Fix session timeout due to timestamp frequency mismatch and activity tracking (#1106)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
Co-authored-by: eiriktsarpalis <2813363+eiriktsarpalis@users.noreply.github.com>

src/ModelContextProtocol.AspNetCore/StatefulSessionManager.cs

@@ -18,7 +18,7 @@ internal sealed partial class StatefulSessionManager(
 
     private readonly TimeProvider _timeProvider = httpServerTransportOptions.Value.TimeProvider;
     private readonly TimeSpan _idleTimeout = httpServerTransportOptions.Value.IdleTimeout;
-    private readonly long _idleTimeoutTicks = httpServerTransportOptions.Value.IdleTimeout.Ticks;
+    private readonly long _idleTimeoutTicks = GetIdleTimeoutInTimestampTicks(httpServerTransportOptions.Value.IdleTimeout, httpServerTransportOptions.Value.TimeProvider);
     private readonly int _maxIdleSessionCount = httpServerTransportOptions.Value.MaxIdleSessionCount;
 
     private readonly object _idlePruningLock = new();
@@ -229,6 +229,15 @@ internal sealed partial class StatefulSessionManager(
         }
     }
 
+    private static long GetIdleTimeoutInTimestampTicks(TimeSpan idleTimeout, TimeProvider timeProvider)
+    {
+        // Convert TimeSpan.Ticks (100-nanosecond intervals) to timestamp ticks based on TimeProvider.TimestampFrequency.
+        // TimeSpan.Ticks uses a fixed frequency of 10,000,000 ticks per second (100ns intervals).
+        // TimeProvider.GetTimestamp() returns ticks based on TimeProvider.TimestampFrequency, which varies by platform
+        // (e.g., ~1,000,000,000 on macOS using nanoseconds, ~10,000,000 on Windows using 100ns intervals).
+        return (long)(idleTimeout.Ticks * timeProvider.TimestampFrequency / (double)TimeSpan.TicksPerSecond);
+    }
+
     [LoggerMessage(Level = LogLevel.Information, Message = "IdleTimeout of {IdleTimeout} exceeded. Closing idle session {SessionId}.")]
     private partial void LogIdleSessionTimeout(string sessionId, TimeSpan idleTimeout);
 

src/ModelContextProtocol.AspNetCore/StreamableHttpSession.cs

@@ -58,6 +58,8 @@ internal sealed class StreamableHttpSession(
                     {
                         sessionManager.DecrementIdleSessionCount();
                     }
+                    // Update LastActivityTicks when acquiring reference in Started state to prevent timeout during active usage
+                    LastActivityTicks = sessionManager.TimeProvider.GetTimestamp();
                     break;
                 case SessionState.Disposed:
                     throw new ObjectDisposedException(nameof(StreamableHttpSession));