feat(loader): mutex-skip + per-instance identity + synthetic Steam identity patches

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSimLoader/Patches/MultiInstancePatches.cs

@@ -0,0 +1,74 @@
+using Cute;
+using HarmonyLib;
+
+namespace SVSimLoader.Patches
+{
+    [HarmonyPatch]
+    public static class MultiInstancePatches
+    {
+        // (1) Defeat the machine-wide single-instance guard. createMutex is private, so target it
+        //     by string name. Prefix returning false skips the original (Application.Quit never runs).
+        [HarmonyPatch(typeof(BootApp), "createMutex")]
+        [HarmonyPrefix]
+        public static bool SkipMutex()
+        {
+            if (!SvSimConfig.SecondaryInstance) return true; // primary/normal: run original
+            Plugin.Log.LogWarning("Multi-instance: skipping BootApp.createMutex single-instance guard.");
+            return false;
+        }
+
+        // (2) Redirect the three identity keys to the per-instance file store. Other keys fall
+        //     through to the original (return true).
+        private static bool IsIdentityKey(string key) =>
+            key == "UDID" || key == "VIEWER_ID" || key == "SHORT_UDID";
+
+        [HarmonyPatch(typeof(SavedataManager), nameof(SavedataManager.GetString))]
+        [HarmonyPrefix]
+        public static bool GetString(string key, string defaultValue, ref string __result)
+        {
+            if (!SvSimConfig.SecondaryInstance || !IsIdentityKey(key)) return true;
+            __result = InstanceIdentityStore.TryGet(key, out var v) ? v : defaultValue;
+            return false;
+        }
+
+        [HarmonyPatch(typeof(SavedataManager), nameof(SavedataManager.SetString))]
+        [HarmonyPrefix]
+        public static bool SetString(string key, string value)
+        {
+            if (!SvSimConfig.SecondaryInstance || !IsIdentityKey(key)) return true;
+            InstanceIdentityStore.Set(key, value);
+            return false;
+        }
+
+        [HarmonyPatch(typeof(SavedataManager), nameof(SavedataManager.GetInt))]
+        [HarmonyPrefix]
+        public static bool GetInt(string key, int defaultValue, ref int __result)
+        {
+            if (!SvSimConfig.SecondaryInstance || !IsIdentityKey(key)) return true;
+            __result = InstanceIdentityStore.TryGet(key, out var v) && int.TryParse(v, out var i) ? i : defaultValue;
+            return false;
+        }
+
+        [HarmonyPatch(typeof(SavedataManager), nameof(SavedataManager.SetInt))]
+        [HarmonyPrefix]
+        public static bool SetInt(string key, int value)
+        {
+            if (!SvSimConfig.SecondaryInstance || !IsIdentityKey(key)) return true;
+            InstanceIdentityStore.Set(key, value.ToString());
+            return false;
+        }
+
+        // (3) Force a synthetic Steam identity. setSTEAMPlatformData runs in Certification.Start();
+        //     a postfix overwrites SteamID/SteamSessionTicket (private setters) via Traverse.
+        [HarmonyPatch(typeof(Certification), "setSTEAMPlatformData")]
+        [HarmonyPostfix]
+        public static void ForceSteamIdentity()
+        {
+            if (!SvSimConfig.SecondaryInstance) return;
+            Traverse.Create(typeof(Certification)).Property("SteamID").SetValue(SvSimConfig.FakeSteamId);
+            Traverse.Create(typeof(Certification)).Property("SteamSessionTicket").SetValue(SvSimConfig.FakeTicket);
+            Plugin.Log.LogWarning(
+                $"Multi-instance: forced SteamID={SvSimConfig.FakeSteamId}, ticket={SvSimConfig.FakeTicket}.");
+        }
+    }
+}