Add SEP-2549 caching hints (ttlMs and cacheScope) to cacheable results (#1623)

Co-authored-by: Tarek Mahmoud Sayed <tarekms@ntdev.microsoft.com>

tests/ModelContextProtocol.Tests/Protocol/CacheableResultClientServerTests.cs

@@ -0,0 +1,93 @@
+using Microsoft.Extensions.DependencyInjection;
+using ModelContextProtocol.Client;
+using ModelContextProtocol.Protocol;
+using ModelContextProtocol.Server;
+
+namespace ModelContextProtocol.Tests.Protocol;
+
+/// <summary>
+/// End-to-end tests verifying that SEP-2549 caching hints set by a server on cacheable results
+/// are observed by a connected client.
+/// </summary>
+public class CacheableResultClientServerTests(ITestOutputHelper testOutputHelper)
+    : ClientServerTestBase(testOutputHelper)
+{
+    protected override void ConfigureServices(ServiceCollection services, IMcpServerBuilder mcpServerBuilder)
+    {
+        mcpServerBuilder
+            .WithListToolsHandler((_, _) => new ValueTask<ListToolsResult>(new ListToolsResult
+            {
+                Tools = [new Tool { Name = "echo" }],
+                TimeToLive = TimeSpan.FromMinutes(5),
+                CacheScope = CacheScope.Public,
+            }))
+            .WithListPromptsHandler((_, _) => new ValueTask<ListPromptsResult>(new ListPromptsResult
+            {
+                Prompts = [new Prompt { Name = "greet" }],
+            }))
+            .WithListResourcesHandler((_, _) => new ValueTask<ListResourcesResult>(new ListResourcesResult
+            {
+                Resources = [new Resource { Uri = "test://resource", Name = "resource" }],
+            }))
+            .WithReadResourceHandler((request, _) => new ValueTask<ReadResourceResult>(new ReadResourceResult
+            {
+                Contents = [new TextResourceContents { Uri = request.Params!.Uri!, Text = "hi" }],
+                TimeToLive = TimeSpan.FromSeconds(30),
+                CacheScope = CacheScope.Private,
+            }));
+    }
+
+    [Fact]
+    public async Task ListTools_PropagatesCachingHints_ToClient()
+    {
+        await using var client = await CreateMcpClientForServer();
+
+        var result = await client.ListToolsAsync(
+            new ListToolsRequestParams(),
+            TestContext.Current.CancellationToken);
+
+        Assert.Equal(TimeSpan.FromMinutes(5), result.TimeToLive);
+        Assert.Equal(CacheScope.Public, result.CacheScope);
+    }
+
+    [Fact]
+    public async Task ReadResource_PropagatesCachingHints_ToClient()
+    {
+        await using var client = await CreateMcpClientForServer();
+
+        var result = await client.ReadResourceAsync(
+            "test://resource",
+            cancellationToken: TestContext.Current.CancellationToken);
+
+        Assert.Equal(TimeSpan.FromSeconds(30), result.TimeToLive);
+        Assert.Equal(CacheScope.Private, result.CacheScope);
+    }
+
+    [Fact]
+    public async Task ListPrompts_WhenHandlerOmitsHints_ServerInjectsConservativeDefaults()
+    {
+        await using var client = await CreateMcpClientForServer();
+
+        var result = await client.ListPromptsAsync(
+            new ListPromptsRequestParams(),
+            TestContext.Current.CancellationToken);
+
+        // SEP-2549: the handler left the hints unset, so the server fills in conservative defaults
+        // (immediately stale, not shareable) rather than omitting the now-required fields.
+        Assert.Equal(TimeSpan.Zero, result.TimeToLive);
+        Assert.Equal(CacheScope.Private, result.CacheScope);
+    }
+
+    [Fact]
+    public async Task ListResources_WhenHandlerOmitsHints_ServerInjectsConservativeDefaults()
+    {
+        await using var client = await CreateMcpClientForServer();
+
+        var result = await client.ListResourcesAsync(
+            new ListResourcesRequestParams(),
+            TestContext.Current.CancellationToken);
+
+        Assert.Equal(TimeSpan.Zero, result.TimeToLive);
+        Assert.Equal(CacheScope.Private, result.CacheScope);
+    }
+}