The dev leaf route wrote the URL's parts into the page's <title> and the
element's profile-config attribute, refusing only .. and /. A quote or a
tag in a crafted link broke out of the attribute on a publicly reachable
dev server. Each part must now have the shape every bundle, profile and
instance id has, before it reaches either; the title is escaped too.
check:dev-leaf-escape drives the plugin's own middleware: every leaf the
dev manifest advertises is still served in both URL forms, hostile parts
are refused in every position, and the title escapes on its own.
