[SystemService] Write notice skip flag as byte (#346)

The Gen5 caller supplies a one-byte flag. Preserve pointer and memory-fault behavior while writing only that byte, and cover a seeded guest-memory boundary that rejects the former four-byte write.

src/SharpEmu.Libs/SystemService/SystemServiceExports.cs

@@ -38,8 +38,8 @@ public static class SystemServiceExports
         }
 
         // No system notice screen to skip in the emulator; report "do not skip".
-        Span<byte> flagBytes = stackalloc byte[sizeof(int)];
+        Span<byte> flagBytes = stackalloc byte[1];
-        BinaryPrimitives.WriteInt32LittleEndian(flagBytes, 0);
+        flagBytes[0] = 0;
         return ctx.Memory.TryWrite(flagAddress, flagBytes)
             ? ctx.SetReturn(0)
             : ctx.SetReturn((int)OrbisGen2Result.ORBIS_GEN2_ERROR_MEMORY_FAULT);

tests/SharpEmu.Libs.Tests/SystemService/SystemServiceExportsTests.cs

@@ -0,0 +1,29 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.HLE;
+using SharpEmu.Libs.SystemService;
+using Xunit;
+
+namespace SharpEmu.Libs.Tests.SystemService;
+
+public sealed class SystemServiceExportsTests
+{
+    private const ulong MemoryBase = 0x1_0000_0000;
+
+    [Fact]
+    public void GetNoticeScreenSkipFlagWritesOneByteAtMemoryBoundary()
+    {
+        var memory = new FakeCpuMemory(MemoryBase, 1);
+        var context = new CpuContext(memory, Generation.Gen5);
+        Assert.True(memory.TryWrite(MemoryBase, new byte[] { 0xA5 }));
+        context[CpuRegister.Rdi] = MemoryBase;
+
+        Assert.Equal(0, SystemServiceExports.SystemServiceGetNoticeScreenSkipFlag(context));
+        Assert.Equal(0UL, context[CpuRegister.Rax]);
+
+        Span<byte> flag = stackalloc byte[1];
+        Assert.True(memory.TryRead(MemoryBase, flag));
+        Assert.Equal(0, flag[0]);
+    }
+}