feat(backend): Django + OpenCode 백엔드 추가 — 5_django_backend/

앱이 기대하는 base-backend 계약(envelope·JWT·/chat/stream SSE)을 그대로 구현.
Django 는 로그인·세션 미러(SQLite/PG)·OpenCode 이벤트 번역만 맡고, 답변은 전용
OpenCode 인스턴스(opencode/ workspace, codeassist 에이전트)가 만듦.
- accounts: 이메일 로그인, access 60분 / refresh 14일, entra/config 는 501
- chat: 세션 목록·검색·메시지·취소 + POST /chat/stream 어댑터(part.delta→token,
  idle→usage/done, 클라 끊겨도 턴 감시 태스크가 DB 마무리, 첫 이벤트 60초 타임아웃)
- OpenCode 1.18 멀티 프로젝트라 모든 요청에 ?directory= 부착
- docs-lib 에 OpenCode SDK 1.18.6 타입 원본, pytest 32

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

5_django_backend/common/envelope.py

@@ -0,0 +1,154 @@
+"""
+응답 envelope — 프론트 `types/api.ts` 의 CommonResponse 와 1:1.
+
+{
+  success, statusCode, code, message, data, counts, errors, timestamp, meta
+}
+
+- DRF 뷰: 그냥 `Response(data)` 하면 EnvelopeRenderer 가 감쌈.
+  목록은 `Response(paged(items, page, limit, total))` — data=items, meta 채워짐.
+- DRF 예외: envelope_exception_handler 가 success:false 로 감쌈. code 는 CodedError 로 지정.
+- 순수 Django async 뷰(스트림): `json_error()` 로 직접 만듦.
+"""
+
+from datetime import datetime, timezone
+
+from django.http import JsonResponse
+from rest_framework.exceptions import APIException
+from rest_framework.renderers import JSONRenderer
+
+_LIST_MARK = "__paged__"
+
+
+def _now() -> str:
+    return datetime.now(timezone.utc).isoformat().replace("+00:00", "Z")
+
+
+def envelope(
+    *,
+    success: bool,
+    status_code: int,
+    data=None,
+    code: str | None = None,
+    message: str | None = None,
+    errors: list[str] | None = None,
+    counts: int | None = None,
+    meta: dict | None = None,
+) -> dict:
+    return {
+        "success": success,
+        "statusCode": status_code,
+        "code": code,
+        "message": message,
+        "data": data,
+        "counts": counts,
+        "errors": errors or [],
+        "timestamp": _now(),
+        "meta": meta,
+    }
+
+
+def paged(items: list, page: int, limit: int, total: int) -> dict:
+    """목록 응답용. Renderer 가 data=items, meta=페이지 정보로 풀어줌."""
+    pages = (total + limit - 1) // limit if limit > 0 else 0
+    return {
+        _LIST_MARK: True,
+        "items": items,
+        "counts": total,
+        "meta": {
+            "currentPage": page,
+            "pageSize": limit,
+            "totalItems": total,
+            "totalPages": pages,
+            "hasNextPage": page < pages,
+            "hasPreviousPage": page > 1,
+        },
+    }
+
+
+def _is_wrapped(data) -> bool:
+    return isinstance(data, dict) and "success" in data and "statusCode" in data
+
+
+class EnvelopeRenderer(JSONRenderer):
+    def render(self, data, accepted_media_type=None, renderer_context=None):
+        response = (renderer_context or {}).get("response")
+        status_code = getattr(response, "status_code", 200)
+        if _is_wrapped(data):
+            body = data
+        elif isinstance(data, dict) and data.get(_LIST_MARK):
+            body = envelope(
+                success=True,
+                status_code=status_code,
+                data=data["items"],
+                counts=data["counts"],
+                meta=data["meta"],
+            )
+        else:
+            body = envelope(success=True, status_code=status_code, data=data)
+        return super().render(body, accepted_media_type, renderer_context)
+
+
+class CodedError(APIException):
+    """상태코드 + 프론트가 분기하는 code 문자열을 같이 던짐."""
+
+    def __init__(self, status_code: int, code: str, message: str):
+        super().__init__(detail=message)
+        self.status_code = status_code
+        self.code_name = code
+
+
+_DEFAULT_CODES = {
+    400: "VALIDATION_ERROR",
+    401: "UNAUTHORIZED",
+    403: "FORBIDDEN",
+    404: "NOT_FOUND",
+    405: "METHOD_NOT_ALLOWED",
+    409: "CONFLICT",
+    501: "NOT_IMPLEMENTED",
+    502: "UPSTREAM_ERROR",
+    503: "UPSTREAM_UNAVAILABLE",
+}
+
+
+def _flatten(data) -> str:
+    """serializer 검증 오류(dict/list)를 한 줄로."""
+    if isinstance(data, str):
+        return data
+    if isinstance(data, list):
+        return " ".join(_flatten(d) for d in data)
+    if isinstance(data, dict):
+        parts = []
+        for k, v in data.items():
+            msg = _flatten(v)
+            parts.append(msg if k in ("detail", "non_field_errors") else f"{k}: {msg}")
+        return " ".join(parts)
+    return str(data)
+
+
+def envelope_exception_handler(exc, context):
+    # rest_framework.views 는 settings 의 renderer(=이 모듈)를 import 하므로 여기서 늦게 import (순환 방지)
+    from rest_framework.views import exception_handler
+
+    response = exception_handler(exc, context)
+    if response is None:
+        return None
+    code = getattr(exc, "code_name", None) or _DEFAULT_CODES.get(response.status_code, "ERROR")
+    message = _flatten(response.data)
+    response.data = envelope(
+        success=False,
+        status_code=response.status_code,
+        code=code,
+        message=message,
+        errors=[message],
+    )
+    return response
+
+
+def json_error(status_code: int, code: str, message: str) -> JsonResponse:
+    """DRF 안 거치는 async 뷰용."""
+    return JsonResponse(
+        envelope(success=False, status_code=status_code, code=code, message=message, errors=[message]),
+        status=status_code,
+        json_dumps_params={"ensure_ascii": False},
+    )