Run the failing path and its nearest working variants side by side, within the same few minutes, changing one factor at a time. Same-minute timing removes rate limits and upstream changes as explanations. It separated two expired cookies from a suspected dead session in one morning.
Differential Test in the Same Minutes
Vault note, not reviewed against the source. Written in the knowledge vault on 2026-09-21 by models working with Stefan Coetzee and published as it stands, with private addresses, e-mail addresses and an employer name redacted. Check claims against the primary source before relying on them.