♻️ refactor: On-demand MCP connections: remove proactive reconnect, default to available (#11839)

* feat: Implement reconnection staggering and backoff jitter for MCP connections

- Enhanced the reconnection logic in OAuthReconnectionManager to stagger reconnection attempts for multiple servers, reducing the risk of connection storms.
- Introduced a backoff delay with random jitter in MCPConnection to improve reconnection behavior during network issues.
- Updated the ConnectionsRepository to handle multiple server connections concurrently with a defined concurrency limit.

Added tests to ensure the new reconnection strategy works as intended.

* refactor: Update MCP server query configuration for improved data freshness

- Reduced stale time from 5 minutes to 30 seconds to ensure quicker updates on server initialization.
- Enabled refetching on window focus and mount to enhance data accuracy during user interactions.

* ♻️  refactor: On-demand MCP connections; remove proactive reconnection, default to available

  - Remove reconnectServers() from refresh controller (connection storm root cause)
  - Stop gating server selection on connection status; add to selection immediately
  - Render agent panel tools from DB cache, not live connection status
  - Proceed to cached tools on init failure (only gate on OAuth)
  - Remove unused batchToggleServers()
  - Reduce useMCPServersQuery staleTime from 5min to 30s, enable refetchOnMount/WindowFocus

* refactor: Optimize MCP tool initialization and server connection logic

- Adjusted tool initialization to only occur if no cached tools are available, improving efficiency.
- Updated comments for clarity on server connection and tool fetching processes.
- Removed unnecessary connection status checks during server selection to streamline the user experience.

client/src/components/SidePanel/Agents/MCPTools.tsx

@@ -46,7 +46,7 @@ export default function MCPTools({
               return null;
             }
 
-            if (serverInfo.isConnected) {
+            if (serverInfo?.tools?.length && serverInfo.tools.length > 0) {
               return (
                 <MCPTool key={`${serverInfo.serverName}-${agentId}`} serverInfo={serverInfo} />
               );

client/src/components/Tools/MCPToolSelectDialog.tsx

@@ -96,17 +96,17 @@ function MCPToolSelectDialog({
         await new Promise((resolve) => setTimeout(resolve, 500));
       }
 
-      // Then initialize server if needed
+      // Only initialize if no cached tools exist; skip if tools are already available from DB
       const serverInfo = mcpServersMap.get(serverName);
-      if (!serverInfo?.isConnected) {
+      if (!serverInfo?.tools?.length) {
         const result = await initializeServer(serverName);
-        if (result?.success && result.oauthRequired && result.oauthUrl) {
+        if (result?.oauthRequired && result.oauthUrl) {
           setIsInitializing(null);
-          return;
+          return; // OAuth flow must complete first
         }
       }
 
-      // Finally, add tools to form
+      // Add tools to form (refetches from backend's persisted cache)
       await addToolsToForm(serverName);
       setIsInitializing(null);
     } catch (error) {