feat(voice): rotate NPC hint variants per turn

tools/zacus-gateway/main.py

@@ -203,11 +203,14 @@ def load_scenario_hints(scenario: str = "zacus_v3"):
 STEP_SCENE, SCENE_HINTS, INITIAL_STEP = load_scenario_hints(settings.scenario)
 
 
-def _scenario_hint(step_id: str, level: int) -> str:
-    """A hint string for the current step at `level` (1 subtle … 3 near-explicit)."""
+def _scenario_hint(step_id: str, level: int, turn: int = 0) -> str:
+    """A hint string for the current step at `level` (1 subtle … 3 near-explicit).
+
+    Rotates by `turn` through the level's variants so a multi-turn call doesn't
+    repeat the same phrasing."""
     scene = STEP_SCENE.get(step_id or "", "")
     pool = SCENE_HINTS.get(scene, {}).get(max(1, min(3, level)), [])
-    return pool[0] if pool else ""
+    return pool[turn % len(pool)] if pool else ""
 
 
 # NOTE: in-process dict — single uvicorn worker only; multi-worker would need shared store (Redis).
@@ -2202,7 +2205,7 @@ async def voice_reply(
         step = getattr(request.app.state, "current_step", INITIAL_STEP)
         user_turns = sum(1 for m in history if m.get("role") == "user")
         level = max(1, min(3, 1 + (user_turns - 1) // 2))
-        hint = _scenario_hint(step, level)
+        hint = _scenario_hint(step, level, turn=user_turns)
         sys_persona = persona
         if hint:
             sys_persona = (persona + f"\n\nÉNIGME EN COURS (étape {step}, indice niveau "