Add unit tests and implementations for MongoDB index models and OpenAPI metadata

- Implemented `MongoIndexModelTests` to verify index models for various stores.
- Created `OpenApiMetadataFactory` with methods to generate OpenAPI metadata.
- Added tests for `OpenApiMetadataFactory` to ensure expected defaults and URL overrides.
- Introduced `ObserverSurfaceSecrets` and `WebhookSurfaceSecrets` for managing secrets.
- Developed `RuntimeSurfaceFsClient` and `WebhookSurfaceFsClient` for manifest retrieval.
- Added dependency injection tests for `SurfaceEnvironmentRegistration` in both Observer and Webhook contexts.
- Implemented tests for secret resolution in `ObserverSurfaceSecretsTests` and `WebhookSurfaceSecretsTests`.
- Created `EnsureLinkNotMergeCollectionsMigrationTests` to validate MongoDB migration logic.
- Added project files for MongoDB tests and NuGet package mirroring.

tests/Concelier/StellaOps.Concelier.Storage.Mongo.Tests/EnsureLinkNotMergeCollectionsMigrationTests.cs

@@ -0,0 +1,70 @@
+using System.Linq;
+using System.Threading.Tasks;
+using FluentAssertions;
+using Mongo2Go;
+using MongoDB.Bson;
+using MongoDB.Driver;
+using StellaOps.Concelier.Storage.Mongo.Migrations;
+
+namespace StellaOps.Concelier.Storage.Mongo.Tests;
+
+public sealed class EnsureLinkNotMergeCollectionsMigrationTests : IAsyncLifetime
+{
+    private MongoDbRunner _runner = null!;
+    private IMongoDatabase _database = null!;
+
+    public Task InitializeAsync()
+    {
+        _runner = MongoDbRunner.Start(singleNodeReplSet: true);
+        var client = new MongoClient(_runner.ConnectionString);
+        _database = client.GetDatabase("lnm-migration-tests");
+        return Task.CompletedTask;
+    }
+
+    public Task DisposeAsync()
+    {
+        _runner.Dispose();
+        return Task.CompletedTask;
+    }
+
+    [Fact]
+    public async Task CreatesCollectionsAndIndexesIdempotently()
+    {
+        var migration = new EnsureLinkNotMergeCollectionsMigration();
+
+        await migration.ApplyAsync(_database, CancellationToken.None);
+        await migration.ApplyAsync(_database, CancellationToken.None); // idempotent second run
+
+        var collections = await _database.ListCollectionNames().ToListAsync();
+        collections.Should().Contain(new[]
+        {
+            MongoStorageDefaults.Collections.AdvisoryObservations,
+            MongoStorageDefaults.Collections.AdvisoryLinksets
+        });
+
+        var linksetIndexes = await _database
+            .GetCollection<BsonDocument>(MongoStorageDefaults.Collections.AdvisoryLinksets)
+            .Indexes.List()
+            .ToListAsync();
+
+        linksetIndexes.Should().ContainSingle(i => i["name"] == "linkset_tenant_advisory_source" && i["unique"].AsBoolean);
+
+        var obsIndexes = await _database
+            .GetCollection<BsonDocument>(MongoStorageDefaults.Collections.AdvisoryObservations)
+            .Indexes.List()
+            .ToListAsync();
+
+        obsIndexes.Should().Contain(i => i["name"] == "obs_prov_sourceArtifactSha_unique" && i["unique"].AsBoolean);
+
+        var linksetValidator = await GetValidatorAsync(MongoStorageDefaults.Collections.AdvisoryLinksets);
+        linksetValidator.Should().NotBeNull();
+    }
+
+    private async Task<BsonDocument?> GetValidatorAsync(string collection)
+    {
+        var filter = new BsonDocument("name", collection);
+        var cursor = await _database.ListCollectionsAsync(new ListCollectionsOptions { Filter = filter });
+        var doc = await cursor.FirstOrDefaultAsync();
+        return doc?"options"?"validator"?.AsBsonDocument;
+    }
+}

tests/Concelier/StellaOps.Concelier.Storage.Mongo.Tests/StellaOps.Concelier.Storage.Mongo.Tests.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.0" />
+    <PackageReference Include="Mongo2Go" Version="4.1.0" />
+    <PackageReference Include="xunit" Version="2.9.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="FluentAssertions" Version="6.12.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="../../../src/Concelier/__Libraries/StellaOps.Concelier.Storage.Mongo/StellaOps.Concelier.Storage.Mongo.csproj" />
+  </ItemGroup>
+</Project>