feat(pages): Redesign the error pages (backport #581)

[mergify]

What

Redesigns all eight error pages and points the 500 page at the bench's web.error.log.

Before, each page was a logo header over a shadowed card, with the docs link styled as an inline 📄 pseudo-button. Now every page is one shared layout: icon, heading, error line, optional docs button, owner footer.

Page	Status	Icon
bad_gateway.html	502	red
gateway_timeout.html	504	red
internal_server_error.html	500	red
exceeded.html	429	amber
suspended.html / suspended_saas.html	402	amber
deactivated.html	503	amber
home.html	—	neutral

Visited links

Text links carry the plain-html visited purple. The rule is scoped a:not(.button):visited deliberately: a bare a:visited has specificity (0,1,1) and outranks .button's own color: #fff at (0,1,0), which repaints the button's white label purple. The button itself has no visited state — :visited reaches only a few colour properties, never a button's label, and Chrome has partitioned it per top-level site and frame origin since 136.

The 500 page

The traceback for a 500 lands in the bench's web.error.log, so the footer now links straight to /dashboard/benches/<bench>/logs/web.error.log instead of the site's dashboard root.

One static page is shared by every bench on the server, so the page ships __BENCH_NAME__ and the per-bench nginx config substitutes it:

location = /internal_server_error.html {
	root {{ error_pages_directory }};
	sub_filter '__BENCH_NAME__' '{{ bench_name }}';
}

This works because the 500 interception injects <iframe src="/internal_server_error.html"> — a relative URL — so the iframe request carries the failing site's Host and resolves through its own bench's server block.

A side effect worth having: this page no longer needs the window.location.hostname script, making it the one error page immune to the custom-domain problem, where hostname is not the site's name once a custom domain is in front of it. The other pages still have that pre-existing issue.

Also drops the Google Fonts <link> an earlier attempt carried — an external font request would hang on the very networks these pages appear on.

Testing

Verified end to end against a local Frappe Cloud install with a real bench on f1.local.frappe.dev:

• nginx substitution over HTTP — the same file (one md5) served through two hosts returned bench-0004-000023-f1 and bench-0004-000022-f1 respectively
• press.api.bench.log returned {'web.error.log': ...} through the full path: permission check, release-group check, circuit breaker, live agent call
• LogPage.vue derives the release group as bench-${name.split('-')[1]}; confirmed against real records (bench-0004-000023-f1 → bench-0004)
• both template branches (standalone and non-standalone) render the sub_filter correctly

agent/tests/test_pages.py covers the invariants that would silently break a page: no external resources, the scoped visited rule, dashboard links paired with their rewrite script, and every __BENCH_NAME__ matched by a sub_filter in each of its nginx location blocks.

🤖 Generated with Claude Code

---

This is an automatic backport of pull request #581 done by Mergify.

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Changes to be committed:
	modified:   agent/pages/bad_gateway.html
	modified:   agent/pages/gateway_timeout.html
	modified:   agent/pages/home.html
	modified:   agent/pages/internal_server_error.html
	modified:   agent/pages/suspended_saas.html
	new file:   agent/tests/test_pages.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   agent/pages/deactivated.html
	both modified:   agent/pages/exceeded.html
	both modified:   agent/pages/suspended.html

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