feat: 接入 Instance 版本与扩展可用性观测

internal/database/adapter/postgresql/metadata.go

@@ -0,0 +1,48 @@
+/*
+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 postgresql
+
+import (
+	"context"
+
+	"git.ddupan.top/panxiao81/ayatori/internal/database/application"
+)
+
+// 使用 pg_catalog 限定名称，避免管理账号的 search_path 改变查询来源。
+// 一个语句读取版本和可用列表；ARRAY 子查询在无行时返回空数组，而非 NULL。
+// 不查询 pg_extension：已安装集合不能代表服务器提供的全部扩展。
+const inspectMetadataStatement = `
+SELECT
+    pg_catalog.current_setting('server_version'),
+    ARRAY(
+        SELECT name::text
+        FROM pg_catalog.pg_available_extensions
+        ORDER BY name
+    )`
+
+func (d *database) InspectMetadata(ctx context.Context) (application.DatabaseMetadata, error) {
+	var metadata application.DatabaseMetadata
+	err := d.pool.QueryRow(ctx, inspectMetadataStatement).Scan(
+		&metadata.Version,
+		&metadata.AvailableExtensions,
+	)
+	if err != nil {
+		// 不返回部分结果，也不把查询失败转换为“成功观察到空列表”。
+		return application.DatabaseMetadata{}, safeError(err, application.ErrObservation)
+	}
+	return metadata, nil
+}