Project durable workflow handoffs as work items

src/govoplan_workflow_engine/backend/db/models.py

@@ -408,6 +408,13 @@ class WorkflowInstanceStep(Base, TimestampMixin):
             "tenant_id",
             "status",
         ),
+        Index(
+            "ix_workflow_instance_steps_work_assignment",
+            "tenant_id",
+            "status",
+            "work_assignment_kind",
+            "work_assignment_id",
+        ),
     )
 
     id: Mapped[str] = mapped_column(String(36), primary_key=True, default=new_uuid)
@@ -465,6 +472,25 @@ class WorkflowInstanceStep(Base, TimestampMixin):
         String(255),
         nullable=True,
     )
+    work_assignment_kind: Mapped[str | None] = mapped_column(
+        String(40),
+        nullable=True,
+        index=True,
+    )
+    work_assignment_id: Mapped[str | None] = mapped_column(
+        String(255),
+        nullable=True,
+        index=True,
+    )
+    work_assignment_label: Mapped[str | None] = mapped_column(
+        String(500),
+        nullable=True,
+    )
+    work_due_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True),
+        nullable=True,
+        index=True,
+    )
 
     instance: Mapped[WorkflowInstance] = relationship(back_populates="steps")