codewhale/docs/ARCHITECTURE.md

DeepSeek TUI Architecture

This document provides an overview of the DeepSeek TUI architecture for developers and contributors.

Current boundary note:

• crates/tui is still the live end-user runtime for the TUI, runtime API, task manager, and tool execution loop.
• Other workspace crates are being split out incrementally, but they are not yet the sole runtime source of truth.

High-Level Overview

┌─────────────────────────────────────────────────────────────────┐
│                         User Interface                          │
│  ┌─────────────────┐  ┌─────────────────┐  ┌────────────────┐  │
│  │   TUI (ratatui) │  │  One-shot Mode  │  │  Config/CLI    │  │
│  └────────┬────────┘  └────────┬────────┘  └────────┬───────┘  │
└───────────┼─────────────────────┼────────────────────┼──────────┘
            │                     │                    │
            ▼                     ▼                    ▼
┌─────────────────────────────────────────────────────────────────┐
│                        Core Engine                              │
│  ┌─────────────────────────────────────────────────────────┐   │
│  │                    Agent Loop (core/engine.rs)           │   │
│  │  ┌─────────┐  ┌─────────────┐  ┌──────────────────────┐ │   │
│  │  │ Session │  │ Turn Mgmt   │  │ Tool Orchestration   │ │   │
│  │  └─────────┘  └─────────────┘  └──────────────────────┘ │   │
│  └─────────────────────────────────────────────────────────┘   │
└─────────────────────────────────────────────────────────────────┘
            │                     │                    │
            ▼                     ▼                    ▼
┌─────────────────────────────────────────────────────────────────┐
│                     Tool & Extension Layer                      │
│  ┌──────────┐  ┌──────────┐  ┌─────────┐  ┌────────────────┐   │
│  │  Tools   │  │  Skills  │  │  Hooks  │  │  MCP Servers   │   │
│  │ (shell,  │  │ (plugins)│  │ (pre/   │  │  (external)    │   │
│  │  file)   │  │          │  │  post)  │  │                │   │
│  └──────────┘  └──────────┘  └─────────┘  └────────────────┘   │
└─────────────────────────────────────────────────────────────────┘
            │                     │                    │
            ▼                     ▼                    ▼
┌─────────────────────────────────────────────────────────────────┐
│                  Runtime API + Task Management                  │
│  ┌─────────────────────────────┐  ┌──────────────────────────┐  │
│  │ HTTP/SSE Runtime API        │  │ Persistent Task Manager  │  │
│  │ (runtime_api.rs)            │  │ (task_manager.rs)        │  │
│  └─────────────────────────────┘  └──────────────────────────┘  │
└─────────────────────────────────────────────────────────────────┘
            │                     │
            ▼                     ▼
┌─────────────────────────────────────────────────────────────────┐
│                        LLM Layer                                │
│  ┌──────────────────────────────────────────────────────────┐  │
│  │              LLM Client Abstraction (llm_client.rs)       │  │
│  │  ┌─────────────────┐  ┌─────────────────────────────┐    │  │
│  │  │  DeepSeek Client │  │  Compatible Client (DeepSeek)│    │  │
│  │  │   (client.rs)   │  │       (client.rs)           │    │  │
│  │  └─────────────────┘  └─────────────────────────────┘    │  │
│  └──────────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────────┘

Module Organization

Entry Point

• main.rs - CLI argument parsing (clap), configuration loading, entry point routing

Core Components

• core/ - Main engine components
  • engine.rs - Engine state, operation handling, message processing
  • engine/turn_loop.rs - Streaming turn loop and tool execution orchestration
  • engine/capacity_flow.rs - Capacity guardrail checkpoints and interventions
  • session.rs - Session state management
  • turn.rs - Turn-based conversation handling
  • events.rs - Event system for UI updates
  • ops.rs - Core operations

Configuration

• config.rs - Configuration loading, profiles, environment variables
• settings.rs - Runtime settings management

Workspace Crates

• crates/tools - Shared tool invocation primitives, including tool result/error/capability types used by the TUI runtime.

LLM Integration

• client.rs - HTTP client for DeepSeek's documented OpenAI-compatible Chat Completions API
• llm_client.rs - Abstract LLM client trait with retry logic
• models.rs - Data structures for API requests/responses

DeepSeek API Endpoints

DeepSeek exposes OpenAI-compatible endpoints. The CLI uses:

• https://api.deepseek.com/v1/chat/completions - normal and streaming model turns
• https://api.deepseek.com/v1/models - live model discovery and health checks

https://api.deepseek.com/v1 is accepted for OpenAI SDK compatibility, and https://api.deepseek.com/beta can be configured for beta-only features such as strict tool mode, chat prefix completion, and FIM completion. The public DeepSeek docs do not document a Responses API path for this workflow; the engine drives turns through Chat Completions.

Tool System

• tools/ - Built-in tool implementations
  • mod.rs - Tool registry and common types
  • shell.rs - Shell command execution
  • file.rs - File read/write operations
  • todo.rs - Todo list management
  • plan.rs - Planning tools
  • subagent.rs - Sub-agent spawning
  • spec.rs - Tool specifications

Extension Systems

• mcp.rs - Model Context Protocol client for external tool servers
• skills.rs - Plugin/skill loading and execution
• hooks.rs - Pre/post execution hooks with conditions

User Interface

• tui/ - Terminal UI components (ratatui-based)

  • app.rs - Application state and message handling
  • ui.rs - Event handling, streaming state, and rendering logic
  • approval.rs - Tool approval dialog
  • clipboard.rs - Clipboard handling
  • streaming.rs - Streaming text collector

• ui.rs - Legacy/simple UI utilities

Security

• sandbox/ - macOS sandboxing support
  • mod.rs - Sandbox type definitions
  • policy.rs - Sandbox policy configuration
  • seatbelt.rs - macOS Seatbelt profile generation

Utilities

• utils.rs - Common utilities
• logging.rs - Logging infrastructure
• compaction.rs - Context compaction for long conversations
• pricing.rs - Cost estimation
• prompts.rs - System prompt templates
• project_doc.rs - Project documentation handling
• session.rs - Session serialization
• runtime_api.rs - HTTP/SSE runtime API (deepseek serve --http)
• runtime_threads.rs - Durable thread/turn/item store + replayable event timeline
• task_manager.rs - Durable queue, worker pool, task timelines and artifacts

Data Flow

Interactive Session

1. User input received in TUI
2. Input processed by core/engine.rs
3. Message sent to LLM via llm_client.rs
4. Response streamed back, parsed in client.rs
5. Tool calls extracted and executed via tools/
6. Hooks triggered before/after tool execution
7. Results aggregated and sent back to LLM
8. Final response rendered in TUI

Crash Recovery + Offline Queue

1. Before sending user input, the TUI writes a checkpoint snapshot to ~/.deepseek/sessions/checkpoints/latest.json
2. Startup remains fresh by default; prior sessions are resumed explicitly via --resume/--continue (or Ctrl+R in TUI)
3. While degraded/offline, new prompts are queued in-memory and mirrored to ~/.deepseek/sessions/checkpoints/offline_queue.json
4. Queue edits (/queue ...) are persisted continuously so drafts and queued prompts survive restarts
5. Successful turn completion clears the active checkpoint and writes a durable session snapshot
6. Agent/Yolo turns also take pre/post-turn side-git workspace snapshots under ~/.deepseek/snapshots/<project_hash>/<worktree_hash>/.git; /restore N and revert_turn restore file state without changing conversation history or the user's .git

Tool Execution

1. LLM requests tool via tool_use content block
2. Tool registry looks up handler
3. Pre-execution hooks run
4. Approval requested if needed (non-yolo mode)
5. Tool executed (possibly sandboxed on macOS)
6. Post-execution hooks run
7. Result returned to agent loop

Background Tasks

1. Client enqueues task (/task add ... or POST /v1/tasks)
2. task_manager.rs persists task + queue entry under ~/.deepseek/tasks
3. Worker picks queued task (bounded pool), transitions to running
4. Task creates/uses a runtime thread and starts a runtime turn
5. runtime_threads.rs persists thread/turn/item records + monotonic event sequence
6. Timeline/tool summaries/artifact references are persisted incrementally
7. Final state (completed|failed|canceled) is durable and queryable via TUI/API

Runtime Thread/Turn Timeline

1. API/TUI creates or resumes a thread (/v1/threads*)
2. Turn starts on the thread (/v1/threads/{id}/turns)
3. Engine events are mapped to item lifecycle events (item.started|item.delta|item.completed)
4. Interrupt/steer operations apply to the active turn only
5. Compaction (auto/manual) is emitted as context_compaction item lifecycle
6. Clients replay history and resume with /v1/threads/{id}/events?since_seq=<n>

Durable Schema Gates

• session_manager.rs, runtime_threads.rs, and task_manager.rs embed schema_version on persisted records.
• On load, newer schema versions are rejected with explicit errors instead of silently truncating/overwriting data.
• This allows safe forward migrations and prevents corruption when binaries and stored state are out of sync.

Extension Points

Adding a New Tool

1. Create handler in tools/
2. Register in tools/registry.rs
3. Add tool specification (name, description, input schema)

Adding an MCP Server

1. Configure in ~/.deepseek/mcp.json
2. Server auto-discovered at startup
3. Tools exposed to LLM automatically

Creating a Skill

1. Create skill directory with SKILL.md
2. Define skill prompt and optional scripts
3. Place in ~/.deepseek/skills/

Adding Hooks

Configure in ~/.deepseek/config.toml:

[[hooks]]
event = "tool_call_before"
command = "echo 'Running tool: $TOOL_NAME'"

Key Design Decisions

1. Streaming-first: All LLM responses stream for responsiveness
2. Tool safety: Non-YOLO mode requires approval for destructive operations, including side-effectful MCP tools
3. Extensibility: MCP, skills, and hooks allow customization without code changes
4. Cross-platform: Core works on Linux/macOS/Windows, sandboxing macOS-only
5. Minimal dependencies: Careful dependency selection for build speed
6. Local-first runtime API: HTTP/SSE endpoints are intended for trusted localhost access and are served by the crates/tui runtime today

Configuration Files

• ~/.deepseek/config.toml - Main configuration
• /etc/deepseek/managed_config.toml - Optional managed defaults layer (Unix)
• /etc/deepseek/requirements.toml - Optional allowed-policy constraints (Unix)
• ~/.deepseek/mcp.json - MCP server configuration
• ~/.deepseek/skills/ - User skills directory
• ~/.deepseek/sessions/ - Session history
• ~/.deepseek/sessions/checkpoints/ - Crash checkpoint + offline queue persistence
• ~/.deepseek/snapshots/ - Side-git pre/post-turn workspace snapshots for /restore and revert_turn
• ~/.deepseek/tasks/ - Background task records, queue, timelines, artifacts
• ~/.deepseek/audit.log - Append-only audit events for credential + approval/elevation actions