ensureUrlIsNotOutdated() replaces the URL with httpRoot ("/") once the
layout state diverges from the state recorded after load. That behaviour
exists so an outdated shortlink path (/z/...) doesn't linger in the
address bar, but since #8166 started running the shared state-tracking in
embedded mode too, it also fired inside /e iframes: the first edit (or
any state churn) silently rewrote the iframe's URL to "/" with no hash.
Browsers that restore an iframe's session-history URL when the parent
page reloads (Firefox does) then loaded the full site instead of the
embed: the default language example plus the privacy-policy popup, since
cookies are unreadable in a cross-site iframe.
Skip the rewrite entirely in embedded mode, and add Cypress coverage for
embeds: the intended code loads, the /e#state URL survives state
changes, and the "Edit on Compiler Explorer" link still tracks edits
(the behaviour #8166 added).
Fixes#8896
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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