Reject status page custom CSS containing @import or a url() / image-set()
/ image() / cross-fade() whose target is http(s) or protocol-relative,
while allowing data: and relative URLs. The check normalizes comments and
CSS escapes first so obfuscated forms cannot slip past. Enforced in the
create/update body validation.
Bound customCSS to 100000 characters on both the client schema and the
server body validation (the server is the enforcement boundary; multer's
1MB field cap was the only limit), regenerate the OpenAPI spec, and add
a validation test suite covering acceptance, clearing, the length cap,
and type rejection.