In conversational flows, a falsy return from an overridden route_turn()
fell back to the sticky state.last_intent from a previous turn, silently
re-running the prior turn's handler for an unhandled input.
The fallback exists for the legacy default_intents path, where
receive_user_message() classifies the intent fresh each turn. Track that
per-turn classification in _turn_classified_intent (cleared on every turn
reset) and route on it instead, so a falsy route_turn() now falls through
to the built-in answer_from_history/converse defaults and never reuses
stale routing state.
Fixes EPD-176.
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Lorenze Jay <63378463+lorenzejay@users.noreply.github.com>
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