First live run (cheunart) tripped the drift guard: "no posts and no recognizable
feed container". The browser-saved page was normal (6 posts + posts_container-list),
so the parser was fine — our live HTTP fetch got a different response. Cause: the
client set X-Requested-With: XMLHttpRequest (+ a JSON Accept) session-wide, so the
initial creator-page GET was sent as an XHR. SubscribeStar (Rails) content-
negotiates an XHR full-page request to a non-HTML body → no container → drift.
Fix: the session now uses browser-like navigation headers (Accept: html, NO
X-Requested-With); the XHR header + JSON Accept are applied PER-REQUEST only on
the "load more" endpoint (which is a genuine XHR). Drift message now reports the
response length + a JSON hint so a recurrence is self-explaining. Regression test
pins the header split (navigation initial GET, XHR load-more).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
bvandeusen
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