Refactor Repl.Core: organize files, extract CoreReplApp engines, fix new analyzers

.editorconfig

@@ -82,3 +82,31 @@ dotnet_naming_symbols.private_fields.applicable_accessibilities = private
 
 dotnet_naming_style.camel_case_underscore.required_prefix = _
 dotnet_naming_style.camel_case_underscore.capitalization = camel_case
+
+# CAxxxx analyzers
+dotnet_diagnostic.CA1066.severity = warning
+dotnet_diagnostic.CA1068.severity = warning
+dotnet_diagnostic.CA1819.severity = suggestion # byte[] in record DTOs is acceptable; ImmutableArray<byte> would be too invasive
+dotnet_diagnostic.CA1823.severity = warning
+dotnet_diagnostic.CA2207.severity = warning
+
+# IDExxxx analyzers
+dotnet_diagnostic.IDE1006.severity = warning
+
+# Meziantou Analyzers
+dotnet_diagnostic.MA0032.severity = suggestion # CancellationToken is good practice but shouldn't block compilation
+dotnet_diagnostic.MA0045.severity = warning # Do not use blocking calls in a sync method (need to make calling method async)
+dotnet_diagnostic.MA0080.severity = error # Use a cancellation token using .WithCancellation()
+dotnet_diagnostic.MA0155.severity = error # No async void
+dotnet_diagnostic.MA0162.severity = error # Correctly use Process.Start()
+dotnet_diagnostic.MA0167.severity = warning # Force usage of TimeProvider whenever possible
+dotnet_diagnostic.MA0168.severity = error # Correctly use readonly structs
+dotnet_diagnostic.MA0171.severity = warning # Don't use the ugly .HasValue on nullable types
+dotnet_diagnostic.MA0180.severity = warning # Correctly use ILogging types
+dotnet_diagnostic.MA0181.severity = none # Explicit casts are idiomatic in low-level serialization/rendering code
+dotnet_diagnostic.MA0186.severity = warning # Correctly use [NotNullWhen()]
+
+# Relax certain analyzers in test projects and samples — intentional sync patterns are common.
+[{src/Repl.IntegrationTests/**.cs,src/Repl.McpTests/**.cs,src/Repl.Tests/**.cs,src/Repl.ShellCompletionTestHost/**.cs,samples/**/**.cs}]
+dotnet_diagnostic.MA0045.severity = suggestion
+dotnet_diagnostic.MA0167.severity = suggestion

samples/08-mcp-server/Program.cs

@@ -47,7 +47,7 @@ The email must be unique across all contacts.
 	contact.Map("delete {id:int}",
 		async ([Description("Contact numeric id")] int id, Repl.Interaction.IReplInteractionChannel interaction, CancellationToken ct) =>
 		{
-			if (!await interaction.AskConfirmationAsync("confirm", $"Delete contact {id}?", options: new(ct)))
+			if (!await interaction.AskConfirmationAsync("confirm", $"Delete contact {id}?", options: new(CancellationToken: ct)))
 			{
 				return Results.Cancelled("Delete cancelled by user.");
 			}

src/Repl.Core/AmbientCommandDefinition.cs

@@ -3,7 +3,7 @@ namespace Repl;
 /// <summary>
 /// Defines a custom ambient command available in all interactive scopes.
 /// </summary>
-public sealed class AmbientCommandDefinition
+internal sealed class AmbientCommandDefinition
 {
 	/// <summary>
 	/// Gets the command name (matched case-insensitively).