feat(sprint6b): блоки D+F — pending_guard, guard-индикаторы в UI, race-condition fix

- _eval_pending_guard() — вычисляет активный guard при незаполненных слотах
- pending_guard добавлен в ThreadStateInfo (ответы /chat и /threads/:id)
- ValidationEventInfo получил guard_name / missing_slots / guard_description
- Sandbox: amber-блок «guard активен», подсветка в validation-событиях
- openThread() защищён от race condition: if (activeThreadId !== id) return
  (исключает отрисовку устаревшего треда после переключения на новый)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/chat_service.py

@@ -111,6 +111,38 @@ async def _resolve_current_step(
     return await intent_step_service.get_first_step(session, intent_id)
 
 
+def _eval_pending_guard(
+    current_step: "IntentStep | None",
+    slots: dict,
+) -> "dict | None":
+    """Возвращает описание активного guard'а если триггер сработал, но слоты ещё не заполнены."""
+    if current_step is None:
+        return None
+    guards = intent_step_service.parse_guards(current_step)
+    if not guards:
+        return None
+    for guard_name, guard_def in guards.items():
+        if not isinstance(guard_def, dict):
+            continue
+        trigger_slot = guard_def.get("trigger_slot")
+        trigger_value = guard_def.get("trigger_value")
+        required_slots: list[str] = guard_def.get("required_slots", [])
+        slot_val = slots.get(trigger_slot) if trigger_slot else None
+        if isinstance(slot_val, str) and slot_val.lower() in ("true", "false"):
+            slot_val = slot_val.lower() == "true"
+        triggered = (trigger_slot is None) or (slot_val == trigger_value)
+        if not triggered:
+            continue
+        missing = [s for s in required_slots if not slots.get(s)]
+        if missing:
+            return {
+                "guard_name": guard_name,
+                "description": guard_def.get("description", ""),
+                "missing_slots": missing,
+            }
+    return None
+
+
 async def send_message(
     session: AsyncSession,
     vectorstore: VectorStoreService,
@@ -586,6 +618,7 @@ async def send_message(
             "suspended_intent": snapshot.get("suspended_intent"),
             "resumable_step_code": snapshot.get("resumable_step_code"),
             "resumable_slots": snapshot.get("resumable_slots", {}),
+            "pending_guard": _eval_pending_guard(current_step, snapshot["slots"]),
         },
         "bounces": bounce_log,
         "validation_events": validation_events,
@@ -690,6 +723,19 @@ async def get_thread_detail(session: AsyncSession, thread_id: int) -> dict | Non
         })
 
     state = await thread_state_service.load_snapshot(session, thread_id)
+    # Вычисляем pending_guard для текущего состояния треда
+    pending_guard = None
+    if state.get("current_step_code") and state.get("current_intent_code"):
+        from db.models import Intent as _Intent
+        intent_obj = (await session.execute(
+            select(_Intent).where(_Intent.code == state["current_intent_code"])
+        )).scalar_one_or_none()
+        if intent_obj:
+            cur_step = await intent_step_service.get_step_by_code(
+                session, intent_obj.id, state["current_step_code"]
+            )
+            pending_guard = _eval_pending_guard(cur_step, state.get("slots", {}))
+    state["pending_guard"] = pending_guard
     return {
         "id": thread.id,
         "name": thread.name,