fix: don't cache "not found" binary result, use ref lock for pagination

- platform.ts: only cache positive findClaudeBinary results so a fresh
  CLI install is detected immediately on next check
- ChatView.tsx: use useRef as atomic lock to prevent double-fetch from
  rapid clicks on "Load earlier messages"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 7418

src/components/chat/ChatView.tsx

@@ -31,6 +31,7 @@ export function ChatView({ sessionId, initialMessages = [], initialHasMore = fal
   const [messages, setMessages] = useState<Message[]>(initialMessages);
   const [hasMore, setHasMore] = useState(initialHasMore);
   const [loadingMore, setLoadingMore] = useState(false);
+  const loadingMoreRef = useRef(false);
   const [streamingContent, setStreamingContent] = useState('');
   const [isStreaming, setIsStreaming] = useState(false);
   const [toolUses, setToolUses] = useState<ToolUseInfo[]>([]);
@@ -113,7 +114,9 @@ export function ChatView({ sessionId, initialMessages = [], initialHasMore = fal
   }, [initialHasMore]);
 
   const loadEarlierMessages = useCallback(async () => {
-    if (loadingMore || !hasMore || messages.length === 0) return;
+    // Use ref as atomic lock to prevent double-fetch from rapid clicks
+    if (loadingMoreRef.current || !hasMore || messages.length === 0) return;
+    loadingMoreRef.current = true;
     setLoadingMore(true);
     try {
       // Use _rowid of the earliest message as cursor
@@ -128,9 +131,10 @@ export function ChatView({ sessionId, initialMessages = [], initialHasMore = fal
         setMessages(prev => [...data.messages, ...prev]);
       }
     } finally {
+      loadingMoreRef.current = false;
       setLoadingMore(false);
     }
-  }, [sessionId, messages, hasMore, loadingMore]);
+  }, [sessionId, messages, hasMore]);
 
   const stopStreaming = useCallback(() => {
     abortControllerRef.current?.abort();

src/lib/platform.ts

@@ -95,14 +95,16 @@ export function getExpandedPath(): string {
   return parts.join(path.delimiter);
 }
 
-// TTL cache for findClaudeBinary to avoid repeated filesystem probes
+// TTL cache for findClaudeBinary to avoid repeated filesystem probes.
+// Only caches "found" results; "not found" is never cached so a fresh
+// install is detected immediately on the next check.
 let _cachedBinaryPath: string | undefined | null = null; // null = not cached
 let _cachedBinaryTimestamp = 0;
 const BINARY_CACHE_TTL = 60_000; // 60 seconds
 
 /**
  * Find and validate the Claude CLI binary.
- * Results are cached for 60s to avoid redundant filesystem probes on every poll.
+ * Positive results are cached for 60s; negative results are never cached.
  */
 export function findClaudeBinary(): string | undefined {
   const now = Date.now();
@@ -111,8 +113,13 @@ export function findClaudeBinary(): string | undefined {
   }
 
   const found = _findClaudeBinaryUncached();
-  _cachedBinaryPath = found;
-  _cachedBinaryTimestamp = now;
+  if (found) {
+    _cachedBinaryPath = found;
+    _cachedBinaryTimestamp = now;
+  } else {
+    // Don't cache "not found" — user may install CLI any moment
+    _cachedBinaryPath = null;
+  }
   return found;
 }