Replace concrete collection types with interfaces in public API surface

src/ModelContextProtocol.Core/Authentication/DynamicClientRegistrationResponse.cs

@@ -23,7 +23,7 @@ public sealed class DynamicClientRegistrationResponse
     /// Gets or initializes the redirect URIs for the client.
     /// </summary>
     [JsonPropertyName("redirect_uris")]
-    public string[]? RedirectUris { get; init; }
+    public IList<string>? RedirectUris { get; init; }
 
     /// <summary>
     /// Gets or initializes the token endpoint authentication method.
@@ -35,13 +35,13 @@ public sealed class DynamicClientRegistrationResponse
     /// Gets or initializes the grant types that the client will use.
     /// </summary>
     [JsonPropertyName("grant_types")]
-    public string[]? GrantTypes { get; init; }
+    public IList<string>? GrantTypes { get; init; }
 
     /// <summary>
     /// Gets or initializes the response types that the client will use.
     /// </summary>
     [JsonPropertyName("response_types")]
-    public string[]? ResponseTypes { get; init; }
+    public IList<string>? ResponseTypes { get; init; }
 
     /// <summary>
     /// Gets or initializes the timestamp at which the client ID was issued.

src/ModelContextProtocol.Core/Authentication/ProtectedResourceMetadata.cs

@@ -35,7 +35,7 @@ public sealed class ProtectedResourceMetadata
     /// OPTIONAL.
     /// </remarks>
     [JsonPropertyName("authorization_servers")]
-    public List<string> AuthorizationServers { get; set; } = [];
+    public IList<string> AuthorizationServers { get; set; } = [];
 
     /// <summary>
     /// Gets or sets the supported bearer token methods.
@@ -48,7 +48,7 @@ public sealed class ProtectedResourceMetadata
     /// OPTIONAL.
     /// </remarks>
     [JsonPropertyName("bearer_methods_supported")]
-    public List<string> BearerMethodsSupported { get; set; } = ["header"];
+    public IList<string> BearerMethodsSupported { get; set; } = ["header"];
 
     /// <summary>
     /// Gets or sets the supported scopes.
@@ -61,7 +61,7 @@ public sealed class ProtectedResourceMetadata
     /// RECOMMENDED.
     /// </remarks>
     [JsonPropertyName("scopes_supported")]
-    public List<string> ScopesSupported { get; set; } = [];
+    public IList<string> ScopesSupported { get; set; } = [];
 
     /// <summary>
     /// Gets or sets the URL of the protected resource's JSON Web Key (JWK) Set document.
@@ -85,7 +85,7 @@ public sealed class ProtectedResourceMetadata
     /// OPTIONAL. No default algorithms are implied if this entry is omitted. The value "none" MUST NOT be used.
     /// </remarks>
     [JsonPropertyName("resource_signing_alg_values_supported")]
-    public List<string>? ResourceSigningAlgValuesSupported { get; set; }
+    public IList<string>? ResourceSigningAlgValuesSupported { get; set; }
 
     /// <summary>
     /// Gets or sets the human-readable name of the protected resource intended for display to the end user.
@@ -157,7 +157,7 @@ public sealed class ProtectedResourceMetadata
     /// OPTIONAL.
     /// </remarks>
     [JsonPropertyName("authorization_details_types_supported")]
-    public List<string>? AuthorizationDetailsTypesSupported { get; set; }
+    public IList<string>? AuthorizationDetailsTypesSupported { get; set; }
 
     /// <summary>
     /// Gets or sets the list of the JWS algorithm values supported by the resource server for validating DPoP proof JWTs.
@@ -170,7 +170,7 @@ public sealed class ProtectedResourceMetadata
     /// OPTIONAL.
     /// </remarks>
     [JsonPropertyName("dpop_signing_alg_values_supported")]
-    public List<string>? DpopSigningAlgValuesSupported { get; set; }
+    public IList<string>? DpopSigningAlgValuesSupported { get; set; }
 
     /// <summary>
     /// Gets or sets a value indicating whether the protected resource always requires the use of DPoP-bound access tokens.

src/ModelContextProtocol.Core/Protocol/ContentBlock.cs

@@ -693,7 +693,7 @@ public sealed class ToolResultContentBlock : ContentBlock
     /// audio, resource links, and embedded resources.
     /// </remarks>
     [JsonPropertyName("content")]
-    public required List<ContentBlock> Content { get; set; }
+    public required IList<ContentBlock> Content { get; set; }
 
     /// <summary>
     /// Gets or sets an optional structured result object.

src/ModelContextProtocol.Core/Protocol/ListTasksRequestParams.cs

@@ -30,5 +30,5 @@ public sealed class ListTasksResult : PaginatedResult
     /// Gets or sets the list of tasks.
     /// </summary>
     [JsonPropertyName("tasks")]
-    public required McpTask[] Tasks { get; set; }
+    public required IList<McpTask> Tasks { get; set; }
 }

src/ModelContextProtocol.Core/Server/McpServer.Methods.cs

@@ -462,7 +462,7 @@ public async ValueTask<IList<McpTask>> ListTasksAsync(
             var taskResults = await ListTasksAsync(requestParams, cancellationToken).ConfigureAwait(false);
             if (tasks is null)
             {
-                tasks = new List<McpTask>(taskResults.Tasks.Length);
+                tasks = new List<McpTask>(taskResults.Tasks.Count);
             }
 
             foreach (var mcpTask in taskResults.Tasks)

tests/ModelContextProtocol.Tests/Protocol/ListTasksResultTests.cs

@@ -38,7 +38,7 @@ public static void ListTasksResult_SerializationRoundTrip()
         // Assert
         Assert.NotNull(deserialized);
         Assert.NotNull(deserialized.Tasks);
-        Assert.Equal(2, deserialized.Tasks.Length);
+        Assert.Equal(2, deserialized.Tasks.Count);
         Assert.Equal(original.Tasks[0].TaskId, deserialized.Tasks[0].TaskId);
         Assert.Equal(original.Tasks[1].TaskId, deserialized.Tasks[1].TaskId);
         Assert.Equal(original.NextCursor, deserialized.NextCursor);

tests/ModelContextProtocol.Tests/Server/InMemoryMcpTaskStoreTests.cs

@@ -353,7 +353,7 @@ public async Task ListTasksAsync_ReturnsAllTasks()
         var result = await store.ListTasksAsync(cancellationToken: TestContext.Current.CancellationToken);
 
         // Assert
-        Assert.Equal(2, result.Tasks.Length);
+        Assert.Equal(2, result.Tasks.Count);
         Assert.Contains(result.Tasks, t => t.TaskId == task1.TaskId);
         Assert.Contains(result.Tasks, t => t.TaskId == task2.TaskId);
         Assert.Null(result.NextCursor);
@@ -397,9 +397,9 @@ public async Task ListTasksAsync_SupportsPagination()
         var secondPageResult = await store.ListTasksAsync(cursor: firstPageResult.NextCursor, cancellationToken: TestContext.Current.CancellationToken);
 
         // Assert
-        Assert.Equal(100, firstPageResult.Tasks.Length);
+        Assert.Equal(100, firstPageResult.Tasks.Count);
         Assert.NotNull(firstPageResult.NextCursor);
-        Assert.Equal(50, secondPageResult.Tasks.Length);
+        Assert.Equal(50, secondPageResult.Tasks.Count);
         Assert.Null(secondPageResult.NextCursor);
     }
 
@@ -779,11 +779,11 @@ public async Task ListTasksAsync_PaginationWithCustomPageSize()
         var result3 = await store.ListTasksAsync(cursor: result2.NextCursor, cancellationToken: TestContext.Current.CancellationToken);
 
         // Assert
-        Assert.Equal(10, result1.Tasks.Length);
+        Assert.Equal(10, result1.Tasks.Count);
         Assert.NotNull(result1.NextCursor);
-        Assert.Equal(10, result2.Tasks.Length);
+        Assert.Equal(10, result2.Tasks.Count);
         Assert.NotNull(result2.NextCursor);
-        Assert.Equal(5, result3.Tasks.Length);
+        Assert.Equal(5, result3.Tasks.Count);
         Assert.Null(result3.NextCursor);
 
         // Verify no duplicates across pages
@@ -854,7 +854,7 @@ public async Task ListTasksAsync_ConsistentWithExpiredTasksRemovedBetweenPages()
         var result2 = await store.ListTasksAsync(cursor: result1.NextCursor, cancellationToken: TestContext.Current.CancellationToken);
 
         // Assert - First page should have 5 tasks, second page should have 0 (all expired)
-        Assert.Equal(5, result1.Tasks.Length);
+        Assert.Equal(5, result1.Tasks.Count);
         Assert.NotNull(result1.NextCursor);
         Assert.Empty(result2.Tasks);
         Assert.Null(result2.NextCursor);
@@ -874,7 +874,7 @@ public async Task ListTasksAsync_KeysetPaginationMaintainsConsistencyWithNewTask
 
         // Get first page
         var result1 = await store.ListTasksAsync(cancellationToken: TestContext.Current.CancellationToken);
-        Assert.Equal(5, result1.Tasks.Length);
+        Assert.Equal(5, result1.Tasks.Count);
 
         // Add more tasks between pages (these should appear in later queries, not retroactively in page 2)
         for (int i = 10; i < 15; i++)
@@ -886,7 +886,7 @@ public async Task ListTasksAsync_KeysetPaginationMaintainsConsistencyWithNewTask
         var result2 = await store.ListTasksAsync(cursor: result1.NextCursor, cancellationToken: TestContext.Current.CancellationToken);
 
         // Assert - Second page should have 5 tasks from original set
-        Assert.Equal(5, result2.Tasks.Length);
+        Assert.Equal(5, result2.Tasks.Count);
         Assert.NotNull(result2.NextCursor);
 
         // Verify no overlap between pages
@@ -1128,14 +1128,14 @@ public async Task ListTasksAsync_KeysetPaginationWorksWithIdenticalTimestamps()
         var result1 = await store.ListTasksAsync(cancellationToken: TestContext.Current.CancellationToken);
 
         // Assert - First page should have 5 tasks
-        Assert.Equal(5, result1.Tasks.Length);
+        Assert.Equal(5, result1.Tasks.Count);
         Assert.NotNull(result1.NextCursor);
 
         // Get second page using cursor
         var result2 = await store.ListTasksAsync(cursor: result1.NextCursor, cancellationToken: TestContext.Current.CancellationToken);
 
         // Assert - Second page should have 5 tasks
-        Assert.Equal(5, result2.Tasks.Length);
+        Assert.Equal(5, result2.Tasks.Count);
         Assert.Null(result2.NextCursor); // No more pages
 
         // Verify no overlap between pages
@@ -1180,7 +1180,7 @@ public async Task ListTasksAsync_TasksCreatedAfterFirstPageWithSameTimestampAppe
 
         // Get first page - should have 5 tasks with a cursor
         var result1 = await store.ListTasksAsync(cancellationToken: TestContext.Current.CancellationToken);
-        Assert.Equal(5, result1.Tasks.Length);
+        Assert.Equal(5, result1.Tasks.Count);
         Assert.NotNull(result1.NextCursor);
 
         // Now create 5 more tasks AFTER we got the first page cursor