fix: keep a global's canonical token visible across case-mode changes

IsGlobalOptionAliasHidden checked membership in HiddenAliases using
the currently active comparer, with no distinction between the
canonical token and an alias. A global registered under case-sensitive
parsing with canonical --tenant and a case-distinct hidden alias
--TENANT (a legal registration at that point) had its canonical token
incorrectly classified as hidden the moment parsing switched to
case-insensitive, because "--tenant" then compares equal to the
already-hidden "--TENANT" under the new comparer.

GlobalOptionBuilder.HiddenAlias's own contract promises the canonical
token stays visible; only Hidden() on the whole definition may retract
it. The canonical-identity check must use Ordinal specifically: using
the effective (now case-insensitive) comparer for it would also exempt
the "--TENANT" alias string itself from its own HiddenAliases
membership, undoing the fix for the entry the caller actually asked to
hide.

Author: carldebilly

src/Repl.Core/ParsingOptions.cs

@@ -257,8 +257,20 @@ internal void SetGlobalOptionAliasHidden(string canonicalName, string alias, boo
 		_customTokenOwnershipCache = null;
 	}
 
+	// The canonical token's visibility is governed solely by the definition's own IsHidden, never
+	// by HiddenAliases: a case-distinct hidden alias (registered while case-sensitive) can become
+	// equivalent to the canonical token once parsing switches to case-insensitive, and without this
+	// guard that would incorrectly hide the canonical spelling too.
+	//
+	// The canonical check is deliberately Ordinal, not the effective comparer: the effective
+	// comparer is exactly what makes "--TENANT" equivalent to canonical "--tenant" once parsing
+	// turns case-insensitive, and using it here would ALSO exempt that distinct alias string from
+	// its own HiddenAliases membership — the opposite of what HiddenAlias("--TENANT") asked for.
+	// Ordinal identifies only the canonical spelling itself; every other alias string still falls
+	// through to the normal effective-comparer membership check below.
 	internal bool IsGlobalOptionAliasHidden(GlobalOptionDefinition definition, string token) =>
-		definition.HiddenAliases.Contains(token, ResolveOptionTokenComparer());
+		!string.Equals(token, definition.CanonicalToken, StringComparison.Ordinal)
+		&& definition.HiddenAliases.Contains(token, ResolveOptionTokenComparer());
 
 	private StringComparer ResolveOptionTokenComparer() =>
 		OptionCaseSensitivity == ReplCaseSensitivity.CaseInsensitive

src/Repl.IntegrationTests/Given_HelpDiscovery.cs

@@ -279,6 +279,26 @@ public void When_GlobalAliasIsUnhiddenThroughEquivalentCasing_Then_OneRepresenta
 		upper.Text.Should().Contain("north");
 	}
 
+	[TestMethod]
+	[Description("A global registered under case-sensitive parsing with canonical --tenant and a case-distinct hidden alias --TENANT must keep its canonical token visible after switching to case-insensitive parsing: the canonical token's visibility is governed by the definition's own IsHidden, never by HiddenAliases becoming case-equivalent to it.")]
+	public void When_CaseDistinctHiddenAliasBecomesEquivalentToCanonicalAfterModeChange_Then_CanonicalStaysVisible()
+	{
+		var sut = ReplApp.Create();
+		sut.Options(options =>
+			options.Parsing.AddGlobalOption<string>("tenant", aliases: ["--TENANT"]));
+		sut.Options(options => options.Parsing.GlobalOption("tenant").HiddenAlias("--TENANT"));
+		sut.Options(options => options.Parsing.OptionCaseSensitivity = ReplCaseSensitivity.CaseInsensitive);
+		sut.Map("show", static string (IGlobalOptionsAccessor globals) => globals.GetValue<string>("tenant") ?? "none");
+
+		var help = ConsoleCaptureHelper.Capture(() => sut.Run(["--help", "--no-logo"]));
+		var canonical = ConsoleCaptureHelper.Capture(() => sut.Run(["--tenant", "acme", "show", "--no-logo"]));
+
+		help.Text.Should().Contain("--tenant");
+		help.Text.Should().NotContain("--TENANT");
+		canonical.ExitCode.Should().Be(0, canonical.Text);
+		canonical.Text.Should().Contain("acme");
+	}
+
 	[TestMethod]
 	[Description("A hidden command option stays bindable when explicitly provided but is omitted from command help.")]
 	public void When_CommandOptionIsHidden_Then_HelpOmitsItAndExplicitInvocationStillBinds()