세션 평가·라이브코치·교수자 분석 라운드 마감 + 문서 정리 + 코드품질 리팩터

- 누적 작업트리 커밋: 회기 평가 복구·durable 저장, 라이브 코치 이력/근거, 교수자 학생분석, 음성 비언어 메타, PII 마스킹, 운영 티켓/헬스 등
- 문서: 완료 기록 docs/archive/ 냉동 보관, docs/ 단일 인덱스(docs/README.md)+통합 TODO(docs/TODO.md)로 정리
- 리팩터(행위 보존): Stage enum SSOT(taxonomy 소유·state_machine re-export), store recent/masked_turns 중복 제거, speaker_ko_label 단일 헬퍼, _list_sessions N+1 제거(state/turns 배치 + 턴평가 하이드레이션 배치)
- 검증: 백엔드 pytest 352 passed, _list_sessions E2E chromium-single-run 2 passed

apps/api/app/routes/voice.py

@@ -18,7 +18,7 @@ import hashlib
 import time
 from typing import Optional
 
-from fastapi import APIRouter, WebSocket, WebSocketDisconnect
+from fastapi import APIRouter, WebSocket, WebSocketDisconnect, HTTPException
 from fastapi.responses import JSONResponse
 from starlette.websockets import WebSocketState
 
@@ -97,6 +97,13 @@ _PROVIDER_EVENT_TAXONOMY = {
     "noise": ("background_noise", "audio_quality"),
     "background_noise": ("background_noise", "audio_quality"),
 }
+
+
+def _is_turn_persistence_unavailable(exc: Exception) -> bool:
+    if not isinstance(exc, HTTPException) or exc.status_code != 503:
+        return False
+    detail = str(exc.detail or "")
+    return "turn append" in detail and "persistence unavailable" in detail
 _PROVIDER_EVENT_TYPE_FIELDS = ("event_type", "type", "kind", "label")
 
 
@@ -303,7 +310,18 @@ async def voice_ws(websocket: WebSocket) -> None:
     except WebSocketDisconnect:
         pass
     except Exception as e:
-        await _safe_send_json(websocket, {"type": "error", "detail": f"voice ws error: {e}"})
+        if _is_turn_persistence_unavailable(e):
+            await _safe_send_json(
+                websocket,
+                {
+                    "type": "error",
+                    "code": "turn_persistence_unavailable",
+                    "detail": "voice turn persistence unavailable; retry the utterance",
+                },
+            )
+            await _safe_send_json(websocket, {"type": "state", "state": "idle"})
+        else:
+            await _safe_send_json(websocket, {"type": "error", "detail": f"voice ws error: {e}"})
     finally:
         await _safe_close(websocket)
 
@@ -609,6 +627,17 @@ async def _principal_from_websocket(websocket: WebSocket) -> Principal | None:
     )
 
 
+async def _practice_access_error(principal: Principal) -> str | None:
+    if (
+        principal.profile_completed_at is None
+        and not await user_onboarding_complete(principal.user_id)
+    ):
+        return "onboarding_required"
+    if principal.consent_at is None and not await user_has_consent(principal.user_id):
+        return "consent_required"
+    return None
+
+
 async def _bind_session(
     websocket: WebSocket,
     principal: Principal,
@@ -616,6 +645,9 @@ async def _bind_session(
     """Bind an existing session or create a dev-only voice session."""
     qp = websocket.query_params
     explicit_preset = qp.get("preset")
+    access_error = await _practice_access_error(principal)
+    if access_error is not None:
+        return None, None, access_error, {}
 
     session_id = qp.get("session_id")
     if session_id:
@@ -636,13 +668,6 @@ async def _bind_session(
     persona_code = qp.get("persona_code")
     if not persona_code:
         return None, None, "session_id or persona_code query required", {}
-    if (
-        principal.profile_completed_at is None
-        and not await user_onboarding_complete(principal.user_id)
-    ):
-        return None, None, "onboarding_required", {}
-    if principal.consent_at is None and not await user_has_consent(principal.user_id):
-        return None, None, "consent_required", {}
     try:
         catalog_persona = await get_catalog_persona(persona_code)
     except Exception: