Fix navigation dropdowns

src/Elastic.Documentation.Navigation/Isolated/Node/FolderNavigation.cs

@@ -38,7 +38,7 @@ public class FolderNavigation<TModel>(
 	public int NavigationIndex { get; set; }
 
 	/// <inheritdoc />
-	public string Id { get; } = ShortId.Create(parentPath);
+	public string Id { get; private set; } = null!;
 
 	/// <inheritdoc />
 	public ILeafNavigationItem<TModel> Index { get; private set; } = null!;
@@ -50,6 +50,9 @@ internal void SetNavigationItems(IReadOnlyCollection<INavigationItem> navigation
 	{
 		var indexNavigation = navigationItems.QueryIndex<TModel>(this, $"{FolderPath}/index.md", out navigationItems);
 		Index = indexNavigation;
+		// Include NavigationRoot.Id to ensure uniqueness across docsets in assembler builds
+		// (URLs alone aren't unique until path prefixes are applied by SiteNavigation)
+		Id = ShortId.Create(NavigationRoot.Id, Index.Url);
 		NavigationItems = navigationItems;
 	}
 }

src/Elastic.Documentation.Navigation/Isolated/Node/TableOfContentsNavigation.cs

@@ -28,7 +28,8 @@ INavigationHomeProvider homeProvider
 		Parent = parent;
 		Hidden = false;
 		IsUsingNavigationDropdown = false;
-		Id = ShortId.Create(parentPath);
+		// Id will be set in SetNavigationItems using Index.Url for uniqueness
+		Id = null!;
 		ParentPath = parentPath;
 		PathPrefix = pathPrefix;
 
@@ -103,7 +104,8 @@ internal void SetNavigationItems(IReadOnlyCollection<INavigationItem> navigation
 	{
 		var indexNavigation = navigationItems.QueryIndex<TModel>(this, $"{ParentPath}/index.md", out navigationItems);
 		Index = indexNavigation;
-		Id = ShortId.Create(indexNavigation.Url);
+		// Include NavigationRoot.Id to ensure uniqueness across docsets in assembler builds
+		Id = ShortId.Create(NavigationRoot.Id, Index.Url);
 		NavigationItems = navigationItems;
 	}
 }

src/Elastic.Documentation.Navigation/Isolated/Node/VirtualFileNavigation.cs

@@ -34,7 +34,8 @@ public class VirtualFileNavigation<TModel>(TModel model, IFileInfo fileInfo, Vir
 	public int NavigationIndex { get; set; }
 
 	/// <inheritdoc />
-	public string Id { get; } = ShortId.Create(args.RelativePathToDocumentationSet);
+	// Include NavigationRoot.Id to ensure uniqueness across docsets in assembler builds
+	public string Id => ShortId.Create(NavigationRoot.Id, Index.Url);
 
 	/// <inheritdoc />
 	public ILeafNavigationItem<TModel> Index { get; } =

tests/Navigation.Tests/Assembler/SiteNavigationTests.cs

@@ -166,6 +166,103 @@ public void SitePrefixAppliedToNavigationItemUrls(string? sitePrefix, string exp
 		observabilityItem.Url.Should().Be(expectedObservabilityUrl, $"sitePrefix '{sitePrefix}' should result in URL '{expectedObservabilityUrl}'");
 	}
 
+	[Fact]
+	public void NavigationNodeIdsAreUniqueAcrossDocsets()
+	{
+		// This test verifies that navigation node IDs are unique even when
+		// multiple docsets have folders with the same relative path.
+		// This is critical because IDs are used as HTML id attributes.
+
+		// Create two docsets, each with a "getting-started" folder at the same relative path
+		var fileSystem = new MockFileSystem();
+
+		// Docset 1: product-a with getting-started folder
+		var productADir = "/checkouts/current/product-a";
+		// language=yaml
+		var productADocset = """
+		                     project: product-a
+		                     toc:
+		                       - file: index.md
+		                       - folder: getting-started
+		                         children:
+		                           - file: index.md
+		                           - file: quick-start.md
+		                     """;
+		fileSystem.AddFile($"{productADir}/docs/docset.yml", new MockFileData(productADocset));
+		fileSystem.AddFile($"{productADir}/docs/index.md", new MockFileData("# Product A"));
+		fileSystem.AddFile($"{productADir}/docs/getting-started/index.md", new MockFileData("# Getting Started A"));
+		fileSystem.AddFile($"{productADir}/docs/getting-started/quick-start.md", new MockFileData("# Quick Start A"));
+
+		// Docset 2: product-b with getting-started folder (same relative path!)
+		var productBDir = "/checkouts/current/product-b";
+		// language=yaml
+		var productBDocset = """
+		                     project: product-b
+		                     toc:
+		                       - file: index.md
+		                       - folder: getting-started
+		                         children:
+		                           - file: index.md
+		                           - file: tutorial.md
+		                     """;
+		fileSystem.AddFile($"{productBDir}/docs/docset.yml", new MockFileData(productBDocset));
+		fileSystem.AddFile($"{productBDir}/docs/index.md", new MockFileData("# Product B"));
+		fileSystem.AddFile($"{productBDir}/docs/getting-started/index.md", new MockFileData("# Getting Started B"));
+		fileSystem.AddFile($"{productBDir}/docs/getting-started/tutorial.md", new MockFileData("# Tutorial B"));
+
+		// Create navigation for both docsets
+		var productAContext = SiteNavigationTestFixture.CreateContext(fileSystem, productADir, output);
+		var productADocsetFile = DocumentationSetFile.LoadAndResolve(productAContext.Collector, fileSystem.FileInfo.New($"{productADir}/docs/docset.yml"), fileSystem);
+		var productANav = new DocumentationSetNavigation<IDocumentationFile>(productADocsetFile, productAContext, GenericDocumentationFileFactory.Instance);
+
+		var productBContext = SiteNavigationTestFixture.CreateContext(fileSystem, productBDir, output);
+		var productBDocsetFile = DocumentationSetFile.LoadAndResolve(productBContext.Collector, fileSystem.FileInfo.New($"{productBDir}/docs/docset.yml"), fileSystem);
+		var productBNav = new DocumentationSetNavigation<IDocumentationFile>(productBDocsetFile, productBContext, GenericDocumentationFileFactory.Instance);
+
+		// Get the "getting-started" folders from each docset
+		var productAGettingStarted = productANav.NavigationItems.First()
+			.Should().BeOfType<FolderNavigation<IDocumentationFile>>().Subject;
+		var productBGettingStarted = productBNav.NavigationItems.First()
+			.Should().BeOfType<FolderNavigation<IDocumentationFile>>().Subject;
+
+		// Both folders have the same relative path within their docsets
+		productAGettingStarted.FolderPath.Should().Be("getting-started");
+		productBGettingStarted.FolderPath.Should().Be("getting-started");
+
+		// But they MUST have different IDs because they resolve to different URLs
+		// Product A: /product-a/getting-started
+		// Product B: /product-b/getting-started
+		productAGettingStarted.Id.Should().NotBe(productBGettingStarted.Id,
+			"folders with the same relative path but in different docsets should have different IDs " +
+			"because they have different URLs");
+
+		// Also verify in assembled navigation context
+		// language=yaml
+		var siteNavYaml = """
+		                  toc:
+		                    - toc: product-a://
+		                      path_prefix: /product-a
+		                    - toc: product-b://
+		                      path_prefix: /product-b
+		                  """;
+		var siteNavFile = SiteNavigationFile.Deserialize(siteNavYaml);
+		var documentationSets = new List<IDocumentationSetNavigation> { productANav, productBNav };
+		var siteContext = SiteNavigationTestFixture.CreateContext(fileSystem, productADir, output);
+		var siteNavigation = new SiteNavigation(siteNavFile, siteContext, documentationSets, sitePrefix: null);
+
+		// Use production YieldAll() to collect all navigation items
+		var allNodeItems = ((INavigationTraversable)siteNavigation).YieldAll()
+			.OfType<INodeNavigationItem<INavigationModel, INavigationItem>>()
+			.ToList();
+
+		// Verify all IDs are unique
+		var allIds = allNodeItems.Select(n => n.Id).ToList();
+		var uniqueIds = allIds.Distinct().ToList();
+		uniqueIds.Should().HaveCount(allIds.Count,
+			$"all navigation node IDs should be unique in assembled navigation. " +
+			$"Found duplicates: {string.Join(", ", allIds.GroupBy(id => id).Where(g => g.Count() > 1).Select(g => $"ID '{g.Key}' appears {g.Count()} times"))}");
+	}
+
 	[Theory]
 	[InlineData(null, "/observability", "/search")]
 	[InlineData("docs", "/docs/observability", "/docs/search")]

tests/Navigation.Tests/Isolation/NavigationStructureTests.cs

@@ -362,4 +362,5 @@ void VisitNavigationItems(INavigationItem item)
 
 		context.Diagnostics.Should().BeEmpty();
 	}
+
 }