test: add 'max' → 'xhigh' test cases for reasoning effort normalization

Cover the DeepSeek reasoning_effort 'max' alias in:
- TestExtractOpenAIReasoningEffortFromBody
- TestExtractCCReasoningEffortFromBody
- TestExtractResponsesReasoningEffortFromBody

backend/internal/service/gateway_forward_as_chat_completions_test.go

@@ -29,6 +29,12 @@ func TestExtractCCReasoningEffortFromBody(t *testing.T) {
 		require.Equal(t, "xhigh", *got)
 	})
 
+	t.Run("DeepSeek max", func(t *testing.T) {
+		got := extractCCReasoningEffortFromBody([]byte(`{"reasoning_effort":"Max"}`))
+		require.NotNil(t, got)
+		require.Equal(t, "xhigh", *got)
+	})
+
 	t.Run("missing effort", func(t *testing.T) {
 		require.Nil(t, extractCCReasoningEffortFromBody([]byte(`{"model":"gpt-5"}`)))
 	})

backend/internal/service/gateway_forward_as_responses_test.go

@@ -21,6 +21,10 @@ func TestExtractResponsesReasoningEffortFromBody(t *testing.T) {
 	require.NotNil(t, got)
 	require.Equal(t, "high", *got)
 
+	maxGot := ExtractResponsesReasoningEffortFromBody([]byte(`{"model":"deepseek-v4-pro","reasoning":{"effort":"max"}}`))
+	require.NotNil(t, maxGot)
+	require.Equal(t, "xhigh", *maxGot)
+
 	require.Nil(t, ExtractResponsesReasoningEffortFromBody([]byte(`{"model":"claude-sonnet-4.5"}`)))
 }
 

backend/internal/service/openai_gateway_service_hotpath_test.go

@@ -595,6 +595,13 @@ func TestExtractOpenAIReasoningEffortFromBody(t *testing.T) {
 			wantNil:   false,
 			wantValue: "xhigh",
 		},
+		{
+			name:      "DeepSeek max 归一化为 xhigh",
+			body:      []byte(`{"reasoning_effort":"max"}`),
+			model:     "deepseek-v4-pro",
+			wantNil:   false,
+			wantValue: "xhigh",
+		},
 		{
 			name:    "minimal 归一化为空",
 			body:    []byte(`{"reasoning":{"effort":"minimal"}}`),