feat: Enhance Stream Management with Abort Functionality

- Updated the abort endpoint to support aborting ongoing generation streams using either streamId or conversationId.
- Introduced a new mutation hook `useAbortStreamMutation` for client-side integration.
- Added `useStreamStatus` query to monitor stream status and facilitate resuming conversations.
- Enhanced `useChatHelpers` to incorporate abort functionality when stopping generation.
- Improved `useResumableSSE` to handle stream errors and token refresh seamlessly.
- Updated `useResumeOnLoad` to check for active streams and resume conversations appropriately.

client/src/data-provider/SSE/index.ts

@@ -0,0 +1,2 @@
+export * from './queries';
+export * from './mutations';

client/src/data-provider/SSE/mutations.ts

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+import { useMutation } from '@tanstack/react-query';
+import { request } from 'librechat-data-provider';
+
+export interface AbortStreamParams {
+  /** The stream ID to abort (if known) */
+  streamId?: string;
+  /** The conversation ID to abort (backend will look up the job) */
+  conversationId?: string;
+}
+
+export interface AbortStreamResponse {
+  success: boolean;
+  aborted?: string;
+  error?: string;
+}
+
+/**
+ * Abort an ongoing generation stream.
+ * The backend will emit a `done` event with `aborted: true` to the SSE stream,
+ * allowing the client to handle cleanup via the normal event flow.
+ *
+ * Can pass either streamId or conversationId - backend will find the job.
+ */
+export const abortStream = async (params: AbortStreamParams): Promise<AbortStreamResponse> => {
+  console.log('[abortStream] Calling abort endpoint with params:', params);
+  const result = (await request.post('/api/agents/chat/abort', params)) as AbortStreamResponse;
+  console.log('[abortStream] Abort response:', result);
+  return result;
+};
+
+/**
+ * React Query mutation hook for aborting a generation stream.
+ * Use this when the user explicitly clicks the stop button.
+ */
+export function useAbortStreamMutation() {
+  return useMutation({
+    mutationFn: abortStream,
+  });
+}

client/src/data-provider/SSE/queries.ts

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+import { useQuery } from '@tanstack/react-query';
+import { request } from 'librechat-data-provider';
+import type { Agents } from 'librechat-data-provider';
+
+export interface StreamStatusResponse {
+  active: boolean;
+  streamId?: string;
+  status?: 'running' | 'complete' | 'error' | 'aborted';
+  chunkCount?: number;
+  aggregatedContent?: Array<{ type: string; text?: string }>;
+  createdAt?: number;
+  resumeState?: Agents.ResumeState;
+}
+
+/**
+ * Query key for stream status
+ */
+export const streamStatusQueryKey = (conversationId: string) => ['streamStatus', conversationId];
+
+/**
+ * Fetch stream status for a conversation
+ */
+export const fetchStreamStatus = async (conversationId: string): Promise<StreamStatusResponse> => {
+  console.log('[fetchStreamStatus] Fetching status for:', conversationId);
+  const result = await request.get<StreamStatusResponse>(
+    `/api/agents/chat/status/${conversationId}`,
+  );
+  console.log('[fetchStreamStatus] Result:', result);
+  return result;
+};
+
+/**
+ * React Query hook for checking if a conversation has an active generation stream.
+ * Only fetches when conversationId is provided and resumable streams are enabled.
+ */
+export function useStreamStatus(conversationId: string | undefined, enabled = true) {
+  return useQuery({
+    queryKey: streamStatusQueryKey(conversationId || ''),
+    queryFn: () => fetchStreamStatus(conversationId!),
+    enabled: !!conversationId && enabled,
+    staleTime: 1000, // Consider stale after 1 second
+    refetchOnMount: true,
+    refetchOnWindowFocus: true,
+    retry: false,
+  });
+}