fix(tags): only hide shadow tags in production builds

The TagsPlugin's summary already documented that shadow tags are hidden
"in production", but the implementation keyed the decision off serve vs.
build (hideShadow = shadow && !(IsServe && shadow_on_serve)). That hid
shadow tags on every non-serve build, including dev/nonprod deploys, so
authors lost visibility of Draft/Internal/ToDo tags on the preview site.

Gate hiding on Options.IsProduction so shadow tags are:
- visible in `serve` and dev (non-prod) builds, and
- hidden only in production (`--prod`) builds,
with shadow_on_serve still keeping them visible under `serve --prod`.

Add regression tests covering the production/development/serve cases.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Netdocs

src/Netdocs.Plugins/TagsPlugin.cs

@@ -31,7 +31,10 @@ public void Configure(IPluginContext ctx)
 
     public Task OnBuildStartAsync(SiteContext site, CancellationToken ct)
     {
-        var hideShadow = _shadow && !(site.Options.IsServe && _shadowOnServe);
+        // Shadow tags are hidden only in production builds, so authors still see Draft/Internal/
+        // ToDo tags on the dev site and in `serve`. `shadow_on_serve` keeps them visible even when
+        // serving a production build (e.g. `serve --prod`).
+        var hideShadow = _shadow && site.Options.IsProduction && !(site.Options.IsServe && _shadowOnServe);
         var index = new SortedDictionary<string, List<Page>>(StringComparer.OrdinalIgnoreCase);
 
         foreach (var page in site.Pages)

tests/Netdocs.Core.Tests/TagsPluginTests.cs

@@ -45,12 +45,14 @@ public void AddAsset(string sourcePath, string destRelative) { }
         FrontMatter = new Dictionary<string, object?>(),
     };
 
-    private static SiteContext BuildSite(params Page[] pages)
+    private static SiteContext BuildSite(params Page[] pages) => BuildSite(new BuildOptions(), pages);
+
+    private static SiteContext BuildSite(BuildOptions options, params Page[] pages)
     {
         var site = new SiteContext
         {
             Config = new SiteConfig { ProjectRoot = Path.GetTempPath() },
-            Options = new BuildOptions(),
+            Options = options,
             LoggerFactory = NullLoggerFactory.Instance,
         };
         foreach (var p in pages) site.Pages.Add(p);
@@ -64,6 +66,18 @@ private static TagsPlugin Configured()
         return plugin;
     }
 
+    private static TagsPlugin ConfiguredWithShadow()
+    {
+        var plugin = new TagsPlugin();
+        plugin.Configure(new FakeContext(new Dictionary<string, object?>
+        {
+            ["export"] = false,
+            ["shadow"] = true,
+            ["shadow_tags"] = new List<object?> { "Draft", "Internal", "ToDo" },
+        }));
+        return plugin;
+    }
+
     [Fact]
     public async Task BareMarker_RendersFullIndex()
     {
@@ -175,4 +189,46 @@ public async Task Heading_Anchor_SlugifiesSpacesAndPunctuationPerSegment()
         Assert.Contains("{ #tag:energy-monitoring }", index.RawMarkdown);
         Assert.Contains("{ #tag:development/net }", index.RawMarkdown);
     }
+
+    [Fact]
+    public async Task ShadowTags_HiddenInProductionBuild()
+    {
+        var draft = Tagged("draft.md", "Draft Page", "Draft", "Process");
+        var index = Marker("tags/index.md", "<!-- material/tags -->");
+        var site = BuildSite(new BuildOptions { IsProduction = true }, draft, index);
+
+        await ConfiguredWithShadow().OnBuildStartAsync(site, CancellationToken.None);
+
+        // The shadow tag is dropped from the index, but non-shadow tags on the same page remain.
+        Assert.DoesNotContain("## Draft", index.RawMarkdown);
+        Assert.Contains("## Process", index.RawMarkdown);
+        Assert.Equal(new[] { "Process" }, (IEnumerable<string>)draft.Meta["tags"]!);
+    }
+
+    [Fact]
+    public async Task ShadowTags_VisibleInDevelopmentBuild()
+    {
+        var draft = Tagged("draft.md", "Draft Page", "Draft", "Process");
+        var index = Marker("tags/index.md", "<!-- material/tags -->");
+        // Non-production build (e.g. the nonprod/dev deploy) keeps shadow tags visible.
+        var site = BuildSite(new BuildOptions { IsProduction = false }, draft, index);
+
+        await ConfiguredWithShadow().OnBuildStartAsync(site, CancellationToken.None);
+
+        Assert.Contains("## Draft", index.RawMarkdown);
+        Assert.Contains("## Process", index.RawMarkdown);
+    }
+
+    [Fact]
+    public async Task ShadowTags_VisibleWhenServingProductionBuild()
+    {
+        var draft = Tagged("draft.md", "Draft Page", "Draft");
+        var index = Marker("tags/index.md", "<!-- material/tags -->");
+        // shadow_on_serve (default true) keeps them visible even under `serve --prod`.
+        var site = BuildSite(new BuildOptions { IsProduction = true, IsServe = true }, draft, index);
+
+        await ConfiguredWithShadow().OnBuildStartAsync(site, CancellationToken.None);
+
+        Assert.Contains("## Draft", index.RawMarkdown);
+    }
 }