Fix local process enumeration when Windows reports PID zero

CHANGELOG.md

@@ -27,6 +27,10 @@ ship.
 
 ### Changed
 
+- **Local process enumeration.** Ignore nonpositive operating-system process IDs, including the Windows idle
+  pseudo-process, before filtering and truncation. Unfiltered listings now return attachable process identities
+  instead of failing when the local catalog contains PID 0.
+
 ### Security
 
 ### Deployment

libs/CheatEngine.Client.Core/Domains/LocalProcessCatalog.cs

@@ -48,6 +48,13 @@ internal static bool TryEnumerate(
 					return Cancel(out result, out failure);
 				}
 
+				// Windows reports the Idle pseudo-process as PID 0. LocalProcessId deliberately models only usable,
+				// positive process identifiers, so omit system and malformed host rows before they affect the bound.
+				if (process.Id <= 0)
+				{
+					continue;
+				}
+
 				if (Matches(request, process))
 				{
 					matches.Add(process);

tests/CheatEngine.Client.Core.Tests/Domains/LocalProcessHostTests.cs

@@ -1,6 +1,8 @@
 using System.Diagnostics;
 
 using CheatEngine.Client.Core.Domains;
+using CheatEngine.Client.Processes;
+using CheatEngine.Client.Results;
 
 namespace CheatEngine.Client.Core.Tests.Domains;
 
@@ -41,4 +43,21 @@ public void GetLocalProcessesContainsCopiedMetadataForTheCurrentManagedProcess()
 
 		Assert.Equal(current.ProcessName, currentSnapshot.Name);
 	}
+
+	[Fact]
+	public void LocalCatalogSkipsSystemPseudoProcessesWhileRetainingTheCurrentProcess()
+	{
+		using Process current = Process.GetCurrentProcess();
+		LocalProcessHost host = new();
+
+		bool succeeded = LocalProcessCatalog.TryEnumerate(host,
+			new LocalProcessEnumerationRequest(int.MaxValue), out LocalProcessEnumerationResult result,
+			out CheatEngineFailure failure, TestContext.Current.CancellationToken);
+
+		Assert.True(succeeded);
+		Assert.Equal(default, failure);
+		Assert.Contains(result.Processes, process =>
+			process.Id.Value == current.Id && process.Name == current.ProcessName);
+		Assert.All(result.Processes, process => Assert.True(process.Id.Value > 0));
+	}
 }

tests/CheatEngine.Client.Core.Tests/Domains/ProcessClientLocalProcessesTests.cs

@@ -37,6 +37,46 @@ public void GetLocalProcessesReturnsBoundedOrderedCopiedLocalMetadata()
 		Assert.Empty(port.TargetCalls);
 	}
 
+	[Fact]
+	public void GetLocalProcessesSkipsSystemAndMalformedRowsBeforeApplyingTheBound()
+	{
+		(ProcessClient client, FakeLocalProcessHost host, FakeRuntimeObservationPort port) = Create(
+		[
+			new LocalProcessInfo(0, "System Idle Process", null),
+			new LocalProcessInfo(-1, "malformed", null),
+			new LocalProcessInfo(52, "alpha-worker", "C:\\fixtures\\alpha-worker.exe"),
+			new LocalProcessInfo(43, "alpha-server", "C:\\fixtures\\alpha-server.exe")
+		]);
+
+		LocalProcessEnumerationResult result = client.GetLocalProcesses(
+			new LocalProcessEnumerationRequest(1), TestContext.Current.CancellationToken);
+
+		Assert.True(result.IsTruncated);
+		LocalProcessSnapshot snapshot = Assert.Single(result.Processes);
+		Assert.Equal(new LocalProcessId(43), snapshot.Id);
+		Assert.Equal("alpha-server", snapshot.Name);
+		Assert.Equal(1, host.GetLocalProcessesCalls);
+		Assert.Empty(port.Calls);
+		Assert.Empty(port.TargetCalls);
+	}
+
+	[Fact]
+	public void GetLocalProcessesReturnsAnEmptyPageWhenOnlyNonpositiveHostRowsMatch()
+	{
+		(ProcessClient client, FakeLocalProcessHost host, _) = Create(
+		[
+			new LocalProcessInfo(0, "System Idle Process", null),
+			new LocalProcessInfo(-4, "malformed", null)
+		]);
+
+		LocalProcessEnumerationResult result = client.GetLocalProcesses(
+			new LocalProcessEnumerationRequest(1), TestContext.Current.CancellationToken);
+
+		Assert.Empty(result.Processes);
+		Assert.False(result.IsTruncated);
+		Assert.Equal(1, host.GetLocalProcessesCalls);
+	}
+
 	[Fact]
 	public void TryGetLocalProcessesReportsACancellationAsNotStartedBeforeReadingTheLocalCatalog()
 	{