diff --git a/internal/adapter/openai/file_refs.go b/internal/adapter/openai/file_refs.go
index 6f31ee6..adf49e1 100644
--- a/internal/adapter/openai/file_refs.go
+++ b/internal/adapter/openai/file_refs.go
@@ -52,8 +52,18 @@ func appendOpenAIRefFileIDs(out *[]string, seen map[string]struct{}, raw any) {
 				addOpenAIRefFileID(out, seen, fileID)
 			}
 		}
+		// Recurse into potential containers. Note: we do NOT recurse into 'content' or 'input'
+		// if they are plain strings (handled by the top-level switch), but they are usually
+		// nested inside the map branch anyway.
+		// To be safe, we only recurse into these known container keys.
 		for _, key := range []string{"ref_file_ids", "file_ids", "attachments", "messages", "input", "content", "files", "items", "data", "source"} {
 			if nested, ok := x[key]; ok {
+				// If it's a message content that is a string, we must NOT treat it as an ID.
+				if key == "content" || key == "input" {
+					if _, ok := nested.(string); ok {
+						continue
+					}
+				}
 				appendOpenAIRefFileIDs(out, seen, nested)
 			}
 		}
diff --git a/internal/deepseek/client_completion.go b/internal/deepseek/client_completion.go
index cab2cab..c27a88f 100644
--- a/internal/deepseek/client_completion.go
+++ b/internal/deepseek/client_completion.go
@@ -51,6 +51,7 @@ func (c *Client) streamPost(ctx context.Context, doer trans.Doer, url string, he
 	if err != nil {
 		return nil, err
 	}
+	headers = c.jsonHeaders(headers)
 	clients := c.requestClientsFromContext(ctx)
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(b))
 	if err != nil {
diff --git a/internal/deepseek/constants.go b/internal/deepseek/constants.go
index 961c3cf..577725f 100644
--- a/internal/deepseek/constants.go
+++ b/internal/deepseek/constants.go
@@ -25,6 +25,7 @@ var defaultBaseHeaders = map[string]string{
 	"Host":              "chat.deepseek.com",
 	"User-Agent":        "DeepSeek/1.8.0 Android/35",
 	"Accept":            "application/json",
+	"Content-Type":      "application/json",
 	"x-client-platform": "android",
 	"x-client-version":  "1.8.0",
 	"x-client-locale":   "zh_CN",