Practice/deck editing mostly there

SVSim.EmulatedEntrypoint/Services/ISteamServer.cs

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+namespace SVSim.EmulatedEntrypoint.Services;
+
+/// <summary>
+/// Thin wrapper around the static <c>Steamworks.SteamServer</c> API. Exists purely so
+/// <see cref="SteamSessionService"/> can be unit-tested — Facepunch.Steamworks is a static
+/// class with process-global state that can't be mocked or run twice in the same test host.
+///
+/// Only the operations <see cref="SteamSessionService"/> actually invokes are exposed. Add
+/// methods here as needed rather than expanding the surface speculatively.
+/// </summary>
+public interface ISteamServer
+{
+    /// <summary>Initialize the underlying Steam game server with the given app id. Idempotent.</summary>
+    void Initialize(int appId);
+
+    /// <summary>
+    /// Open an auth session for the given steam id with the given ticket bytes. Returns true
+    /// when Steam accepts the ticket. Returns false on any rejection — most commonly the
+    /// "duplicate request" case (the steam id already has an open session on this server),
+    /// which is the failure mode <see cref="SteamSessionService"/> resolves by calling
+    /// <see cref="EndSession"/> first.
+    /// </summary>
+    bool BeginAuthSession(byte[] ticket, ulong steamId);
+
+    /// <summary>
+    /// Close any active auth session for this steam id. Safe to call when no session exists
+    /// (Steam SDK no-ops). Must be called before a second <see cref="BeginAuthSession"/> for
+    /// the same steam id or Steam will reject the new call as a duplicate request.
+    /// </summary>
+    void EndSession(ulong steamId);
+
+    /// <summary>Tear down the game server. Implicitly ends every open auth session.</summary>
+    void Shutdown();
+}