Streamable HTTP resumability + redelivery + SSE polling via server-side disconnect (#1077)

Co-authored-by: Stephen Halter <halter73@gmail.com>

src/ModelContextProtocol.AspNetCore/HttpServerTransportOptions.cs

@@ -43,6 +43,21 @@ public class HttpServerTransportOptions
     /// </remarks>
     public bool Stateless { get; set; }
 
+    /// <summary>
+    /// Gets or sets the event store for resumability support.
+    /// When set, events are stored and can be replayed when clients reconnect with a Last-Event-ID header.
+    /// </summary>
+    /// <remarks>
+    /// When configured, the server will:
+    /// <list type="bullet">
+    /// <item><description>Generate unique event IDs for each SSE message</description></item>
+    /// <item><description>Store events for later replay</description></item>
+    /// <item><description>Replay missed events when a client reconnects with a Last-Event-ID header</description></item>
+    /// <item><description>Send priming events to establish resumability before any actual messages</description></item>
+    /// </list>
+    /// </remarks>
+    public ISseEventStreamStore? EventStreamStore { get; set; }
+
     /// <summary>
     /// Gets or sets a value that indicates whether the server uses a single execution context for the entire session.
     /// </summary>