fix(chat): stabilize assistant add flow and location routing

CLAUDE.md

@@ -75,10 +75,11 @@ Run in this exact order:
 - CSRF handling: use `/auth/csrf/` + `X-CSRFToken`
 - Chat providers: dynamic catalog from `GET /api/chat/providers/`; configured in `CHAT_PROVIDER_CONFIG`
 - Chat model override: dropdown selector fed by `GET /api/chat/providers/{provider}/models/`; persisted in `localStorage` key `voyage_chat_model_prefs`; backend accepts optional `model` param in `send_message`
-- Chat context: collection chats inject collection UUID + multi-stop itinerary context; system prompt guides `get_trip_details`-first reasoning and confirms only before first `add_to_itinerary`
+- Chat context: collection chats inject collection UUID + multi-stop itinerary context; system prompt guides `get_trip_details`-first reasoning and confirms only before first `add_to_itinerary`; `search_places` prompt guard requires the LLM to have a concrete location string before calling the tool (asks clarifying question otherwise)
 - Chat tool output: `role=tool` messages hidden from display; tool outputs render as concise summaries; persisted tool rows reconstructed on reload via `rebuildConversationMessages()`
 - Chat error surfacing: `_safe_error_payload()` maps LiteLLM exceptions to sanitized user-safe categories (never forwards raw `exc.message`)
 - Invalid tool calls (missing required args) are detected and short-circuited with a user-visible error — not replayed into history
+- Geocoding: `background_geocode_and_assign()` runs in a thread after Location save; populates `region`, `city`, `country`, and also fills `Location.location` from reverse geocode `display_name` (truncated to field max_length) if blank or different
 
 ## Conventions
 - Do **not** attempt to fix known test/configuration issues as part of feature work.