fix: persist uploads on Render disk and show missing file notice

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/components/detail/ExcelPreview.tsx

@@ -48,6 +48,9 @@ export function ExcelPreview({ fileId, fileName }: ExcelPreviewProps) {
     return (
       <div className="flex h-full w-full flex-col items-center justify-center gap-3 p-6 text-center">
         <p className="text-lg text-white/60">{error}</p>
+        <p className="text-sm text-white/40">
+          서버 재배포 등으로 파일이 삭제되었을 수 있습니다. 단계 수정에서 다시 첨부해 주세요.
+        </p>
         <a
           href={fileDownloadUrl(fileId)}
           className="rounded bg-white/10 px-4 py-2 text-sm font-bold text-white hover:bg-white/20"

frontend/src/components/detail/ResultPreview.tsx

@@ -1,7 +1,7 @@
 import { useState, useEffect, useCallback } from 'react';
 import { createPortal } from 'react-dom';
 import { ExcelPreview } from './ExcelPreview';
-import { fileViewUrl } from '../../lib/apiClient';
+import { fileDownloadUrl, fileViewUrl } from '../../lib/apiClient';
 import { openLinkOnRightMonitor } from '../../lib/dualMonitor';
 import { fileDisplayName, isExcelFile, isVideoFile } from '../../lib/fileDisplay';
 import type { FileRecord, MilestoneLink } from '../../types';
@@ -12,10 +12,32 @@ interface ResultPreviewProps {
   hasSelectedStage: boolean;
 }
 
+function FileMissingNotice({ label, fileId }: { label: string; fileId: string }) {
+  return (
+    <div className="flex max-w-lg flex-col items-center gap-3 px-6 text-center">
+      <p className="text-xl font-bold text-white/70">{label}</p>
+      <p className="text-base leading-relaxed text-white/45">
+        첨부 파일을 서버에서 찾을 수 없습니다.
+        <br />
+        코드 배포·서버 재시작 시 파일이 삭제될 수 있습니다.
+        <br />
+        단계 수정에서 같은 파일을 다시 첨부해 주세요.
+      </p>
+      <a
+        href={fileDownloadUrl(fileId)}
+        className="rounded-lg bg-white/10 px-4 py-2 text-sm font-bold text-white/80 hover:bg-white/20"
+      >
+        다운로드 재시도
+      </a>
+    </div>
+  );
+}
+
 export function ResultPreview({ files, links, hasSelectedStage }: ResultPreviewProps) {
   const [fileId, setFileId] = useState<string | null>(null);
   const [zoom, setZoom] = useState(1);
   const [fullscreen, setFullscreen] = useState(false);
+  const [fileMissing, setFileMissing] = useState(false);
 
   useEffect(() => {
     if (files.length > 0) {
@@ -27,6 +49,25 @@ export function ResultPreview({ files, links, hasSelectedStage }: ResultPreviewP
   }, [files]);
 
   const activeFile = fileId ? files.find((f) => f.id === fileId) ?? null : null;
+
+  useEffect(() => {
+    if (!activeFile || isExcelFile(activeFile)) {
+      setFileMissing(false);
+      return;
+    }
+    let cancelled = false;
+    setFileMissing(false);
+    fetch(fileViewUrl(activeFile.id), { method: 'HEAD' })
+      .then((res) => {
+        if (!cancelled) setFileMissing(!res.ok);
+      })
+      .catch(() => {
+        if (!cancelled) setFileMissing(true);
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [activeFile?.id, activeFile?.mimetype]);
   const fileIndex = activeFile ? files.findIndex((f) => f.id === activeFile.id) : -1;
   const isImage = activeFile?.mimetype.includes('image') ?? false;
   const isVideo = activeFile ? isVideoFile(activeFile) : false;
@@ -54,6 +95,9 @@ export function ResultPreview({ files, links, hasSelectedStage }: ResultPreviewP
       if (isExcel) {
         return <ExcelPreview fileId={activeFile.id} fileName={label} />;
       }
+      if (fileMissing) {
+        return <FileMissingNotice label={label} fileId={activeFile.id} />;
+      }
       const src = fileViewUrl(activeFile.id);
       if (isImage) {
         return (
@@ -63,12 +107,19 @@ export function ResultPreview({ files, links, hasSelectedStage }: ResultPreviewP
             className="max-h-full max-w-full object-contain transition-transform duration-150"
             style={{ transform: `scale(${zoom})` }}
             draggable={false}
+            onError={() => setFileMissing(true)}
           />
         );
       }
       if (isVideo) {
         return (
-          <video src={src} controls className="max-h-full max-w-full" title={label} />
+          <video
+            src={src}
+            controls
+            className="max-h-full max-w-full"
+            title={label}
+            onError={() => setFileMissing(true)}
+          />
         );
       }
       return (