Plugin admin page declared with path "/" never gets the sidebar active state (hits the official forms plugin)

[marks-zyz]

What happens

A plugin admin page declared with path: "/" never gets the active state in the sidebar. The link works and the page renders; only the highlight is missing, so the sidebar shows no selected item while you are on that page.

This hits the official @emdash-cms/plugin-forms: its first page is declared as { path: "/", label: "Forms" }, and "Forms" stays unhighlighted while /plugins/emdash-forms is open. Its second page (/submissions) highlights correctly.

Repro

1. Any admin with a plugin that declares an admin page with path: "/" (the shipped forms plugin does).
2. Click the item in the sidebar under Plugins.
3. The page loads, the URL becomes /_emdash/admin/plugins/<id>, and no sidebar item is marked active.

Measured on emdash 0.36.0 / @emdash-cms/admin 0.36.0, in astro dev, by reading data-active on the sidebar anchors:

/_emdash/admin/plugins/emdash-forms/submissions  -> data-active="true"
/_emdash/admin/plugins/emdash-forms              -> no data-active

Cause

packages/admin/src/components/Sidebar.tsx:364 builds the target by concatenation:

pluginItems.push({
  to: `/plugins/${pluginId}${page.path}`,
  ...

With page.path === "/" that yields /plugins/<id>/, with a trailing slash. The router renders and navigates to the normalized path (/plugins/<id>, no trailing slash), but isItemActive compares the raw to against the current path (Sidebar.tsx:226):

return path === "/"
  ? currentPath === "/"
  : currentPath === path || currentPath.startsWith(`${path}/`);

"/plugins/emdash-forms" === "/plugins/emdash-forms/" is false, and startsWith("/plugins/emdash-forms//") is false too, so the item can never match.

Suggested fix

Normalize the trailing slash on both sides in isItemActive, keeping the special case for the admin root:

const TRAILING_SLASHES = /\/+$/;

function stripTrailingSlash(value: string): string {
  return value.length > 1 ? value.replace(TRAILING_SLASHES, "") : value;
}

export function isItemActive(itemPath: string, currentPath: string): boolean {
  const queryIndex = itemPath.indexOf("?");
  const raw = queryIndex === -1 ? itemPath : itemPath.slice(0, queryIndex);
  const path = stripTrailingSlash(raw);
  const current = stripTrailingSlash(currentPath);
  return path === "/"
    ? current === "/"
    : current === path || current.startsWith(`${path}/`);
}

That keeps every existing case (the function is exported and covered by packages/admin/tests/components/Sidebar.test.tsx) and fixes any item whose to ends in a slash, not just plugin pages.

Happy to send this as a PR with a test for the path: "/" case if you want it in this shape.

Workaround for plugin authors

Declare the page with a real segment (path: "/status") instead of "/".