Fix macOS CI hang and flaky idle session pruning test

On macOS, the createdump tool hangs indefinitely due to ptrace/SIP
restrictions when invoked by grandchild .NET processes that inherit
DOTNET_DbgEnableMiniDump=1 from dotnet test --blame-crash.

- Suppress mini-dump generation on macOS only for conformance child
  processes (the runtime still prints crash diagnostics to stderr)
- Add 5-minute process timeout to conformance test runners as a
  safety net against any future hangs
- Fix race in IdleSessions_ArePruned_AfterIdleTimeout where the
  background pruning task hadn't completed before the assertion

Author: stephentoub

src/ModelContextProtocol.Core/Client/StreamableHttpClientSessionTransport.cs

@@ -1,5 +1,6 @@
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
+using System.Diagnostics;
 using System.Net.Http.Headers;
 using System.Net.ServerSentEvents;
 using System.Text.Json;
@@ -239,7 +240,19 @@ await SendGetSseRequestWithRetriesAsync(
             if (shouldDelay)
             {
                 var delay = state.RetryInterval ?? _options.DefaultReconnectionInterval;
-                await Task.Delay(delay, cancellationToken).ConfigureAwait(false);
+
+                // Subtract time already elapsed since the SSE stream ended to more accurately
+                // honor the retry interval. Without this, processing overhead (HTTP response
+                // disposal, condition checks, etc.) inflates the observed reconnection delay.
+                if (state.StreamEndedTimestamp != 0)
+                {
+                    delay -= ElapsedSince(state.StreamEndedTimestamp);
+                }
+
+                if (delay > TimeSpan.Zero)
+                {
+                    await Task.Delay(delay, cancellationToken).ConfigureAwait(false);
+                }
             }
             shouldDelay = true;
 
@@ -336,9 +349,11 @@ private async Task<SseResponse> ProcessSseResponseAsync(
         }
         catch (Exception ex) when (ex is IOException or HttpRequestException)
         {
+            state.StreamEndedTimestamp = Stopwatch.GetTimestamp();
             return new() { IsNetworkError = true };
         }
 
+        state.StreamEndedTimestamp = Stopwatch.GetTimestamp();
         return default;
     }
 
@@ -435,6 +450,8 @@ private sealed class SseStreamState
     {
         public string? LastEventId { get; set; }
         public TimeSpan? RetryInterval { get; set; }
+        /// <summary>Timestamp (via Stopwatch.GetTimestamp()) when the last SSE stream ended, used to discount processing overhead from the retry delay.</summary>
+        public long StreamEndedTimestamp { get; set; }
     }
 
     /// <summary>
@@ -445,4 +462,13 @@ private readonly struct SseResponse
         public JsonRpcMessageWithId? Response { get; init; }
         public bool IsNetworkError { get; init; }
     }
+
+    private static TimeSpan ElapsedSince(long stopwatchTimestamp)
+    {
+#if NET
+        return Stopwatch.GetElapsedTime(stopwatchTimestamp);
+#else
+        return TimeSpan.FromSeconds((double)(Stopwatch.GetTimestamp() - stopwatchTimestamp) / Stopwatch.Frequency);
+#endif
+    }
 }

tests/Common/Utils/NodeHelpers.cs

@@ -83,10 +83,11 @@ public static ProcessStartInfo ConformanceTestStartInfo(string arguments)
         var repoRoot = FindRepoRoot();
         var binPath = Path.Combine(repoRoot, "node_modules", ".bin", "conformance");
 
+        ProcessStartInfo startInfo;
         if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
         {
             // On Windows, node_modules/.bin contains .cmd shims that can be executed directly
-            return new ProcessStartInfo
+            startInfo = new ProcessStartInfo
             {
                 FileName = $"{binPath}.cmd",
                 Arguments = arguments,
@@ -98,7 +99,7 @@ public static ProcessStartInfo ConformanceTestStartInfo(string arguments)
         }
         else
         {
-            return new ProcessStartInfo
+            startInfo = new ProcessStartInfo
             {
                 FileName = binPath,
                 Arguments = arguments,
@@ -108,6 +109,21 @@ public static ProcessStartInfo ConformanceTestStartInfo(string arguments)
                 CreateNoWindow = true
             };
         }
+
+        // On macOS, disable .NET mini-dump file generation for child processes. When
+        // dotnet test runs with --blame-crash, it sets DOTNET_DbgEnableMiniDump=1 in the
+        // environment. This is inherited by grandchild .NET processes (e.g. ConformanceClient
+        // launched via node). On macOS, the createdump tool can hang indefinitely due to
+        // ptrace/SIP restrictions, causing the entire test run to hang. Disabling mini-dumps
+        // only suppresses the dump file creation; the runtime still prints crash diagnostics
+        // (stack traces, signal info, etc.) to stderr, which the test captures.
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+        {
+            startInfo.Environment["DOTNET_DbgEnableMiniDump"] = "0";
+            startInfo.Environment["COMPlus_DbgEnableMiniDump"] = "0";
+        }
+
+        return startInfo;
     }
 
     /// <summary>

tests/ModelContextProtocol.AspNetCore.Tests/ClientConformanceTests.cs

@@ -103,7 +103,20 @@ public async Task RunConformanceTest(string scenario)
         process.BeginOutputReadLine();
         process.BeginErrorReadLine();
 
-        await process.WaitForExitAsync();
+        using var cts = new CancellationTokenSource(TimeSpan.FromMinutes(5));
+        try
+        {
+            await process.WaitForExitAsync(cts.Token);
+        }
+        catch (OperationCanceledException)
+        {
+            process.Kill(entireProcessTree: true);
+            return (
+                Success: false,
+                Output: outputBuilder.ToString(),
+                Error: errorBuilder.ToString() + "\nProcess timed out after 5 minutes and was killed."
+            );
+        }
 
         return (
             Success: process.ExitCode == 0,

tests/ModelContextProtocol.AspNetCore.Tests/ServerConformanceTests.cs

@@ -167,7 +167,20 @@ private void StartConformanceServer()
         process.BeginOutputReadLine();
         process.BeginErrorReadLine();
 
-        await process.WaitForExitAsync();
+        using var cts = new CancellationTokenSource(TimeSpan.FromMinutes(5));
+        try
+        {
+            await process.WaitForExitAsync(cts.Token);
+        }
+        catch (OperationCanceledException)
+        {
+            process.Kill(entireProcessTree: true);
+            return (
+                Success: false,
+                Output: outputBuilder.ToString(),
+                Error: errorBuilder.ToString() + "\nProcess timed out after 5 minutes and was killed."
+            );
+        }
 
         return (
             Success: process.ExitCode == 0,

tests/ModelContextProtocol.AspNetCore.Tests/StreamableHttpServerConformanceTests.cs

@@ -473,8 +473,19 @@ public async Task IdleSessions_ArePruned_AfterIdleTimeout()
         // Add 5 seconds to idle timeout to account for the interval of the PeriodicTimer.
         fakeTimeProvider.Advance(TimeSpan.FromHours(2) + TimeSpan.FromSeconds(5));
 
-        using var response = await HttpClient.PostAsync("", JsonContent(EchoRequest), TestContext.Current.CancellationToken);
-        Assert.Equal(HttpStatusCode.NotFound, response.StatusCode);
+        // The background IdleTrackingBackgroundService prunes sessions asynchronously after
+        // the timer tick fires. Poll until pruning completes and the session returns NotFound.
+        var deadline = DateTime.UtcNow + TestConstants.DefaultTimeout;
+        HttpStatusCode statusCode;
+        do
+        {
+            await Task.Delay(100, TestContext.Current.CancellationToken);
+            using var response = await HttpClient.PostAsync("", JsonContent(EchoRequest), TestContext.Current.CancellationToken);
+            statusCode = response.StatusCode;
+        }
+        while (statusCode != HttpStatusCode.NotFound && DateTime.UtcNow < deadline);
+
+        Assert.Equal(HttpStatusCode.NotFound, statusCode);
     }
 
     [Fact]