fix: eliminate SSE buffering through Nginx proxy

Add 2 KB padding comment after headers to push past proxy buffer
threshold, enable TCP_NODELAY on the socket, and remove erroneous
chunked_transfer_encoding off from Nginx that caused full response
buffering.

backend/src/routes/import.ts

@@ -32,6 +32,15 @@ function sseWrite(res: import('express').Response, data: Record<string, unknown>
   res.write(`data: ${JSON.stringify(data)}\n\n`);
 }
 
+/**
+ * Send a 2 KB comment block to push past any proxy buffering threshold.
+ * Nginx and other reverse proxies often buffer the first few KB before
+ * starting to stream — this padding forces the initial flush.
+ */
+function ssePadding(res: import('express').Response) {
+  res.write(`: ${' '.repeat(2048)}\n\n`);
+}
+
 const router = Router();
 
 router.post(
@@ -60,7 +69,9 @@ router.post(
       res.setHeader('Cache-Control', 'no-cache');
       res.setHeader('Connection', 'keep-alive');
       res.setHeader('X-Accel-Buffering', 'no');
+      res.socket?.setNoDelay(true);
       res.flushHeaders();
+      ssePadding(res);
 
       try {
         const converted = await convertPdfToStatementStreaming(
@@ -79,12 +90,6 @@ router.post(
           return;
         }
 
-        sseWrite(res, {
-          stage: 'import',
-          progress: 88,
-          message: 'Импорт в базу данных...',
-        });
-
         const result = await importStatement(converted);
         if (isValidationError(result)) {
           sseWrite(res, {

backend/src/services/pdfToStatement.ts

@@ -137,7 +137,7 @@ export async function convertPdfToStatement(
     return {
       status: 502,
       error: 'BAD_GATEWAY',
-      message: 'Временная ошибка конвертации',
+      message: extractLlmErrorMessage(err),
     };
   }
 }
@@ -146,7 +146,7 @@ export type ProgressStage = 'pdf' | 'llm' | 'import';
 export type OnProgress = (stage: ProgressStage, progress: number, message: string) => void;
 
 const LLM_PROGRESS_MIN = 10;
-const LLM_PROGRESS_MAX = 85;
+const LLM_PROGRESS_MAX = 98;
 const LLM_PROGRESS_RANGE = LLM_PROGRESS_MAX - LLM_PROGRESS_MIN;
 const THROTTLE_MS = 300;
 
@@ -248,11 +248,25 @@ export async function convertPdfToStatementStreaming(
     return {
       status: 502,
       error: 'BAD_GATEWAY',
-      message: 'Временная ошибка конвертации',
+      message: extractLlmErrorMessage(err),
     };
   }
 }
 
+function extractLlmErrorMessage(err: unknown): string {
+  const raw = String(
+    (err as Record<string, unknown>)?.message ??
+    (err as Record<string, Record<string, unknown>>)?.error?.message ?? '',
+  );
+  if (/context.length|n_ctx|too.many.tokens|maximum.context/i.test(raw)) {
+    return 'PDF-файл слишком большой для обработки. Попробуйте файл с меньшим количеством операций или используйте модель с большим контекстным окном.';
+  }
+  if (/timeout|timed?\s*out|ETIMEDOUT|ECONNREFUSED/i.test(raw)) {
+    return 'LLM-сервер не отвечает. Проверьте, что сервер запущен и доступен.';
+  }
+  return 'Временная ошибка конвертации';
+}
+
 function parseConversionResult(content: string): StatementFile | PdfConversionError {
   const jsonMatch = content.match(/\{[\s\S]*\}/);
   const jsonStr = jsonMatch ? jsonMatch[0] : content;

frontend/nginx.conf

@@ -15,7 +15,6 @@ server {
         proxy_connect_timeout 5s;
         proxy_read_timeout 600s;
         proxy_buffering off;
-        chunked_transfer_encoding off;
         client_max_body_size 15m;
     }
 

frontend/src/components/ImportModal.tsx

@@ -66,13 +66,11 @@ export function ImportModal({ onClose, onDone }: Props) {
         onClose();
       }
     } else {
-      if (result || importState.error) clearImport();
       onClose();
     }
   };
 
   const handleDone = () => {
-    clearImport();
     onDone();
   };
 

frontend/src/components/Layout.tsx

@@ -4,7 +4,7 @@ import { useAuth } from '../context/AuthContext';
 import { useImport } from '../context/ImportContext';
 
 function ImportProgressBar() {
-  const { importState, clearImport } = useImport();
+  const { importState, clearImport, openModal } = useImport();
   const [visible, setVisible] = useState(false);
   const hideTimerRef = useRef<ReturnType<typeof setTimeout> | undefined>(undefined);
 
@@ -31,9 +31,9 @@ function ImportProgressBar() {
 
   const handleClick = useCallback(() => {
     if (hideTimerRef.current) clearTimeout(hideTimerRef.current);
+    openModal();
     setVisible(false);
-    clearImport();
+  }, [openModal]);
-  }, [clearImport]);
 
   if (!visible) return null;
 

frontend/src/context/ImportContext.tsx

@@ -20,6 +20,9 @@ export interface ImportProgress {
 
 interface ImportContextValue {
   importState: ImportProgress;
+  showModal: boolean;
+  openModal: () => void;
+  closeModal: () => void;
   startImport: (file: File) => void;
   clearImport: () => void;
 }
@@ -35,8 +38,12 @@ const ImportContext = createContext<ImportContextValue | null>(null);
 
 export function ImportProvider({ children }: { children: ReactNode }) {
   const [importState, setImportState] = useState<ImportProgress>(INITIAL);
+  const [showModal, setShowModal] = useState(false);
   const runningRef = useRef(false);
 
+  const openModal = useCallback(() => setShowModal(true), []);
+  const closeModal = useCallback(() => setShowModal(false), []);
+
   const startImport = useCallback((file: File) => {
     if (runningRef.current) return;
     runningRef.current = true;
@@ -92,7 +99,9 @@ export function ImportProvider({ children }: { children: ReactNode }) {
   }, []);
 
   return (
-    <ImportContext.Provider value={{ importState, startImport, clearImport }}>
+    <ImportContext.Provider value={{
+      importState, showModal, openModal, closeModal, startImport, clearImport,
+    }}>
       {children}
     </ImportContext.Provider>
   );

frontend/src/pages/HistoryPage.tsx

@@ -18,6 +18,7 @@ import { TransactionTable } from '../components/TransactionTable';
 import { Pagination } from '../components/Pagination';
 import { EditTransactionModal } from '../components/EditTransactionModal';
 import { ImportModal } from '../components/ImportModal';
+import { useImport } from '../context/ImportContext';
 import { toISODate } from '../utils/format';
 
 const PARAM_KEYS = [
@@ -125,7 +126,7 @@ export function HistoryPage() {
   const [accounts, setAccounts] = useState<Account[]>([]);
   const [categories, setCategories] = useState<Category[]>([]);
   const [editingTx, setEditingTx] = useState<Transaction | null>(null);
-  const [showImport, setShowImport] = useState(false);
+  const { showModal: showImport, openModal: openImport, closeModal: closeImport, clearImport } = useImport();
 
   useEffect(() => {
     getAccounts().then(setAccounts).catch(() => {});
@@ -197,7 +198,8 @@ export function HistoryPage() {
   };
 
   const handleImportDone = () => {
-    setShowImport(false);
+    closeImport();
+    clearImport();
     fetchData();
     getAccounts().then(setAccounts).catch(() => {});
   };
@@ -208,7 +210,7 @@ export function HistoryPage() {
         <h1>История операций</h1>
         <button
           className="btn btn-primary"
-          onClick={() => setShowImport(true)}
+          onClick={openImport}
         >
           Импорт выписки
         </button>
@@ -262,7 +264,7 @@ export function HistoryPage() {
 
       {showImport && (
         <ImportModal
-          onClose={() => setShowImport(false)}
+          onClose={closeImport}
           onDone={handleImportDone}
         />
       )}