How do I tell which deploy was live when a session failed?

Match the session’s own timestamp against your deploy history: the version live at that moment is whichever one’s deploy window contains the time the session ran, not whichever version is live now. This only works if you can reconstruct that window, so it depends on keeping a deploy log or commit history with real timestamps, not just a changelog of what shipped eventually. Once you have the version, you have the actual code, prompt, and configuration that produced the failing session, which is the input every other step of the investigation needs: you can’t test whether a candidate change explains a failure without knowing what was actually running when it happened. Without this, timing gets fuzzy fast; two changes shipped an hour apart can both look plausible, and only the deploy window tells you which one was actually live when the failure happened.

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