Both endpoints were declared as bare relative paths ("admin/users/theme",
"admin/users/switch-tenant") and handed to postForm(), which normalizes
through `new URL(value, window.location.href)`. On a deep route like
/de/admin/permissions that resolves to /de/admin/admin/users/theme —
404 → 302 to error page → HTML response → JSON.parse throws → the theme
toggle reverts visually. The tenant switcher had the same latent bug.
- Topbar renders data-theme-url and data-switch-tenant-url via lurl(), so
both carry the locale-aware root-anchored path.
- Tenant switcher reads data-switch-tenant-url from the switcher root
(matching the theme-menu convention) and passes it through to
switchTenant(); fail-fast warning if the attribute is missing.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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