F1: add reusable task backend resources and migrate task tools

backend/db/models.py

@@ -177,6 +177,7 @@ class Assistant(Base):
     prompt: Mapped[str] = mapped_column(Text, default="")    # prompt
     dynamic_variable_definitions: Mapped[dict] = mapped_column(JSON, default=dict)
     built_in_tools: Mapped[dict] = mapped_column(JSONB, default=dict)
+    task_backend: Mapped[dict | None] = mapped_column(JSONB, nullable=True)
     analysis_config: Mapped[dict] = mapped_column(JSONB, default=dict)
     api_url: Mapped[str] = mapped_column(String(512), default="")    # dify / fastgpt
     api_key: Mapped[str] = mapped_column(String(512), default="")    # dify / fastgpt(打码/哨兵)
@@ -237,6 +238,27 @@ class McpServer(Base):
     )
 
 
+class TaskBackendResource(Base):
+    """Reusable connection and execution policy, separate from ordinary tools."""
+
+    __tablename__ = "task_backend_resources"
+    __table_args__ = (
+        CheckConstraint("type IN ('reasoner', 'opencode')", name="ck_task_backend_type"),
+    )
+
+    id: Mapped[str] = mapped_column(String(40), primary_key=True)
+    name: Mapped[str] = mapped_column(String(128))
+    type: Mapped[str] = mapped_column(String(16))
+    description: Mapped[str] = mapped_column(String(2048), default="")
+    config: Mapped[dict] = mapped_column(JSONB, default=dict)
+    secrets: Mapped[dict] = mapped_column(JSONB, default=dict)
+    enabled: Mapped[bool] = mapped_column(Boolean, default=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )
+
+
 class Tool(Base):
     """Reusable LLM tool definition; supported types are executed at runtime."""
 
@@ -248,7 +270,7 @@ class Tool(Base):
             name="uq_tools_mcp_server_remote_name",
         ),
         CheckConstraint(
-            "type IN ('http', 'mcp', 'client', 'task')",
+            "type IN ('http', 'mcp', 'client')",
             name="ck_tools_external_type",
         ),
     )
@@ -655,7 +677,10 @@ class BackgroundTask(Base):
     id: Mapped[str] = mapped_column(String(40), primary_key=True)
     assistant_id: Mapped[str] = mapped_column(String(40), index=True)
     conversation_id: Mapped[str] = mapped_column(String(80), index=True)
-    tool_id: Mapped[str] = mapped_column(String(40))
+    tool_id: Mapped[str] = mapped_column(String(40), default="")
+    backend_id: Mapped[str] = mapped_column(String(40), default="")
+    backend_type: Mapped[str] = mapped_column(String(16), default="opencode")
+    deadline_at: Mapped[str | None] = mapped_column(String(40), nullable=True)
     instruction: Mapped[str] = mapped_column(Text)
     origin_key: Mapped[str] = mapped_column(String(256), unique=True)
     connection: Mapped[dict] = mapped_column(JSONB)