Serves phoenix_kit_catalogue's vendored PDF.js viewer assets through the router.

The catalogue PDF detail page embeds the viewer from /_pdfjs/.... Normally those bytes are served by a Plug.Static mount that mix phoenix_kit.install / mix phoenix_kit.update add to the host endpoint. That mount is fragile — a host that bumps the deps without re-running the task (or whose endpoint gets regenerated by a scaffold script) loses it, and the viewer iframe then 404s with a NoRouteError.

This controller is the router-served fallback. Because it's wired in via phoenix_kit_routes() (the same mechanism behind /file/... and /<prefix>/assets/...), it's present on every host that mounts PhoenixKit at all — no endpoint patch required. When the endpoint Plug.Static mount is present it runs first (endpoint plugs precede the router), so this only handles the fall-through.

Read-only: it streams files from the catalogue app's priv/static/pdfjs/ and nothing else. Path traversal is rejected via Path.safe_relative/1 plus an expanded-prefix check.

Compatibility note

The route is mounted at the root literal /_pdfjs/*path (no URL prefix / locale) so it matches the same URL the catalogue's iframe and the endpoint Plug.Static mount use. A host app that already serves its own /_pdfjs/... would shadow / be shadowed here — but the path is deliberately underscore-prefixed and module-namespaced to avoid collisions, and the route only compiles in when phoenix_kit_catalogue is a dependency.