fix(openai): 空 openai_capabilities 不再排除 OAuth 账号的文本调度（#5530）

backend/internal/service/account.go

@@ -1861,18 +1861,30 @@ func (a *Account) openAIEndpointCapabilitySet() (map[string]bool, bool) {
 		result[value] = true
 	}
 
+	// 空容器（{} / []）与未配置一致：不限制任何能力。
+	// 避免 OAuth 账号因 API 直写/导入/历史数据遗留的空对象而被调度器静默排除（#5530）。
+	// 注意：非空但全 false / 类型异常的数据仍视为「已配置且不含能力」，保持原行为。
 	switch capabilities := raw.(type) {
 	case []any:
+		if len(capabilities) == 0 {
+			return nil, false
+		}
 		for _, item := range capabilities {
 			if value, ok := item.(string); ok {
 				add(value)
 			}
 		}
 	case []string:
+		if len(capabilities) == 0 {
+			return nil, false
+		}
 		for _, value := range capabilities {
 			add(value)
 		}
 	case map[string]any:
+		if len(capabilities) == 0 {
+			return nil, false
+		}
 		for key, value := range capabilities {
 			enabled, ok := value.(bool)
 			if ok && enabled {
@@ -1880,6 +1892,9 @@ func (a *Account) openAIEndpointCapabilitySet() (map[string]bool, bool) {
 			}
 		}
 	case map[string]bool:
+		if len(capabilities) == 0 {
+			return nil, false
+		}
 		for key, enabled := range capabilities {
 			if enabled {
 				add(key)

backend/internal/service/openai_images_test.go

@@ -593,6 +593,67 @@ func TestAccountSupportsOpenAIEndpointCapability(t *testing.T) {
 		require.True(t, account.SupportsOpenAIEndpointCapability(OpenAIEndpointCapabilityEmbeddings))
 	})
 
+	t.Run("空 openai_capabilities（{}）与未配置一致，不排除 OAuth 文本调度", func(t *testing.T) {
+		account := &Account{
+			Platform: PlatformOpenAI,
+			Type:     AccountTypeOAuth,
+			Credentials: map[string]any{
+				"openai_capabilities": map[string]any{},
+			},
+		}
+
+		require.True(t, account.SupportsOpenAIEndpointCapability(OpenAIEndpointCapabilityChatCompletions))
+		require.True(t, account.SupportsOpenAIEndpointCapability(OpenAIEndpointCapabilityResponses))
+	})
+
+	t.Run("空 openai_capabilities（[]any）与未配置一致，不排除 OAuth 文本调度", func(t *testing.T) {
+		account := &Account{
+			Platform: PlatformOpenAI,
+			Type:     AccountTypeOAuth,
+			Credentials: map[string]any{
+				"openai_capabilities": []any{},
+			},
+		}
+
+		require.True(t, account.SupportsOpenAIEndpointCapability(OpenAIEndpointCapabilityChatCompletions))
+	})
+
+	t.Run("空 openai_capabilities（[]string）与未配置一致，不排除 OAuth 文本调度", func(t *testing.T) {
+		account := &Account{
+			Platform: PlatformOpenAI,
+			Type:     AccountTypeOAuth,
+			Credentials: map[string]any{
+				"openai_capabilities": []string{},
+			},
+		}
+
+		require.True(t, account.SupportsOpenAIEndpointCapability(OpenAIEndpointCapabilityChatCompletions))
+	})
+
+	t.Run("非空但全 false 的 map 仍按显式禁用处理，不默认放行", func(t *testing.T) {
+		account := &Account{
+			Platform: PlatformOpenAI,
+			Type:     AccountTypeOAuth,
+			Credentials: map[string]any{
+				"openai_capabilities": map[string]any{"chat_completions": false},
+			},
+		}
+
+		require.False(t, account.SupportsOpenAIEndpointCapability(OpenAIEndpointCapabilityChatCompletions))
+	})
+
+	t.Run("类型异常（字符串）仍视为已配置但不含能力，不默认放行", func(t *testing.T) {
+		account := &Account{
+			Platform: PlatformOpenAI,
+			Type:     AccountTypeOAuth,
+			Credentials: map[string]any{
+				"openai_capabilities": "chat_completions",
+			},
+		}
+
+		require.False(t, account.SupportsOpenAIEndpointCapability(OpenAIEndpointCapabilityChatCompletions))
+	})
+
 	t.Run("未知能力不应默认放行", func(t *testing.T) {
 		account := &Account{
 			Platform: PlatformOpenAI,