fix: reject DXF files missing EOF marker

Add regression coverage for issue #1.

tests/test_r2c.py

@@ -216,6 +216,14 @@ class DrawingReconstructionTests(unittest.TestCase):
                 with self.assertRaisesRegex(ValueError, '관로 단면'):
                     r2c.specification_model(self.model, row)
 
+    def test_upload_rejects_dxf_missing_end_marker(self):
+        lines = self.raw.splitlines(keepends=True)
+        self.assertEqual(lines[-1].strip(), b'EOF')
+        truncated = b''.join(lines[:-2])
+        status, payload = self.api_request(truncated)
+        self.assertEqual(status, 422)
+        self.assertIn('EOF', payload['error'])
+
     def test_spline_validation_and_valid_linear_interpolation(self):
         def spline(weights=('1', '1'), knots=('0', '0', '1', '1'), degree='1'):
             return {'type': 'SPLINE', 'tags': [