fix(#36855/#30300): export 404.html correctly

[SukkaW]

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

The PR fixes #30300 and #36855.

The corresponding integration test case has been added.

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
buildDuration	19.2s	20s	⚠️ +792ms
buildDurationCached	7.8s	7.8s	⚠️ +16ms
nodeModulesSize	475 MB	475 MB	⚠️ +663 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
/ failed reqs	0	0	✓
/ total time (seconds)	4.788	5.11	⚠️ +0.32
/ avg req/sec	522.14	489.28	⚠️ -32.86
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.644	1.722	⚠️ +0.08
/error-in-render avg req/sec	1520.33	1451.54	⚠️ -68.79

Client Bundles (main, webpack)

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
925.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42 kB	42 kB	✓
main-HASH.js gzip	28.8 kB	28.8 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	72.5 kB	72.5 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
_app-HASH.js gzip	1.36 kB	1.36 kB	✓
_error-HASH.js gzip	193 B	193 B	✓
amp-HASH.js gzip	308 B	308 B	✓
css-HASH.js gzip	327 B	327 B	✓
dynamic-HASH.js gzip	2.7 kB	2.7 kB	✓
head-HASH.js gzip	359 B	359 B	✓
hooks-HASH.js gzip	920 B	920 B	✓
image-HASH.js gzip	5.71 kB	5.71 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.65 kB	2.65 kB	✓
routerDirect..HASH.js gzip	320 B	320 B	✓
script-HASH.js gzip	391 B	391 B	✓
withRouter-HASH.js gzip	318 B	318 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	15.9 kB	15.9 kB	✓

Client Build Manifests

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
_buildManifest.js gzip	458 B	458 B	✓
Overall change	458 B	458 B	✓

Rendered Page Sizes

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
index.html gzip	532 B	532 B	✓
link.html gzip	544 B	544 B	✓
withRouter.html gzip	527 B	527 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Default Build with SWC (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
buildDuration	21.7s	21.5s	-224ms
buildDurationCached	7.7s	7.7s	-72ms
nodeModulesSize	475 MB	475 MB	⚠️ +663 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
/ failed reqs	0	0	✓
/ total time (seconds)	4.851	4.777	-0.07
/ avg req/sec	515.37	523.33	+7.96
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.705	1.605	-0.1
/error-in-render avg req/sec	1466.09	1557.83	+91.74

Client Bundles (main, webpack)

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
925.HASH.js gzip	178 B	178 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	29.3 kB	29.3 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	73.2 kB	73.2 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	179 B	179 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	324 B	324 B	✓
dynamic-HASH.js gzip	2.72 kB	2.72 kB	✓
head-HASH.js gzip	357 B	357 B	✓
hooks-HASH.js gzip	921 B	921 B	✓
image-HASH.js gzip	5.8 kB	5.8 kB	✓
index-HASH.js gzip	261 B	261 B	✓
link-HASH.js gzip	2.77 kB	2.77 kB	✓
routerDirect..HASH.js gzip	322 B	322 B	✓
script-HASH.js gzip	392 B	392 B	✓
withRouter-HASH.js gzip	317 B	317 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	16.1 kB	16.1 kB	✓

Client Build Manifests

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
_buildManifest.js gzip	458 B	458 B	✓
Overall change	458 B	458 B	✓

Rendered Page Sizes

	vercel/next.js canary	SukkaW/next.js fix-36855	Change
index.html gzip	527 B	527 B	✓
link.html gzip	542 B	542 B	✓
withRouter.html gzip	524 B	524 B	✓
Overall change	1.59 kB	1.59 kB	✓

Commit: de95c82

[huozhi]

Thank you!