docs(openai): document force HTTP fallback

backend/internal/config/config_test.go

@@ -553,6 +553,15 @@ func TestLoadOpenAIWSClientFirstMessageTimeoutFromEnv(t *testing.T) {
 	require.Equal(t, 120, cfg.Gateway.OpenAIWS.ClientFirstMessageTimeoutSeconds)
 }
 
+func TestLoadOpenAIWSForceHTTPFromEnv(t *testing.T) {
+	resetViperWithJWTSecret(t)
+	t.Setenv("GATEWAY_OPENAI_WS_FORCE_HTTP", "true")
+
+	cfg, err := Load()
+	require.NoError(t, err)
+	require.True(t, cfg.Gateway.OpenAIWS.ForceHTTP)
+}
+
 func TestLoadDefaultOpenAICompactModel(t *testing.T) {
 	resetViperWithJWTSecret(t)
 

backend/internal/service/openai_ws_protocol_resolver_test.go

@@ -87,6 +87,15 @@ func TestOpenAIWSProtocolResolver_Resolve(t *testing.T) {
 		require.Equal(t, "account_force_http", decision.Reason)
 	})
 
+	t.Run("全局强制HTTP无需启用mode router", func(t *testing.T) {
+		cfg := *baseCfg
+		cfg.Gateway.OpenAIWS.ForceHTTP = true
+
+		decision := NewOpenAIWSProtocolResolver(&cfg).Resolve(openAIOAuthEnabled)
+		require.Equal(t, OpenAIUpstreamTransportHTTPSSE, decision.Transport)
+		require.Equal(t, "global_force_http", decision.Reason)
+	})
+
 	t.Run("全局关闭保持HTTP", func(t *testing.T) {
 		cfg := *baseCfg
 		cfg.Gateway.OpenAIWS.Enabled = false