feat(US2): image quad extraction — POST /api/v1/image/extract

- app/models/image_models.py: BBox, QuadrupleItem, ImageExtract{Request,Response}
- app/services/image_service.py: download → base64 LLM → bbox clamp → crop upload
- app/routers/image.py: POST /image/extract handler
- tests: 4 service + 3 router tests, 7/7 passing

tests/test_image_service.py

@@ -0,0 +1,102 @@
+import io
+import json
+import pytest
+import numpy as np
+import cv2
+from unittest.mock import AsyncMock
+
+from app.core.exceptions import LLMParseError
+from app.models.image_models import ImageExtractRequest
+
+
+def _make_test_image_bytes(width=100, height=80) -> bytes:
+    img = np.zeros((height, width, 3), dtype=np.uint8)
+    img[10:50, 10:60] = (255, 0, 0)  # blue rectangle
+    _, buf = cv2.imencode(".jpg", img)
+    return buf.tobytes()
+
+
+SAMPLE_QUADS_JSON = json.dumps([
+    {
+        "subject": "电缆接头",
+        "predicate": "位于",
+        "object": "配电箱左侧",
+        "qualifier": "2024年检修",
+        "bbox": {"x": 10, "y": 10, "w": 40, "h": 30},
+    }
+])
+
+
+@pytest.fixture
+def image_bytes():
+    return _make_test_image_bytes()
+
+
+@pytest.fixture
+def req():
+    return ImageExtractRequest(file_path="image/test.jpg", task_id=1)
+
+
+@pytest.mark.asyncio
+async def test_extract_quads_returns_items(mock_llm, mock_storage, image_bytes, req):
+    mock_storage.download_bytes = AsyncMock(return_value=image_bytes)
+    mock_llm.chat_vision = AsyncMock(return_value=SAMPLE_QUADS_JSON)
+    mock_storage.upload_bytes = AsyncMock(return_value=None)
+
+    from app.services.image_service import extract_quads
+    result = await extract_quads(req, mock_llm, mock_storage)
+
+    assert len(result.items) == 1
+    item = result.items[0]
+    assert item.subject == "电缆接头"
+    assert item.predicate == "位于"
+    assert item.bbox.x == 10
+    assert item.bbox.y == 10
+    assert item.cropped_image_path == "crops/1/0.jpg"
+
+
+@pytest.mark.asyncio
+async def test_crop_is_uploaded(mock_llm, mock_storage, image_bytes, req):
+    mock_storage.download_bytes = AsyncMock(return_value=image_bytes)
+    mock_llm.chat_vision = AsyncMock(return_value=SAMPLE_QUADS_JSON)
+    mock_storage.upload_bytes = AsyncMock(return_value=None)
+
+    from app.services.image_service import extract_quads
+    await extract_quads(req, mock_llm, mock_storage)
+
+    # upload_bytes called once for the crop
+    mock_storage.upload_bytes.assert_called_once()
+    call_args = mock_storage.upload_bytes.call_args
+    assert call_args.args[1] == "crops/1/0.jpg"
+
+
+@pytest.mark.asyncio
+async def test_out_of_bounds_bbox_is_clamped(mock_llm, mock_storage, req):
+    img = _make_test_image_bytes(width=50, height=40)
+    mock_storage.download_bytes = AsyncMock(return_value=img)
+
+    # bbox goes outside image boundary
+    oob_json = json.dumps([{
+        "subject": "test",
+        "predicate": "rel",
+        "object": "obj",
+        "qualifier": None,
+        "bbox": {"x": 30, "y": 20, "w": 100, "h": 100},  # extends beyond 50x40
+    }])
+    mock_llm.chat_vision = AsyncMock(return_value=oob_json)
+    mock_storage.upload_bytes = AsyncMock(return_value=None)
+
+    from app.services.image_service import extract_quads
+    # Should not raise; bbox is clamped
+    result = await extract_quads(req, mock_llm, mock_storage)
+    assert len(result.items) == 1
+
+
+@pytest.mark.asyncio
+async def test_llm_parse_error_raised(mock_llm, mock_storage, image_bytes, req):
+    mock_storage.download_bytes = AsyncMock(return_value=image_bytes)
+    mock_llm.chat_vision = AsyncMock(return_value="bad json {{")
+
+    from app.services.image_service import extract_quads
+    with pytest.raises(LLMParseError):
+        await extract_quads(req, mock_llm, mock_storage)