feat: 接入 Instance 版本与扩展可用性观测

internal/database/application/metadata.go

@@ -0,0 +1,40 @@
+/*
+Copyright 2026.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package application
+
+import "git.ddupan.top/panxiao81/ayatori/internal/database/domain/instance"
+
+// DatabaseMetadata 是一次只读查询的事实，不包含管理权限或 registry 就绪结论。
+// AvailableExtensions 是服务器提供的可用列表，不是已安装列表或安装授权。
+type DatabaseMetadata struct {
+	Version             string
+	AvailableExtensions []string
+}
+
+// MetadataObservation 只在查询成功且有效凭据再次核对一致后产生。
+// target 绑定本次调用，而非连接最初创建时的 generation；零值表示没有观察。
+type MetadataObservation struct {
+	target     instance.ObservationTarget
+	version    string
+	extensions instance.ExtensionSupport
+}
+
+func (o MetadataObservation) Target() instance.ObservationTarget { return o.target }
+func (o MetadataObservation) Version() string                    { return o.version }
+func (o MetadataObservation) Extensions() instance.ExtensionSupport {
+	return o.extensions
+}