Got at least one data fetching method working; turns out, we can't use a patched LogicStack to get the data

Vendor/EmbedIO-3.5.2/Sessions/SessionProxy.cs

@@ -0,0 +1,167 @@
+using System;
+using System.Collections.Generic;
+using EmbedIO.Sessions.Internal;
+
+namespace EmbedIO.Sessions
+{
+    /// <summary>
+    /// Provides the same interface as a session object,
+    /// plus a basic interface to a session manager.
+    /// </summary>
+    /// <remarks>
+    /// A session proxy can be used just as if it were a session object.
+    /// A session is automatically created wherever its data are accessed.
+    /// </remarks>
+    /// <seealso cref="ISessionProxy" />
+    public sealed class SessionProxy : ISessionProxy
+    {
+        private readonly IHttpContext _context;
+        private readonly ISessionManager? _sessionManager;
+
+        private ISession? _session;
+        private bool _onCloseRegistered;
+
+        internal SessionProxy(IHttpContext context, ISessionManager? sessionManager)
+        {
+            _context = context;
+            _sessionManager = sessionManager;
+        }
+
+        /// <summary>
+        /// Returns a "dummy" <see cref="ISessionProxy"/> interface that will always behave as if no session manager has been defined.
+        /// </summary>
+        /// <remarks>
+        /// <para>The returned <see cref="ISessionProxy"/> interface is only useful
+        /// to initialize a non-nullable property of type <see cref="ISessionProxy"/>.</para>
+        /// </remarks>
+        public static ISessionProxy None => DummySessionProxy.Instance;
+
+        /// <inheritdoc/>
+        public bool Exists => _session != null;
+
+        /// <inheritdoc/>
+        public string Id
+        {
+            get
+            {
+                EnsureSessionExists();
+                return _session!.Id;
+            }
+        }
+
+        /// <inheritdoc/>
+        public TimeSpan Duration
+        {
+            get
+            {
+                EnsureSessionExists();
+                return _session!.Duration;
+            }
+        }
+
+        /// <inheritdoc/>
+        public DateTime LastActivity
+        {
+            get
+            {
+                EnsureSessionExists();
+                return _session!.LastActivity;
+            }
+        }
+
+        /// <inheritdoc/>
+        public int Count => _session?.Count ?? 0;
+
+        /// <inheritdoc/>
+        public bool IsEmpty => _session?.IsEmpty ?? true;
+
+        /// <inheritdoc/>
+        public object this[string key]
+        {
+            get
+            {
+                EnsureSessionExists();
+                return _session![key];
+            }
+            set
+            {
+                EnsureSessionExists();
+                _session![key] = value;
+            }
+        }
+
+        /// <inheritdoc/>
+        public void Delete()
+        {
+            EnsureSessionExists();
+
+            if (_session == null)
+                return;
+
+            _sessionManager!.Delete(_context, _session.Id);
+            _session = null;
+        }
+
+        /// <inheritdoc/>
+        public void Regenerate()
+        {
+            if (_session != null)
+                _sessionManager!.Delete(_context, _session.Id);
+
+            EnsureSessionManagerExists();
+            _session = _sessionManager!.Create(_context);
+        }
+
+        /// <inheritdoc/>
+        public void Clear() => _session?.Clear();
+
+        /// <inheritdoc/>
+        public bool ContainsKey(string key)
+        {
+            EnsureSessionExists();
+            return _session!.ContainsKey(key);
+        }
+
+        /// <inheritdoc/>
+        public bool TryGetValue(string key, out object value)
+        {
+            EnsureSessionExists();
+            return _session!.TryGetValue(key, out value);
+        }
+
+        /// <inheritdoc/>
+        public bool TryRemove(string key, out object value)
+        {
+            EnsureSessionExists();
+            return _session!.TryRemove(key, out value);
+        }
+
+        /// <inheritdoc/>
+        public IReadOnlyList<KeyValuePair<string, object>> TakeSnapshot()
+        {
+            EnsureSessionExists();
+            return _session!.TakeSnapshot();
+        }
+
+        private void EnsureSessionManagerExists()
+        {
+            if (_sessionManager == null)
+                throw new InvalidOperationException("No session manager registered in the web server.");
+        }
+
+        private void EnsureSessionExists()
+        {
+            if (_session != null)
+                return;
+
+            EnsureSessionManagerExists();
+            _session = _sessionManager!.Create(_context);
+
+            if (_onCloseRegistered)
+                return;
+
+            _context.OnClose(_sessionManager.OnContextClose);
+            _onCloseRegistered = true;
+        }
+    }
+}