Odin currently advertises general Q&A via the /chat path, which burns API
credits on open-ended questions. Guard it: a text-only message makes NO AI
call — it gets a canned reply telling the user to attach an invoice. The
invoice path (attachments → extract) is unchanged. Removing the guard
re-enables the general /chat path for a later phase.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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