- start_session now RESUMES an existing ACTIVE session for the persona instead of creating
a new one / forcing re-pick of the scenario (keep original scenario+messages).
- send_message falls back to a text-based decision detector (_detect_customer_decision)
because real LLMs rarely emit structured meta.decision — so a customer who says
'ซื้อไม่ไหว'/'no thanks' now actually ENDS the chat as lost (was stuck active forever).
Fragments handled in TH + EN; buy + walk.
All 11 backend suites pass. Rebuilt dist.
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