feat(ticket): 工单协同后端——升级不搬数据、受理到验收、站内通知

- item.kind='ticket' + ticket_ext 1:1，迁移 0003 同时重写 item 状态约束为任务∪工单并集
- 工单状态机与动作权限：受理/开工/提交限办理人，验收限需求人（办理人不能自验）
- 升级时原任务转 blocked，验收通过后自动回流 todo，事件流两侧都留痕
- item_link（父子/相关）与 notification（只发当事人），三张表均开 RLS
- 抽出 serializers.py 复用任务序列化，修复工单响应缺 tags 导致前端白屏
- 评论与 PATCH 放开给工单；conftest 清库前终止残留事务，避免 TRUNCATE 死等锁
- tests/test_tickets.py 11 个用例，全量 57 passed

backend/app/api/items.py

@@ -28,7 +28,9 @@ from ..domain.task import (
 )
 from ..errors import AppError, ErrorCode
 from ..models_task import Activity, Comment, Item, ItemTag, Tag
+from ..models_ticket import TicketExt
 from ..schemas import Pagination, encode_cursor, ok
+from ..serializers import item_out, tag_out, tags_of
 
 router = APIRouter(prefix="/workspaces/{ws_id}/items", tags=["任务"])
 tag_router = APIRouter(prefix="/workspaces/{ws_id}/tags", tags=["标签"])
@@ -76,36 +78,20 @@ class TagIn(BaseModel):
     color: str = Field(default="", max_length=16)
 
 
-# ── 序列化 ──────────────────────────────────────────────────────────────
-def _tag_out(tag: Tag) -> dict[str, Any]:
-    return {"id": str(tag.id), "name": tag.name, "color": tag.color}
-
-
-def _item_out(item: Item, tags: list[Tag] | None = None) -> dict[str, Any]:
-    return {
-        "id": str(item.id),
-        "kind": item.kind,
-        "title": item.title,
-        "body_md": item.body_md,
-        "status": item.status,
-        "priority": item.priority,
-        "creator_id": str(item.creator_id),
-        "assignee_id": str(item.assignee_id) if item.assignee_id else None,
-        "due_at": item.due_at,
-        "completed_at": item.completed_at,
-        "sort_order": item.sort_order,
-        "deleted_at": item.deleted_at,
-        "tags": [_tag_out(t) for t in (tags or [])],
-        "created_at": item.created_at,
-        "updated_at": item.updated_at,
-        "version": item.version,
-    }
+# ── 序列化（与工单接口共用一份，两份拼装迟早会不一致）─────────────────────
+_tag_out = tag_out
+_item_out = item_out
 
 
 # ── 内部工具 ────────────────────────────────────────────────────────────
-async def _load_item(session: AsyncSession, ws_id: uuid.UUID, item_id: uuid.UUID) -> Item:
+async def _load_item(
+    session: AsyncSession,
+    ws_id: uuid.UUID,
+    item_id: uuid.UUID,
+    kinds: tuple[str, ...] = ("task",),
+) -> Item:
     item = await session.get(Item, item_id)
-    if item is None or item.workspace_id != ws_id or item.kind != "task":
+    if item is None or item.workspace_id != ws_id or item.kind not in kinds:
         # 跨租户 / 不存在 / 不是任务，对外一律"不存在"，不泄漏别人有没有这条数据
         raise AppError(ErrorCode.ITEM_NOT_FOUND, "任务不存在")
     return item
@@ -114,20 +100,7 @@ async def _load_item(session: AsyncSession, ws_id: uuid.UUID, item_id: uuid.UUID
 async def _tags_of(
     session: AsyncSession, ws_id: uuid.UUID, item_ids: list[uuid.UUID]
 ) -> dict[uuid.UUID, list[Tag]]:
-    if not item_ids:
-        return {}
-    rows = (
-        await session.execute(
-            select(ItemTag.item_id, Tag)
-            .join(Tag, Tag.id == ItemTag.tag_id)
-            .where(ItemTag.workspace_id == ws_id, ItemTag.item_id.in_(item_ids))
-            .order_by(Tag.name)
-        )
-    ).all()
-    grouped: dict[uuid.UUID, list[Tag]] = {}
-    for item_id, tag in rows:
-        grouped.setdefault(item_id, []).append(tag)
-    return grouped
+    return await tags_of(session, ws_id, item_ids)
 
 
 def _normalize_tag_names(names: list[str]) -> list[str]:
@@ -415,9 +388,9 @@ async def board(
     )
 
 
-@router.get("/{item_id}", summary="任务详情（含最近 50 条事件）")
+@router.get("/{item_id}", summary="事项详情（任务或工单，含最近 50 条事件）")
 async def get_item(item_id: uuid.UUID, ctx: MemberDep, session: SessionDep) -> dict:
-    item = await _load_item(session, ctx.ws_id, item_id)
+    item = await _load_item(session, ctx.ws_id, item_id, ("task", "ticket"))
     tags = await _tags_of(session, ctx.ws_id, [item.id])
     activities = (
         (
@@ -442,6 +415,20 @@ async def get_item(item_id: uuid.UUID, ctx: MemberDep, session: SessionDep) -> d
         }
         for a in activities
     ]
+    if item.kind == "ticket":
+        ext = await session.get(TicketExt, item.id)
+        if ext is not None:
+            data["ticket"] = {
+                "requester_id": str(ext.requester_id),
+                "assignee_id": str(ext.assignee_id),
+                "parent_item_id": str(ext.parent_item_id) if ext.parent_item_id else None,
+                "accepted_at": ext.accepted_at,
+                "submitted_at": ext.submitted_at,
+                "verified_at": ext.verified_at,
+                "verified_by": str(ext.verified_by) if ext.verified_by else None,
+                "reject_count": ext.reject_count,
+                "resolution_md": ext.resolution_md,
+            }
     return ok(data)
 
 
@@ -556,11 +543,12 @@ async def batch_status(body: BatchStatusIn, ctx: MemberDep, session: SessionDep)
     )
 
 
-@router.patch("/{item_id}", summary="修改任务字段（乐观锁）")
+@router.patch("/{item_id}", summary="修改事项字段（乐观锁）")
 async def update_item(
     item_id: uuid.UUID, body: UpdateItemIn, ctx: MemberDep, session: SessionDep
 ) -> dict:
-    item = await _load_item(session, ctx.ws_id, item_id)
+    # 工单也能改标题/优先级/截止/标签；状态必须走 /ticket/* 的动作接口
+    item = await _load_item(session, ctx.ws_id, item_id, ("task", "ticket"))
 
     values: dict[str, Any] = {}
     changes: dict[str, Any] = {}
@@ -662,7 +650,7 @@ async def delete_item(
 async def add_comment(
     item_id: uuid.UUID, body: CommentIn, ctx: MemberDep, session: SessionDep
 ) -> dict:
-    item = await _load_item(session, ctx.ws_id, item_id)
+    item = await _load_item(session, ctx.ws_id, item_id, ("task", "ticket"))
     comment = Comment(
         workspace_id=ctx.ws_id,
         item_id=item.id,
@@ -686,7 +674,7 @@ async def add_comment(
 
 @router.get("/{item_id}/comments", summary="评论列表")
 async def list_comments(item_id: uuid.UUID, ctx: MemberDep, session: SessionDep) -> dict:
-    item = await _load_item(session, ctx.ws_id, item_id)
+    item = await _load_item(session, ctx.ws_id, item_id, ("task", "ticket"))
     rows = (
         (
             await session.execute(