X_AI_PROMPT_SECRET

a Secret was about to be rendered into a prompt

a Secret passed through vars(). Nothing would have leaked — Secret redacts by value, so the template would have received [redacted] and asked the model to reason about it, which is a prompt that reads fine and means something else. The same class of failure as an unfilled {{slot}}, refused for the same reason: loudly, before a token is spent

drop the key from vars() and from the template, or revealSecret(value) in vars() if the model genuinely has to read it