feat: strengthen backup and mobile workflows

backend/models.py

@@ -255,6 +255,52 @@ class Memo(Base):
     deleted_at: Mapped[datetime | None] = mapped_column(UTCDateTime(), nullable=True)
 
 
+class BackupPreflight(Base):
+    __tablename__ = "backup_preflights"
+    id: Mapped[UUID] = mapped_column(primary_key=True, default=new_id)
+    token_hash: Mapped[str] = mapped_column(String(64), unique=True, index=True)
+    user_id: Mapped[UUID] = mapped_column(ForeignKey("users.id", ondelete="CASCADE"), index=True)
+    backup_id: Mapped[UUID] = mapped_column(index=True)
+    archive_sha256: Mapped[str] = mapped_column(String(64))
+    archive_size: Mapped[int] = mapped_column(Integer)
+    staging_path: Mapped[str] = mapped_column(String(1024), unique=True)
+    mode: Mapped[str] = mapped_column(String(16))
+    status: Mapped[str] = mapped_column(String(32), default="pending", index=True)
+    expires_at: Mapped[datetime] = mapped_column(UTCDateTime(), index=True)
+    consumed_at: Mapped[datetime | None] = mapped_column(UTCDateTime(), nullable=True)
+    cleanup_path: Mapped[str | None] = mapped_column(String(1024), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(UTCDateTime(), default=utcnow)
+
+
+class BackupImport(Base):
+    __tablename__ = "backup_imports"
+    __table_args__ = (UniqueConstraint("user_id", "backup_id", name="uq_backup_import_user_backup"),)
+    id: Mapped[UUID] = mapped_column(primary_key=True, default=new_id)
+    user_id: Mapped[UUID] = mapped_column(ForeignKey("users.id", ondelete="CASCADE"), index=True)
+    backup_id: Mapped[UUID] = mapped_column(index=True)
+    archive_sha256: Mapped[str] = mapped_column(String(64))
+    mode: Mapped[str] = mapped_column(String(16))
+    created_at: Mapped[datetime] = mapped_column(UTCDateTime(), default=utcnow)
+
+
+class BackupImportEntity(Base):
+    __tablename__ = "backup_import_entities"
+    __table_args__ = (
+        UniqueConstraint(
+            "user_id", "backup_id", "entity_type", "source_id",
+            name="uq_backup_import_entity_source",
+        ),
+    )
+    id: Mapped[UUID] = mapped_column(primary_key=True, default=new_id)
+    user_id: Mapped[UUID] = mapped_column(ForeignKey("users.id", ondelete="CASCADE"), index=True)
+    backup_id: Mapped[UUID] = mapped_column(index=True)
+    entity_type: Mapped[str] = mapped_column(String(64))
+    source_id: Mapped[UUID] = mapped_column(index=True)
+    target_id: Mapped[UUID] = mapped_column(index=True)
+    content_digest: Mapped[str] = mapped_column(String(64))
+    created_at: Mapped[datetime] = mapped_column(UTCDateTime(), default=utcnow)
+
+
 class AuditLog(Base):
     __tablename__ = "audit_logs"
     id: Mapped[UUID] = mapped_column(primary_key=True, default=new_id)