with

• Astro v 4.8.1

using static generator option in Astro,i.e. output: "static"

default defineConfig({
  site: "https://abc.xyz",
  prefetch: true,
  output: "static"
});

having a tag page on routing oftag/ using getStaticPaths() method

use

src/pages/tag/[tag].astro

---

const { tag } = Astro.params;

export const prerender = false;

export function getStaticPaths() {
  return [
  { params: { tag: "alpha" } }, 
  { params: { tag: "beta" } }
  ];
}

---

<article title={tag || "default" }>
  <span >no tags found</span>
</title>

here tag/alpha and tag/beta works but user type tag/gamma then it reaches to 404 page
desired behavior is not to show 404 but custom message , although url does not change to /404

and in terminal it throw Warning

A getStaticPaths() route pattern was matched, but no matching static path was found for requested path /tag/gamma.

trial 1 adding undefined path

added undefined route

export function getStaticPaths() {
  return [
  { params: { tag: "alpha" } }, 
  { params: { tag: "beta" } },
  { params: { tag: undefined } }
 ];
}

but did not work and gives type error missing parameter “tag” as below

trial 2 using a flag

---
const validTag = ["alpha", "beta" ];
export function getStaticPaths() {
  return [
  { params: { tag: "alpha" } },
  { params: { tag: "beta" } }
];
}

const { tag } = Astro.params;
const isValidTag = validTag.includes(tag);
---
<article title={tag || "default" }>
 {isValidTag ? <p>Valid tag</p> : <p>No tag found</p>}
</article>

this also not working; show 404 page.