Replace the substring _detect_addressee_id helper with a classifier
call for the multi-entity case. The substring helper is kept as a
fast-path for the no-guest case (no LLM round-trip needed when only
one bot is present, preserves throughput).
- New service chat/services/addressee.py wrapping the existing
classifier wrapper. AddresseeDecision carries addressee_id +
confidence + reason; classifier failure falls back to the host with
reason="fallback" (graceful-degradation, matches the relationship_seed
/ interjection pattern).
- chat/web/turns.py post_turn now calls detect_addressee in the
multi-entity branch; 1:1 keeps the substring path.
- tests/test_addressee.py: 3 new tests (guest pick, host pick,
classifier-failure fallback).
- tests/test_turn_flow.py: existing multi-entity tests now feed a
canned addressee response in the queue. The addressee-routing test
is updated to assert classifier-driven routing rather than substring.
Joseph Doherty