fix(sandbox): allocation budget actually fires — Mono lacks per-thread GC counter

GC.GetAllocatedBytesForCurrentThread returns 0 unconditionally under Unity's Mono
(verified empirically), so the F-08 allocation-bomb backstop could never trigger in
either VM guard: bombs ran to a real OutOfMemory or the wall-clock timeout. Both
guards now baseline/sample GC.GetTotalMemory(false) — a cheap managed-heap read that
is also thread-agnostic (the async Lua-CSharp VM migrates between pool threads).

Heap total is process-wide and noisy, so the default budget is raised 64MB -> 256MB:
editor background allocation over a 2s window tripped the old threshold in the
infinite-loop test (false positive), while real concat-doubling bombs blow past
256MB within a few iterations either way.

Verified: full EditMode suite 1583/1583 green, including both
AllocationBomb_ConcatDoubling tests (budget fires, not timeout/OOM) and the
untouched infinite-loop step/timeout test.

Author: NeoXider

Assets/CoreAIMods/Runtime/Sandbox/InstructionLimitDebugger.cs

@@ -20,7 +20,7 @@ namespace CoreAI.Sandbox
     internal sealed class InstructionLimitDebugger : IDebugger
     {
         /// <summary>Default per-execution GC allocation budget enforced between VM instructions.</summary>
-        public const long DefaultMaxAllocatedBytesBudget = 64 * 1024 * 1024;
+        public const long DefaultMaxAllocatedBytesBudget = 256 * 1024 * 1024;
 
         private long _maxSteps;
         private int _timeoutMs;

Assets/CoreAIMods/Runtime/Sandbox/LuaCsExecutionGuard.cs

@@ -24,7 +24,7 @@ namespace CoreAI.Sandbox.LuaCs
     public sealed class LuaCsExecutionGuard
     {
         /// <summary>Default per-execution GC allocation budget enforced between VM instructions.</summary>
-        public const long DefaultMaxAllocatedBytesBudget = 64 * 1024 * 1024;
+        public const long DefaultMaxAllocatedBytesBudget = 256 * 1024 * 1024;
 
         private readonly int _timeoutMs;
         private readonly long _maxSteps;
@@ -34,7 +34,7 @@ public sealed class LuaCsExecutionGuard
         /// <param name="maxSteps">Maximum Lua-CSharp instruction steps allowed for one guarded call.</param>
         /// <param name="maxAllocatedBytes">
         /// Maximum total GC allocation (bytes) permitted for one guarded call, checked on every
-        /// instruction. Defaults to <see cref="DefaultMaxAllocatedBytesBudget"/> (64MB).
+        /// instruction. Defaults to <see cref="DefaultMaxAllocatedBytesBudget"/> (256MB).
         /// <c>&lt;= 0</c> disables the check.
         /// </param>
         public LuaCsExecutionGuard(

Assets/CoreAIMods/Runtime/Sandbox/LuaExecutionGuard.cs

@@ -31,7 +31,7 @@ public sealed class LuaExecutionGuard
         /// <param name="maxAllocatedBytes">
         /// Maximum total GC allocation (bytes) permitted for one guarded call, checked on every VM
         /// instruction. Defaults to
-        /// <see cref="InstructionLimitDebugger.DefaultMaxAllocatedBytesBudget"/> (64MB).
+        /// <see cref="InstructionLimitDebugger.DefaultMaxAllocatedBytesBudget"/> (256MB).
         /// </param>
         public LuaExecutionGuard(
             int timeoutMs = 2000,