diff --git a/backend/auth.py b/backend/auth.py
index 27ab83e..2c0bc65 100644
--- a/backend/auth.py
+++ b/backend/auth.py
@@ -39,7 +39,7 @@ async def issue_session(db: AsyncSession, response: Response, user: User, reques
     db.add(Session(
         token_hash=hash_token(token), user_id=user.id, expires_at=expires,
         ip_address=request.client.host if request and request.client else None,
-        user_agent=request.headers.get("user-agent", "")[:500] if request else None,
+        user_agent=request.headers.get("user-agent", "")[:255] if request else None,
     ))
     await db.commit()
     response.set_cookie(
diff --git a/backend/main.py b/backend/main.py
index 9608830..9c1ba9a 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -39,6 +39,7 @@ from .schemas import (
     ListOut,
     LoginRequest,
     NameUpdate,
+    SessionOut,
     TagCreate,
     TagOut,
     TaskCreate,
@@ -213,7 +214,7 @@ async def logout(
     return Response(status_code=204, headers=response.headers)
 
 
-@app.get("/api/v1/sessions")
+@app.get("/api/v1/sessions", response_model=list[SessionOut])
 async def list_sessions(
     token: str = Depends(session_token),
     user: User = Depends(current_user),
@@ -559,7 +560,7 @@ async def list_tasks(
     if page is not None:
         size = page_size or limit
         items = list((await db.scalars(query.order_by(*ordering).offset((page - 1) * size).limit(size))).all())
-        return TaskPage(items=items, total=total, page=page, page_size=size)
+        return TaskPage(items=await _task_details(db, items), total=total, page=page, page_size=size)
     if cursor:
         created_at, task_id = _decode_cursor(cursor)
         query = query.where(
@@ -569,31 +570,48 @@ async def list_tasks(
     has_more = len(rows) > limit
     items = rows[:limit]
     next_cursor = _encode_cursor(items[-1].created_at, items[-1].id) if has_more else None
-    return TaskPage(items=items, next_cursor=next_cursor, total=total, page=1, page_size=limit)
+    return TaskPage(items=await _task_details(db, items), next_cursor=next_cursor, total=total, page=1, page_size=limit)
 
 
-async def _task_detail(db: AsyncSession, task: Task) -> TaskDetailOut:
-    tags = list(
-        (
-            await db.scalars(
-                select(Tag)
-                .join(TaskTag, TaskTag.tag_id == Tag.id)
-                .where(TaskTag.task_id == task.id)
-                .order_by(Tag.name, Tag.id)
-            )
-        ).all()
-    )
+async def _task_details(db: AsyncSession, tasks: list[Task]) -> list[TaskDetailOut]:
+    if not tasks:
+        return []
+    task_ids = [task.id for task in tasks]
+    tag_rows = (
+        await db.execute(
+            select(TaskTag.task_id, Tag)
+            .join(Tag, Tag.id == TaskTag.tag_id)
+            .where(TaskTag.task_id.in_(task_ids))
+            .order_by(Tag.name, Tag.id)
+        )
+    ).all()
     subtasks = list(
         (
             await db.scalars(
                 select(Task)
-                .where(Task.parent_id == task.id, Task.deleted_at.is_(None))
+                .where(Task.parent_id.in_(task_ids), Task.deleted_at.is_(None))
                 .order_by(Task.position, Task.created_at, Task.id)
             )
         ).all()
     )
-    data = TaskOut.model_validate(task).model_dump()
-    return TaskDetailOut(**data, tags=tags, subtasks=subtasks)
+    tags_by_task: dict[UUID, list[Tag]] = defaultdict(list)
+    subtasks_by_task: dict[UUID, list[Task]] = defaultdict(list)
+    for task_id, tag in tag_rows:
+        tags_by_task[task_id].append(tag)
+    for subtask in subtasks:
+        subtasks_by_task[subtask.parent_id].append(subtask)
+    return [
+        TaskDetailOut(
+            **TaskOut.model_validate(task).model_dump(),
+            tags=tags_by_task[task.id],
+            subtasks=subtasks_by_task[task.id],
+        )
+        for task in tasks
+    ]
+
+
+async def _task_detail(db: AsyncSession, task: Task) -> TaskDetailOut:
+    return (await _task_details(db, [task]))[0]
 
 
 @app.get("/api/v1/tasks/{task_id}", response_model=TaskDetailOut)
@@ -707,7 +725,7 @@ async def list_trash(
     if page is not None:
         size = page_size or limit
         items = list((await db.scalars(query.order_by(*ordering).offset((page - 1) * size).limit(size))).all())
-        return TaskPage(items=items, total=total, page=page, page_size=size)
+        return TaskPage(items=await _task_details(db, items), total=total, page=page, page_size=size)
     if cursor:
         created_at, task_id = _decode_cursor(cursor)
         query = query.where(
@@ -717,7 +735,7 @@ async def list_trash(
     has_more = len(rows) > limit
     items = rows[:limit]
     next_cursor = _encode_cursor(items[-1].created_at, items[-1].id) if has_more else None
-    return TaskPage(items=items, next_cursor=next_cursor, total=total, page=1, page_size=limit)
+    return TaskPage(items=await _task_details(db, items), next_cursor=next_cursor, total=total, page=1, page_size=limit)
 
 
 @app.post("/api/v1/tasks/{task_id}/restore", response_model=TaskDetailOut)
@@ -791,6 +809,9 @@ async def batch_update_tasks(
         raise HTTPException(status_code=404, detail="一个或多个任务不存在")
     if payload.list_id is not None:
         await _owned_list(db, user.id, payload.list_id)
+        standalone_children = [task for task in tasks if task.parent_id is not None]
+        if standalone_children:
+            raise HTTPException(status_code=400, detail="子任务不能脱离父任务单独移动")
     tag_ids = await _validate_tags(db, user.id, payload.tag_ids)
     changes = payload.model_dump(exclude_unset=True, exclude={"task_ids", "tag_ids", "soft_delete"})
     if payload.soft_delete:
@@ -798,9 +819,25 @@ async def batch_update_tasks(
     if changes:
         changes["version"] = Task.version + 1
         changes["updated_at"] = utcnow()
+        target_ids = set(task_ids)
+        if payload.soft_delete:
+            parent_ids = [task.id for task in tasks if task.parent_id is None]
+            if parent_ids:
+                child_ids = list(
+                    (
+                        await db.scalars(
+                            select(Task.id).where(
+                                Task.parent_id.in_(parent_ids),
+                                Task.user_id == user.id,
+                                Task.deleted_at.is_(None),
+                            )
+                        )
+                    ).all()
+                )
+                target_ids.update(child_ids)
         await db.execute(
             update(Task)
-            .where(Task.id.in_(task_ids), Task.user_id == user.id, Task.deleted_at.is_(None))
+            .where(Task.id.in_(target_ids), Task.user_id == user.id, Task.deleted_at.is_(None))
             .values(**changes)
         )
         if payload.list_id is not None:
diff --git a/backend/models.py b/backend/models.py
index eb854e5..7ce95eb 100644
--- a/backend/models.py
+++ b/backend/models.py
@@ -52,7 +52,7 @@ class Session(Base):
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=utcnow)
     last_seen_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=utcnow)
     ip_address: Mapped[str | None] = mapped_column(String(64), nullable=True)
-    user_agent: Mapped[str | None] = mapped_column(String(500), nullable=True)
+    user_agent: Mapped[str | None] = mapped_column(String(255), nullable=True)
 
 
 class Folder(Base):
diff --git a/backend/mvp.py b/backend/mvp.py
index 9e6f387..ce791ca 100644
--- a/backend/mvp.py
+++ b/backend/mvp.py
@@ -17,7 +17,7 @@ from fastapi import APIRouter, Depends, File, HTTPException, Query, Response, Up
 from fastapi.responses import FileResponse
 from icalendar import Calendar
 from pydantic import BaseModel, Field, model_validator
-from sqlalchemy import case, delete, func, select
+from sqlalchemy import case, delete, func, select, update
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from .auth import current_user
@@ -36,6 +36,7 @@ from .models import (
     Tag,
     Task,
     TaskList,
+    TaskTag,
     User,
     new_id,
     utcnow,
@@ -718,29 +719,113 @@ async def export_json(user: User = Depends(current_user), db: AsyncSession = Dep
     def serialize(row, fields):
         return {f: (str(v) if isinstance((v := getattr(row, f)), UUID) else v.isoformat() if isinstance(v, (date, datetime)) else v) for f in fields}
     folders = list((await db.scalars(select(Folder).where(Folder.user_id == user.id))).all()); lists = list((await db.scalars(select(TaskList).where(TaskList.user_id == user.id))).all()); tags = list((await db.scalars(select(Tag).where(Tag.user_id == user.id))).all()); tasks = list((await db.scalars(select(Task).where(Task.user_id == user.id))).all()); habits = list((await db.scalars(select(Habit).where(Habit.user_id == user.id))).all())
-    return {"version": 1, "exported_at": utcnow(), "folders": [serialize(x,["id","name","position","deleted_at"]) for x in folders], "lists": [serialize(x,["id","folder_id","name","is_inbox","position","deleted_at"]) for x in lists], "tags": [serialize(x,["id","name","color"]) for x in tags], "tasks": [serialize(x,["id","list_id","parent_id","title","description","priority","completed","due_at","external_id","deleted_at"]) for x in tasks], "habits": [serialize(x,["id","name","kind","target","max_value","schedule_type","weekdays","month_days","interval_days","start_date","archived_at"]) for x in habits]}
+    return {
+        "version": 1,
+        "exported_at": utcnow(),
+        "folders": [serialize(x, ["id", "name", "position", "deleted_at"]) for x in folders],
+        "lists": [serialize(x, ["id", "folder_id", "name", "is_inbox", "position", "deleted_at"]) for x in lists],
+        "tags": [serialize(x, ["id", "name", "color"]) for x in tags],
+        "tasks": [serialize(x, ["id", "list_id", "parent_id", "title", "description", "priority", "completed", "due_at", "external_id", "deleted_at"]) for x in tasks],
+        "task_tags": [{"task_id": str(x.task_id), "tag_id": str(x.tag_id)} for x in (await db.scalars(select(TaskTag))).all() if x.task_id in {task.id for task in tasks}],
+        "habits": [serialize(x, ["id", "name", "kind", "target", "max_value", "schedule_type", "weekdays", "month_days", "interval_days", "start_date", "archived_at"]) for x in habits],
+    }
 
 
 @router.post("/restore")
 async def restore_json(payload: dict, mode: str = Query("merge", pattern="^(merge|replace)$"), user: User = Depends(current_user), db: AsyncSession = Depends(get_db)):
-    if payload.get("version") != 1: raise HTTPException(422, "不支持的备份版本")
+    if payload.get("version") != 1:
+        raise HTTPException(422, "不支持的备份版本")
     if mode == "replace":
-        await db.execute(delete(Task).where(Task.user_id == user.id)); await db.execute(delete(TaskList).where(TaskList.user_id == user.id)); await db.execute(delete(Folder).where(Folder.user_id == user.id))
+        await db.execute(delete(TaskTag).where(TaskTag.task_id.in_(select(Task.id).where(Task.user_id == user.id))))
+        await db.execute(delete(Task).where(Task.user_id == user.id))
+        await db.execute(delete(Tag).where(Tag.user_id == user.id))
+        await db.execute(delete(Habit).where(Habit.user_id == user.id))
+        await db.execute(delete(TaskList).where(TaskList.user_id == user.id))
+        await db.execute(delete(Folder).where(Folder.user_id == user.id))
     id_map = {}
+    task_id_map = {}
+    tag_id_map = {}
     for raw in payload.get("folders", []):
-        old = raw["id"]; row = Folder(user_id=user.id, name=raw["name"], position=raw.get("position",0)); db.add(row); await db.flush(); id_map[old] = row.id
+        old = raw["id"]
+        row = Folder(user_id=user.id, name=raw["name"], position=raw.get("position", 0))
+        db.add(row)
+        await db.flush()
+        id_map[old] = row.id
     inbox = None
     for raw in payload.get("lists", []):
-        row = TaskList(user_id=user.id, folder_id=id_map.get(raw.get("folder_id")), name=raw["name"], is_inbox=raw.get("is_inbox",False), position=raw.get("position",0)); db.add(row); await db.flush(); id_map[raw["id"]] = row.id
-        if row.is_inbox: inbox = row
-    if not inbox: inbox = TaskList(user_id=user.id, name="收集箱", is_inbox=True); db.add(inbox); await db.flush()
+        row = TaskList(
+            user_id=user.id,
+            folder_id=id_map.get(raw.get("folder_id")),
+            name=raw["name"],
+            is_inbox=raw.get("is_inbox", False),
+            position=raw.get("position", 0),
+        )
+        db.add(row)
+        await db.flush()
+        id_map[raw["id"]] = row.id
+        if row.is_inbox:
+            inbox = row
+    if not inbox:
+        inbox = TaskList(user_id=user.id, name="收集箱", is_inbox=True)
+        db.add(inbox)
+        await db.flush()
+    for raw in payload.get("tags", []):
+        row = Tag(user_id=user.id, name=raw["name"], color=raw.get("color", "#f15a29"))
+        db.add(row)
+        await db.flush()
+        tag_id_map[raw["id"]] = row.id
     restored = 0
+    pending_tasks = []
     for raw in payload.get("tasks", []):
         ext = raw.get("external_id")
         existing = await db.scalar(select(Task).where(Task.user_id == user.id, Task.external_id == ext)) if ext else None
-        if existing and mode == "merge": continue
-        row = Task(user_id=user.id, list_id=id_map.get(raw.get("list_id"), inbox.id), title=raw["title"], description=raw.get("description", ""), priority=raw.get("priority",0), completed=raw.get("completed",False), due_at=datetime.fromisoformat(raw["due_at"]) if raw.get("due_at") else None, external_id=ext); db.add(row); restored += 1
-    audit(db, user.id, "restore", "backup", count=restored, mode=mode); await db.commit(); return {"restored": restored, "mode": mode}
+        if existing and mode == "merge":
+            task_id_map[raw["id"]] = existing.id
+            continue
+        row = Task(
+            user_id=user.id,
+            list_id=id_map.get(raw.get("list_id"), inbox.id),
+            title=raw["title"],
+            description=raw.get("description", ""),
+            priority=raw.get("priority", 0),
+            completed=raw.get("completed", False),
+            due_at=datetime.fromisoformat(raw["due_at"]) if raw.get("due_at") else None,
+            external_id=ext,
+        )
+        db.add(row)
+        await db.flush()
+        task_id_map[raw["id"]] = row.id
+        pending_tasks.append((row.id, raw.get("parent_id")))
+        restored += 1
+    for task_id, old_parent_id in pending_tasks:
+        if old_parent_id and old_parent_id in task_id_map:
+            await db.execute(update(Task).where(Task.id == task_id, Task.user_id == user.id).values(parent_id=task_id_map[old_parent_id]))
+    task_tag_rows = []
+    for raw in payload.get("task_tags", []):
+        task_id = task_id_map.get(raw.get("task_id"))
+        tag_id = tag_id_map.get(raw.get("tag_id"))
+        if task_id and tag_id:
+            task_tag_rows.append(TaskTag(task_id=task_id, tag_id=tag_id))
+    if task_tag_rows:
+        db.add_all(task_tag_rows)
+    for raw in payload.get("habits", []):
+        row = Habit(
+            user_id=user.id,
+            name=raw["name"],
+            kind=raw.get("kind", "boolean"),
+            target=raw.get("target", 1),
+            max_value=raw.get("max_value"),
+            schedule_type=raw.get("schedule_type", "daily"),
+            weekdays=raw.get("weekdays"),
+            month_days=raw.get("month_days"),
+            interval_days=raw.get("interval_days"),
+            start_date=date.fromisoformat(raw["start_date"]),
+            archived_at=datetime.fromisoformat(raw["archived_at"]) if raw.get("archived_at") else None,
+        )
+        db.add(row)
+    audit(db, user.id, "restore", "backup", count=restored, mode=mode)
+    await db.commit()
+    return {"restored": restored, "mode": mode}
 
 
 @router.get("/audit-logs")
diff --git a/backend/schemas.py b/backend/schemas.py
index 6adecc6..463e010 100644
--- a/backend/schemas.py
+++ b/backend/schemas.py
@@ -20,6 +20,17 @@ class UserOut(BaseModel):
     username: str
 
 
+class SessionOut(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+    id: UUID
+    current: bool
+    created_at: datetime
+    last_seen_at: datetime
+    expires_at: datetime
+    ip_address: str | None
+    user_agent: str | None
+
+
 class NameUpdate(BaseModel):
     name: str = Field(min_length=1, max_length=120)
 
@@ -106,7 +117,7 @@ class TaskDetailOut(TaskOut):
 
 
 class TaskPage(BaseModel):
-    items: list[TaskOut]
+    items: list[TaskDetailOut]
     next_cursor: str | None = None
     total: int = 0
     page: int = 1
diff --git a/migrations/versions/0003_mvp_models.py b/migrations/versions/0003_mvp_models.py
index 0696678..6d73d6e 100644
--- a/migrations/versions/0003_mvp_models.py
+++ b/migrations/versions/0003_mvp_models.py
@@ -13,8 +13,14 @@ depends_on = None
 
 
 def upgrade() -> None:
+    bind = op.get_bind()
+    dialect = bind.dialect.name
     op.add_column("tasks", sa.Column("external_id", sa.String(255), nullable=True))
-    op.create_unique_constraint("uq_tasks_external_id", "tasks", ["user_id", "external_id"])
+    if dialect == "sqlite":
+        with op.batch_alter_table("tasks") as batch_op:
+            batch_op.create_unique_constraint("uq_tasks_external_id", ["user_id", "external_id"])
+    else:
+        op.create_unique_constraint("uq_tasks_external_id", "tasks", ["user_id", "external_id"])
 
     op.add_column("sessions", sa.Column("ip_address", sa.String(64), nullable=True))
     op.add_column("sessions", sa.Column("user_agent", sa.String(255), nullable=True))
diff --git a/migrations/versions/0006_remove_duplicate_habit_index.py b/migrations/versions/0006_remove_duplicate_habit_index.py
index 3cfa3f6..f175560 100644
--- a/migrations/versions/0006_remove_duplicate_habit_index.py
+++ b/migrations/versions/0006_remove_duplicate_habit_index.py
@@ -3,6 +3,7 @@ Revision ID: 0006
 Revises: 0005
 """
 
+import sqlalchemy as sa
 from alembic import op
 
 revision = "0006"
@@ -12,12 +13,18 @@ depends_on = None
 
 
 def upgrade() -> None:
-    op.drop_index("ix_habit_logs_habit_day", table_name="habit_logs")
+    bind = op.get_bind()
+    indexes = {index["name"] for index in sa.inspect(bind).get_indexes("habit_logs")}
+    if "ix_habit_logs_habit_day" in indexes:
+        op.drop_index("ix_habit_logs_habit_day", table_name="habit_logs")
 
 
 def downgrade() -> None:
-    op.create_index(
-        "ix_habit_logs_habit_day",
-        "habit_logs",
-        ["habit_id", "day"],
-    )
+    bind = op.get_bind()
+    indexes = {index["name"] for index in sa.inspect(bind).get_indexes("habit_logs")}
+    if "ix_habit_logs_habit_day" not in indexes:
+        op.create_index(
+            "ix_habit_logs_habit_day",
+            "habit_logs",
+            ["habit_id", "day"],
+        )
diff --git a/tests/test_app.py b/tests/test_app.py
index 941caf9..bc2727e 100644
--- a/tests/test_app.py
+++ b/tests/test_app.py
@@ -172,7 +172,10 @@ def test_task_search_tags_subtasks_and_recycle_bin(client):
     assert detail.status_code == 200
     assert detail.json()["tags"][0]["name"] == "重要"
     assert len(detail.json()["subtasks"]) == 1
-    assert len(client.get("/api/v1/tasks", params={"q": "咖啡"}).json()["items"]) == 1
+    listed = client.get("/api/v1/tasks", params={"q": "咖啡"}).json()["items"]
+    assert len(listed) == 1
+    assert listed[0]["tags"][0]["name"] == "重要"
+    assert listed[0]["subtasks"][0]["title"] == "比较价格"
 
     assert client.delete(f"/api/v1/tasks/{parent['id']}").status_code == 204
     trash = client.get("/api/v1/trash").json()["items"]
@@ -197,6 +200,29 @@ def test_batch_complete_and_move(client):
     assert all(row["completed"] and row["list_id"] == other["id"] for row in rows)
 
 
+def test_batch_move_rejects_standalone_subtask_and_delete_cascades(client):
+    client = initialized_client(client)
+    inbox = client.get("/api/v1/lists").json()[0]
+    other = client.post("/api/v1/lists", json={"name": "稍后"}).json()
+    parent = client.post("/api/v1/tasks", json={"title": "父", "list_id": inbox["id"]}).json()
+    child = client.post(
+        "/api/v1/tasks",
+        json={"title": "子", "list_id": inbox["id"], "parent_id": parent["id"]},
+    ).json()
+
+    moved_child = client.post(
+        "/api/v1/tasks/batch", json={"task_ids": [child["id"]], "list_id": other["id"]}
+    )
+    assert moved_child.status_code == 400
+
+    deleted_parent = client.post(
+        "/api/v1/tasks/batch", json={"task_ids": [parent["id"]], "soft_delete": True}
+    )
+    assert deleted_parent.status_code == 200
+    assert client.get(f"/api/v1/tasks/{parent['id']}").status_code == 404
+    assert client.get(f"/api/v1/tasks/{child['id']}").status_code == 404
+
+
 def test_inbox_is_protected_and_deleted_collections_are_hidden(client):
     client = initialized_client(client)
     inbox = client.get("/api/v1/lists").json()[0]
@@ -258,6 +284,37 @@ def test_tags_are_global_searchable_and_validated(client):
     assert invalid.status_code == 404
 
 
+def test_restore_replace_recovers_tags_habits_and_task_links(client):
+    client = initialized_client(client)
+    inbox = client.get("/api/v1/lists").json()[0]
+    tag = client.post("/api/v1/tags", json={"name": "备份标签", "color": "#f15a29"}).json()
+    client.post(
+        "/api/v1/tasks",
+        json={"title": "备份任务", "list_id": inbox["id"], "tag_ids": [tag["id"]]},
+    ).json()
+    client.post(
+        "/api/v1/habits",
+        json={"name": "俯卧撑", "kind": "boolean", "schedule_type": "daily"},
+    ).json()
+    exported = client.get("/api/v1/export")
+    assert exported.status_code == 200
+
+    client.post("/api/v1/tags", json={"name": "现有标签", "color": "#123abc"})
+    client.post(
+        "/api/v1/habits",
+        json={"name": "深蹲", "kind": "boolean", "schedule_type": "daily"},
+    )
+    restored = client.post("/api/v1/restore?mode=replace", json=exported.json())
+    assert restored.status_code == 200
+
+    tags = client.get("/api/v1/tags").json()
+    assert [row["name"] for row in tags] == ["备份标签"]
+    habits = client.get("/api/v1/habits").json()
+    assert [row["name"] for row in habits] == ["俯卧撑"]
+    listed = client.get("/api/v1/tasks", params={"q": "备份任务"}).json()["items"]
+    assert listed[0]["tags"][0]["name"] == "备份标签"
+
+
 def test_recycle_bin_restore_and_permanent_delete_include_subtasks(client):
     client = initialized_client(client)
     inbox = client.get("/api/v1/lists").json()[0]