Add time gap indicators and hash anchor navigation to SessionViewer

Time gaps:
- Insert a horizontal divider with duration label ("12m later",
  "1h 30m later") between consecutive visible messages separated
  by more than 5 minutes
- Computed during the display list build pass alongside redacted
  dividers, so no additional traversal is needed

Hash anchor navigation:
- Each message div now has id="msg-{uuid}" for deep linking
- On load, if the URL contains a #msg-* hash, scroll that message
  into view with smooth centering and a 3-second highlight ring
- Works with the copy-link feature added to MessageBubble headers

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/client/components/SessionViewer.tsx

@@ -58,7 +58,22 @@ export function SessionViewer({
     }
   }, [focusedIndex]);
 
-  // Build display list with redacted dividers.
+  // Auto-scroll to hash anchor on load
+  useEffect(() => {
+    const hash = window.location.hash;
+    if (hash && hash.startsWith("#msg-") && messages.length > 0) {
+      requestAnimationFrame(() => {
+        const el = document.getElementById(hash.slice(1));
+        if (el) {
+          el.scrollIntoView({ behavior: "smooth", block: "center" });
+          el.classList.add("search-match-focused", "rounded-xl");
+          setTimeout(() => el.classList.remove("search-match-focused"), 3000);
+        }
+      });
+    }
+  }, [messages.length]);
+
+  // Build display list with redacted dividers and time gaps.
   // Must be called before any early returns to satisfy Rules of Hooks.
   const displayItems = useMemo(() => {
     if (messages.length === 0) return [];
@@ -67,9 +82,11 @@ export function SessionViewer({
     const items: Array<
       | { type: "message"; message: ParsedMessage; messageIndex: number }
       | { type: "redacted_divider"; key: string }
+      | { type: "time_gap"; key: string; duration: string }
     > = [];
 
     let prevWasRedactedGap = false;
+    let prevTimestamp: string | undefined;
     let messageIndex = 0;
     for (const msg of allMessages) {
       if (redactedUuids.has(msg.uuid)) {
@@ -86,6 +103,20 @@ export function SessionViewer({
         });
         prevWasRedactedGap = false;
       }
+      // Insert time gap indicator if > 5 minutes between visible messages
+      if (prevTimestamp && msg.timestamp) {
+        const currTime = new Date(msg.timestamp).getTime();
+        const prevTime = new Date(prevTimestamp).getTime();
+        const gap = currTime - prevTime;
+        if (!isNaN(gap) && gap > 5 * 60 * 1000) {
+          items.push({
+            type: "time_gap",
+            key: `gap-${msg.uuid}`,
+            duration: formatDuration(gap),
+          });
+        }
+      }
+      if (msg.timestamp) prevTimestamp = msg.timestamp;
       items.push({ type: "message", message: msg, messageIndex });
       messageIndex++;
     }
@@ -154,6 +185,17 @@ export function SessionViewer({
           if (item.type === "redacted_divider") {
             return <RedactedDivider key={item.key} />;
           }
+          if (item.type === "time_gap") {
+            return (
+              <div key={item.key} className="flex items-center gap-3 py-2">
+                <div className="flex-1 h-px bg-border-muted" />
+                <span className="text-caption text-foreground-muted tabular-nums flex-shrink-0">
+                  {item.duration} later
+                </span>
+                <div className="flex-1 h-px bg-border-muted" />
+              </div>
+            );
+          }
           const msg = item.message;
           const isMatch =
             searchQuery &&
@@ -163,6 +205,7 @@ export function SessionViewer({
           return (
             <div
               key={msg.uuid}
+              id={`msg-${msg.uuid}`}
               data-msg-index={item.messageIndex}
               className={`animate-fade-in ${isFocused ? "search-match-focused rounded-xl" : ""}`}
               style={{ animationDelay: `${Math.min(idx * 20, 300)}ms`, animationFillMode: "backwards" }}
@@ -184,3 +227,12 @@ export function SessionViewer({
     </div>
   );
 }
+
+function formatDuration(ms: number): string {
+  const minutes = Math.floor(ms / 60000);
+  if (minutes < 60) return `${minutes}m`;
+  const hours = Math.floor(minutes / 60);
+  const remainMinutes = minutes % 60;
+  if (remainMinutes === 0) return `${hours}h`;
+  return `${hours}h ${remainMinutes}m`;
+}