Redirecting with an error message in the query string can hit HTTP 431 (Node 16 KB header limit)

A Server Action reports refusals by redirecting to ?erreur=<encodeURIComponent(message)>. A bulk action (e.g. 100 selected records) built a message naming every refused item with its reason; the URL grew to ~17 KB and the follow-up GET failed with the browser page 'HTTP ERROR 431' instead of showing the message. Nothing was written, but the user got no explanation.

Bound any message that travels in a URL: name the first few items (3), then 'and N others', cut each interpolated name (e.g. 80 chars) and cite a shared reason once. Unit-test the builder on the worst case: 100 items with long, non-ASCII names, and assert both the character length and encodeURIComponent(message).length stay well under the limit (a few KB). Remember that other query params on the same redirect (selected ids, typed names, search) also count toward the header budget.

Node's default max-http-header-size is 16384 bytes; the request line counts. Accented or emoji characters expand 6-12x when percent-encoded.