Add agent workflow engine foundation and theme-style page switcher.

Introduce WorkflowEngine with state machine, tool registry, and builtin chat template; migrate stream chat to engine callbacks. Move page mode switching to TopBar actions cluster as a ThemeToggle-style dropdown (聊天/工作室/爽文/房间).

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/models/agent.py

@@ -0,0 +1,128 @@
+"""
+Agent workflow engine data models.
+"""
+from __future__ import annotations
+
+from datetime import datetime
+from enum import Enum
+from typing import Any, Awaitable, Callable, Dict, List, Optional
+
+from pydantic import BaseModel, Field
+
+
+class WorkflowTemplateKind(str, Enum):
+    BUILTIN_CHAT = "builtin.chat"
+
+
+class RunStatus(str, Enum):
+    PENDING = "pending"
+    RUNNING = "running"
+    COMPLETED = "completed"
+    FAILED = "failed"
+
+
+class RunEventType(str, Enum):
+    STATE_ENTER = "state_enter"
+    TOOL_START = "tool_start"
+    TOOL_END = "tool_end"
+    WORLD_BOOK_ACTIVE = "worldbook_active"
+    TASKS_CREATED = "tasks_created"
+    CHUNK = "chunk"
+    ERROR = "error"
+    COMPLETE = "complete"
+
+
+class ToolSpec(BaseModel):
+    name: str
+    description: str = ""
+    parameters: Dict[str, Any] = Field(default_factory=dict)
+
+
+class SkillManifest(BaseModel):
+    id: str
+    name: str = ""
+    description: str = ""
+    path: str = ""
+
+
+class WorkflowTemplate(BaseModel):
+    id: str
+    kind: WorkflowTemplateKind
+    name: str = ""
+    description: str = ""
+    version: str = "1.0.0"
+    state_machine_path: str = "state_machine.json"
+    skills: List[SkillManifest] = Field(default_factory=list)
+
+
+class ChatRunBinding(BaseModel):
+    role_name: str
+    chat_name: str
+    template_id: str = WorkflowTemplateKind.BUILTIN_CHAT.value
+
+
+class TurnCallbacks(BaseModel):
+    """Optional async callbacks for streaming / WS events."""
+
+    model_config = {"arbitrary_types_allowed": True}
+
+    on_worldbook_active: Optional[Callable[[List[Any]], Awaitable[None]]] = None
+    on_tasks_created: Optional[Callable[[Dict[str, Any]], Awaitable[None]]] = None
+    on_chunk: Optional[Callable[[str], Awaitable[None]]] = None
+
+
+class TurnContext(BaseModel):
+    """Mutable per-turn execution context passed between tools."""
+
+    model_config = {"arbitrary_types_allowed": True}
+
+    request_data: Dict[str, Any] = Field(default_factory=dict)
+    template_id: str = WorkflowTemplateKind.BUILTIN_CHAT.value
+    run_id: str = ""
+    stream: bool = False
+    callbacks: Optional[TurnCallbacks] = None
+
+    current_role: str = ""
+    current_chat: str = ""
+    user_message: str = ""
+    preset_name: Optional[str] = None
+    character: Any = None
+    active_entries: List[Any] = Field(default_factory=list)
+    chat_history: List[Any] = Field(default_factory=list)
+    prompt_messages: List[Any] = Field(default_factory=list)
+    generated_content: str = ""
+    token_usage: Dict[str, Any] = Field(default_factory=dict)
+    duration: float = 0.0
+    task_ids: Dict[str, Optional[str]] = Field(default_factory=dict)
+    error: Optional[str] = None
+
+
+class WorkflowRun(BaseModel):
+    id: str
+    template_id: str
+    binding: ChatRunBinding
+    status: RunStatus = RunStatus.PENDING
+    started_at: str = Field(default_factory=lambda: datetime.now().isoformat())
+    finished_at: Optional[str] = None
+    current_state: Optional[str] = None
+    result_content: str = ""
+    error: Optional[str] = None
+
+
+class RunEvent(BaseModel):
+    run_id: str
+    type: RunEventType
+    timestamp: str = Field(default_factory=lambda: datetime.now().isoformat())
+    state: Optional[str] = None
+    tool: Optional[str] = None
+    payload: Dict[str, Any] = Field(default_factory=dict)
+
+
+class ChatTurnResult(BaseModel):
+    success: bool
+    content: str = ""
+    error: Optional[str] = None
+    active_entries: List[Any] = Field(default_factory=list)
+    task_ids: Dict[str, Optional[str]] = Field(default_factory=dict)
+    run_id: str = ""
+    workflow_template_id: str = WorkflowTemplateKind.BUILTIN_CHAT.value

backend/models/internal.py

@@ -215,6 +215,10 @@ class ChatHeader(BaseModel):
     messageCount: int = Field(0, description="消息数量")
     ragLibraryId: Optional[str] = Field(None, description="关联的 RAG 历史消息库 ID")
 
+    # Agent workflow engine (optional, backward compatible)
+    workflowTemplateId: Optional[str] = Field(None, description="工作流模板 ID")
+    engineRunId: Optional[str] = Field(None, description="最近一次引擎运行 ID")
+
 
 class ChatMessage(BaseModel):
     """