feat(review): 取证层多源化 + 视觉多图（整体+2x2 象限）

- 新增 evidence_model.py：统一证据模型（source_type + images 列表），访问器兼容旧 image_b64/image_mime 单图字段
- phases/evidence.py：新增 collect() 多源分发 seam（仅 CAD）、capture_images() 整体+等分象限多图（结束复位视口）、sub_windows()
- phases/review.py：多图逐张下采样喂 LLM，payload 增加 source_type
- config.py：EVIDENCE_DETAIL_TILES=4 / EVIDENCE_MAX_IMAGES=5（默认开启多图）
- 新增 tests/test_evidence_model.py，更新 evidence/review 断言与 fakes 归一

tests/test_evidence.py

@@ -55,8 +55,8 @@ def test_collect_frame_assembles_evidence():
     assert ev["dimensions"]["total"] == 2
     assert ev["blocks"]["total"] == 0
     assert ev["polylines"]["total"] == 3
-    assert ev["image_b64"] == "QUJD"
-    assert ev["image_mime"] == "image/png"
+    assert ev["source_type"] == "cad"
+    assert ev["images"] == [{"b64": "QUJD", "mime": "image/png", "label": "overall"}]
 
 
 def test_collect_frame_calls_expected_tools():
@@ -80,12 +80,64 @@ def test_collect_frame_calls_expected_tools():
 def test_collect_frame_without_image():
     ctx = make_ctx(client=build_evidence_client(image=ok_text({})))
     ev = collect_frame(ctx, 1, frame([0, 0, 10, 10]))
-    assert ev["image_b64"] is None
-    assert ev["image_mime"] is None
+    assert ev["images"] == []
 
 
 def test_collect_frame_tolerates_empty_structured_data():
     ctx = make_ctx(client=FakeMcpClient())  # 全部默认 ok_text({})
     ev = collect_frame(ctx, 1, frame([0, 0, 10, 10]))
     assert ev["entities"] == {}
-    assert ev["image_b64"] is None
+    assert ev["images"] == []
+
+
+def test_sub_windows_2x2():
+    from dwg_review.phases.evidence import sub_windows
+
+    win = {"min_x": 0.0, "min_y": 0.0, "max_x": 10.0, "max_y": 10.0}
+    subs = sub_windows(win, 4)
+    assert len(subs) == 4
+    # 行优先：左上 → 右上 → 左下 → 右下
+    assert subs[0] == {"min_x": 0.0, "min_y": 5.0, "max_x": 5.0, "max_y": 10.0}
+    assert subs[1] == {"min_x": 5.0, "min_y": 5.0, "max_x": 10.0, "max_y": 10.0}
+    assert subs[2] == {"min_x": 0.0, "min_y": 0.0, "max_x": 5.0, "max_y": 5.0}
+    assert subs[3] == {"min_x": 5.0, "min_y": 0.0, "max_x": 10.0, "max_y": 5.0}
+
+
+def test_sub_windows_disabled():
+    from dwg_review.phases.evidence import sub_windows
+
+    win = {"min_x": 0.0, "min_y": 0.0, "max_x": 10.0, "max_y": 10.0}
+    assert sub_windows(win, 0) == []
+    assert sub_windows(win, 1) == []
+
+
+def test_collect_frame_captures_multiple_images(monkeypatch):
+    from dwg_review import config
+    from dwg_review.phases.evidence import collect_frame
+
+    monkeypatch.setattr(config, "EVIDENCE_DETAIL_TILES", 4)
+    ctx = make_ctx(client=build_evidence_client())
+    ev = collect_frame(ctx, 1, frame([0, 0, 100, 50]))
+    assert [img["label"] for img in ev["images"]] == [
+        "overall",
+        "tile-1",
+        "tile-2",
+        "tile-3",
+        "tile-4",
+    ]
+
+
+def test_collect_dispatches_cad_source():
+    from dwg_review.phases.evidence import collect
+
+    ctx = make_ctx(client=build_evidence_client())
+    ev = collect(ctx, 1, frame([0, 0, 10, 10]))
+    assert ev is not None
+    assert ev["source_type"] == "cad"
+
+
+def test_collect_returns_none_for_unsupported_source():
+    from dwg_review.phases.evidence import collect
+
+    ctx = make_ctx(client=FakeMcpClient())
+    assert collect(ctx, 1, {"source_type": "pdf", "bbox": [0, 0, 1, 1]}) is None