++) {
     const node = nodes[i];
     const id = node.id;
-    if (!id) {
+    if (!id || seen.has(id)) {
       continue;
     }
+    seen.add(id);
     const msg = messagesById.get(id);
     entries.push(msg ? buildEntry(id, msg) : buildFallbackEntry(node, id));
   }
@@ -105,64 +107,67 @@ function computeTargetScroll(
   return Math.max(0, Math.min(target, max));
 }
 
+type RibDims = { baseW: number; baseH: number; peakW: number; peakH: number };
+
+const RIB_END: RibDims = { baseW: 4, baseH: 4, peakW: 6, peakH: 6 };
+const RIB_MESSAGE: RibDims = { baseW: 16, baseH: 3, peakW: 52, peakH: 6 };
+
+/** Vertical falloff radius (content-space px) over which neighbouring ribs magnify. */
+const MAG_INFLUENCE = 50;
+/** Delay before the shared preview first opens; subsequent moves reposition instantly. */
+const TOOLTIP_OPEN_DELAY = 60;
+
+export function ribDimsFor(entry: MessageEntry): RibDims {
+  return entry.isEnd ? RIB_END : RIB_MESSAGE;
+}
+
+/** Cosine bell: 1 at the pointer, easing to 0 at the influence radius. */
+export function magnifyFalloff(distance: number, influence: number): number {
+  if (distance >= influence) {
+    return 0;
+  }
+  return 0.5 * (1 + Math.cos((Math.PI * distance) / influence));
+}
+
 const indicatorButtonClasses = cn(
-  'flex h-[5px] items-center justify-center rounded-sm',
+  'flex h-1.5 w-full items-center justify-end rounded-sm',
   'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-border-xheavy',
 );
 
 const MessageIndicator = memo(function MessageIndicator({
   entry,
-  isActive,
+  isHighlighted,
   isCurrent,
   label,
-  hoverText,
   onSelect,
 }: {
   entry: MessageEntry;
-  isActive: boolean;
+  isHighlighted: boolean;
   isCurrent: boolean;
   label: string;
-  hoverText: string;
   onSelect: (id: string) => void;
 }) {
+  const baseSize = entry.isEnd ? 'h-1 w-1' : 'h-[3px] w-4';
   return (
-    <HoverCard openDelay={150}>
-      <HoverCardTrigger asChild>
-        <button
-          type="button"
-          onClick={() => onSelect(entry.id)}
-          className={cn(indicatorButtonClasses, entry.isEnd || !entry.isUser ? 'w-6' : 'w-4')}
-          aria-label={label}
-          aria-current={isCurrent ? 'true' : undefined}
-          data-msg-id={entry.id}
-        >
-          {entry.isEnd ? (
-            <span
-              className={cn(
-                'block rounded-full transition-all duration-200',
-                isActive
-                  ? 'h-1.5 w-1.5 bg-gray-800 dark:bg-gray-100'
-                  : 'h-1 w-1 bg-gray-400 dark:bg-gray-500',
-              )}
-            />
-          ) : (
-            <span
-              className={cn(
-                'block w-full rounded-full transition-all duration-200',
-                isActive
-                  ? 'h-[5px] bg-gray-800 dark:bg-gray-100'
-                  : 'h-[3px] bg-gray-400 dark:bg-gray-500',
-              )}
-            />
-          )}
-        </button>
-      </HoverCardTrigger>
-      <HoverCardPortal>
-        <HoverCardContent side="left" sideOffset={12} className="z-[999] max-w-[280px] px-3 py-2">
-          <p className="line-clamp-3 text-xs text-text-secondary">{hoverText}</p>
-        </HoverCardContent>
-      </HoverCardPortal>
-    </HoverCard>
+    <button
+      type="button"
+      onClick={(e) => {
+        e.stopPropagation();
+        onSelect(entry.id);
+      }}
+      className={indicatorButtonClasses}
+      aria-label={label}
+      aria-current={isCurrent ? 'true' : undefined}
+      data-msg-id={entry.id}
+    >
+      <span
+        className={cn(
+          'block rounded-full',
+          baseSize,
+          isHighlighted ? 'bg-gray-800 dark:bg-gray-100' : 'bg-gray-400 dark:bg-gray-500',
+        )}
+      />
+    </button>
   );
 });
 
@@ -215,6 +220,30 @@ function MessageNav({ scrollableRef }: { scrollableRef: React.RefObject<HTMLDivE
   const navRef = useRef<HTMLElement>(null);
   const dragCleanupRef = useRef<(() => void) | null>(null);
   const suppressClickRef = useRef(false);
+  const isDraggingRef = useRef(false);
+
+  const ribLayoutRef = useRef<
+    Array<{ id: string; line: HTMLElement; center: number; dims: RibDims }>
+  >([]);
+  const pointerYRef = useRef<number | null>(null);
+  const magRafRef = useRef<number | null>(null);
+  const reducedMotionRef = useRef(false);
+  const focusedIdRef = useRef<string | null>(null);
+  const tipShownRef = useRef(false);
+  const tipTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+  const tipElRef = useRef<HTMLDivElement | null>(null);
+  const tipPosRef = useRef({ top: 0, right: 0 });
+
+  const [tip, setTip] = useState<{ id: string; top: number; right: number } | null>(null);
+  const [hoveredId, setHoveredId] = useState<string | null>(null);
+
+  const entryById = useMemo(() => {
+    const map = new Map<string, MessageEntry>();
+    for (let i = 0; i < entries.length; i++) {
+      map.set(entries[i].id, entries[i]);
+    }
+    return map;
+  }, [entries]);
 
   const getCurrentVisibleId = useCallback((): string | null => {
     let nextId: string | null = null;
@@ -346,6 +375,13 @@ function MessageNav({ scrollableRef }: { scrollableRef: React.RefObject<HTMLDivE
     [scrollToStart, focusMessage],
   );
 
+  const handleColumnClick = useCallback(() => {
+    const id = focusedIdRef.current;
+    if (id) {
+      handleSelect(id);
+    }
+  }, [handleSelect]);
+
   const focusNav = useCallback((): boolean => {
     const nav = navRef.current;
     if (!nav) {
@@ -398,6 +434,7 @@ function MessageNav({ scrollableRef }: { scrollableRef: React.RefObject<HTMLDivE
         document.removeEventListener('pointercancel', onUp);
         window.removeEventListener('blur', onBlur);
         dragCleanupRef.current = null;
+        isDraggingRef.current = false;
         if (wasDragging) {
           suppressClickRef.current = true;
           window.setTimeout(() => {
@@ -419,6 +456,7 @@ function MessageNav({ scrollableRef }: { scrollableRef: React.RefObject<HTMLDivE
             return;
           }
           state.dragging = true;
+          isDraggingRef.current = true;
         }
         scrubTo(ev.clientY);
       }
@@ -445,6 +483,236 @@ function MessageNav({ scrollableRef }: { scrollableRef: React.RefObject<HTMLDivE
 
   useEffect(() => () => dragCleanupRef.current?.(), []);
 
+  useEffect(() => {
+    const mq = window.matchMedia('(prefers-reduced-motion: reduce)');
+    reducedMotionRef.current = mq.matches;
+    const onChange = () => {
+      reducedMotionRef.current = mq.matches;
+    };
+    if (typeof mq.addEventListener === 'function') {
+      mq.addEventListener('change', onChange);
+      return () => mq.removeEventListener('change', onChange);
+    }
+    mq.addListener(onChange);
+    return () => mq.removeListener(onChange);
+  }, []);
+
+  const measureRibs = useCallback(() => {
+    const col = columnRef.current;
+    if (!col) {
+      return;
+    }
+    const colRect = col.getBoundingClientRect();
+    const scrollTop = col.scrollTop;
+    const layout: Array<{ id: string; line: HTMLElement; center: number; dims: RibDims }> = [];
+    const kids = col.children;
+    for (let i = 0; i < kids.length; i++) {
+      const button = kids[i] as HTMLElement;
+      const id = button.getAttribute('data-msg-id');
+      const line = button.firstElementChild as HTMLElement | null;
+      const entry = id ? entryById.get(id) : undefined;
+      if (!id || !line || !entry) {
+        continue;
+      }
+      const rect = button.getBoundingClientRect();
+      layout.push({
+        id,
+        line,
+        center: rect.top - colRect.top + scrollTop + rect.height / 2,
+        dims: ribDimsFor(entry),
+      });
+    }
+    ribLayoutRef.current = layout;
+  }, [entryById]);
+
+  useEffect(() => {
+    const raf = requestAnimationFrame(measureRibs);
+    const col = columnRef.current;
+    const resize = col ? new ResizeObserver(measureRibs) : null;
+    if (col && resize) {
+      resize.observe(col);
+    }
+    return () => {
+      cancelAnimationFrame(raf);
+      resize?.disconnect();
+    };
+  }, [entries, measureRibs]);
+
+  const positionTip = useCallback((top: number, right: number) => {
+    tipPosRef.current = { top, right };
+    const el = tipElRef.current;
+    if (el) {
+      el.style.top = `${top}px`;
+      el.style.right = `${right}px`;
+    }
+  }, []);
+
+  const revealTip = useCallback(
+    (id: string | null) => {
+      if (!id || !entryById.has(id)) {
+        setTip(null);
+        return;
+      }
+      setTip({ id, top: tipPosRef.current.top, right: tipPosRef.current.right });
+    },
+    [entryById],
+  );
+
+  const clearTooltip = useCallback(() => {
+    if (tipTimerRef.current) {
+      clearTimeout(tipTimerRef.current);
+      tipTimerRef.current = null;
+    }
+    if (focusedIdRef.current !== null) {
+      focusedIdRef.current = null;
+      setHoveredId(null);
+    }
+    if (tipShownRef.current) {
+      tipShownRef.current = false;
+      setTip(null);
+    }
+  }, []);
+
+  const focusTooltip = useCallback(
+    (id: string, top: number, right: number) => {
+      positionTip(top, right);
+      if (focusedIdRef.current === id) {
+        return;
+      }
+      focusedIdRef.current = id;
+      setHoveredId(id);
+      if (tipShownRef.current) {
+        revealTip(id);
+        return;
+      }
+      if (tipTimerRef.current) {
+        return;
+      }
+      tipTimerRef.current = setTimeout(() => {
+        tipTimerRef.current = null;
+        tipShownRef.current = true;
+        revealTip(focusedIdRef.current);
+      }, TOOLTIP_OPEN_DELAY);
+    },
+    [positionTip, revealTip],
+  );
+
+  const applyMagnify = useCallback(() => {
+    magRafRef.current = null;
+    const col = columnRef.current;
+    const layout = ribLayoutRef.current;
+    const py = pointerYRef.current;
+    if (!col || py == null || layout.length === 0) {
+      return;
+    }
+    const reduce = reducedMotionRef.current;
+    const colRect = col.getBoundingClientRect();
+    const scrollTop = col.scrollTop;
+    let nearestId: string | null = null;
+    let nearestD = Number.POSITIVE_INFINITY;
+    let nearestCenter = 0;
+    for (let i = 0; i < layout.length; i++) {
+      const rib = layout[i];
+      const d = Math.abs(py - rib.center);
+      if (d < nearestD) {
+        nearestD = d;
+        nearestId = rib.id;
+        nearestCenter = rib.center;
+      }
+      if (reduce) {
+        continue;
+      }
+      const t = magnifyFalloff(d, MAG_INFLUENCE);
+      const dims = rib.dims;
+      rib.line.style.transition = 'none';
+      rib.line.style.width = `${(dims.baseW + (dims.peakW - dims.baseW) * t).toFixed(2)}px`;
+      rib.line.style.height = `${(dims.baseH + (dims.peakH - dims.baseH) * t).toFixed(2)}px`;
+    }
+    if (nearestId != null && nearestD <= MAG_INFLUENCE && !isDraggingRef.current) {
+      const top = colRect.top - scrollTop + nearestCenter;
+      const right = window.innerWidth - colRect.left + 8;
+      focusTooltip(nearestId, top, right);
+    } else {
+      clearTooltip();
+    }
+  }, [focusTooltip, clearTooltip]);
+
+  const resetMagnify = useCallback(() => {
+    const layout = ribLayoutRef.current;
+    for (let i = 0; i < layout.length; i++) {
+      const line = layout[i].line;
+      line.style.transition = 'width 140ms ease-out, height 140ms ease-out';
+      line.style.width = '';
+      line.style.height = '';
+    }
+  }, []);
+
+  const handlePointerMove = useCallback(
+    (e: React.PointerEvent<HTMLDivElement>) => {
+      const col = columnRef.current;
+      if (!col) {
+        return;
+      }
+      const rect = col.getBoundingClientRect();
+      pointerYRef.current = e.clientY - rect.top + col.scrollTop;
+      if (magRafRef.current == null) {
+        magRafRef.current = requestAnimationFrame(applyMagnify);
+      }
+    },
+    [applyMagnify],
+  );
+
+  const handlePointerLeave = useCallback(() => {
+    pointerYRef.current = null;
+    if (magRafRef.current != null) {
+      cancelAnimationFrame(magRafRef.current);
+      magRafRef.current = null;
+    }
+    resetMagnify();
+    clearTooltip();
+  }, [resetMagnify, clearTooltip]);
+
+  const handleColumnFocus = useCallback(
+    (e: React.FocusEvent<HTMLDivElement>) => {
+      const col = columnRef.current;
+      const target = e.target as HTMLElement;
+      if (!col || !target.getAttribute?.('data-msg-id')) {
+        return;
+      }
+      const colRect = col.getBoundingClientRect();
+      const rect = target.getBoundingClientRect();
+      pointerYRef.current = rect.top - colRect.top + col.scrollTop + rect.height / 2;
+      if (magRafRef.current == null) {
+        magRafRef.current = requestAnimationFrame(applyMagnify);
+      }
+    },
+    [applyMagnify],
+  );
+
+  const handleColumnBlur = useCallback(
+    (e: React.FocusEvent<HTMLDivElement>) => {
+      const col = columnRef.current;
+      const next = e.relatedTarget as Node | null;
+      if (col && next && col.contains(next)) {
+        return;
+      }
+      handlePointerLeave();
+    },
+    [handlePointerLeave],
+  );
+
+  useEffect(
+    () => () => {
+      if (magRafRef.current != null) {
+        cancelAnimationFrame(magRafRef.current);
+      }
+      if (tipTimerRef.current) {
+        clearTimeout(tipTimerRef.current);
+      }
+    },
+    [],
+  );
+
   useEffect(() => {
     refreshEntries();
 
@@ -831,6 +1099,12 @@ function MessageNav({ scrollableRef }: { scrollableRef: React.RefObject<HTMLDivE
     return null;
   }
 
+  const tipEntry = tip ? entryById.get(tip.id) : undefined;
+  let tipText = '';
+  if (tipEntry) {
+    tipText = tipEntry.isEnd ? localize('com_ui_scroll_to_bottom') : tipEntry.preview;
+  }
+
   return (
     <nav
       ref={navRef}
@@ -838,10 +1112,9 @@ function MessageNav({ scrollableRef }: { scrollableRef: React.RefObject<HTMLDivE
       aria-keyshortcuts="Shift+Alt+M"
       className={cn(
         'group/nav absolute right-2 top-1/2 z-40 hidden max-h-[min(24rem,calc(100%-2rem))]',
-        '-translate-y-1/2 flex-col items-center gap-1.5 rounded-full px-1 py-2 md:flex',
+        '-translate-y-1/2 flex-col items-end gap-1.5 px-1.5 py-2 md:flex',
         'opacity-30 transition-opacity duration-300',
-        'hover:bg-black/5 hover:opacity-100 dark:hover:bg-white/5',
-        'focus-within:bg-black/5 focus-within:opacity-100 dark:focus-within:bg-white/5',
+        'focus-within:opacity-100 hover:opacity-100',
       )}
     >
       <button
@@ -857,7 +1130,12 @@ function MessageNav({ scrollableRef }: { scrollableRef: React.RefObject<HTMLDivE
       <div
         ref={columnRef}
         onPointerDown={handlePointerDown}
-        className="flex min-h-0 cursor-grab touch-none select-none flex-col items-center gap-1.5 overflow-y-auto active:cursor-grabbing [&::-webkit-scrollbar]:hidden"
+        onPointerMove={handlePointerMove}
+        onPointerLeave={handlePointerLeave}
+        onFocus={handleColumnFocus}
+        onBlur={handleColumnBlur}
+        onClick={handleColumnClick}
+        className="flex min-h-0 w-14 cursor-pointer touch-none select-none flex-col items-stretch gap-1.5 overflow-y-auto [&::-webkit-scrollbar]:hidden"
         style={{ scrollbarWidth: 'none', msOverflowStyle: 'none' }}
       >
         {entries.map((entry) => {
@@ -869,15 +1147,16 @@ function MessageNav({ scrollableRef }: { scrollableRef: React.RefObject<HTMLDivE
                   : 'com_ui_message_nav_go_to_assistant',
                 { 0: entry.preview.slice(0, 30) },
               );
+          const isHighlighted =
+            hoveredId != null ? hoveredId === entry.id : visibleIds.has(entry.id);
           return (
             <MessageIndicator
               key={entry.id}
               entry={entry}
-              isActive={visibleIds.has(entry.id)}
+              isHighlighted={isHighlighted}
               isCurrent={currentId === entry.id}
               onSelect={handleSelect}
               label={label}
-              hoverText={entry.isEnd ? label : entry.preview}
             />
           );
         })}
@@ -892,6 +1171,24 @@ function MessageNav({ scrollableRef }: { scrollableRef: React.RefObject<HTMLDivE
       >
         <ChevronDown className="h-4 w-4" />
       </button>
+      {tip &&
+        createPortal(
+          <div
+            ref={tipElRef}
+            role="tooltip"
+            style={{
+              position: 'fixed',
+              top: tip.top,
+              right: tip.right,
+              transform: 'translateY(-50%)',
+              zIndex: 999,
+            }}
+            className="pointer-events-none max-w-[280px] rounded-md border border-border-medium bg-surface-secondary px-3 py-2 text-text-secondary shadow-lg"
+          >
+            <p className="line-clamp-3 text-xs">{tipText}</p>
+          </div>,
+          document.body,
+        )}
     </nav>
   );
 }

client/src/components/Chat/Messages/__tests__/MessageNav.spec.tsx

@@ -38,18 +38,31 @@ jest.mock('~/hooks', () => ({
       opts ? `${key}|${JSON.stringify(opts)}` : key,
 }));
 
+// The nav no longer renders HoverCard, but `~/utils` transitively imports the
+// dual CJS/ESM @librechat/client whose dist pulls ESM-only @ariakit subpaths
+// that jest cannot resolve. Stub the module so the unit under test stays isolated.
 jest.mock('@librechat/client', () => ({
   HoverCard: ({ children }: { children: ReactNode }) => <>{children}</>,
   HoverCardTrigger: ({ children, asChild }: { children: ReactNode; asChild?: boolean }) =>
     asChild ? children : <div>{children}</div>,
   HoverCardPortal: ({ children }: { children: ReactNode }) => <>{children}</>,
-  HoverCardContent: ({ children, className }: { children: ReactNode; className?: string }) => (
-    <div data-testid="hover-card-content" className={className}>
-      {children}
-    </div>
-  ),
+  HoverCardContent: ({ children }: { children: ReactNode }) => <div>{children}</div>,
 }));
 
+if (typeof window.matchMedia !== 'function') {
+  window.matchMedia = (query: string) =>
+    ({
+      matches: false,
+      media: query,
+      onchange: null,
+      addEventListener: () => {},
+      removeEventListener: () => {},
+      addListener: () => {},
+      removeListener: () => {},
+      dispatchEvent: () => false,
+    }) as unknown as MediaQueryList;
+}
+
 type IOEntry = Pick<IntersectionObserverEntry, 'target' | 'isIntersecting'>;
 
 class MockIntersectionObserver {
@@ -110,7 +123,13 @@ if (typeof (global as { PointerEvent?: unknown }).PointerEvent === 'undefined')
     PointerEventPolyfill;
 }
 
-import MessageNav from '../MessageNav';
+import type { TMessage } from 'librechat-data-provider';
+import MessageNav, {
+  buildEntry,
+  buildFallbackEntry,
+  magnifyFalloff,
+  ribDimsFor,
+} from '../MessageNav';
 
 function buildMessage(overrides: Partial<TestMessage> = {}): TestMessage {
   return {
@@ -122,6 +141,8 @@ function buildMessage(overrides: Partial<TestMessage> = {}): TestMessage {
   };
 }
 
+const asTMessage = (m: TestMessage): TMessage => m as unknown as TMessage;
+
 function buildDom(messages: TestMessage[]): {
   scrollable: HTMLDivElement;
   content: HTMLDivElement;
@@ -229,51 +250,27 @@ describe('MessageNav', () => {
         'c',
       ]);
     });
-  });
 
-  describe('indicator styling', () => {
-    it('uses narrower width for user turns and wider for assistant turns', () => {
-      const messages = [
-        buildMessage({ messageId: 'u', text: 'user msg', isCreatedByUser: true }),
-        buildMessage({ messageId: 'a', text: 'assistant msg' }),
-        buildMessage({ messageId: 'u2', text: 'more user', isCreatedByUser: true }),
-      ];
-      const { container } = renderNav(messages);
-      const [userInd, assistantInd] = container.querySelectorAll('[data-msg-id]');
-      expect(userInd.className).toContain('w-4');
-      expect(userInd.className).not.toContain('w-6');
-      expect(assistantInd.className).toContain('w-6');
-      expect(assistantInd.className).not.toContain('w-4');
-    });
-  });
-
-  describe('preview text', () => {
-    it('uses message text from React Query data when available', () => {
-      const messages = [
-        buildMessage({ messageId: 'a', text: 'alpha-preview', isCreatedByUser: true }),
-        buildMessage({ messageId: 'b', text: 'bravo-preview' }),
-        buildMessage({ messageId: 'c', text: 'charlie-preview', isCreatedByUser: true }),
-      ];
-      const { container } = renderNav(messages);
-      const previews = container.querySelectorAll('[data-testid="hover-card-content"] p');
-      expect(previews).toHaveLength(3);
-      expect(previews[0]).toHaveTextContent('alpha-preview');
-      expect(previews[1]).toHaveTextContent('bravo-preview');
-    });
-
-    it('falls back to DOM text when a message is not in React Query data', () => {
+    it('renders one rib per message even when a message nests duplicate .message-render nodes', () => {
       mockUseGetMessagesByConvoId.mockReturnValue({ data: [] });
       const scrollable = document.createElement('div');
       scrollable.className = 'scrollbar-gutter-stable';
       const content = document.createElement('div');
       scrollable.appendChild(content);
-      for (const [i, id] of ['x', 'y', 'z'].entries()) {
+      for (const [i, id] of ['a', 'b', 'c'].entries()) {
         const div = document.createElement('div');
         div.id = id;
         div.className = 'message-render';
-        div.textContent = `dom-text-${id}`;
-        Object.defineProperty(div, 'offsetTop', { value: i * 200 });
-        Object.defineProperty(div, 'offsetHeight', { value: 150 });
+        div.textContent = `msg-${id}`;
+        if (id === 'b') {
+          const part = document.createElement('div');
+          part.id = id;
+          part.className = 'message-render';
+          part.textContent = 'msg-b-part';
+          div.appendChild(part);
+        }
+        Object.defineProperty(div, 'offsetTop', { value: i * 200, configurable: true });
+        Object.defineProperty(div, 'offsetHeight', { value: 150, configurable: true });
         content.appendChild(div);
       }
       document.body.appendChild(scrollable);
@@ -283,39 +280,107 @@ describe('MessageNav', () => {
         jest.advanceTimersByTime(250);
       });
 
-      const previews = container.querySelectorAll('[data-testid="hover-card-content"] p');
-      expect(previews[0]).toHaveTextContent('dom-text-x');
-      expect(previews[2]).toHaveTextContent('dom-text-z');
+      const indicators = container.querySelectorAll('[data-msg-id]');
+      expect(Array.from(indicators).map((el) => el.getAttribute('data-msg-id'))).toEqual([
+        'a',
+        'b',
+        'c',
+      ]);
+    });
+  });
+
+  describe('indicator styling', () => {
+    it('gives every message rib the same short resting width regardless of role', () => {
+      const messages = [
+        buildMessage({ messageId: 'u', text: 'user msg', isCreatedByUser: true }),
+        buildMessage({ messageId: 'a', text: 'assistant msg' }),
+        buildMessage({ messageId: 'u2', text: 'more user', isCreatedByUser: true }),
+      ];
+      const { container } = renderNav(messages);
+      const [userInd, assistantInd] = container.querySelectorAll('[data-msg-id]');
+      const userLine = userInd.querySelector('span');
+      const assistantLine = assistantInd.querySelector('span');
+      expect(userLine?.className).toContain('w-4');
+      expect(assistantLine?.className).toContain('w-4');
+    });
+  });
+
+  describe('preview text', () => {
+    it('uses message text from React Query data when available', () => {
+      const entry = buildEntry(
+        'a',
+        asTMessage(buildMessage({ messageId: 'a', text: 'alpha-preview' })),
+      );
+      expect(entry.preview).toBe('alpha-preview');
+    });
+
+    it('falls back to DOM text content for messages without React Query data', () => {
+      const node = document.createElement('div');
+      node.className = 'message-render';
+      node.textContent = 'dom-text-x';
+      const entry = buildFallbackEntry(node, 'x');
+      expect(entry.preview).toBe('dom-text-x');
+      expect(entry.isUser).toBe(false);
+    });
+
+    it('marks fallback entries containing a user turn as user messages', () => {
+      const node = document.createElement('div');
+      node.className = 'message-render';
+      const turn = document.createElement('div');
+      turn.className = 'user-turn';
+      turn.textContent = 'hi';
+      node.appendChild(turn);
+      expect(buildFallbackEntry(node, 'u').isUser).toBe(true);
     });
 
     it('truncates previews longer than 80 chars with an ellipsis', () => {
-      const long = 'a'.repeat(120);
-      const messages = [
-        buildMessage({ messageId: 'a', text: long, isCreatedByUser: true }),
-        buildMessage({ messageId: 'b', text: 'short' }),
-        buildMessage({ messageId: 'c', text: 'also short', isCreatedByUser: true }),
-      ];
-      const { container } = renderNav(messages);
-      const preview = container.querySelectorAll('[data-testid="hover-card-content"] p')[0];
-      const text = preview?.textContent ?? '';
-      expect(text.endsWith('...')).toBe(true);
-      expect(text.length).toBe(83);
+      const entry = buildEntry(
+        'a',
+        asTMessage(buildMessage({ messageId: 'a', text: 'a'.repeat(120) })),
+      );
+      expect(entry.preview.endsWith('...')).toBe(true);
+      expect(entry.preview.length).toBe(83);
     });
 
     it('skips sparse content entries when deriving preview text', () => {
-      const messages = [
-        buildMessage({
-          messageId: 'a',
-          text: '',
-          isCreatedByUser: true,
-          content: [undefined, { type: 'text', text: 'content-preview' }],
-        }),
-        buildMessage({ messageId: 'b', text: 'bravo' }),
-        buildMessage({ messageId: 'c', text: 'charlie', isCreatedByUser: true }),
-      ];
-      const { container } = renderNav(messages);
-      const preview = container.querySelectorAll('[data-testid="hover-card-content"] p')[0];
-      expect(preview).toHaveTextContent('content-preview');
+      const entry = buildEntry(
+        'a',
+        asTMessage(
+          buildMessage({
+            messageId: 'a',
+            text: '',
+            content: [undefined, { type: 'text', text: 'content-preview' }],
+          }),
+        ),
+      );
+      expect(entry.preview).toBe('content-preview');
+    });
+  });
+
+  describe('rib magnification', () => {
+    it('peaks at the pointer and decays to zero at the influence radius', () => {
+      expect(magnifyFalloff(0, 50)).toBeCloseTo(1);
+      expect(magnifyFalloff(50, 50)).toBe(0);
+      expect(magnifyFalloff(100, 50)).toBe(0);
+    });
+
+    it('decreases monotonically with distance within the radius', () => {
+      const near = magnifyFalloff(10, 50);
+      const mid = magnifyFalloff(25, 50);
+      const far = magnifyFalloff(40, 50);
+      expect(near).toBeGreaterThan(mid);
+      expect(mid).toBeGreaterThan(far);
+    });
+
+    it('magnifies every message rib uniformly and keeps the end marker square', () => {
+      const user = ribDimsFor({ id: 'u', isUser: true, preview: '' });
+      const assistant = ribDimsFor({ id: 'a', isUser: false, preview: '' });
+      const end = ribDimsFor({ id: 'e', isUser: false, preview: '', isEnd: true });
+      expect(assistant.baseW).toBe(user.baseW);
+      expect(assistant.peakW).toBe(user.peakW);
+      expect(user.peakW).toBeGreaterThan(user.baseW);
+      expect(end.baseW).toBe(end.baseH);
+      expect(end.peakW).toBe(end.peakH);
     });
   });
 
@@ -395,10 +460,8 @@ describe('MessageNav', () => {
       expect(current).toHaveLength(1);
       expect(current[0]).toHaveAttribute('data-msg-id', 'a');
 
-      for (const id of ['a', 'b', 'c']) {
-        const indicator = container.querySelector(`[data-msg-id="${id}"] span`);
-        expect(indicator?.className).toContain('h-[5px]');
-      }
+      const activeLine = container.querySelector('[aria-current="true"] span');
+      expect(activeLine?.className).toContain('bg-gray-800');
     });
 
     it('chevron buttons expose a disabled state when there is nothing to navigate to', () => {
@@ -759,6 +822,176 @@ describe('MessageNav', () => {
     });
   });
 
+  describe('click to jump', () => {
+    it('jumps to the hovered (focused) message when the column is clicked off a rib line', () => {
+      const messages = [
+        buildMessage({ messageId: 'a', text: 'alpha', isCreatedByUser: true }),
+        buildMessage({ messageId: 'b', text: 'bravo' }),
+        buildMessage({ messageId: 'c', text: 'charlie', isCreatedByUser: true }),
+      ];
+      const { container, scrollable } = renderNav(messages);
+      const column = container.querySelector('nav > div') as HTMLDivElement;
+      column.getBoundingClientRect = () => ({ top: 0, bottom: 50, height: 50 }) as DOMRect;
+
+      const writes: number[] = [];
+      Object.defineProperty(scrollable, 'scrollTop', {
+        get: () => 0,
+        set: (v: number) => writes.push(v),
+        configurable: true,
+      });
+
+      act(() => {
+        fireEvent.pointerMove(column, { pointerId: 1, clientY: 5 });
+        jest.advanceTimersByTime(120);
+      });
+
+      act(() => {
+        fireEvent.click(column);
+        jest.advanceTimersByTime(32);
+      });
+
+      expect(writes.length).toBeGreaterThan(0);
+    });
+
+    it('highlights only the hovered rib white, dimming the rest', () => {
+      const messages = [
+        buildMessage({ messageId: 'a', text: 'alpha', isCreatedByUser: true }),
+        buildMessage({ messageId: 'b', text: 'bravo' }),
+        buildMessage({ messageId: 'c', text: 'charlie', isCreatedByUser: true }),
+      ];
+      const { container } = renderNav(messages);
+      const column = container.querySelector('nav > div') as HTMLDivElement;
+      column.getBoundingClientRect = () => ({ top: 0, bottom: 50, height: 50 }) as DOMRect;
+
+      act(() => {
+        fireEvent.pointerMove(column, { pointerId: 1, clientY: 5 });
+        jest.advanceTimersByTime(20);
+      });
+
+      const ribs = Array.from(container.querySelectorAll('[data-msg-id]'));
+      const white = ribs.filter((r) => r.querySelector('span')?.className.includes('bg-gray-800'));
+      expect(white).toHaveLength(1);
+      expect(white[0]).toHaveAttribute('data-msg-id', 'a');
+    });
+  });
+
+  describe('keyboard accessibility', () => {
+    function setupFocusableNav() {
+      const messages = [
+        buildMessage({ messageId: 'a', text: 'alpha', isCreatedByUser: true }),
+        buildMessage({ messageId: 'b', text: 'bravo' }),
+        buildMessage({ messageId: 'c', text: 'charlie', isCreatedByUser: true }),
+      ];
+      const result = renderNav(messages);
+      const column = result.container.querySelector('nav > div') as HTMLDivElement;
+      column.getBoundingClientRect = () => ({ top: 0, bottom: 50, height: 50 }) as DOMRect;
+      return { ...result, column };
+    }
+
+    it('highlights and previews a rib when it receives keyboard focus, like hover', () => {
+      const { container, column } = setupFocusableNav();
+      const ribA = container.querySelector('[data-msg-id="a"]') as HTMLElement;
+
+      act(() => {
+        ribA.dispatchEvent(new FocusEvent('focusin', { bubbles: true }));
+        jest.advanceTimersByTime(80);
+      });
+
+      expect(ribA.querySelector('span')?.className).toContain('bg-gray-800');
+      const tip = document.body.querySelector('[role="tooltip"]');
+      expect(tip).not.toBeNull();
+      expect(tip).toHaveTextContent('alpha');
+      expect(column).toBeDefined();
+    });
+
+    it('clears the highlight and preview when focus leaves the rail', () => {
+      const { container } = setupFocusableNav();
+      const ribA = container.querySelector('[data-msg-id="a"]') as HTMLElement;
+
+      act(() => {
+        ribA.dispatchEvent(new FocusEvent('focusin', { bubbles: true }));
+        jest.advanceTimersByTime(80);
+      });
+      act(() => {
+        ribA.dispatchEvent(
+          new FocusEvent('focusout', { bubbles: true, relatedTarget: document.body }),
+        );
+      });
+
+      expect(document.body.querySelector('[role="tooltip"]')).toBeNull();
+      const white = Array.from(container.querySelectorAll('[data-msg-id] span')).filter((s) =>
+        s.className.includes('bg-gray-800'),
+      );
+      expect(white).toHaveLength(0);
+    });
+  });
+
+  describe('preview live sync', () => {
+    it('refreshes the open tooltip text when the hovered message updates in place', () => {
+      const messages = [
+        buildMessage({ messageId: 'a', text: 'alpha', isCreatedByUser: true }),
+        buildMessage({ messageId: 'b', text: 'bravo' }),
+        buildMessage({ messageId: 'c', text: 'charlie', isCreatedByUser: true }),
+      ];
+      const { container } = renderNav(messages);
+      const column = container.querySelector('nav > div') as HTMLDivElement;
+      column.getBoundingClientRect = () => ({ top: 0, bottom: 50, height: 50 }) as DOMRect;
+
+      act(() => {
+        fireEvent.pointerMove(column, { pointerId: 1, clientY: 5 });
+        jest.advanceTimersByTime(80);
+      });
+      expect(document.body.querySelector('[role="tooltip"]')).toHaveTextContent('alpha');
+
+      // Message text updates in place (e.g. streaming). A re-render happens without
+      // the pointer leaving the rail; the tooltip should reflect the new preview.
+      mockUseGetMessagesByConvoId.mockReturnValue({
+        data: [
+          buildMessage({ messageId: 'a', text: 'alpha streamed more', isCreatedByUser: true }),
+          buildMessage({ messageId: 'b', text: 'bravo' }),
+          buildMessage({ messageId: 'c', text: 'charlie', isCreatedByUser: true }),
+        ],
+      });
+      const io = MockIntersectionObserver.last();
+      act(() => {
+        io!.trigger([{ target: document.getElementById('a')!, isIntersecting: true }]);
+        jest.advanceTimersByTime(20);
+      });
+      act(() => {
+        jest.advanceTimersByTime(260);
+      });
+
+      expect(document.body.querySelector('[role="tooltip"]')).toHaveTextContent(
+        'alpha streamed more',
+      );
+    });
+  });
+
+  describe('browser compatibility', () => {
+    it('uses legacy MediaQueryList listeners when addEventListener is unavailable', () => {
+      const original = window.matchMedia;
+      const addListener = jest.fn();
+      const removeListener = jest.fn();
+      window.matchMedia = (() => ({ matches: false, addListener, removeListener })) as never;
+      try {
+        const messages = [
+          buildMessage({ messageId: 'a', text: 'alpha', isCreatedByUser: true }),
+          buildMessage({ messageId: 'b', text: 'bravo' }),
+          buildMessage({ messageId: 'c', text: 'charlie', isCreatedByUser: true }),
+        ];
+        let result: ReturnType<typeof renderNav> | undefined;
+        expect(() => {
+          result = renderNav(messages);
+        }).not.toThrow();
+        expect(addListener).toHaveBeenCalledTimes(1);
+        result?.unmount();
+        expect(removeListener).toHaveBeenCalledTimes(1);
+      } finally {
+        window.matchMedia = original;
+      }
+    });
+  });
+
   describe('drag to scroll', () => {
     function setupDraggableNav() {
       const messages = Array.from({ length: 5 }, (_, i) =>