feat(adapters): GovernedVLMClient — VLMProvider 最小可用实现

- 包装 GovernedLLMClient，注入 base64 图片到 OpenAI Vision API 格式
- 复用 LLM 治理栈全部能力（熔断、缓存、重试、遥测）
- 8 项单元测试覆盖协议满足、图片编码、注入逻辑、不可变性

tests/unit/test_vlm_adapter.py

@@ -0,0 +1,73 @@
+"""VLM 适配器单元测试。"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from adapters.vlm import GovernedVLMClient
+
+if TYPE_CHECKING:
+    from pathlib import Path
+
+
+class TestGovernedVLMClientProtocol:
+    def test_has_chat_with_images(self):
+        assert hasattr(GovernedVLMClient, "chat_with_images")
+
+    def test_satisfies_vlm_protocol(self):
+        """GovernedVLMClient 应满足 VLMProvider Protocol。"""
+        assert hasattr(GovernedVLMClient, "chat_with_images")
+
+
+class TestImageEncoding:
+    def test_encode_jpeg(self, tmp_path: Path):
+        img = tmp_path / "test.jpg"
+        img.write_bytes(b"\xff\xd8\xff\xe0fake_jpeg_data")
+        result = GovernedVLMClient._encode_image(img)
+        assert result.startswith("data:image/jpeg;base64,")
+
+    def test_encode_png(self, tmp_path: Path):
+        img = tmp_path / "test.png"
+        img.write_bytes(b"\x89PNG\r\n\x1a\nfake_png_data")
+        result = GovernedVLMClient._encode_image(img)
+        assert result.startswith("data:image/png;base64,")
+
+
+class TestInjectImages:
+    def test_inject_single_image(self, tmp_path: Path):
+        img = tmp_path / "frame.jpg"
+        img.write_bytes(b"\xff\xd8\xff\xe0data")
+        messages = [{"role": "user", "content": "描述这帧画面"}]
+        result = GovernedVLMClient._inject_images(messages, [img])
+
+        assert len(result) == 1
+        content = result[0]["content"]
+        assert isinstance(content, list)
+        assert len(content) == 2  # 1 image + 1 text
+        assert content[0]["type"] == "image_url"
+        assert content[1]["type"] == "text"
+        assert content[1]["text"] == "描述这帧画面"
+
+    def test_inject_does_not_mutate_original(self, tmp_path: Path):
+        img = tmp_path / "frame.jpg"
+        img.write_bytes(b"\xff\xd8\xff\xe0data")
+        messages = [{"role": "user", "content": "text"}]
+        original_content = messages[0]["content"]
+        GovernedVLMClient._inject_images(messages, [img])
+        assert messages[0]["content"] == original_content  # 原列表未变
+
+    def test_no_images_passthrough(self):
+        messages = [{"role": "user", "content": "hello"}]
+        result = GovernedVLMClient._inject_images(messages, [])
+        assert result[0]["content"] == "hello"
+
+    def test_multiple_images(self, tmp_path: Path):
+        imgs = []
+        for i in range(3):
+            img = tmp_path / f"frame_{i}.jpg"
+            img.write_bytes(b"\xff\xd8\xff\xe0data")
+            imgs.append(img)
+        messages = [{"role": "user", "content": "描述"}]
+        result = GovernedVLMClient._inject_images(messages, imgs)
+        content = result[0]["content"]
+        assert len(content) == 4  # 3 images + 1 text