转换器: 图片内容块跨协议互转保留(base64/url)

- 支持 OpenAI image_url ↔ Anthropic image.source(base64/url) 双向转换
- messages→chat / responses→chat 不再丢弃图片块, 保留图文原始顺序
- chat→messages 的 data URL 拆成 base64 source(media_type+data)
- chat→responses 的 image_url 转 input_image
- responses↔messages 经 chat 中转, 六方向全覆盖
- 新增多图/顺序回归测试

Co-Authored-By: Claude <noreply@anthropic.com>

server/internal/proxy/convert/json_chat.go

@@ -137,9 +137,11 @@ func chatMsgToAnthropic(m chatMsg) any {
 					var url string
 					if iu, ok := b["image_url"].(map[string]any); ok {
 						url, _ = iu["url"].(string)
+					} else if s, ok := b["image_url"].(string); ok {
+						url = s
 					}
 					if url != "" {
-						blocks = append(blocks, map[string]any{"type": "image", "source": map[string]any{"type": "url", "url": url}})
+						blocks = append(blocks, anthropicImageBlock(url))
 					}
 				}
 			}
@@ -229,12 +231,18 @@ func anthropicMsgToChat(role string, content json.RawMessage) []any {
 	if json.Unmarshal(content, &blocks) == nil && blocks != nil {
 		var out []any
 		var textParts []string
+		var contentBlocks []any // text / image_url 块，保留原始顺序
 		var toolCalls []any
 		for _, b := range blocks {
 			switch b["type"] {
 			case "text":
 				if t, _ := b["text"].(string); t != "" {
 					textParts = append(textParts, t)
+					contentBlocks = append(contentBlocks, map[string]any{"type": "text", "text": t})
+				}
+			case "image":
+				if cb := chatImageBlock(b); cb != nil {
+					contentBlocks = append(contentBlocks, cb)
 				}
 			case "tool_use":
 				id, _ := b["id"].(string)
@@ -254,9 +262,19 @@ func anthropicMsgToChat(role string, content json.RawMessage) []any {
 				out = append(out, map[string]any{"role": "tool", "tool_call_id": callID, "content": res})
 			}
 		}
-		if len(textParts) > 0 || len(toolCalls) > 0 {
+		hasImage := false
+		for _, cb := range contentBlocks {
+			if m, _ := cb.(map[string]any); m["type"] == "image_url" {
+				hasImage = true
+				break
+			}
+		}
+		if hasImage || len(textParts) > 0 || len(toolCalls) > 0 {
 			msg := map[string]any{"role": role}
-			if len(textParts) > 0 {
+			switch {
+			case hasImage:
+				msg["content"] = contentBlocks
+			case len(textParts) > 0:
 				msg["content"] = strings.Join(textParts, "")
 			}
 			if len(toolCalls) > 0 {
@@ -416,6 +434,58 @@ func intOrNil(p *int, def int) any {
 	return *p
 }
 
+// splitDataURL 解析 data:media_type;base64,data 形式的 URL；非该形式返回 ok=false。
+func splitDataURL(url string) (media, data string, ok bool) {
+	if !strings.HasPrefix(url, "data:") {
+		return "", "", false
+	}
+	i := strings.Index(url, ";base64,")
+	if i < 0 {
+		return "", "", false
+	}
+	return url[len("data:"):i], url[i+len(";base64,"):], true
+}
+
+// chatImageBlock 把 Anthropic image 块转 OpenAI image_url 块。
+// 仅支持 base64 与 url source；其他类型（如 Files API 的 file_id）不支持，跳过。
+func chatImageBlock(b map[string]any) any {
+	src, ok := b["source"].(map[string]any)
+	if !ok {
+		return nil
+	}
+	switch src["type"] {
+	case "base64":
+		media, _ := src["media_type"].(string)
+		data, _ := src["data"].(string)
+		if data == "" {
+			return nil
+		}
+		if media == "" {
+			media = "image/png"
+		}
+		return map[string]any{"type": "image_url", "image_url": map[string]any{"url": "data:" + media + ";base64," + data}}
+	case "url":
+		url, _ := src["url"].(string)
+		if url == "" {
+			return nil
+		}
+		return map[string]any{"type": "image_url", "image_url": map[string]any{"url": url}}
+	}
+	return nil
+}
+
+// anthropicImageBlock 把 OpenAI image_url 的 url 转 Anthropic image 块。
+// data URL → base64 source；http(s) URL → url source。
+func anthropicImageBlock(url string) any {
+	if media, data, ok := splitDataURL(url); ok {
+		if media == "" {
+			media = "image/png"
+		}
+		return map[string]any{"type": "image", "source": map[string]any{"type": "base64", "media_type": media, "data": data}}
+	}
+	return map[string]any{"type": "image", "source": map[string]any{"type": "url", "url": url}}
+}
+
 func rawOrObject(raw json.RawMessage) any {
 	if len(raw) == 0 || string(raw) == "null" {
 		return map[string]any{}