[CLAUDE] App+Infra+Api+FE: Attachment upload E2E

Foundation file-storage:
- IFileStorage interface (Application) — SaveAsync/OpenReadAsync/
  DeleteAsync/Exists. Future swap cho S3/Azure Blob không đổi caller.
- LocalFileStorage (Infrastructure) — resolve Uploads:RootPath từ
  config, path-traversal guard (resolved full path phải stay in root),
  tự tạo directory khi save.
- DI: singleton (stateless).
- Config: dev "uploads", prod "C:\inetpub\solution-erp\uploads".

CQRS:
- UploadContractAttachmentCommand: validate size <=20MB + MIME whitelist
  (pdf, doc/docx, xls/xlsx, png/jpg/jpeg/webp). Sanitize filename
  (strip path components + invalid FS chars + leading dots). Storage
  path: contracts/{contractId}/{attId}_{safeFileName}.
- DownloadContractAttachmentQuery: trả Stream + FileName + ContentType.
- DeleteContractAttachmentCommand: best-effort file delete sau DB remove
  (orphan cleanup job có thể sweep sau).

Api:
- POST /api/contracts/{id}/attachments — multipart/form-data, field
  'file' + form fields 'purpose' + 'note'. RequestSizeLimit 25MB
  (validator enforces 20MB).
- GET /api/contracts/{id}/attachments/{attId}/download — File() stream.
- DELETE /api/contracts/{id}/attachments/{attId}.

FE ContractAttachmentsSection (both apps, identical):
- Drag-drop zone với dragging highlight (brand-500 border + brand-50 bg)
- Purpose selector (DraftExport / ScannedSigned / SealedCopy / Other)
- List có icon per MIME (FileText/Image/File), filename, metadata
  (purpose · size · createdAt), download button (fetch blob + trigger
  browser save với auth header), delete button (confirm dialog)
- Empty state hint về use-case ("bản scan HĐ đã ký ở phase In ký…")

Integrated vào cả 2 ContractDetailPage — ngay dưới phần comments,
trước sidebar lịch sử duyệt.

Unblock E2E workflow: users giờ có thể upload bản scan ký (DangInKy),
scan đóng dấu (DangDongDau) — phase transitions có bằng chứng thật.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fe-admin/src/components/ContractAttachmentsSection.tsx

@@ -0,0 +1,224 @@
+import { useRef, useState, type ChangeEvent, type DragEvent } from 'react'
+import { useMutation, useQueryClient } from '@tanstack/react-query'
+import { toast } from 'sonner'
+import { Paperclip, Upload, Download, Trash2, FileText, Image as ImageIcon, File as FileIcon } from 'lucide-react'
+import { api, TOKEN_KEY } from '@/lib/api'
+import { getErrorMessage } from '@/lib/apiError'
+import { Button } from '@/components/ui/Button'
+import { Select } from '@/components/ui/Select'
+import { EmptyState } from '@/components/EmptyState'
+import type { ContractAttachment } from '@/types/contracts'
+import { cn } from '@/lib/cn'
+
+const PurposeLabel: Record<number, string> = {
+  1: 'File gốc (draft export)',
+  2: 'Bản scan đã ký',
+  3: 'Bản scan đã đóng dấu',
+  99: 'Khác',
+}
+
+const PURPOSES = [1, 2, 3, 99] as const
+
+function fmtSize(n: number) {
+  if (n < 1024) return `${n} B`
+  if (n < 1024 * 1024) return `${(n / 1024).toFixed(1)} KB`
+  return `${(n / (1024 * 1024)).toFixed(1)} MB`
+}
+
+function iconFor(contentType: string) {
+  if (contentType.startsWith('image/')) return ImageIcon
+  if (contentType.includes('pdf') || contentType.includes('word') || contentType.includes('document'))
+    return FileText
+  return FileIcon
+}
+
+const BASE_URL = (import.meta.env.VITE_API_BASE_URL ?? '') + '/api'
+
+export function ContractAttachmentsSection({
+  contractId,
+  attachments,
+  canEdit = true,
+}: {
+  contractId: string
+  attachments: ContractAttachment[]
+  canEdit?: boolean
+}) {
+  const qc = useQueryClient()
+  const inputRef = useRef<HTMLInputElement>(null)
+  const [dragging, setDragging] = useState(false)
+  const [purpose, setPurpose] = useState<number>(2)
+
+  const upload = useMutation({
+    mutationFn: async (file: File) => {
+      const form = new FormData()
+      form.append('file', file)
+      form.append('purpose', String(purpose))
+      const res = await api.post(`/contracts/${contractId}/attachments`, form, {
+        headers: { 'Content-Type': 'multipart/form-data' },
+      })
+      return res.data
+    },
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['contract', contractId] })
+      toast.success('Upload thành công')
+    },
+    onError: err => toast.error(`Upload lỗi: ${getErrorMessage(err)}`),
+  })
+
+  const del = useMutation({
+    mutationFn: async (attId: string) => api.delete(`/contracts/${contractId}/attachments/${attId}`),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['contract', contractId] })
+      toast.success('Đã xóa')
+    },
+    onError: err => toast.error(`Xóa lỗi: ${getErrorMessage(err)}`),
+  })
+
+  function handleFiles(files: FileList | null) {
+    if (!files || files.length === 0) return
+    // Upload each file sequentially so the server respects its own rate limits
+    for (const f of Array.from(files)) upload.mutate(f)
+  }
+
+  function onDrop(e: DragEvent<HTMLDivElement>) {
+    e.preventDefault()
+    setDragging(false)
+    if (!canEdit) return
+    handleFiles(e.dataTransfer.files)
+  }
+
+  function onPick(e: ChangeEvent<HTMLInputElement>) {
+    handleFiles(e.target.files)
+    // Reset so same file can be re-picked if needed
+    e.target.value = ''
+  }
+
+  async function download(att: ContractAttachment) {
+    // Blob fetch via fetch API so we can include auth header + trigger browser save
+    const token = localStorage.getItem(TOKEN_KEY)
+    const res = await fetch(`${BASE_URL}/contracts/${contractId}/attachments/${att.id}/download`, {
+      headers: token ? { Authorization: `Bearer ${token}` } : {},
+    })
+    if (!res.ok) {
+      toast.error(`Tải xuống lỗi (HTTP ${res.status})`)
+      return
+    }
+    const blob = await res.blob()
+    const url = URL.createObjectURL(blob)
+    const a = document.createElement('a')
+    a.href = url
+    a.download = att.fileName
+    document.body.appendChild(a)
+    a.click()
+    a.remove()
+    URL.revokeObjectURL(url)
+  }
+
+  return (
+    <section className="rounded-xl border border-slate-200 bg-white p-5 shadow-sm">
+      <div className="mb-3 flex items-center justify-between">
+        <h2 className="flex items-center gap-2 text-sm font-semibold text-slate-700">
+          <Paperclip className="h-4 w-4" />
+          Tệp đính kèm ({attachments.length})
+        </h2>
+        {canEdit && (
+          <div className="flex items-center gap-2">
+            <Select value={purpose} onChange={e => setPurpose(Number(e.target.value))} className="h-8 w-48 text-xs">
+              {PURPOSES.map(p => (
+                <option key={p} value={p}>
+                  {PurposeLabel[p]}
+                </option>
+              ))}
+            </Select>
+          </div>
+        )}
+      </div>
+
+      {canEdit && (
+        <div
+          onDragOver={e => {
+            e.preventDefault()
+            setDragging(true)
+          }}
+          onDragLeave={() => setDragging(false)}
+          onDrop={onDrop}
+          onClick={() => inputRef.current?.click()}
+          className={cn(
+            'mb-3 cursor-pointer rounded-lg border-2 border-dashed px-4 py-6 text-center transition',
+            dragging ? 'border-brand-500 bg-brand-50' : 'border-slate-300 bg-slate-50/50 hover:bg-slate-50',
+          )}
+        >
+          <Upload className="mx-auto h-5 w-5 text-slate-400" />
+          <div className="mt-2 text-sm font-medium text-slate-600">
+            Kéo thả file vào đây hoặc <span className="text-brand-600">chọn file</span>
+          </div>
+          <div className="mt-0.5 text-xs text-slate-400">PDF / DOCX / XLSX / PNG / JPG · tối đa 20 MB</div>
+          <input
+            ref={inputRef}
+            type="file"
+            multiple
+            onChange={onPick}
+            className="hidden"
+            accept=".pdf,.doc,.docx,.xls,.xlsx,.png,.jpg,.jpeg,.webp"
+          />
+          {upload.isPending && (
+            <div className="mt-2 text-xs text-brand-600">Đang upload…</div>
+          )}
+        </div>
+      )}
+
+      {attachments.length === 0 && !canEdit && (
+        <EmptyState icon={Paperclip} title="Chưa có tệp đính kèm nào" />
+      )}
+
+      {attachments.length > 0 && (
+        <ul className="divide-y divide-slate-100">
+          {attachments.map(a => {
+            const Icon = iconFor(a.contentType)
+            return (
+              <li key={a.id} className="flex items-center gap-3 py-2.5">
+                <div className="flex h-9 w-9 shrink-0 items-center justify-center rounded-md bg-slate-100 text-slate-500">
+                  <Icon className="h-4 w-4" />
+                </div>
+                <div className="min-w-0 flex-1">
+                  <div className="truncate text-sm font-medium text-slate-700">{a.fileName}</div>
+                  <div className="text-xs text-slate-400">
+                    {PurposeLabel[a.purpose] ?? '—'} · {fmtSize(a.fileSize)} ·{' '}
+                    {new Date(a.createdAt).toLocaleString('vi-VN', { dateStyle: 'short', timeStyle: 'short' })}
+                  </div>
+                </div>
+                <div className="flex shrink-0 gap-1">
+                  <button
+                    onClick={() => download(a)}
+                    className="flex h-8 w-8 items-center justify-center rounded-md text-slate-500 transition hover:bg-slate-100 hover:text-slate-700"
+                    title="Tải xuống"
+                  >
+                    <Download className="h-4 w-4" />
+                  </button>
+                  {canEdit && (
+                    <button
+                      onClick={() => {
+                        if (window.confirm(`Xóa tệp "${a.fileName}"?`)) del.mutate(a.id)
+                      }}
+                      disabled={del.isPending}
+                      className="flex h-8 w-8 items-center justify-center rounded-md text-slate-500 transition hover:bg-red-50 hover:text-red-600"
+                      title="Xóa"
+                    >
+                      <Trash2 className="h-4 w-4" />
+                    </button>
+                  )}
+                </div>
+              </li>
+            )
+          })}
+        </ul>
+      )}
+
+      {canEdit && attachments.length === 0 && (
+        <div className="py-2 text-center text-xs text-slate-400">
+          Ví dụ: bản scan HĐ đã ký ở phase "Đang in ký", bản đóng dấu ở phase "Đang đóng dấu".
+        </div>
+      )}
+    </section>
+  )
+}