feat(webui): extend shared explorer tree actions

webui/tests/explorer-tree.test.tsx

@@ -0,0 +1,55 @@
+function assert(condition: unknown, message = "assertion failed"): void {
+  if (!condition) throw new Error(message);
+}
+
+function count(markup: string, pattern: RegExp): number {
+  return markup.match(pattern)?.length ?? 0;
+}
+
+import { renderToStaticMarkup } from "react-dom/server";
+import ExplorerTree from "../src/components/ExplorerTree";
+import IconButton from "../src/components/IconButton";
+
+type TestNode = {
+  id: string;
+  label: string;
+  children: TestNode[];
+};
+
+function noop() {}
+
+const alpha: TestNode = { id: "alpha", label: "Alpha", children: [] };
+const beta: TestNode = { id: "beta", label: "Beta", children: [] };
+alpha.children.push(beta);
+beta.children.push(alpha);
+
+const markup = renderToStaticMarkup(
+  <ExplorerTree
+    nodes={[alpha, alpha]}
+    getNodeId={(node) => node.id}
+    getNodeLabel={(node) => node.label}
+    getNodeChildren={(node) => node.children}
+    activeId="beta"
+    collapsible={false}
+    onOpen={noop}
+    renderNodeContent={(node) => <span>{`node-${node.id}`}</span>}
+    renderNodeActions={(node) => (
+      <IconButton label={`Add below ${node.label}`} icon={<span>+</span>} onClick={noop} />
+    )}
+  />
+);
+
+assert(markup.includes("node-alpha"), "the root node is rendered");
+assert(markup.includes("node-beta"), "non-collapsible trees render descendants without expansion state");
+assert(count(markup, /node-alpha/g) === 1, "a cycle does not render an ancestor again");
+assert(count(markup, /node-beta/g) === 1, "duplicate paths do not duplicate descendants");
+assert(count(markup, /explorer-tree-toggle-static/g) === 2, "non-collapsible nodes render static tree affordances");
+assert(!markup.includes('<button type="button" class="explorer-tree-toggle'), "non-collapsible nodes do not expose dead toggle buttons");
+assert(markup.includes("explorer-tree-node-wrap file-tree-node-wrap has-actions"), "rows reserve a sibling action column only when used");
+assert(markup.includes('class="explorer-tree-actions" role="group"'), "node actions expose group semantics");
+assert(markup.includes('aria-label="Add below Alpha"'), "node action controls retain accessible labels");
+assert(
+  /node-alpha<\/span><\/button><div class="explorer-tree-actions"/.test(markup),
+  "node actions are siblings of the node button instead of nested interactive content"
+);
+assert(markup.includes('aria-current="true"'), "the active node is exposed to assistive technology");