#region AgentChat.Contracts [C:4] [TYPE ADR] [SEMANTICS contracts,modules,agent-chat,langgraph,final]
@BRIEF Final module contracts — LangGraph `create_react_agent()`, `@tool`, `interrupt()`/`Command(resume=...)`, `PostgresSaver`, structured JSON metadata, dual-identity RBAC.

## Backend

| Contract | C | File | Notes |
|----------|---|------|-------|
| AgentChat.GradioApp | C4 | `backend/src/agent/app.py` | `gr.ChatInterface(type="messages", multimodal=True, additional_inputs=[gr.Textbox("conversation_id"), gr.Textbox("action")], examples=[["Покажи дашборды",null,null],["Статус системы",null,null]])`. Handler: `def handler(message, history, request: gr.Request, conversation_id=None, action=None)`. Per-user lock via in-memory dict (no global concurrency_limit — Gradio handles concurrent users by default). |
| AgentChat.GradioApp.Handler | C4 | ↑ | Creates `create_react_agent()` with PostgresSaver. `astream_events(config={"configurable":{"thread_id":conversation_id}})`. Resume: detects `action="confirm"/"deny"` in additional_inputs, loads checkpoint, invokes `Command(resume=...)`. |
| AgentChat.LangGraph.Setup | C4 | `backend/src/agent/langgraph_setup.py` | `create_react_agent(model, tools=ALL_TOOLS, checkpointer=PostgresSaver(conn_string))`. `interrupt_before=DANGEROUS_TOOLS`. Wrapped in `RunnableWithMessageHistory`. No custom middleware. |
| AgentChat.Tools | C4 | `backend/src/agent/tools.py` | Native `@tool` functions. Each: Pydantic `BaseModel` args_schema, calls FastAPI REST with dual-identity headers (`Authorization: service JWT` + `X-User-JWT: user JWT`). |
| AgentChat.Middleware | C3 | `backend/src/agent/middleware.py` | `LoggingMiddleware` only (audit trail). |
| AgentChat.Document.Parser | C3 | `backend/src/agent/document_parser.py` | pdfplumber (PDF) + openpyxl (XLSX). |
| AgentChat.Api.Conversations | C3 | `backend/src/api/routes/agent_conversations.py` | CRUD (list, history, create, archive) + multi-tab gate `GET .../conversations/{id}/active`. |
| AgentChat.Api.ServiceToken | C3 | `backend/src/api/routes/auth.py` | `POST /api/auth/service-token` — returns service JWT (role `agent`). |
| Models.Agent | C2 | `backend/src/models/agent.py` | AgentConversation, AgentMessage. |
| Schemas.Agent | C1 | `backend/src/schemas/agent.py` | Pydantic: ConversationItem, ConversationListResponse, MessageItem, HistoryResponse, DeleteResponse. |

## Frontend

| Contract | C | File | Notes |
|----------|---|------|-------|
| AgentChat.Model | C4 | `frontend/src/lib/models/AgentChatModel.svelte.ts` | `submit("/chat", {text,files}, [conversationId, action])` lifecycle. Structured `ChatMessage.metadata` parsing. HITL resume via second submit with `additional_inputs[1]="confirm"/"deny"`. No tabRole, no follower. |
| AgentChat.Panel | C4 | `frontend/src/lib/components/assistant/AssistantChatPanel.svelte` | `Client.connect("/api/agent/gradio")`, `submit()`, metadata-based rendering of tool cards + confirmation cards. |
| AgentChat.Page | C3 | `frontend/src/routes/agent/+page.svelte` | Two-column layout: conversation list (240px) + chat area. |
| AgentChat.ConversationList | C3 | `frontend/src/lib/components/assistant/ConversationList.svelte` | Search, infinite scroll, date grouping, archive action. |
| AgentChat.ToolCallCard | C2 | `frontend/src/lib/components/assistant/ToolCallCard.svelte` | Props from `metadata.type="tool_start"/"tool_end"/"tool_error"`. |
| AgentChat.ConfirmationCard | C3 | `frontend/src/lib/components/assistant/ConfirmationCard.svelte` | Renders on `metadata.type="confirm_required"`. Calls second `submit()` with `additional_inputs=[conversation_id, "confirm"/"deny"]`. |

## Contracts Removed (vs prior versions)
- `AgentChat.LangChain.Setup` → renamed to `AgentChat.LangGraph.Setup`
- `HumanInTheLoopMiddleware` → replaced by `interrupt_before=DANGEROUS_TOOLS` (LangGraph native)
- `__resume__` field → replaced by `additional_inputs[1]="confirm"/"deny"`

#endregion AgentChat.Contracts