Maybe Runtime subsystem done

2026-06-04 08:19:50 +08:00
parent 06100b0561
commit 6b17a884e5
43 changed files with 7687 additions and 0 deletions
--- a/.gitignore
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/target
+prototype/
--- a/Cargo.lock
+++ b/Cargo.lock
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -0,0 +1,52 @@
+[package]
+name = "everjoy"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+# TUI rendering
+ratatui = "0.29"
+crossterm = "0.28"
+tui-textarea = "0.7"
+tui-term = "0.2"
+
+# Async + network
+tokio = { version = "1.4", features = ["full"] }
+reqwest = { version = "0.12", features = ["json", "stream", "rustls-tls"] }
+tokio-tungstenite = "0.26"
+futures = "0.3"
+
+# Serialization + Agent protocol
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+schemars = "0.8"
+async-trait = "0.1"
+
+# Data persistence
+rusqlite = { version = "0.34", features = ["bundled", "chrono"] }
+chrono = { version = "0.4", features = ["serde"] }
+uuid = { version = "1.16", features = ["v4", "serde"] }
+
+# Text + files
+ropey = "1.6"
+pulldown-cmark = "0.13"
+syntect = "5.2"
+notify = "8.0"
+ignore = "0.4"
+walkdir = "2.5"
+
+# Config + utilities
+toml = "0.8"
+directories = "5.0"
+regex = "1.11"
+which = "7.0"
+tempfile = "3.19"
+glob = "0.3"
+
+# Infrastructure
+anyhow = "1.0"
+thiserror = "2.0"
+parking_lot = "0.12"
+indexmap = "2.7"
+
+[dev-dependencies]
--- a/NOTES.MD
+++ b/NOTES.MD
@@ -0,0 +1 @@
+i18n support
--- a/TECH_STACK.md
+++ b/TECH_STACK.md
@@ -0,0 +1,361 @@
+# Everjoy Tech Stack
+
+> **Everjoy is not only an IDE but a completely fresh AI workflow.**
+> 
+> An ideal agent tool with a TUI interacting interface, divided into several workspaces:
+> file editing, vibe interacting, and project/life management.
+
+---
+
+## 1. TUI 渲染与交互框架
+
+| 库 | 用途 |
+|----|------|
+| **ratatui** | TUI 渲染核心，多工作区布局、面板分割、状态管理 |
+| **crossterm** | 跨平台输入输出（键鼠事件、颜色、光标、屏幕缓冲） |
+| **tui-textarea** | 编辑器工作区的文本编辑组件 |
+| **tui-term** | 内置终端面板（Agent 执行命令时展示实时输出） |
+
+### 为什么选 ratatui
+
+- 工作区（Workspace）需要复杂布局：侧边栏 + 编辑区 + AI 对话面板 + 状态栏
+- 支持鼠标点击切换面板、拖拽分割线
+- 活跃的组件生态，适合快速组装多面板界面
+
+```bash
+cargo add ratatui crossterm tui-textarea tui-term
+```
+
+---
+
+## 2. 异步运行时与网络通信
+
+| 库 | 用途 |
+|----|------|
+| **tokio** | 异步运行时，同时处理 UI 事件、AI 流式响应、文件监听 |
+| **reqwest** | HTTP 客户端，调用 LLM API（OpenAI、Claude、本地 Ollama 等） |
+| **tokio-tungstenite** | WebSocket 客户端（实时连接、本地服务通信） |
+| **futures** | 流处理工具 |
+
+### AI 流式响应处理
+
+```bash
+cargo add tokio --features full
+cargo add reqwest --features json,stream,rustls-tls
+cargo add tokio-tungstenite
+cargo add futures
+```
+
+---
+
+## 3. Agent 核心引擎
+
+这是 Everjoy 的灵魂。不依赖现有框架，自研一个轻量但可扩展的 Agent 循环。
+
+### 核心架构
+
+```
+┌─────────────┐     ┌─────────────┐     ┌─────────────┐
+│  Observer   │ --> │   Thinker   │ --> │   Actor     │
+│  (观察环境)  │     │  (推理决策)  │     │  (执行动作)  │
+└─────────────┘     └─────────────┘     └─────────────┘
+       ^                                      |
+       └────────────── Feedback <─────────────┘
+```
+
+### Agent 相关依赖
+
+| 库 | 用途 |
+|----|------|
+| **serde** + **serde_json** | LLM API 请求/响应的结构化序列化 |
+| **schemars** | 为工具函数生成 JSON Schema，供 LLM function calling 使用 |
+| **async-trait** | Agent 组件的异步 trait 抽象 |
+
+```bash
+cargo add serde --features derive
+cargo add serde_json
+cargo add schemars
+cargo add async-trait
+```
+
+### 工具系统（Tools）
+
+Agent 需要能操作环境的工具集：
+
+| 工具 | 实现方式 |
+|------|---------|
+| 文件读写 | `std::fs` + `ropey`（大文件） |
+| 命令执行 | `tokio::process::Command` + `tui-term` 展示输出 |
+| 代码搜索 | `regex` + `ignore`（支持 .gitignore） |
+| 网络请求 | `reqwest`（Agent 自主查询文档/API） |
+| 任务管理 | 调用 SQLite 存储层（见第 5 节） |
+
+```bash
+cargo add regex ignore
+```
+
+---
+
+## 4. 记忆系统（Memory）
+
+Agent 不能金鱼脑。需要短期对话记忆 + 长期知识记忆。
+
+### 短期记忆：对话上下文
+
+直接维护 `Vec<Message>`，按 token 限制滑动窗口截断。
+
+### 长期记忆：向量检索
+
+| 库 | 用途 |
+|----|------|
+| **rusqlite** | 主数据库（对话历史、任务、配置、笔记） |
+| **sqlite-vec** 或 **pgvector 本地版** | 向量存储与相似度检索 |
+| **fastembed-rs** | 本地文本 Embedding（不依赖外部 API） |
+
+> 如果追求极简，可以先只用 SQLite 全文搜索（`fts5`），后期再上向量。
+
+```bash
+cargo add rusqlite --features bundled
+# 向量检索后续按需添加
+```
+
+---
+
+## 5. 数据持久化层
+
+Everjoy 管理项目和人生，需要稳定的数据层。
+
+| 库 | 用途 |
+|----|------|
+| **rusqlite** | 嵌入式数据库，存储一切 |
+| **chrono** | 时间处理、截止日期、日历事件 |
+| **uuid** | 任务/对话/项目的唯一标识 |
+
+### 数据库表设计（初版）
+
+```sql
+-- 对话历史
+CREATE TABLE conversations (
+    id TEXT PRIMARY KEY,
+    title TEXT,
+    created_at DATETIME,
+    updated_at DATETIME
+);
+
+CREATE TABLE messages (
+    id TEXT PRIMARY KEY,
+    conversation_id TEXT,
+    role TEXT,  -- 'user' | 'assistant' | 'system' | 'tool'
+    content TEXT,
+    tool_calls TEXT,  -- JSON
+    created_at DATETIME
+);
+
+-- 任务/项目管理
+CREATE TABLE tasks (
+    id TEXT PRIMARY KEY,
+    title TEXT,
+    description TEXT,
+    status TEXT,  -- 'todo' | 'doing' | 'done' | 'archived'
+    priority INTEGER,
+    due_date DATETIME,
+    project TEXT,
+    tags TEXT,  -- JSON array
+    created_at DATETIME
+);
+
+-- 笔记/知识
+CREATE TABLE notes (
+    id TEXT PRIMARY KEY,
+    title TEXT,
+    content TEXT,
+    tags TEXT,
+    linked_file TEXT,
+    created_at DATETIME
+);
+```
+
+```bash
+cargo add chrono --features serde
+cargo add uuid --features v4,serde
+```
+
+---
+
+## 6. 内容渲染与解析
+
+| 库 | 用途 |
+|----|------|
+| **pulldown-cmark** | 解析 AI 回复的 Markdown，渲染到 TUI 面板 |
+| **syntect** | 代码块语法高亮（Markdown 中的 ```rust 块） |
+| **syntect-tui** | syntect 与 ratatui 的桥接 |
+
+> AI 回复基本是 Markdown，需要解析成 ratatui 的 `Text`/`Span` 结构渲染。
+
+```bash
+cargo add pulldown-cmark
+cargo add syntect syntect-tui
+```
+
+---
+
+## 7. 文件系统与项目感知
+
+| 库 | 用途 |
+|----|------|
+| **ropey** | 大文件高效编辑（编辑工作区核心） |
+| **notify** | 监听文件变化，Agent 实时感知项目改动 |
+| **ignore** | 按 .gitignore 规则遍历文件树 |
+| **walkdir** | 目录遍历 |
+
+```bash
+cargo add ropey notify ignore walkdir
+```
+
+---
+
+## 8. 配置管理
+
+| 库 | 用途 |
+|----|------|
+| **toml** | 用户配置（AI API key、主题、快捷键、Agent 人设） |
+| **serde** | 配置反序列化 |
+| **directories** | 跨平台定位配置目录 `~/.config/everjoy/` |
+
+### 配置文件结构
+
+```toml
+# ~/.config/everjoy/config.toml
+[ai]
+provider = "openai"
+api_key = "sk-..."
+model = "gpt-4o"
+stream = true
+
+[agent]
+personality = "你是一位高效且略带幽默的编程伙伴..."
+auto_execute_tools = false  -- 危险操作需确认
+
+[ui]
+theme = "everforest"
+sidebar_width = 30
+editor_tab_size = 4
+
+[keymap]
+"ctrl+space" = "toggle_agent_panel"
+"ctrl+shift+a" = "ask_agent"
+```
+
+```bash
+cargo add toml serde --features derive directories
+```
+
+---
+
+## 9. 实用工具库
+
+| 库 | 用途 |
+|----|------|
+| **anyhow** | 快速原型期的错误处理 |
+| **thiserror** | 后期结构化错误定义 |
+| **parking_lot** | 更轻量的同步原语 |
+| **indexmap** | 有序 HashMap（保持面板顺序、配置项顺序） |
+| **which** | 查找系统命令路径（检查 git、node 等是否存在） |
+| **tempfile** | 临时文件（Agent 编辑前备份） |
+| **glob** | 文件通配匹配 |
+
+```bash
+cargo add anyhow thiserror parking_lot indexmap which tempfile glob
+```
+
+---
+
+## 10. 完整 Cargo.toml
+
+```toml
+[package]
+name = "everjoy"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+# TUI 渲染
+ratatui = "0.29"
+crossterm = "0.28"
+tui-textarea = "0.7"
+tui-term = "0.2"
+
+# 异步 + 网络
+tokio = { version = "1.4", features = ["full"] }
+reqwest = { version = "0.12", features = ["json", "stream", "rustls-tls"] }
+tokio-tungstenite = "0.26"
+futures = "0.3"
+
+# 序列化 + Agent 协议
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+schemars = "0.8"
+async-trait = "0.1"
+
+# 数据持久化
+rusqlite = { version = "0.34", features = ["bundled", "chrono"] }
+chrono = { version = "0.4", features = ["serde"] }
+uuid = { version = "1.16", features = ["v4", "serde"] }
+
+# 文本 + 文件
+ropey = "1.6"
+pulldown-cmark = "0.13"
+syntect = "5.2"
+# syntect-tui = "..."  # 视情况选择或自研桥接
+notify = "8.0"
+ignore = "0.4"
+walkdir = "2.5"
+
+# 配置 + 工具
+toml = "0.8"
+directories = "5.0"
+regex = "1.11"
+which = "7.0"
+tempfile = "3.19"
+glob = "0.3"
+
+# 基础设施
+anyhow = "1.0"
+thiserror = "2.0"
+parking_lot = "0.12"
+indexmap = "2.7"
+
+[dev-dependencies]
+# 测试工具后续添加
+```
+
+---
+
+## 12. 关键设计决策
+
+| 维度 | 决策 | 理由 |
+|------|------|------|
+| **编辑模式** | **非模态**（直接打字） | 开箱即用，AI 随时可介入 |
+| **Agent 架构** | **自研 ReAct 循环** | 现有框架太重，自研更灵活 |
+| **LLM 接入** | **多 Provider 抽象** | 支持 OpenAI/Claude/Ollama/本地模型 |
+| **流式响应** | **SSE 实时渲染** | AI 思考过程实时展示在对话面板 |
+| **数据存储** | **SQLite 单文件** | 用户项目 + 人生数据一盘棋 |
+| **工具执行** | **人工确认 + 自动执行分级** | 读文件自动，写文件/执行命令需确认 |
+| **文件编辑** | **临时缓冲 + 用户确认写入** | Agent 的修改先预览，用户 OK 再落盘 |
+
+---
+
+## 13. 开发里程碑（建议）
+
+| 阶段 | 目标 | 核心组件 |
+|------|------|---------|
+| **MVP** | TUI 多面板 + 基本编辑器 + 能聊天的 Agent | ratatui, tui-textarea, reqwest, 简单 ReAct |
+| **v0.2** | 文件工具 + 项目内代码问答 | ropey, ignore, notify, 文件读写工具 |
+| **v0.3** | 任务/笔记管理 + SQLite 持久化 | rusqlite, chrono, 任务面板 |
+| **v0.4** | 内嵌终端 + Agent 自主执行命令 | tui-term, tokio-process, 命令工具 |
+| **v0.5** | 记忆系统 + 跨对话上下文 | sqlite-vec, embedding, 长期记忆检索 |
+
+---
+
+*for Hoshu Chiu & Everjoy Chiu 🐕*
+*Just have fun with Everjoy.*
--- a/doc/Architecture-Runtime-and-Plugin.md
+++ b/doc/Architecture-Runtime-and-Plugin.md
@@ -0,0 +1,218 @@
+# Everjoy Architecture: Runtime Subsystem + Plugin Subsystem
+
+## Design Principle
+
+**Separate concerns:**
+- **Runtime Subsystem** = the engine. Defines interfaces, manages lifecycle, routes events, schedules rendering. Everything (built-in + external) depends on it.
+- **Plugin Subsystem** = the adapter. Loads external code, translates C-ABI ↔ Rust trait. Only external modules go through it.
+
+```
+┌─────────────────────────────────────────┐
+│         Runtime Subsystem               │
+│  (supporter for everything)             │
+├─────────────────────────────────────────┤
+│  Module Registry                        │
+│  - PanelProvider registry               │
+│  - MenuItem registry                    │
+│  - StatusWidget registry                │
+│  - Tool registry                        │
+├─────────────────────────────────────────┤
+│  Lifecycle Manager                      │
+│  - init → render → event → hide →      │
+│    show → shutdown                      │
+├─────────────────────────────────────────┤
+│  Event Router                           │
+│  - Layer 1: System shortcuts            │
+│  - Layer 2: Focused PanelProvider       │
+│  - Layer 3: Global shortcuts / Menubar  │
+├─────────────────────────────────────────┤
+│  Render Scheduler                       │
+│  - Calls Provider::render() each frame  │
+│  - Blits cell grid → Buffer for         │
+│    external providers                   │
+└─────────────────────────────────────────┘
+              ↑ ↓ traits
+┌─────────────────────────────────────────┐
+│         Plugin Subsystem                │
+│  (loader + translator)                  │
+├─────────────────────────────────────────┤
+│  Extension Loader                       │
+│  - Scan plugin directory                │
+│  - Load .wasm / .so / static            │
+│  - Symbol resolution                    │
+├─────────────────────────────────────────┤
+│  Translation Layer                      │
+│  - C-ABI ↔ Rust trait                   │
+│  - EjSurface memory management          │
+│  - Cell grid → Buffer blitting          │
+│  - Style resolution                     │
+│  - Panic isolation                      │
+└─────────────────────────────────────────┘
+```
+
+---
+
+## Runtime Subsystem
+
+Defines the **trait interfaces** that all modules must satisfy. Built-in modules implement these directly. External modules satisfy them via the Plugin Subsystem.
+
+### Core Traits
+
+```rust
+/// Anything that can render into a panel
+pub trait PanelProvider: Send {
+    fn init(&mut self, ctx: &mut dyn ProviderCtx);
+    fn render(&mut self, area: Rect, buf: &mut Buffer);
+    fn handle_event(&mut self, event: Event) -> EventResult;
+    fn focus_changed(&mut self, focused: bool);
+    fn hide(&mut self);
+    fn show(&mut self);
+    fn shutdown(&mut self);
+    fn can_open(&self, context: &OpenContext) -> bool;
+    fn keep_alive_on_hide(&self) -> bool { false }
+}
+
+/// Callable by Agents
+pub trait Tool: Send {
+    fn name(&self) -> &str;
+    fn description(&self) -> &str;
+    fn schema(&self) -> ToolSchema;           // JSON Schema for LLM function calling
+    fn execute(&self, input: ToolInput) -> ToolOutput;
+}
+
+/// Menubar entry
+pub trait MenuItem: Send {
+    fn id(&self) -> &str;
+    fn label(&self) -> &str;
+    fn parent(&self) -> Option<&str>;
+    fn shortcut(&self) -> Option<&str>;
+    fn invoke(&self);
+}
+
+/// Status bar widget
+pub trait StatusWidget: Send {
+    fn id(&self) -> &str;
+    fn position(&self) -> StatusPosition;
+    fn render(&self, area: Rect, buf: &mut Buffer);
+}
+```
+
+### Module Registry
+
+```rust
+pub struct ModuleRegistry {
+    panel_providers: HashMap<String, Box<dyn PanelProvider>>,
+    menu_items: Vec<Box<dyn MenuItem>>,
+    status_widgets: Vec<Box<dyn StatusWidget>>,
+    tools: HashMap<String, Box<dyn Tool>>,
+}
+```
+
+Built-in modules register directly:
+
+```rust
+// In everjoy/src/main.rs or a built-in module initializer
+runtime.register_panel_provider("editor", Box::new(EditorProvider::new()));
+runtime.register_panel_provider("terminal", Box::new(TerminalProvider::new()));
+runtime.register_panel_provider("tasktree", Box::new(TaskTreeProvider::new()));
+runtime.register_tool("read_file", Box::new(ReadFileTool));
+runtime.register_menu_item(Box::new(QuitMenuItem));
+```
+
+### Lifecycle (Runtime-managed)
+
+```
+Load (built-in = static init, external = via Plugin Subsystem)
+    ↓
+bootstrap() — register all contributions
+    ↓
+Running — render / event / command loop
+    ↓
+Unload — shutdown() all providers, unregister all contributions
+```
+
+---
+
+## Plugin Subsystem
+
+Only responsible for **external modules**. Built-in modules never touch it.
+
+### Extension Loader
+
+```rust
+pub struct ExtensionLoader {
+    plugin_dir: PathBuf,
+}
+
+impl ExtensionLoader {
+    pub fn scan_and_load(&self, runtime: &mut Runtime) -> Result<()> {
+        for entry in fs::read_dir(&self.plugin_dir)? {
+            let path = entry?.path();
+            let plugin = self.load(&path)?;
+            plugin.bootstrap(runtime.registrar())?;
+        }
+        Ok(())
+    }
+
+    fn load(&self, path: &Path) -> Result<Box<dyn Plugin>> {
+        match path.extension() {
+            Some("wasm") => self.load_wasm(path),
+            Some("so") | Some("dll") => self.load_dylib(path),
+            _ => Err("Unknown plugin format"),
+        }
+    }
+}
+```
+
+### Translation Layer
+
+For external plugins (especially WASM), the Plugin Subsystem provides a translation layer:
+
+```rust
+/// Wraps a C-ABI / WASM plugin into Runtime-compatible traits
+pub struct TranslatedProvider {
+    wasm_instance: wasmtime::Instance,
+    // ... cached function handles
+}
+
+impl PanelProvider for TranslatedProvider {
+    fn render(&mut self, area: Rect, buf: &mut Buffer) {
+        // 1. Allocate EjSurface
+        let mut surface = EjSurface::new(area.width, area.height);
+        // 2. Call plugin's C render function
+        self.call_render(&mut surface);
+        // 3. Blit cell grid into ratatui Buffer
+        self.blit(&surface, area, buf);
+    }
+    // ... other methods translated similarly
+}
+```
+
+### Key Rule
+
+> **Built-in modules implement Runtime traits directly.**
+> **External modules are wrapped by Plugin Subsystem to satisfy Runtime traits.**
+
+```rust
+// Built-in: direct trait implementation
+runtime.register_panel_provider("editor", Box::new(EditorProvider::new()));
+
+// External: loaded via Plugin Subsystem, wrapped to satisfy trait
+let plugin = plugin_subsystem.load("image-viewer.wasm")?;
+let provider = plugin.create_provider("image-viewer.main")?;
+runtime.register_panel_provider("image-viewer", Box::new(provider));
+//                        ^^^^ provider here is a TranslatedProvider
+//                              that implements PanelProvider
+```
+
+---
+
+## Summary
+
+| Concern | Runtime Subsystem | Plugin Subsystem |
+|---------|-------------------|------------------|
+| **Defines** | Trait interfaces | Loading + translation mechanism |
+| **Used by** | Everyone (built-in + external) | Only external modules |
+| **Manages** | Registry, lifecycle, events, render | File I/O, WASM runtime, FFI |
+| **Depends on** | ratatui, crossterm, tokio | wasmtime / libloading, Runtime traits |
+| **Can be omitted?** | No — without it, no app | Yes — without it, only built-in modules work |
--- a/doc/Architecture.md
+++ b/doc/Architecture.md
@@ -0,0 +1,414 @@
+# Everjoy Architecture
+
+## Overview
+
+Everjoy is a TUI IDE with an AI-native workflow. The architecture separates concerns into four subsystems:
+
+```
+┌─────────────────────────────────────────────────────────────┐
+│                      UI Framework                            │
+│  - Layout, focus, render scheduling                         │
+│  - Menubar, Status Bar, Splash Screen                       │
+│  - Panel management (Sidebar | Main | Agent)                │
+├─────────────────────────────────────────────────────────────┤
+│                   Runtime Subsystem                          │
+│  - Trait definitions (Provider, Tool, Plugin)               │
+│  - Module Registry (providers, tools, menu, status)         │
+│  - Lifecycle management                                     │
+│  - Command dispatch (Provider → App)                        │
+├─────────────────────────────────────────────────────────────┤
+│                   Agent Framework                            │
+│  - Multi-agent orchestration                                │
+│  - Role system (Secretary, Driver, Executor...)             │
+│  - Tool invocation via LLM function calling                 │
+│  - Memory & context management                              │
+├─────────────────────────────────────────────────────────────┤
+│                   Plugin Subsystem                           │
+│  - Extension loader (.wasm / .so / static)                  │
+│  - C-ABI ↔ Rust trait translation                           │
+│  - Optional — built-in modules don't use it                 │
+└─────────────────────────────────────────────────────────────┘
+```
+
+---
+
+## 1. Runtime Subsystem
+
+The foundation. Defines what modules can do and manages their lifecycle.
+
+### 1.1 Core Traits
+
+```rust
+/// A plugin registers its contributions during bootstrap
+pub trait Plugin: Send {
+    fn bootstrap(registrar: &mut dyn Registrar);
+}
+
+/// Where content comes from (file, URL, memory)
+pub enum Source {
+    File { path: PathBuf },
+    Url  { url: String },
+    Memory { name: String, data: Vec<u8> },
+}
+
+/// Actions a Provider can request from the system
+pub enum Command {
+    /// Present content in a panel. System bids providers on that panel.
+    Present { panel: PanelType, source: Source, mime_hint: Option<String> },
+
+    /// Launch a tool/session by id. Direct dispatch, no bidding.
+    Launch { panel: PanelType, tool_id: String, params: serde_json::Value },
+
+    FocusPanel(PanelType),
+    ShowMessage { msg: String, level: MessageLevel },
+}
+
+/// Renders content into a panel
+pub trait PanelProvider: Send {
+    fn id(&self) -> &str;
+    fn init(&mut self);
+    fn render(&mut self, area: Rect, buf: &mut Buffer);
+    /// Returns (handled?, commands to dispatch)
+    fn handle_event(&mut self, event: Event) -> (EventResult, Vec<Command>);
+    fn focus_changed(&mut self, focused: bool);
+    fn hide(&mut self);
+    fn show(&mut self);
+    fn shutdown(&mut self);
+    /// Score how well this provider handles the source. 0 = cannot handle.
+    fn can_open(&self, source: &Source, mime_hint: Option<&str>) -> i32;
+    fn keep_alive_on_hide(&self) -> bool { false }
+}
+
+/// Callable by Agents via LLM function calling
+pub trait Tool: Send {
+    fn name(&self) -> &str;
+    fn description(&self) -> &str;
+    fn schema(&self) -> ToolSchema;
+    fn execute(&self, input: ToolInput) -> ToolOutput;
+}
+```
+
+### 1.2 Registrar
+
+```rust
+pub trait Registrar {
+    fn register_provider(&mut self, desc: ProviderDesc, factory: ProviderFactory);
+    fn register_tool(&mut self, desc: ToolDesc, handler: Box<dyn Tool>);
+    fn register_menu_item(&mut self, desc: MenuItemDesc, handler: Box<dyn Fn() + Send>);
+    fn register_status_widget(&mut self, desc: StatusWidgetDesc, render: Box<dyn Fn(Rect, &mut Buffer) + Send>);
+}
+```
+
+### 1.3 Command Pattern (replaces ProviderCtx)
+
+**Removed:** `ProviderCtx` trait. Providers no longer call into the system via a context object.
+
+**New:** Providers return `Vec<Command>` from `handle_event()`. The App (main.rs) is the sole dispatcher.
+
+Why: `ProviderCtx::open_file()` was an implicit black-box router — the caller didn't know which provider would handle the file, and adding new providers required modifying core code. The Command pattern makes every intent explicit and traceable.
+
+```rust
+// Before: implicit, hard-coded routing
+fn handle_event(&mut self, ev: Event) -> EventResult {
+    self.ctx.open_file("main.rs");  // who handles this? nobody knows
+    Consumed
+}
+
+// After: explicit intent, App decides
+fn handle_event(&mut self, ev: Event) -> (EventResult, Vec<Command>) {
+    let cmd = Command::Present {
+        panel: PanelType::Main,
+        source: Source::File { path: "main.rs".into() },
+        mime_hint: None,
+    };
+    (Consumed, vec![cmd])
+}
+```
+
+### 1.4 Module Registry
+
+```rust
+pub struct ModuleRegistry {
+    pub panel_providers: HashMap<String, RegisteredProvider>,
+    pub tools: HashMap<String, Box<dyn Tool>>,
+    pub menu_items: Vec<Box<dyn MenuItem>>,
+    pub status_widgets: Vec<Box<dyn StatusWidget>>,
+}
+
+pub struct RegisteredProvider {
+    pub desc: ProviderDesc,
+    pub factory: ProviderFactory,
+    pub instance: Option<Box<dyn PanelProvider>>,
+}
+```
+
+Key methods:
+- `providers_for_panel(panel) -> Vec<&RegisteredProvider>` — filter by panel type
+- `ensure_instance(id) -> Option<&mut Box<dyn PanelProvider>>` — lazy instantiate
+- `find_best_provider(panel, source, mime_hint) -> Option<(String, i32)>` — bid scoring
+- `shutdown_all()` — graceful teardown
+
+### 1.5 Lifecycle
+
+```
+Load
+  ├─ Built-in: registered into ModuleRegistry at App startup
+  └─ External: via Plugin Subsystem
+    ↓
+Bootstrap (Plugin::bootstrap)
+  ├─ Register providers (with panel type + capabilities)
+  ├─ Register tools
+  ├─ Register menu items
+  └─ Register status widgets
+    ↓
+Running
+  ├─ Render loop: App asks registry for active provider per panel, calls render()
+  ├─ Event loop: App routes to focused provider, receives Commands, dispatches
+  ├─ Tool calls: Agent Framework → Tool::execute()
+  └─ Present/Launch: App bids/routes to the best provider
+    ↓
+Unload (atomic)
+  ├─ Provider::shutdown() for all active providers
+  ├─ Unregister all contributions
+  └─ Plugin::shutdown()
+```
+
+---
+
+## 2. Plugin Subsystem
+
+Optional subsystem for external modules. Built-in modules implement Runtime traits directly.
+
+### 2.1 Architecture
+
+```
+External Plugin (.wasm / .so)
+    ↓
+Plugin Subsystem
+  ├─ Extension Loader: file I/O, symbol resolution
+  └─ Translation Layer
+      ├─ C-ABI ↔ Rust trait
+      ├─ EjSurface memory management
+      ├─ Cell grid → Buffer blitting
+      └─ Panic isolation
+    ↓
+Runtime Subsystem (receives Box<dyn PanelProvider>, Box<dyn Tool>)
+```
+
+### 2.2 Key Rule
+
+> Built-in modules implement Runtime traits directly.
+> External modules are wrapped by Plugin Subsystem to satisfy Runtime traits.
+
+---
+
+## 3. UI Framework
+
+Manages what the user sees and how they interact.
+
+### 3.1 Layout
+
+```
+┌─────────────────────────────────────────────────────────────┐
+│  _F_ile  _E_dit  _V_iew  _A_gent  _H_elp                   │  Menubar
+├──────────┬──────────────────────────────┬───────────────────┤
+│ 📁 src   │ 📁 src > main.rs             │ 🤖 Agent Chat     │
+│ 📄 Cargo │ [File Editor]                │ Claude GPT-4 Local│
+│ 📄 doc   │                              │ ───────────────── │
+│ 📁 targ  │  fn main() {                 │ You: ...          │
+│          │      let x = 42;             │ Claude: ...       │
+│          │  }                           │                   │
+│          │                              │ Quick Links:      │
+│          │                              │ [agents.md] ...   │
+│          │                              │                   │
+├──────────┴──────────────────────────────┴───────────────────┤
+│  main.rs | Rust | UTF-8 | Ln 3, Col 10 | [Main]             │  Status Bar
+└─────────────────────────────────────────────────────────────┘
+```
+
+- **Sidebar** — 20% width, FileTree (navigate files, Enter to open in Main)
+- **Main Panel** — 52% width, dynamic content (Editor, Terminal, etc.)
+- **Agent Panel** — 28% width, chat + quick links
+- **Menubar** — 1 row, underlined capitals for Alt+ shortcuts
+- **Status Bar** — 1 row, file info + focused panel
+
+### 3.2 Focus Management
+
+| Input | Action |
+|-------|--------|
+| `Alt` | Focus Menubar |
+| `Ctrl+J` | Focus Sidebar |
+| `Ctrl+K` | Focus Main Panel |
+| `Ctrl+L` | Focus Agent Panel |
+| Mouse click | Focus clicked panel directly |
+
+### 3.3 Panel State
+
+- **Main Panel** — dynamic provider, single content area
+- **Provider switching** — `hide()` old, `show()` new, old may `keep_alive_on_hide()`
+- **Navigation** — stack-based history, no tab bar (too heavy for TUI)
+- **Bidding** — when `Command::Present` arrives, all providers on the target panel score themselves via `can_open()`. Highest score wins.
+
+### 3.4 Event Routing
+
+```
+Layer 1: System shortcuts (Ctrl+Q quit) — intercepted by App
+Layer 2: Menubar — if active
+Layer 3: Focus shortcuts (Ctrl+J/K/L) — intercepted by App
+Layer 4: Focused PanelProvider → returns (EventResult, Vec<Command>)
+Layer 5: App dispatches returned Commands
+```
+
+### 3.5 Render Order
+
+Per frame:
+1. Clear
+2. Menubar
+3. Panel backgrounds (uniform dark)
+4. Sidebar Provider::render()
+5. Main Panel Provider::render()
+6. Agent Panel Provider::render()
+7. Status Bar
+
+---
+
+## 4. Agent Framework
+
+### 4.1 Role System
+
+Managed by core system, not plugins.
+
+| Role | Icon | Purpose | Trigger |
+|------|------|---------|---------|
+| Secretary | 👤 | User conversation | Always |
+| Driver | 🧭 | Exploration, curiosity | Auto |
+| NegFeedback | 🛡️ | Error detection | Auto |
+| Executor | ⚡ | Command execution | Auto |
+
+### 4.2 Tool Invocation
+
+Agent → LLM function calling → Tool Registry → Tool::execute() → result → Agent
+
+Tools are registered by plugins. The Agent Framework queries the Tool Registry for available tools and generates JSON Schema for the LLM.
+
+---
+
+## 5. Data Flows
+
+### 5.1 User Opens a File
+
+```
+User navigates to main.rs in Sidebar (FileTree)
+  → FileTreeProvider::handle_event(Enter)
+  → Returns Command::Present {
+        panel: Main,
+        source: Source::File { path: "src/main.rs" }
+    }
+  → App::dispatch_command()
+  → App asks registry: find_best_provider(Main, File("main.rs"), "text/rust")
+  → EditorProvider::can_open(File, "text/rust") = 100
+  → TerminalProvider::can_open(File, ...) = 0
+  → Editor wins
+  → App hides old Main provider, shows Editor
+  → EditorProvider.render()
+```
+
+### 5.2 Agent Opens a File
+
+```
+Agent decides to open src/main.rs
+  → LLM function calling: "open_file" tool
+  → Tool Registry finds "open_file"
+  → OpenFileTool.execute(path: "src/main.rs")
+    → Read file from disk
+    → Returns Command::Present { panel: Main, source: File(...) }
+  → App dispatches → routes to EditorProvider
+  → Tool returns "File opened" to Agent
+```
+
+### 5.3 Provider Renders a Frame
+
+```
+UI Framework render loop
+  → Determine panel areas from layout
+  → Look up active provider id per panel from App.active_providers
+  → Ask registry for instance
+  → Sidebar area → FileTreeProvider::render(area, buf)
+  → Main area → EditorProvider::render(area, buf) (or whoever is active)
+  → Agent area → AgentChatProvider::render(area, buf)
+  → Draw Menubar and Status Bar
+```
+
+---
+
+## 6. Directory Structure
+
+```
+ everjoy/
+ ├── src/
+ │   ├── main.rs                 # Entry point, App event loop, Command dispatch
+ │   ├── lib.rs                  # Public API
+ │   │
+ │   ├── runtime/                # Runtime Subsystem
+ │   │   ├── mod.rs
+ │   │   ├── traits.rs           # Plugin, PanelProvider, Tool, Command, Source
+ │   │   ├── registry.rs         # ModuleRegistry, provider bidding
+ │   │   ├── lifecycle.rs        # Provider lifecycle management
+ │   │   └── ctx.rs              # RuntimeServices (ProviderCtx removed)
+ │   │
+ │   ├── ui/                     # UI Framework
+ │   │   ├── mod.rs
+ │   │   ├── layout.rs           # Panel sizing
+ │   │   ├── focus.rs            # Focus management
+ │   │   ├── router.rs           # Event routing (legacy, to be removed)
+ │   │   ├── scheduler.rs        # Render scheduling
+ │   │   ├── menubar.rs          # Menubar rendering
+ │   │   ├── statusbar.rs        # Status bar rendering
+ │   │   └── splash.rs           # Splash screen
+ │   │
+ │   ├── agent/                  # Agent Framework
+ │   │   ├── mod.rs
+ │   │   ├── roles.rs            # Agent role definitions
+ │   │   ├── orchestrator.rs     # Multi-agent coordination
+ │   │   ├── memory.rs           # Short/long-term memory
+ │   │   └── tools.rs            # Tool invocation for LLM
+ │   │
+ │   ├── plugin/                 # Plugin Subsystem
+ │   │   ├── mod.rs
+ │   │   ├── loader.rs           # ExtensionLoader (.wasm / .so)
+ │   │   ├── translator.rs       # C-ABI ↔ Rust trait
+ │   │   ├── surface.rs          # EjSurface, cell grid
+ │   │   └── panic.rs            # Panic isolation
+ │   │
+ │   └── builtin/                # Built-in modules
+ │       ├── editor/
+ │       ├── terminal/
+ │       ├── tasktree/
+ │       ├── agentchat/
+ │       └── filetree/
+ │
+ ├── doc/
+ │   └── Architecture.md         # This file
+ │
+ └── Cargo.toml
+```
+
+---
+
+## 7. Key Design Decisions
+
+| Decision | Choice | Rationale |
+|----------|--------|-----------|
+| Provider → System comms | **Command pattern** | Explicit intents, no hidden routing, easy to log/intercept |
+| Content routing | **Bidding (can_open score)** | Multiple providers can compete; new providers need no core changes |
+| Provider rendering | Dual-track | Built-in direct Buffer, external cell grid |
+| Event routing | 5-layer | System → Menubar → Focus shortcuts → Provider → Command dispatch |
+| Tool lifecycle | Plugin-level | Independent of Provider activation |
+| Main Panel | Single content | No tab bar, stack nav, keep_alive_on_hide |
+| Workspaces | Not in MVP | Manual provider switching sufficient |
+| Plugin loading | Eager + config | All at startup, user-configurable blacklist |
+| Focus | Keyboard + mouse | Ctrl+J/K/L for panels (avoids terminal tab interception) |
+
+---
+
+*Architecture approved? If yes, this becomes the authoritative spec.*
--- a/doc/Plugin-Lifecycle-Tool-vs-Provider.md
+++ b/doc/Plugin-Lifecycle-Tool-vs-Provider.md
@@ -0,0 +1,157 @@
+# Tool vs Provider: Different Lifecycles
+
+## The Problem
+
+> "How can text plugin receive a tool call when it is not activated to main panel?"
+
+**Answer: Tool and Provider have different lifecycles.**
+
+```
+Plugin (EditorPlugin) ── lives as long as the app runs (or until plugin is unloaded)
+├── Tool: open_file           ── always available
+├── Tool: save_file           ── always available
+├── Tool: find_and_replace    ── always available
+│
+└── Provider: EditorProvider  ── created/destroyed per Main Panel instance
+    ├── Instance A (showing main.rs)
+    ├── Instance B (showing lib.rs)  ← if we support split later
+    └── destroyed when user closes the file
+```
+
+## Key Insight
+
+**Tool is registered at Plugin level, not Provider level.**
+
+```rust
+pub trait Plugin {
+    fn bootstrap(registrar: &mut dyn Registrar);
+}
+
+pub trait Registrar {
+    // Tool lives with the Plugin
+    fn register_tool(&mut self, desc: ToolDesc, handler: Box<dyn Tool>);
+    
+    // Provider is a factory — created on demand when panel needs it
+    fn register_provider(&mut self, desc: ProviderDesc, factory: ProviderFactory);
+}
+```
+
+## How It Works
+
+### Plugin State (Shared)
+
+```rust
+pub struct EditorPlugin {
+    // Plugin-level state: all open documents
+    documents: HashMap<PathBuf, Document>,
+    config: EditorConfig,
+}
+
+impl Plugin for EditorPlugin {
+    fn bootstrap(registrar: &mut dyn Registrar) {
+        let plugin = Arc::new(Mutex::new(EditorPlugin::new()));
+        
+        // Register tools — these live with the plugin, not any provider instance
+        registrar.register_tool(
+            ToolDesc { name: "open_file", ... },
+            Box::new(OpenFileTool { plugin: plugin.clone() }),
+        );
+        registrar.register_tool(
+            ToolDesc { name: "find_and_replace", ... },
+            Box::new(FindReplaceTool { plugin: plugin.clone() }),
+        );
+        
+        // Register provider factory
+        registrar.register_provider(
+            ProviderDesc { id: "editor", panel: PanelType::Main, ... },
+            Box::new(move |_| Box::new(EditorProvider::new(plugin.clone()))),
+        );
+    }
+}
+```
+
+### Tool Execution (Always Available)
+
+```rust
+pub struct OpenFileTool {
+    plugin: Arc<Mutex<EditorPlugin>>,
+}
+
+impl Tool for OpenFileTool {
+    fn execute(&self, input: ToolInput) -> ToolOutput {
+        let path = input.args["path"].as_str().unwrap();
+        let content = std::fs::read_to_string(path).unwrap();
+        
+        // 1. Store in plugin-level state
+        self.plugin.lock().documents.insert(path.into(), Document::new(content));
+        
+        // 2. Request UI to open this file in Main Panel
+        //    This goes through a UI action, not the tool system
+        runtime.ui_actions().open_file(path);
+        
+        ToolOutput::ok("File opened")
+    }
+}
+```
+
+### Provider Render (Reads from Shared State)
+
+```rust
+pub struct EditorProvider {
+    plugin: Arc<Mutex<EditorPlugin>>,
+    current_file: PathBuf,
+}
+
+impl PanelProvider for EditorProvider {
+    fn render(&mut self, area: Rect, buf: &mut Buffer) {
+        let plugin = self.plugin.lock();
+        let doc = plugin.documents.get(&self.current_file).unwrap();
+        // render document content
+    }
+}
+```
+
+## Lifecycle Comparison
+
+| | Tool | Provider |
+|---|---|---|
+| **Registered by** | Plugin | Plugin |
+| **Created when** | Plugin bootstrap | Panel needs to display content |
+| **Destroyed when** | Plugin unload | Panel switches away (unless keep_alive) |
+| **Can be called when** | Always | Only when panel is active (render/event) |
+| **Has state** | Yes, Plugin-level shared state | Yes, instance-level state (cursor, scroll) |
+
+## Agent Opens a File: Full Flow
+
+```
+Agent: "Open src/main.rs"
+    → LLM decides to call tool "open_file"
+    → Tool Registry finds "open_file" (registered by EditorPlugin)
+    → OpenFileTool.execute(path: "src/main.rs")
+        → Read file from disk
+        → Store in EditorPlugin.documents
+        → Call ui_actions.open_file("src/main.rs")
+            → UI Framework: Main Panel provider = "editor"
+            → UI Framework: EditorProvider.current_file = "src/main.rs"
+            → EditorProvider.init()
+            → EditorProvider.render() — reads from shared state
+    → Tool returns "File opened" to Agent
+    → Agent displays "I've opened src/main.rs for you"
+```
+
+## Why This Matters
+
+**Without this separation:**
+- Agent calls `open_file` → Editor Provider not active → crash or no-op
+- Tool must wait for Provider to be created → Agent workflow broken
+
+**With this separation:**
+- Tool operates on Plugin-level state, independent of UI
+- UI switches to Provider after Tool completes
+- Provider renders from shared state
+
+## Design Rule
+
+> **Plugin = shared state + tools + provider factory.**
+> **Tool = operates on shared state, always callable.**
+> **Provider = renders shared state into a panel, only active when visible.**
--- a/src/agent/memory.rs
+++ b/src/agent/memory.rs
@@ -0,0 +1,12 @@
+/// Short-term and long-term memory for agents.
+pub struct MemorySystem;
+
+impl MemorySystem {
+    pub fn new() -> Self {
+        Self
+    }
+
+    // TODO: conversation context sliding window
+    // TODO: vector embedding for long-term retrieval
+    // TODO: SQLite storage
+}
--- a/src/agent/mod.rs
+++ b/src/agent/mod.rs
@@ -0,0 +1,4 @@
+pub mod memory;
+pub mod orchestrator;
+pub mod roles;
+pub mod tools;
--- a/src/agent/orchestrator.rs
+++ b/src/agent/orchestrator.rs
@@ -0,0 +1,12 @@
+/// Coordinates multiple agents and dispatches tasks.
+pub struct Orchestrator;
+
+impl Orchestrator {
+    pub fn new() -> Self {
+        Self
+    }
+
+    // TODO: task decomposition
+    // TODO: agent assignment
+    // TODO: result aggregation
+}
--- a/src/agent/roles.rs
+++ b/src/agent/roles.rs
@@ -0,0 +1,62 @@
+use ratatui::style::Color;
+
+/// Agent role definition. Managed by core system, not plugins.
+pub struct AgentRole {
+    pub id: String,
+    pub name: String,
+    pub icon: String,
+    pub color: Color,
+    pub system_prompt: String,
+    pub tools: Vec<String>,
+    pub trigger: TriggerMode,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum TriggerMode {
+    Always,
+    OnUserRequest,
+    OnEvent(String),
+    Auto,
+}
+
+/// Built-in roles.
+pub fn builtin_roles() -> Vec<AgentRole> {
+    vec![
+        AgentRole {
+            id: "secretary".into(),
+            name: "Secretary".into(),
+            icon: "👤".into(),
+            color: Color::Cyan,
+            system_prompt: "You are a helpful assistant...".into(),
+            tools: vec![],
+            trigger: TriggerMode::Always,
+        },
+        AgentRole {
+            id: "driver".into(),
+            name: "Driver".into(),
+            icon: "🧭".into(),
+            color: Color::Yellow,
+            system_prompt: "You are a curious explorer...".into(),
+            tools: vec!["search_web".into(), "read_file".into()],
+            trigger: TriggerMode::Auto,
+        },
+        AgentRole {
+            id: "negfeedback".into(),
+            name: "NegFeedback".into(),
+            icon: "🛡️".into(),
+            color: Color::Red,
+            system_prompt: "You check for errors and potential issues...".into(),
+            tools: vec![],
+            trigger: TriggerMode::Auto,
+        },
+        AgentRole {
+            id: "executor".into(),
+            name: "Executor".into(),
+            icon: "⚡".into(),
+            color: Color::Magenta,
+            system_prompt: "You execute commands and tasks...".into(),
+            tools: vec!["run_shell".into()],
+            trigger: TriggerMode::Auto,
+        },
+    ]
+}
--- a/src/agent/tools.rs
+++ b/src/agent/tools.rs
@@ -0,0 +1,15 @@
+use crate::runtime::{ToolInput, ToolOutput};
+
+/// Invokes tools on behalf of agents via LLM function calling.
+pub struct ToolInvoker;
+
+impl ToolInvoker {
+    pub fn new() -> Self {
+        Self
+    }
+
+    pub fn invoke(&self, _name: &str, _input: ToolInput) -> ToolOutput {
+        // TODO: look up tool in registry, execute, return result
+        ToolOutput::err("not implemented")
+    }
+}
--- a/src/builtin/agentchat/mod.rs
+++ b/src/builtin/agentchat/mod.rs
@@ -0,0 +1,277 @@
+use crate::runtime::{Command, EventResult, PanelProvider, Source};
+use crossterm::event::{Event, KeyCode, KeyModifiers};
+use ratatui::{
+    buffer::Buffer,
+    layout::{Constraint, Direction, Layout, Rect},
+    style::{Color, Modifier, Style},
+    text::{Line, Span},
+    widgets::{Block, Borders, Paragraph, Widget, Wrap},
+};
+
+#[derive(Clone, Debug)]
+pub(crate) struct ChatMessage {
+    pub(crate) role: String,
+    pub(crate) content: String,
+}
+
+pub struct AgentChatProvider {
+    pub(crate) messages: Vec<ChatMessage>,
+    pub(crate) input_buffer: String,
+    cursor_pos: usize,
+    scroll_offset: usize,
+    pub(crate) selected_backend: usize,
+    backends: Vec<String>,
+}
+
+impl AgentChatProvider {
+    pub fn new() -> Self {
+        let mut provider = Self {
+            messages: vec![
+                ChatMessage {
+                    role: "user".into(),
+                    content: "write a sorting function".into(),
+                },
+                ChatMessage {
+                    role: "assistant".into(),
+                    content: "Here's a clean implementation:\n\nfn sort<T: Ord>(list: &mut [T]) {\n    list.sort();\n}\n\nOr if you want a custom quicksort:\n\nfn quicksort<T: Ord>(arr: &mut [T]) {\n    if arr.len() <= 1 { return; }\n    let pivot = arr.len() - 1;\n    // ... partition and recurse\n}".into(),
+                },
+            ],
+            input_buffer: String::new(),
+            cursor_pos: 0,
+            scroll_offset: 0,
+            selected_backend: 0,
+            backends: vec!["Claude".into(), "GPT-4".into(), "Local".into()],
+        };
+        provider.scroll_to_bottom();
+        provider
+    }
+
+    fn scroll_to_bottom(&mut self) {
+        self.scroll_offset = self.messages.len().saturating_sub(1);
+    }
+
+    fn add_message(&mut self, role: &str, content: &str) {
+        self.messages.push(ChatMessage {
+            role: role.into(),
+            content: content.into(),
+        });
+        self.scroll_to_bottom();
+    }
+
+    fn handle_input(&mut self, c: char) {
+        self.input_buffer.insert(self.cursor_pos, c);
+        self.cursor_pos += 1;
+    }
+
+    fn handle_backspace(&mut self) {
+        if self.cursor_pos > 0 {
+            self.cursor_pos -= 1;
+            self.input_buffer.remove(self.cursor_pos);
+        }
+    }
+
+    fn handle_delete(&mut self) {
+        if self.cursor_pos < self.input_buffer.len() {
+            self.input_buffer.remove(self.cursor_pos);
+        }
+    }
+
+    fn move_cursor(&mut self, delta: isize) {
+        if delta < 0 {
+            self.cursor_pos = self.cursor_pos.saturating_sub((-delta) as usize);
+        } else {
+            self.cursor_pos = (self.cursor_pos + delta as usize).min(self.input_buffer.len());
+        }
+    }
+
+    fn submit(&mut self) {
+        let text = self.input_buffer.trim().to_string();
+        if !text.is_empty() {
+            self.add_message("user", &text);
+            self.add_message(
+                "assistant",
+                &format!("[{}] Processing: {}...", self.backends[self.selected_backend], text),
+            );
+        }
+        self.input_buffer.clear();
+        self.cursor_pos = 0;
+    }
+
+    fn cycle_backend(&mut self) {
+        self.selected_backend = (self.selected_backend + 1) % self.backends.len();
+    }
+
+    fn message_lines(&self) -> Vec<Line<'_>> {
+        let mut lines = Vec::new();
+        for msg in &self.messages {
+            let (label, label_color) = match msg.role.as_str() {
+                "user" => ("You:", Color::White),
+                "assistant" => ("Agent:", Color::Green),
+                "system" => ("System:", Color::Yellow),
+                _ => ("??:", Color::DarkGray),
+            };
+            lines.push(Line::styled(
+                label.to_string(),
+                Style::default().fg(label_color).add_modifier(Modifier::BOLD),
+            ));
+            for content_line in msg.content.lines() {
+                lines.push(Line::styled(
+                    content_line.to_string(),
+                    Style::default().fg(Color::Rgb(200, 200, 200)),
+                ));
+            }
+            lines.push(Line::from(""));
+        }
+        lines
+    }
+}
+
+impl PanelProvider for AgentChatProvider {
+    fn as_any(&self) -> &dyn std::any::Any { self }
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any { self }
+
+    fn id(&self) -> &str { "agentchat" }
+
+    fn render(&mut self, area: Rect, buf: &mut Buffer) {
+        let vertical = Layout::default()
+            .direction(Direction::Vertical)
+            .constraints([
+                Constraint::Length(1),
+                Constraint::Min(0),
+                Constraint::Length(1),
+                Constraint::Length(2),
+                Constraint::Length(4),
+            ])
+            .split(area);
+
+        let tabs: Vec<Span> = self
+            .backends
+            .iter()
+            .enumerate()
+            .flat_map(|(i, name)| {
+                let style = if i == self.selected_backend {
+                    Style::default()
+                        .bg(Color::Rgb(60, 60, 60))
+                        .fg(Color::Rgb(204, 204, 204))
+                        .add_modifier(Modifier::BOLD)
+                } else {
+                    Style::default().fg(Color::DarkGray)
+                };
+                vec![Span::raw(" "), Span::styled(format!("{} ", name), style)]
+            })
+            .collect();
+        Paragraph::new(Line::from(tabs))
+            .style(Style::default().bg(Color::Rgb(35, 35, 35)))
+            .render(vertical[0], buf);
+
+        let all_lines = self.message_lines();
+        let visible_height = vertical[1].height as usize;
+        let line_count = all_lines.len();
+
+        let scroll_offset = if self.scroll_offset + visible_height > line_count {
+            line_count.saturating_sub(visible_height)
+        } else {
+            self.scroll_offset
+        };
+
+        let visible_lines: Vec<Line> = all_lines
+            .iter()
+            .skip(scroll_offset)
+            .take(visible_height)
+            .cloned()
+            .collect();
+
+        Paragraph::new(visible_lines)
+            .style(Style::default().bg(Color::Rgb(25, 25, 25)))
+            .wrap(Wrap { trim: false })
+            .render(vertical[1], buf);
+
+        let sep = Block::default()
+            .borders(Borders::TOP)
+            .border_style(Color::Rgb(60, 60, 60));
+        sep.render(vertical[2], buf);
+
+        let input_lines = vec![
+            Line::from(vec![
+                Span::styled(
+                    "> ",
+                    Style::default().fg(Color::Green).add_modifier(Modifier::BOLD),
+                ),
+                Span::raw(&self.input_buffer),
+            ]),
+            Line::styled(
+                "Enter to send  |  Ctrl+B cycle backend  |  PgUp/PgDn scroll",
+                Style::default().fg(Color::DarkGray),
+            ),
+        ];
+        Paragraph::new(input_lines)
+            .style(Style::default().bg(Color::Rgb(25, 25, 25)))
+            .render(vertical[3], buf);
+
+        let links = Paragraph::new(vec![
+            Line::from(""),
+            Line::from(vec![
+                Span::styled("[agents.md]", Style::default().fg(Color::Cyan)),
+                Span::raw("  "),
+                Span::styled("[soul.md]", Style::default().fg(Color::Cyan)),
+            ]),
+            Line::from(vec![
+                Span::styled("[memory.json]", Style::default().fg(Color::Cyan)),
+                Span::raw("  "),
+                Span::styled("[context.md]", Style::default().fg(Color::Cyan)),
+            ]),
+        ])
+        .block(
+            Block::default()
+                .title(" Quick Links ")
+                .borders(Borders::TOP)
+                .border_style(Color::Rgb(60, 60, 60)),
+        )
+        .style(Style::default().bg(Color::Rgb(25, 25, 25)));
+        links.render(vertical[4], buf);
+    }
+
+    fn handle_event(&mut self, event: Event) -> (EventResult, Vec<Command>) {
+        let commands = Vec::new();
+        if let Event::Key(key) = event {
+            if key.code == KeyCode::Char('b') && key.modifiers.contains(KeyModifiers::CONTROL) {
+                self.cycle_backend();
+                return (EventResult::Consumed, commands);
+            }
+            match key.code {
+                KeyCode::Char(c) => { self.handle_input(c); return (EventResult::Consumed, commands); }
+                KeyCode::Backspace => { self.handle_backspace(); return (EventResult::Consumed, commands); }
+                KeyCode::Delete => { self.handle_delete(); return (EventResult::Consumed, commands); }
+                KeyCode::Enter => { self.submit(); return (EventResult::Consumed, commands); }
+                KeyCode::Left => { self.move_cursor(-1); return (EventResult::Consumed, commands); }
+                KeyCode::Right => { self.move_cursor(1); return (EventResult::Consumed, commands); }
+                KeyCode::Home => { self.cursor_pos = 0; return (EventResult::Consumed, commands); }
+                KeyCode::End => { self.cursor_pos = self.input_buffer.len(); return (EventResult::Consumed, commands); }
+                KeyCode::PageUp => {
+                    self.scroll_offset = self.scroll_offset.saturating_sub(5);
+                    return (EventResult::Consumed, commands);
+                }
+                KeyCode::PageDown => {
+                    let max = self.messages.len().saturating_sub(1);
+                    self.scroll_offset = (self.scroll_offset + 5).min(max);
+                    return (EventResult::Consumed, commands);
+                }
+                _ => {}
+            }
+        }
+        (EventResult::PassThrough, commands)
+    }
+
+    fn focus_changed(&mut self, _focused: bool) {}
+    fn hide(&mut self) {}
+    fn show(&mut self) {}
+    fn shutdown(&mut self) {}
+
+    fn can_open(&self, _source: &Source, _mime_hint: Option<&str>) -> i32 {
+        // AgentChat doesn't compete for content presentation
+        0
+    }
+}
+
+#[cfg(test)]
+mod tests;
--- a/src/builtin/agentchat/tests.rs
+++ b/src/builtin/agentchat/tests.rs
@@ -0,0 +1,65 @@
+use crate::builtin::agentchat::AgentChatProvider;
+use crate::runtime::PanelProvider;
+use crossterm::event::{Event, KeyCode, KeyEvent, KeyModifiers};
+
+fn char_event(c: char) -> Event {
+    Event::Key(KeyEvent::from(KeyCode::Char(c)))
+}
+
+fn key_event(code: KeyCode) -> Event {
+    Event::Key(KeyEvent::from(code))
+}
+
+fn ctrl_event(c: char) -> Event {
+    Event::Key(KeyEvent {
+        code: KeyCode::Char(c),
+        modifiers: KeyModifiers::CONTROL,
+        kind: crossterm::event::KeyEventKind::Press,
+        state: crossterm::event::KeyEventState::empty(),
+    })
+}
+
+#[test]
+fn agentchat_has_initial_messages() {
+    let chat = AgentChatProvider::new();
+    assert!(!chat.messages.is_empty());
+}
+
+#[test]
+fn agentchat_typing() {
+    let mut chat = AgentChatProvider::new();
+    chat.handle_event(char_event('h'));
+    chat.handle_event(char_event('i'));
+    assert_eq!(chat.input_buffer, "hi");
+}
+
+#[test]
+fn agentchat_submit_adds_message() {
+    let mut chat = AgentChatProvider::new();
+    let before = chat.messages.len();
+    chat.handle_event(char_event('t'));
+    chat.handle_event(char_event('e'));
+    chat.handle_event(char_event('s'));
+    chat.handle_event(char_event('t'));
+    chat.handle_event(key_event(KeyCode::Enter));
+    let after = chat.messages.len();
+    assert!(after > before);
+    assert_eq!(chat.input_buffer, "");
+}
+
+#[test]
+fn agentchat_cycle_backend() {
+    let mut chat = AgentChatProvider::new();
+    let first = chat.selected_backend;
+    chat.handle_event(ctrl_event('b'));
+    assert_ne!(chat.selected_backend, first);
+}
+
+#[test]
+fn agentchat_empty_submit_ignored() {
+    let mut chat = AgentChatProvider::new();
+    let before = chat.messages.len();
+    chat.handle_event(key_event(KeyCode::Enter));
+    let after = chat.messages.len();
+    assert_eq!(after, before);
+}
--- a/src/builtin/editor/mod.rs
+++ b/src/builtin/editor/mod.rs
@@ -0,0 +1,271 @@
+use crate::runtime::{Command, EventResult, PanelProvider, Source};
+use crossterm::event::{Event, KeyCode, KeyModifiers};
+use ratatui::{
+    buffer::Buffer,
+    layout::{Constraint, Direction, Layout, Rect},
+    style::{Color, Style},
+    text::{Line, Span},
+    widgets::{Paragraph, Widget},
+};
+
+pub struct EditorProvider {
+    lines: Vec<String>,
+    cursor_line: usize,
+    cursor_col: usize,
+    scroll_offset: usize,
+    filename: String,
+    modified: bool,
+}
+
+impl EditorProvider {
+    pub fn new() -> Self {
+        let code = vec![
+            "// main.rs".into(),
+            "".into(),
+            "fn main() {".into(),
+            "    let data = fetch_data();".into(),
+            "    process(&data);".into(),
+            "    println!(\"done\");".into(),
+            "}".into(),
+            "".into(),
+            "fn fetch_data() -> Vec<i32> {".into(),
+            "    vec![1, 2, 3]".into(),
+            "}".into(),
+            "".into(),
+            "fn process(data: &[i32]) {".into(),
+            "    let sum: i32 = data.iter().sum();".into(),
+            "    println!(\"sum = {}\", sum);".into(),
+            "}".into(),
+        ];
+        Self {
+            lines: code,
+            cursor_line: 2,
+            cursor_col: 9,
+            scroll_offset: 0,
+            filename: "main.rs".into(),
+            modified: false,
+        }
+    }
+
+    pub fn cursor_line(&self) -> usize { self.cursor_line + 1 }
+    pub fn cursor_col(&self) -> usize { self.cursor_col + 1 }
+    pub fn filename(&self) -> &str { &self.filename }
+    pub fn is_modified(&self) -> bool { self.modified }
+
+    fn move_cursor(&mut self, dx: isize, dy: isize) {
+        if dy != 0 {
+            let new_line = if dy < 0 {
+                self.cursor_line.saturating_sub((-dy) as usize)
+            } else {
+                (self.cursor_line + dy as usize).min(self.lines.len().saturating_sub(1))
+            };
+            self.cursor_line = new_line;
+            let line_len = self.lines.get(self.cursor_line).map(|l| l.len()).unwrap_or(0);
+            self.cursor_col = self.cursor_col.min(line_len);
+        }
+        if dx != 0 {
+            let line_len = self.lines.get(self.cursor_line).map(|l| l.len()).unwrap_or(0);
+            if dx < 0 {
+                self.cursor_col = self.cursor_col.saturating_sub((-dx) as usize);
+            } else {
+                self.cursor_col = (self.cursor_col + dx as usize).min(line_len);
+            }
+        }
+    }
+
+    fn ensure_cursor_visible(&mut self, visible_height: usize) {
+        if self.cursor_line >= self.scroll_offset + visible_height {
+            self.scroll_offset = self.cursor_line.saturating_sub(visible_height - 1);
+        } else if self.cursor_line < self.scroll_offset {
+            self.scroll_offset = self.cursor_line;
+        }
+    }
+}
+
+impl PanelProvider for EditorProvider {
+    fn as_any(&self) -> &dyn std::any::Any { self }
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any { self }
+
+    fn id(&self) -> &str { "editor" }
+
+    fn render(&mut self, area: Rect, buf: &mut Buffer) {
+        let horizontal = Layout::default()
+            .direction(Direction::Horizontal)
+            .constraints([Constraint::Length(4), Constraint::Min(0)])
+            .split(area);
+
+        let gutter_area = horizontal[0];
+        let content_area = horizontal[1];
+        let visible_height = content_area.height as usize;
+
+        self.ensure_cursor_visible(visible_height);
+
+        let gutter_lines: Vec<Line> = (self.scroll_offset
+            ..(self.scroll_offset + visible_height).min(self.lines.len()))
+            .map(|i| {
+                let num = format!("{:>3} ", i + 1);
+                let style = if i == self.cursor_line {
+                    Style::default().fg(Color::Cyan).add_modifier(ratatui::style::Modifier::BOLD)
+                } else {
+                    Style::default().fg(Color::DarkGray)
+                };
+                Line::styled(num, style)
+            })
+            .collect();
+        Paragraph::new(gutter_lines).render(gutter_area, buf);
+
+        let content_lines: Vec<Line> = self
+            .lines
+            .iter()
+            .skip(self.scroll_offset)
+            .take(visible_height)
+            .enumerate()
+            .map(|(i, line)| {
+                let absolute_line = self.scroll_offset + i;
+                let is_current = absolute_line == self.cursor_line;
+                let bg = if is_current { Some(Color::Rgb(40, 40, 40)) } else { None };
+                highlight_rust_line(line, bg)
+            })
+            .collect();
+        Paragraph::new(content_lines).render(content_area, buf);
+    }
+
+    fn handle_event(&mut self, event: Event) -> (EventResult, Vec<Command>) {
+        let commands = Vec::new();
+        if let Event::Key(key) = event {
+            match key.code {
+                KeyCode::Up => { self.move_cursor(0, -1); return (EventResult::Consumed, commands); }
+                KeyCode::Down => { self.move_cursor(0, 1); return (EventResult::Consumed, commands); }
+                KeyCode::Left => { self.move_cursor(-1, 0); return (EventResult::Consumed, commands); }
+                KeyCode::Right => { self.move_cursor(1, 0); return (EventResult::Consumed, commands); }
+                KeyCode::Home => { self.cursor_col = 0; return (EventResult::Consumed, commands); }
+                KeyCode::End => {
+                    let line_len = self.lines.get(self.cursor_line).map(|l| l.len()).unwrap_or(0);
+                    self.cursor_col = line_len;
+                    return (EventResult::Consumed, commands);
+                }
+                KeyCode::PageUp => { self.move_cursor(0, -10); return (EventResult::Consumed, commands); }
+                KeyCode::PageDown => { self.move_cursor(0, 10); return (EventResult::Consumed, commands); }
+                KeyCode::Char('g') if key.modifiers.contains(KeyModifiers::CONTROL) => {
+                    self.cursor_line = 0; self.cursor_col = 0;
+                    return (EventResult::Consumed, commands);
+                }
+                _ => {}
+            }
+        }
+        (EventResult::PassThrough, commands)
+    }
+
+    fn focus_changed(&mut self, _focused: bool) {}
+    fn hide(&mut self) {}
+    fn show(&mut self) {}
+    fn shutdown(&mut self) {}
+
+    fn can_open(&self, source: &Source, mime_hint: Option<&str>) -> i32 {
+        let mime = mime_hint
+            .map(|m| m.to_string())
+            .or_else(|| source.mime_hint());
+        match mime.as_deref() {
+            Some("text/rust") | Some("text/plain") | Some("text/toml") | Some("text/markdown")
+            | Some("text/x-shellscript") | Some("text/x-python") | Some("text/javascript")
+            | Some("text/typescript") | Some("application/json") => 100,
+            Some(m) if m.starts_with("text/") => 50,
+            _ => 0,
+        }
+    }
+}
+
+fn highlight_rust_line(line: &str, bg: Option<Color>) -> Line<'_> {
+    let base_style = Style::default().bg(bg.unwrap_or(Color::Reset));
+    if line.trim().starts_with("//") {
+        return Line::styled(line.to_string(), base_style.fg(Color::DarkGray));
+    }
+
+    let keywords = ["fn", "let", "mut", "use", "pub", "struct", "impl", "if", "else", "for", "while", "match", "return", "self", "Self", "where", "async", "await", "trait", "enum", "type", "const", "static", "move", "ref", "dyn"];
+    let types = ["i32", "i64", "u32", "u64", "f32", "f64", "bool", "char", "str", "String", "Vec", "Option", "Result", "Box", "HashMap", "Path", "PathBuf"];
+    let builtins = ["println!", "format!", "vec!", "panic!", "todo!", "unimplemented!", "assert!"];
+
+    let mut spans = Vec::new();
+    let mut remaining = line;
+
+    while !remaining.is_empty() {
+        let mut found = false;
+
+        if remaining.starts_with('"') {
+            if let Some(end) = remaining[1..].find('"') {
+                let lit = &remaining[..end + 2];
+                spans.push(Span::styled(lit.to_string(), base_style.fg(Color::Green)));
+                remaining = &remaining[end + 2..];
+                found = true;
+            }
+        }
+
+        if !found {
+            for kw in &keywords {
+                if remaining.starts_with(kw) {
+                    let after = &remaining[kw.len()..];
+                    if after.is_empty() || !after.starts_with(|c: char| c.is_alphanumeric() || c == '_') {
+                        spans.push(Span::styled(kw.to_string(), base_style.fg(Color::Magenta)));
+                        remaining = after;
+                        found = true;
+                        break;
+                    }
+                }
+            }
+        }
+        if !found {
+            for t in &types {
+                if remaining.starts_with(t) {
+                    let after = &remaining[t.len()..];
+                    if after.is_empty() || !after.starts_with(|c: char| c.is_alphanumeric() || c == '_') {
+                        spans.push(Span::styled(t.to_string(), base_style.fg(Color::Yellow)));
+                        remaining = after;
+                        found = true;
+                        break;
+                    }
+                }
+            }
+        }
+        if !found {
+            for b in &builtins {
+                if remaining.starts_with(b) {
+                    spans.push(Span::styled(b.to_string(), base_style.fg(Color::Cyan)));
+                    remaining = &remaining[b.len()..];
+                    found = true;
+                    break;
+                }
+            }
+        }
+
+        if !found && remaining.starts_with(|c: char| c.is_ascii_digit()) {
+            let end = remaining.find(|c: char| !c.is_ascii_digit()).unwrap_or(remaining.len());
+            let num = &remaining[..end];
+            spans.push(Span::styled(num.to_string(), base_style.fg(Color::Yellow)));
+            remaining = &remaining[end..];
+            found = true;
+        }
+
+        if !found {
+            if let Some(i) = remaining.find(|c: char| !c.is_alphanumeric() && c != '_') {
+                if remaining[i..].starts_with('(') && i > 0 {
+                    let name = &remaining[..i];
+                    spans.push(Span::styled(name.to_string(), base_style.fg(Color::Cyan)));
+                    remaining = &remaining[i..];
+                    found = true;
+                }
+            }
+        }
+
+        if !found {
+            let ch = remaining.chars().next().unwrap();
+            let s = ch.to_string();
+            spans.push(Span::styled(s, base_style.fg(Color::Rgb(204, 204, 204))));
+            remaining = &remaining[ch.len_utf8()..];
+        }
+    }
+
+    Line::from(spans)
+}
+
+#[cfg(test)]
+mod tests;
--- a/src/builtin/editor/tests.rs
+++ b/src/builtin/editor/tests.rs
@@ -0,0 +1,59 @@
+use crate::builtin::editor::EditorProvider;
+use crate::runtime::PanelProvider;
+use crossterm::event::{Event, KeyCode, KeyEvent};
+
+fn key_event(code: KeyCode) -> Event {
+    Event::Key(KeyEvent::from(code))
+}
+
+#[test]
+fn editor_cursor_moves() {
+    let mut editor = EditorProvider::new();
+    let start_line = editor.cursor_line();
+    let start_col = editor.cursor_col();
+    editor.handle_event(key_event(KeyCode::Down));
+    assert!(editor.cursor_line() > start_line || editor.cursor_line() == start_line);
+    editor.handle_event(key_event(KeyCode::Right));
+    assert!(editor.cursor_col() > start_col || editor.cursor_col() == start_col);
+}
+
+#[test]
+fn editor_cursor_bounded() {
+    let mut editor = EditorProvider::new();
+    for _ in 0..100 { editor.handle_event(key_event(KeyCode::Up)); }
+    for _ in 0..100 { editor.handle_event(key_event(KeyCode::Left)); }
+    assert_eq!(editor.cursor_line(), 1);
+    assert_eq!(editor.cursor_col(), 1);
+}
+
+#[test]
+fn editor_consumes_arrow_keys() {
+    let mut editor = EditorProvider::new();
+    for code in [KeyCode::Up, KeyCode::Down, KeyCode::Left, KeyCode::Right] {
+        let (result, _) = editor.handle_event(key_event(code));
+        assert!(
+            matches!(result, crate::runtime::EventResult::Consumed),
+            "Expected Consumed for {:?}", code
+        );
+    }
+}
+
+#[test]
+fn editor_has_filename() {
+    let editor = EditorProvider::new();
+    assert_eq!(editor.filename(), "main.rs");
+}
+
+#[test]
+fn editor_can_open_text_files() {
+    let editor = EditorProvider::new();
+    let source = crate::runtime::Source::File { path: "test.rs".into() };
+    assert!(editor.can_open(&source, Some("text/rust")) > 0);
+}
+
+#[test]
+fn editor_rejects_binary_files() {
+    let editor = EditorProvider::new();
+    let source = crate::runtime::Source::File { path: "image.png".into() };
+    assert_eq!(editor.can_open(&source, Some("image/png")), 0);
+}
--- a/src/builtin/filetree/mod.rs
+++ b/src/builtin/filetree/mod.rs
@@ -0,0 +1,304 @@
+use std::fs;
+use std::path::{Path, PathBuf};
+
+use crate::runtime::{Command, EventResult, PanelProvider, Source};
+use crossterm::event::{Event, KeyCode};
+use ratatui::{
+    buffer::Buffer,
+    layout::Rect,
+    style::{Color, Modifier, Style},
+    text::{Line, Span},
+    widgets::{Paragraph, Widget, Wrap},
+};
+
+// ---------------------------------------------------------------------------
+// FileNode
+// ---------------------------------------------------------------------------
+
+#[derive(Debug, Clone)]
+pub(crate) struct FileNode {
+    pub(crate) name: String,
+    pub(crate) path: PathBuf,
+    pub(crate) is_dir: bool,
+    pub(crate) expanded: bool,
+    pub(crate) children: Vec<FileNode>,
+    pub(crate) depth: usize,
+}
+
+impl FileNode {
+    fn from_path(path: &Path, depth: usize) -> Option<Self> {
+        let name = path.file_name()?.to_string_lossy().to_string();
+        let is_dir = path.is_dir();
+        Some(Self {
+            name,
+            path: path.to_path_buf(),
+            is_dir,
+            expanded: depth == 0,
+            children: Vec::new(),
+            depth,
+        })
+    }
+
+    fn load_children(&mut self) {
+        if !self.is_dir || !self.children.is_empty() {
+            return;
+        }
+        let Ok(entries) = fs::read_dir(&self.path) else { return };
+        let mut children: Vec<_> = entries
+            .filter_map(|e| e.ok())
+            .filter_map(|e| FileNode::from_path(&e.path(), self.depth + 1))
+            .collect();
+        children.sort_by(|a, b| {
+            match (a.is_dir, b.is_dir) {
+                (true, false) => std::cmp::Ordering::Less,
+                (false, true) => std::cmp::Ordering::Greater,
+                _ => a.name.cmp(&b.name),
+            }
+        });
+        self.children = children;
+    }
+
+    fn toggle(&mut self) {
+        if self.is_dir {
+            self.expanded = !self.expanded;
+            if self.expanded {
+                self.load_children();
+            }
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// FileTreeProvider
+// ---------------------------------------------------------------------------
+
+pub struct FileTreeProvider {
+    root: FileNode,
+    pub(crate) selected: usize,
+    pub(crate) scroll_offset: usize,
+}
+
+impl FileTreeProvider {
+    pub fn new() -> Self {
+        let cwd = std::env::current_dir().unwrap_or_else(|_| PathBuf::from("."));
+        let mut root = FileNode::from_path(&cwd, 0).unwrap_or_else(|| FileNode {
+            name: ".".into(),
+            path: cwd.clone(),
+            is_dir: true,
+            expanded: true,
+            children: Vec::new(),
+            depth: 0,
+        });
+        root.load_children();
+        Self {
+            root,
+            selected: 0,
+            scroll_offset: 0,
+        }
+    }
+
+    pub(crate) fn flat_nodes(&self) -> Vec<&FileNode> {
+        let mut result = Vec::new();
+        Self::collect_visible(&self.root, &mut result);
+        result
+    }
+
+    fn collect_visible<'a>(node: &'a FileNode, out: &mut Vec<&'a FileNode>) {
+        out.push(node);
+        if node.expanded {
+            for child in &node.children {
+                Self::collect_visible(child, out);
+            }
+        }
+    }
+
+    fn node_by_index_mut(&mut self, idx: usize) -> Option<&mut FileNode> {
+        let mut stack = vec![&mut self.root];
+        let mut count = 0;
+        while let Some(node) = stack.pop() {
+            if count == idx {
+                return Some(node);
+            }
+            count += 1;
+            if node.expanded {
+                for child in node.children.iter_mut().rev() {
+                    stack.push(child);
+                }
+            }
+        }
+        None
+    }
+
+    fn move_selection(&mut self, delta: isize) {
+        let flat = self.flat_nodes();
+        if flat.is_empty() {
+            return;
+        }
+        let new_idx = if delta < 0 {
+            self.selected.saturating_sub((-delta) as usize)
+        } else {
+            (self.selected + delta as usize).min(flat.len().saturating_sub(1))
+        };
+        self.selected = new_idx;
+    }
+}
+
+impl PanelProvider for FileTreeProvider {
+    fn as_any(&self) -> &dyn std::any::Any { self }
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any { self }
+
+    fn id(&self) -> &str { "filetree" }
+
+    fn render(&mut self, area: Rect, buf: &mut Buffer) {
+        let visible_height = area.height as usize;
+
+        self.scroll_offset = if self.selected >= self.scroll_offset + visible_height {
+            self.selected.saturating_sub(visible_height - 1)
+        } else if self.selected < self.scroll_offset {
+            self.selected
+        } else {
+            self.scroll_offset
+        };
+
+        let flat = self.flat_nodes();
+        let lines: Vec<Line> = flat
+            .iter()
+            .skip(self.scroll_offset)
+            .take(visible_height)
+            .enumerate()
+            .map(|(i, node)| {
+                let absolute_idx = self.scroll_offset + i;
+                let is_selected = absolute_idx == self.selected;
+
+                let indent = "  ".repeat(node.depth);
+                let prefix = if node.is_dir {
+                    if node.expanded { "📂 " } else { "📁 " }
+                } else {
+                    "  "
+                };
+                let icon = if node.is_dir { "" } else { file_icon(&node.name) };
+
+                let name_style = if is_selected {
+                    Style::default()
+                        .fg(Color::Black)
+                        .bg(Color::Cyan)
+                        .add_modifier(Modifier::BOLD)
+                } else if node.is_dir {
+                    Style::default().fg(Color::Yellow).add_modifier(Modifier::BOLD)
+                } else {
+                    Style::default().fg(Color::Rgb(204, 204, 204))
+                };
+
+                Line::from(vec![
+                    Span::styled(indent, Style::default().fg(Color::DarkGray)),
+                    Span::raw(prefix),
+                    Span::styled(format!("{}{}", icon, node.name), name_style),
+                ])
+            })
+            .collect();
+
+        let title = format!(" 📁 {} ", self.root.name);
+        let block = ratatui::widgets::Block::default()
+            .title(title)
+            .borders(ratatui::widgets::Borders::NONE);
+
+        Paragraph::new(lines)
+            .block(block)
+            .wrap(Wrap { trim: false })
+            .render(area, buf);
+    }
+
+    fn handle_event(&mut self, event: Event) -> (EventResult, Vec<Command>) {
+        let mut commands = Vec::new();
+        if let Event::Key(key) = event {
+            match key.code {
+                KeyCode::Up => {
+                    self.move_selection(-1);
+                    return (EventResult::Consumed, commands);
+                }
+                KeyCode::Down => {
+                    self.move_selection(1);
+                    return (EventResult::Consumed, commands);
+                }
+                KeyCode::Left => {
+                    let parent_path = self.node_by_index_mut(self.selected)
+                        .filter(|n| n.depth > 0 && !(n.is_dir && n.expanded))
+                        .map(|n| n.path.parent().map(|p| p.to_path_buf()));
+
+                    if let Some(Some(parent)) = parent_path {
+                        let flat = self.flat_nodes();
+                        for (i, n) in flat.iter().enumerate() {
+                            if n.path == parent {
+                                self.selected = i;
+                                break;
+                            }
+                        }
+                    } else if let Some(node) = self.node_by_index_mut(self.selected) {
+                        if node.is_dir && node.expanded {
+                            node.toggle();
+                        }
+                    }
+                    return (EventResult::Consumed, commands);
+                }
+                KeyCode::Right | KeyCode::Enter => {
+                    if let Some(node) = self.node_by_index_mut(self.selected) {
+                        if node.is_dir {
+                            node.toggle();
+                        } else {
+                            // Emit a command to open this file in Main panel
+                            commands.push(Command::Present {
+                                panel: crate::runtime::PanelType::Main,
+                                source: Source::File { path: node.path.clone() },
+                                mime_hint: None,
+                            });
+                        }
+                    }
+                    return (EventResult::Consumed, commands);
+                }
+                KeyCode::Char(' ') => {
+                    if let Some(node) = self.node_by_index_mut(self.selected) {
+                        if node.is_dir {
+                            node.toggle();
+                        }
+                    }
+                    return (EventResult::Consumed, commands);
+                }
+                _ => {}
+            }
+        }
+        (EventResult::PassThrough, commands)
+    }
+
+    fn focus_changed(&mut self, _focused: bool) {}
+    fn hide(&mut self) {}
+    fn show(&mut self) {}
+    fn shutdown(&mut self) {}
+
+    fn can_open(&self, _source: &Source, _mime_hint: Option<&str>) -> i32 {
+        // FileTree doesn't compete for content; it's always the sidebar navigator
+        0
+    }
+}
+
+fn file_icon(name: &str) -> &'static str {
+    if name.ends_with(".rs") {
+        "🦀 "
+    } else if name.ends_with(".toml") || name.ends_with(".lock") {
+        "⚙️  "
+    } else if name.ends_with(".md") {
+        "📝 "
+    } else if name.ends_with(".json") {
+        "📋 "
+    } else if name.ends_with(".sh") || name.ends_with(".bash") {
+        "🐚 "
+    } else if name.ends_with(".py") {
+        "🐍 "
+    } else if name.ends_with(".js") || name.ends_with(".ts") {
+        "📜 "
+    } else {
+        "📄 "
+    }
+}
+
+#[cfg(test)]
+mod tests;
--- a/src/builtin/filetree/tests.rs
+++ b/src/builtin/filetree/tests.rs
@@ -0,0 +1,71 @@
+use crate::builtin::filetree::FileTreeProvider;
+use crate::runtime::PanelProvider;
+use crossterm::event::{Event, KeyCode, KeyEvent};
+
+fn key_event(code: KeyCode) -> Event {
+    Event::Key(KeyEvent::from(code))
+}
+
+#[test]
+fn filetree_starts_at_root() {
+    let tree = FileTreeProvider::new();
+    let flat = tree.flat_nodes();
+    assert!(!flat.is_empty());
+    assert_eq!(flat[0].depth, 0);
+}
+
+#[test]
+fn filetree_navigate_down() {
+    let mut tree = FileTreeProvider::new();
+    let before = tree.flat_nodes().len();
+    assert!(before > 0);
+    tree.handle_event(key_event(KeyCode::Down));
+}
+
+#[test]
+fn filetree_expand_collapse() {
+    let mut tree = FileTreeProvider::new();
+    let flat = tree.flat_nodes();
+    let first_dir_idx = flat.iter().position(|n| n.is_dir).unwrap_or(0);
+    for _ in 0..first_dir_idx {
+        tree.handle_event(key_event(KeyCode::Down));
+    }
+    let before = tree.flat_nodes().len();
+    tree.handle_event(key_event(KeyCode::Left));
+    let after_collapse = tree.flat_nodes().len();
+    tree.handle_event(key_event(KeyCode::Right));
+    let after_expand = tree.flat_nodes().len();
+    assert!(after_expand >= after_collapse);
+}
+
+#[test]
+fn filetree_consumes_navigation_keys() {
+    let mut tree = FileTreeProvider::new();
+    let (result, _) = tree.handle_event(key_event(KeyCode::Down));
+    assert!(matches!(result, crate::runtime::EventResult::Consumed));
+    let (result, _) = tree.handle_event(key_event(KeyCode::Up));
+    assert!(matches!(result, crate::runtime::EventResult::Consumed));
+}
+
+#[test]
+fn filetree_passes_unknown_keys() {
+    let mut tree = FileTreeProvider::new();
+    let (result, _) = tree.handle_event(key_event(KeyCode::Char('x')));
+    assert!(matches!(result, crate::runtime::EventResult::PassThrough));
+}
+
+#[test]
+fn filetree_enter_emits_present_command() {
+    let mut tree = FileTreeProvider::new();
+    // Move to first file (not directory)
+    let flat = tree.flat_nodes();
+    let first_file_idx = flat.iter().position(|n| !n.is_dir);
+    if let Some(idx) = first_file_idx {
+        for _ in 0..idx {
+            tree.handle_event(key_event(KeyCode::Down));
+        }
+        let (_, commands) = tree.handle_event(key_event(KeyCode::Enter));
+        assert!(!commands.is_empty());
+        assert!(matches!(&commands[0], crate::runtime::Command::Present { .. }));
+    }
+}
--- a/src/builtin/mod.rs
+++ b/src/builtin/mod.rs
@@ -0,0 +1,5 @@
+pub mod agentchat;
+pub mod editor;
+pub mod filetree;
+pub mod tasktree;
+pub mod terminal;
--- a/src/builtin/tasktree/mod.rs
+++ b/src/builtin/tasktree/mod.rs
@@ -0,0 +1,83 @@
+use crate::runtime::{Command, EventResult, PanelProvider, Source};
+use crossterm::event::Event;
+use ratatui::{
+    buffer::Buffer,
+    layout::{Constraint, Direction, Layout, Rect},
+    style::{Color, Style},
+    text::{Line, Span},
+    widgets::{Paragraph, Widget, Wrap},
+};
+
+pub struct TaskTreeProvider;
+
+impl TaskTreeProvider {
+    pub fn new() -> Self { Self }
+}
+
+impl PanelProvider for TaskTreeProvider {
+    fn as_any(&self) -> &dyn std::any::Any { self }
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any { self }
+
+    fn id(&self) -> &str { "tasktree" }
+
+    fn render(&mut self, area: Rect, buf: &mut Buffer) {
+        let vertical = Layout::default()
+            .direction(Direction::Vertical)
+            .constraints([Constraint::Length(1), Constraint::Min(0)])
+            .split(area);
+
+        let tabs = Paragraph::new("[Tree]  [Chain]  [By Agent]")
+            .style(Style::default().fg(Color::DarkGray));
+        tabs.render(vertical[0], buf);
+
+        let content = Paragraph::new(vec![
+            Line::from(""),
+            agent_line("👤", "Secretary", Color::Cyan, "idle", Color::Green),
+            task_line(" └─", "✅", Color::Green, "Explain API to user"),
+            Line::from(""),
+            agent_line("🧭", "Driver", Color::Yellow, "work", Color::Yellow),
+            task_line(" ├─", "🟡", Color::Yellow, "Research async patterns"),
+            task_line(" └─", "⚪", Color::DarkGray, "Check error handling"),
+            Line::from(""),
+            agent_line("🛡️", "NegFeedback", Color::Red, "idle", Color::Green),
+            task_line(" └─", "✅", Color::Green, "Flag race condition"),
+            Line::from(""),
+            agent_line("⚡", "Executor", Color::Magenta, "work", Color::Yellow),
+            task_line(" └─", "🟡", Color::Yellow, "cargo test..."),
+            Line::from(""),
+            Line::from("3 idle | 2 work").style(Style::default().fg(Color::DarkGray)),
+        ])
+        .wrap(Wrap { trim: true });
+
+        content.render(vertical[1], buf);
+    }
+
+    fn handle_event(&mut self, _event: Event) -> (EventResult, Vec<Command>) {
+        (EventResult::PassThrough, Vec::new())
+    }
+
+    fn focus_changed(&mut self, _focused: bool) {}
+    fn hide(&mut self) {}
+    fn show(&mut self) {}
+    fn shutdown(&mut self) {}
+
+    fn can_open(&self, _source: &Source, _mime_hint: Option<&str>) -> i32 { 0 }
+}
+
+fn agent_line<'a>(icon: &'a str, name: &'a str, name_color: Color, status: &'a str, status_color: Color) -> Line<'a> {
+    Line::from(vec![
+        Span::raw(icon),
+        Span::raw(" "),
+        Span::styled(name, Style::default().fg(name_color).add_modifier(ratatui::style::Modifier::BOLD)),
+        Span::raw(" "),
+        Span::styled(format!("● {}", status), Style::default().fg(status_color)),
+    ])
+}
+
+fn task_line<'a>(indent: &'a str, icon: &'a str, icon_color: Color, text: &'a str) -> Line<'a> {
+    Line::from(vec![
+        Span::styled(indent, Style::default().fg(Color::DarkGray)),
+        Span::styled(format!("{} ", icon), Style::default().fg(icon_color)),
+        Span::raw(text),
+    ])
+}
--- a/src/builtin/terminal/mod.rs
+++ b/src/builtin/terminal/mod.rs
@@ -0,0 +1,266 @@
+use crate::runtime::{Command, EventResult, PanelProvider, Source};
+use crossterm::event::{Event, KeyCode};
+use ratatui::{
+    buffer::Buffer,
+    layout::{Constraint, Rect},
+    style::{Color, Style},
+    text::{Line, Span},
+    widgets::{Block, Borders, Paragraph, Widget},
+};
+
+pub struct TerminalProvider {
+    pub(crate) lines: Vec<String>,
+    pub(crate) scroll_offset: usize,
+    pub(crate) input_buffer: String,
+    cursor_pos: usize,
+    pub(crate) history: Vec<String>,
+    pub(crate) history_index: Option<usize>,
+}
+
+impl TerminalProvider {
+    pub fn new() -> Self {
+        let mut provider = Self {
+            lines: vec![
+                "Everjoy v0.1.0 — Integrated Terminal".into(),
+                "Type 'help' for available commands".into(),
+                "".into(),
+            ],
+            scroll_offset: 0,
+            input_buffer: String::new(),
+            cursor_pos: 0,
+            history: Vec::new(),
+            history_index: None,
+        };
+        provider.add_line("$ echo 'Hello, Everjoy!'");
+        provider.add_line("Hello, Everjoy!");
+        provider.add_line("");
+        provider.add_line("$ cargo build");
+        provider.add_line("   Compiling everjoy v0.1.0");
+        provider.add_line("    Finished `dev` profile [unoptimized] target(s) in 2.34s");
+        provider.add_line("");
+        provider
+    }
+
+    fn add_line(&mut self, line: impl Into<String>) {
+        self.lines.push(line.into());
+        let visible = 20usize;
+        if self.lines.len() > visible {
+            self.scroll_offset = self.lines.len() - visible;
+        }
+    }
+
+    fn handle_input(&mut self, c: char) {
+        self.input_buffer.insert(self.cursor_pos, c);
+        self.cursor_pos += 1;
+        self.history_index = None;
+    }
+
+    fn handle_backspace(&mut self) {
+        if self.cursor_pos > 0 {
+            self.cursor_pos -= 1;
+            self.input_buffer.remove(self.cursor_pos);
+        }
+    }
+
+    fn handle_delete(&mut self) {
+        if self.cursor_pos < self.input_buffer.len() {
+            self.input_buffer.remove(self.cursor_pos);
+        }
+    }
+
+    fn move_cursor(&mut self, delta: isize) {
+        if delta < 0 {
+            self.cursor_pos = self.cursor_pos.saturating_sub((-delta) as usize);
+        } else {
+            self.cursor_pos = (self.cursor_pos + delta as usize).min(self.input_buffer.len());
+        }
+    }
+
+    fn submit(&mut self) {
+        let cmd = self.input_buffer.trim().to_string();
+        if !cmd.is_empty() {
+            self.history.push(cmd.clone());
+            self.add_line(format!("$ {}", cmd));
+            self.process_command(&cmd);
+        } else {
+            self.add_line("$ ");
+        }
+        self.input_buffer.clear();
+        self.cursor_pos = 0;
+        self.history_index = None;
+    }
+
+    fn process_command(&mut self, cmd: &str) {
+        match cmd {
+            "help" => {
+                self.add_line("Available commands:");
+                self.add_line("  help      Show this help message");
+                self.add_line("  clear     Clear terminal output");
+                self.add_line("  pwd       Print working directory");
+                self.add_line("  ls        List files");
+                self.add_line("  agents    List active agents");
+                self.add_line("  version   Show version info");
+            }
+            "clear" => { self.lines.clear(); }
+            "pwd" => {
+                if let Ok(dir) = std::env::current_dir() {
+                    self.add_line(dir.display().to_string());
+                }
+            }
+            "ls" => {
+                if let Ok(entries) = std::fs::read_dir(".") {
+                    let mut names: Vec<_> = entries
+                        .filter_map(|e| e.ok())
+                        .map(|e| e.file_name().to_string_lossy().to_string())
+                        .collect();
+                    names.sort();
+                    for name in names {
+                        let is_dir = std::path::Path::new(&name).is_dir();
+                        self.add_line(format!("{}{}", if is_dir { "📁 " } else { "  " }, name));
+                    }
+                }
+            }
+            "agents" => {
+                self.add_line("Active agents:");
+                self.add_line("  👤 Secretary    — idle");
+                self.add_line("  🧭 Driver       — working");
+                self.add_line("  🛡️ NegFeedback  — idle");
+                self.add_line("  ⚡ Executor     — working");
+            }
+            "version" => {
+                self.add_line("Everjoy v0.1.0");
+                self.add_line("Built with Rust + Ratatui");
+            }
+            _ => {
+                self.add_line(format!("Command not found: {}", cmd));
+                self.add_line("Type 'help' for available commands");
+            }
+        }
+        self.add_line("");
+    }
+
+    fn prev_history(&mut self) {
+        if self.history.is_empty() { return; }
+        let idx = match self.history_index {
+            Some(i) if i > 0 => i - 1,
+            Some(_) => 0,
+            None => self.history.len() - 1,
+        };
+        self.history_index = Some(idx);
+        self.input_buffer = self.history[idx].clone();
+        self.cursor_pos = self.input_buffer.len();
+    }
+
+    fn next_history(&mut self) {
+        if let Some(idx) = self.history_index {
+            if idx + 1 < self.history.len() {
+                self.history_index = Some(idx + 1);
+                self.input_buffer = self.history[idx + 1].clone();
+                self.cursor_pos = self.input_buffer.len();
+            } else {
+                self.history_index = None;
+                self.input_buffer.clear();
+                self.cursor_pos = 0;
+            }
+        }
+    }
+}
+
+impl PanelProvider for TerminalProvider {
+    fn as_any(&self) -> &dyn std::any::Any { self }
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any { self }
+
+    fn id(&self) -> &str { "terminal" }
+
+    fn render(&mut self, area: Rect, buf: &mut Buffer) {
+        let vertical = ratatui::layout::Layout::default()
+            .direction(ratatui::layout::Direction::Vertical)
+            .constraints([Constraint::Min(0), Constraint::Length(1)])
+            .split(area);
+
+        let output_area = vertical[0];
+        let input_area = vertical[1];
+        let visible_lines = output_area.height as usize;
+        if self.lines.len() > visible_lines {
+            self.scroll_offset = self.scroll_offset.min(self.lines.len() - visible_lines);
+        }
+
+        let output_lines: Vec<Line> = self
+            .lines
+            .iter()
+            .skip(self.scroll_offset)
+            .take(visible_lines)
+            .map(|l| {
+                if l.starts_with("$") {
+                    Line::from(vec![
+                        Span::styled("$", Style::default().fg(Color::Green).add_modifier(ratatui::style::Modifier::BOLD)),
+                        Span::styled(&l[1..], Style::default().fg(Color::Rgb(204, 204, 204))),
+                    ])
+                } else if l.starts_with("Error") || l.starts_with("Command not found") {
+                    Line::styled(l.clone(), Style::default().fg(Color::Red))
+                } else if l.starts_with("   Compiling") || l.starts_with("    Finished") {
+                    Line::styled(l.clone(), Style::default().fg(Color::Cyan))
+                } else {
+                    Line::styled(l.clone(), Style::default().fg(Color::Rgb(200, 200, 200)))
+                }
+            })
+            .collect();
+
+        Paragraph::new(output_lines)
+            .block(Block::default().borders(Borders::NONE))
+            .render(output_area, buf);
+
+        let input = Paragraph::new(vec![Line::from(vec![
+            Span::styled("$ ", Style::default().fg(Color::Green).add_modifier(ratatui::style::Modifier::BOLD)),
+            Span::raw(&self.input_buffer),
+        ])])
+        .style(Style::default().bg(Color::Rgb(35, 35, 35)));
+        input.render(input_area, buf);
+    }
+
+    fn handle_event(&mut self, event: Event) -> (EventResult, Vec<Command>) {
+        let commands = Vec::new();
+        if let Event::Key(key) = event {
+            match key.code {
+                KeyCode::Char(c) => { self.handle_input(c); return (EventResult::Consumed, commands); }
+                KeyCode::Backspace => { self.handle_backspace(); return (EventResult::Consumed, commands); }
+                KeyCode::Delete => { self.handle_delete(); return (EventResult::Consumed, commands); }
+                KeyCode::Enter => { self.submit(); return (EventResult::Consumed, commands); }
+                KeyCode::Left => { self.move_cursor(-1); return (EventResult::Consumed, commands); }
+                KeyCode::Right => { self.move_cursor(1); return (EventResult::Consumed, commands); }
+                KeyCode::Home => { self.cursor_pos = 0; return (EventResult::Consumed, commands); }
+                KeyCode::End => { self.cursor_pos = self.input_buffer.len(); return (EventResult::Consumed, commands); }
+                KeyCode::Up => { self.prev_history(); return (EventResult::Consumed, commands); }
+                KeyCode::Down => { self.next_history(); return (EventResult::Consumed, commands); }
+                KeyCode::PageUp => {
+                    let visible = 10;
+                    self.scroll_offset = self.scroll_offset.saturating_sub(visible);
+                    return (EventResult::Consumed, commands);
+                }
+                KeyCode::PageDown => {
+                    let visible = 10;
+                    let max = self.lines.len().saturating_sub(visible);
+                    self.scroll_offset = (self.scroll_offset + visible).min(max);
+                    return (EventResult::Consumed, commands);
+                }
+                _ => {}
+            }
+        }
+        (EventResult::PassThrough, commands)
+    }
+
+    fn focus_changed(&mut self, _focused: bool) {}
+    fn hide(&mut self) {}
+    fn show(&mut self) {}
+    fn shutdown(&mut self) {}
+
+    fn can_open(&self, _source: &Source, _mime_hint: Option<&str>) -> i32 {
+        // Terminal doesn't compete for content presentation
+        0
+    }
+
+    fn keep_alive_on_hide(&self) -> bool { true }
+}
+
+#[cfg(test)]
+mod tests;
--- a/src/builtin/terminal/tests.rs
+++ b/src/builtin/terminal/tests.rs
@@ -0,0 +1,62 @@
+use crate::builtin::terminal::TerminalProvider;
+use crate::runtime::PanelProvider;
+use crossterm::event::{Event, KeyCode, KeyEvent};
+
+fn char_event(c: char) -> Event {
+    Event::Key(KeyEvent::from(KeyCode::Char(c)))
+}
+
+fn key_event(code: KeyCode) -> Event {
+    Event::Key(KeyEvent::from(code))
+}
+
+#[test]
+fn terminal_has_initial_content() {
+    let term = TerminalProvider::new();
+    assert!(!term.lines.is_empty());
+}
+
+#[test]
+fn terminal_typing_accumulates() {
+    let mut term = TerminalProvider::new();
+    term.handle_event(char_event('h'));
+    term.handle_event(char_event('i'));
+    assert_eq!(term.input_buffer, "hi");
+}
+
+#[test]
+fn terminal_backspace_works() {
+    let mut term = TerminalProvider::new();
+    term.handle_event(char_event('a'));
+    term.handle_event(char_event('b'));
+    term.handle_event(key_event(KeyCode::Backspace));
+    assert_eq!(term.input_buffer, "a");
+}
+
+#[test]
+fn terminal_submit_clears_buffer() {
+    let mut term = TerminalProvider::new();
+    term.handle_event(char_event('l'));
+    term.handle_event(char_event('s'));
+    term.handle_event(key_event(KeyCode::Enter));
+    assert_eq!(term.input_buffer, "");
+}
+
+#[test]
+fn terminal_help_command() {
+    let mut term = TerminalProvider::new();
+    for c in "help".chars() { term.handle_event(char_event(c)); }
+    let lines_before = term.lines.len();
+    term.handle_event(key_event(KeyCode::Enter));
+    let lines_after = term.lines.len();
+    assert!(lines_after > lines_before);
+}
+
+#[test]
+fn terminal_history_navigation() {
+    let mut term = TerminalProvider::new();
+    for c in "test".chars() { term.handle_event(char_event(c)); }
+    term.handle_event(key_event(KeyCode::Enter));
+    term.handle_event(key_event(KeyCode::Up));
+    assert_eq!(term.input_buffer, "test");
+}
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -0,0 +1,5 @@
+pub mod agent;
+pub mod builtin;
+pub mod plugin;
+pub mod runtime;
+pub mod ui;
--- a/src/main.rs
+++ b/src/main.rs
@@ -0,0 +1,414 @@
+use std::collections::HashMap;
+use std::io::{self, stdout};
+
+use anyhow::Result;
+use crossterm::{
+    event::{self, Event, KeyCode, KeyModifiers},
+    terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
+    ExecutableCommand,
+};
+use ratatui::{
+    backend::CrosstermBackend,
+    layout::{Constraint, Direction, Layout, Rect},
+    style::Color,
+    widgets::Widget,
+    Terminal,
+};
+
+use everjoy::builtin;
+use everjoy::runtime::{
+    Capability, Command, EventResult, ModuleRegistry, PanelType, ProviderDesc, Registrar,
+};
+use everjoy::ui;
+
+enum AppState {
+    Splash,
+    Main,
+}
+
+struct App {
+    state: AppState,
+    layout: ui::LayoutManager,
+    focus: ui::focus::FocusManager,
+    menubar: ui::menubar::Menubar,
+    statusbar: ui::statusbar::StatusBar,
+    splash: ui::splash::SplashScreen,
+    registry: ModuleRegistry,
+    /// Current active provider id per panel.
+    active_providers: HashMap<PanelType, String>,
+}
+
+impl App {
+    fn new() -> Self {
+        let mut registry = ModuleRegistry::default();
+
+        // Register built-in providers
+        registry.register_provider(
+            ProviderDesc {
+                id: "filetree".into(),
+                name: "File Tree".into(),
+                panel: PanelType::Sidebar,
+                capabilities: vec![Capability::Render, Capability::HandleEvent],
+            },
+            Box::new(|| Box::new(builtin::filetree::FileTreeProvider::new())),
+        );
+        registry.register_provider(
+            ProviderDesc {
+                id: "editor".into(),
+                name: "Editor".into(),
+                panel: PanelType::Main,
+                capabilities: vec![Capability::Render, Capability::HandleEvent],
+            },
+            Box::new(|| Box::new(builtin::editor::EditorProvider::new())),
+        );
+        registry.register_provider(
+            ProviderDesc {
+                id: "terminal".into(),
+                name: "Terminal".into(),
+                panel: PanelType::Main,
+                capabilities: vec![Capability::Render, Capability::HandleEvent],
+            },
+            Box::new(|| Box::new(builtin::terminal::TerminalProvider::new())),
+        );
+        registry.register_provider(
+            ProviderDesc {
+                id: "agentchat".into(),
+                name: "Agent Chat".into(),
+                panel: PanelType::Agent,
+                capabilities: vec![Capability::Render, Capability::HandleEvent],
+            },
+            Box::new(|| Box::new(builtin::agentchat::AgentChatProvider::new())),
+        );
+
+        // Default active providers
+        let mut active_providers: HashMap<PanelType, String> = HashMap::new();
+        active_providers.insert(PanelType::Sidebar, "filetree".into());
+        active_providers.insert(PanelType::Main, "editor".into());
+        active_providers.insert(PanelType::Agent, "agentchat".into());
+
+        // Ensure all default providers are instantiated
+        for id in active_providers.values() {
+            let _ = registry.ensure_instance(id);
+        }
+
+        Self {
+            state: AppState::Splash,
+            layout: ui::LayoutManager::default(),
+            focus: ui::focus::FocusManager::default(),
+            menubar: ui::menubar::Menubar::default(),
+            statusbar: ui::statusbar::StatusBar::default(),
+            splash: ui::splash::SplashScreen,
+            registry,
+            active_providers,
+        }
+    }
+
+    fn run(&mut self, terminal: &mut Terminal<CrosstermBackend<io::Stdout>>) -> Result<()> {
+        loop {
+            self.update_statusbar();
+            terminal.draw(|frame| self.render(frame.area(), frame.buffer_mut()))?;
+
+            if event::poll(std::time::Duration::from_millis(16))? {
+                let ev = event::read()?;
+                if self.handle_event(ev) {
+                    break;
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn update_statusbar(&mut self) {
+        // Pull state from the active Main provider if it's an editor
+        if let Some(id) = self.active_providers.get(&PanelType::Main) {
+            if let Some(inst) = self.registry.ensure_instance(id) {
+                if let Some(editor) = inst.as_any().downcast_ref::<builtin::editor::EditorProvider>() {
+                    self.statusbar.filename = editor.filename().to_string();
+                    self.statusbar.cursor_line = editor.cursor_line();
+                    self.statusbar.cursor_col = editor.cursor_col();
+                    if editor.is_modified() {
+                        self.statusbar.filename.push_str(" [+]");
+                    }
+                }
+            }
+        }
+
+        // Focus info
+        self.statusbar.focused_panel = match self.focus.panel {
+            PanelType::Sidebar => "Sidebar".into(),
+            PanelType::Main => "Main".into(),
+            PanelType::Agent => "Agent".into(),
+        };
+    }
+
+    fn render(&mut self, area: Rect, buf: &mut ratatui::buffer::Buffer) {
+        match self.state {
+            AppState::Splash => {
+                self.splash.render(area, buf);
+            }
+            AppState::Main => {
+                self.render_main(area, buf);
+            }
+        }
+    }
+
+    fn render_main(&mut self, area: Rect, buf: &mut ratatui::buffer::Buffer) {
+        let vertical = Layout::default()
+            .direction(Direction::Vertical)
+            .constraints([
+                Constraint::Length(1),
+                Constraint::Min(0),
+                Constraint::Length(1),
+            ])
+            .split(area);
+
+        let menubar_area = vertical[0];
+        let body_area = vertical[1];
+        let status_area = vertical[2];
+
+        self.menubar.render(menubar_area, buf);
+
+        let panels = self.layout.compute(body_area);
+
+        let sidebar_title = match self.focus.panel {
+            PanelType::Sidebar => " Sidebar * ",
+            _ => " Sidebar ",
+        };
+        let main_title = match self.focus.panel {
+            PanelType::Main => " Main * ",
+            _ => " Main ",
+        };
+        let agent_title = match self.focus.panel {
+            PanelType::Agent => " Agent * ",
+            _ => " Agent ",
+        };
+
+        self.draw_panel_frame(panels.sidebar, buf, sidebar_title);
+        self.draw_panel_frame(panels.main, buf, main_title);
+        self.draw_panel_frame(panels.agent, buf, agent_title);
+
+        let sidebar_inner = inner_rect(panels.sidebar);
+        let main_inner = inner_rect(panels.main);
+        let agent_inner = inner_rect(panels.agent);
+
+        // Fill panel backgrounds
+        for inner in [sidebar_inner, main_inner, agent_inner] {
+            for y in inner.top()..inner.bottom() {
+                for x in inner.left()..inner.right() {
+                    buf[(x, y)].set_bg(Color::Rgb(25, 25, 25));
+                }
+            }
+        }
+
+        self.render_provider(PanelType::Sidebar, sidebar_inner, buf);
+        self.render_provider(PanelType::Main, main_inner, buf);
+        self.render_provider(PanelType::Agent, agent_inner, buf);
+
+        self.statusbar.render(status_area, buf);
+    }
+
+    fn render_provider(&mut self, panel: PanelType, area: Rect, buf: &mut ratatui::buffer::Buffer) {
+        if let Some(id) = self.active_providers.get(&panel) {
+            if let Some(inst) = self.registry.ensure_instance(id) {
+                inst.render(area, buf);
+            }
+        }
+    }
+
+    fn draw_panel_frame(&self, area: Rect, buf: &mut ratatui::buffer::Buffer, title: &str) {
+        use ratatui::style::{Color, Style};
+        use ratatui::widgets::{Block, Borders};
+
+        let block = Block::default()
+            .title(title)
+            .borders(Borders::ALL)
+            .border_style(Style::default().fg(Color::DarkGray));
+        block.render(area, buf);
+    }
+
+    fn handle_event(&mut self, ev: Event) -> bool {
+        if let Event::Key(key) = &ev {
+            if key.code == KeyCode::Char('q') && key.modifiers.contains(KeyModifiers::CONTROL) {
+                return true;
+            }
+        }
+
+        match self.state {
+            AppState::Splash => {
+                if let Event::Key(_) = ev {
+                    self.state = AppState::Main;
+                }
+                false
+            }
+            AppState::Main => self.handle_main_event(ev),
+        }
+    }
+
+    fn handle_main_event(&mut self, ev: Event) -> bool {
+        // Menubar
+        if self.menubar.is_active() {
+            if self.menubar.handle_event(&ev) {
+                return false;
+            }
+        } else if let Event::Key(key) = &ev {
+            if key.modifiers.contains(KeyModifiers::ALT) {
+                if self.menubar.handle_event(&ev) {
+                    return false;
+                }
+            }
+        }
+
+        // Focus shortcuts
+        if let Event::Key(key) = &ev {
+            if key.modifiers.contains(KeyModifiers::CONTROL) {
+                match key.code {
+                    KeyCode::Char('j') => {
+                        self.set_focus(PanelType::Sidebar);
+                        return false;
+                    }
+                    KeyCode::Char('k') => {
+                        self.set_focus(PanelType::Main);
+                        return false;
+                    }
+                    KeyCode::Char('l') => {
+                        self.set_focus(PanelType::Agent);
+                        return false;
+                    }
+                    _ => {}
+                }
+            }
+        }
+
+        // Route to focused provider
+        let focused = self.focus.panel;
+        let commands = if let Some(id) = self.active_providers.get(&focused) {
+            if let Some(inst) = self.registry.ensure_instance(id) {
+                let (result, cmds) = inst.handle_event(ev.clone());
+                if matches!(result, EventResult::PassThrough) {
+                    if let Event::Key(key) = &ev {
+                        if key.modifiers.contains(KeyModifiers::ALT) {
+                            let _ = self.menubar.handle_event(&ev);
+                        }
+                    }
+                }
+                cmds
+            } else {
+                Vec::new()
+            }
+        } else {
+            Vec::new()
+        };
+
+        for cmd in commands {
+            self.dispatch_command(cmd);
+        }
+
+        false
+    }
+
+    fn set_focus(&mut self, panel: PanelType) {
+        let old = self.focus.panel;
+        if old == panel {
+            return;
+        }
+        self.focus.focus_panel(panel);
+
+        // Notify old provider
+        if let Some(id) = self.active_providers.get(&old) {
+            if let Some(inst) = self.registry.ensure_instance(id) {
+                inst.focus_changed(false);
+            }
+        }
+        // Notify new provider
+        if let Some(id) = self.active_providers.get(&panel) {
+            if let Some(inst) = self.registry.ensure_instance(id) {
+                inst.focus_changed(true);
+            }
+        }
+    }
+
+    fn dispatch_command(&mut self, cmd: Command) {
+        match cmd {
+            Command::Present {
+                panel,
+                source,
+                mime_hint,
+            } => {
+                let guessed = source.mime_hint();
+                let mime_str = mime_hint.as_deref().or(guessed.as_deref());
+                if let Some((id, _score)) =
+                    self.registry.find_best_provider(panel, &source, mime_str)
+                {
+                    // Hide current provider on this panel if different
+                    if let Some(old_id) = self.active_providers.get(&panel) {
+                        if old_id != &id {
+                            if let Some(inst) = self.registry.ensure_instance(old_id) {
+                                inst.hide();
+                            }
+                        }
+                    }
+                    self.active_providers.insert(panel, id.clone());
+                    if let Some(inst) = self.registry.ensure_instance(&id) {
+                        inst.show();
+                        if self.focus.panel == panel {
+                            inst.focus_changed(true);
+                        }
+                    }
+                }
+            }
+            Command::Launch { panel, tool_id, .. } => {
+                // Direct dispatch by provider id
+                if let Some(old_id) = self.active_providers.get(&panel) {
+                    if old_id != &tool_id {
+                        if let Some(inst) = self.registry.ensure_instance(old_id) {
+                            inst.hide();
+                        }
+                    }
+                }
+                self.active_providers.insert(panel, tool_id.clone());
+                if let Some(inst) = self.registry.ensure_instance(&tool_id) {
+                    inst.show();
+                    if self.focus.panel == panel {
+                        inst.focus_changed(true);
+                    }
+                }
+            }
+            Command::FocusPanel(panel) => {
+                self.set_focus(panel);
+            }
+            Command::ShowMessage { msg, level } => {
+                let color = match level {
+                    everjoy::runtime::MessageLevel::Info => Color::Cyan,
+                    everjoy::runtime::MessageLevel::Warn => Color::Yellow,
+                    everjoy::runtime::MessageLevel::Error => Color::Red,
+                };
+                self.statusbar.message = Some((msg, color));
+            }
+        }
+    }
+}
+
+fn inner_rect(area: Rect) -> Rect {
+    Rect {
+        x: area.x.saturating_add(1),
+        y: area.y.saturating_add(1),
+        width: area.width.saturating_sub(2),
+        height: area.height.saturating_sub(2),
+    }
+}
+
+fn main() -> Result<()> {
+    enable_raw_mode()?;
+    stdout().execute(EnterAlternateScreen)?;
+    let mut terminal = Terminal::new(CrosstermBackend::new(stdout()))?;
+
+    let mut app = App::new();
+    let result = app.run(&mut terminal);
+
+    // Shutdown all providers before exit
+    app.registry.shutdown_all();
+
+    disable_raw_mode()?;
+    stdout().execute(LeaveAlternateScreen)?;
+    result
+}
--- a/src/plugin/loader.rs
+++ b/src/plugin/loader.rs
@@ -0,0 +1,22 @@
+use std::path::{Path, PathBuf};
+
+/// Loads external plugins (.wasm, .so, .dll).
+pub struct ExtensionLoader {
+    plugin_dir: PathBuf,
+}
+
+impl ExtensionLoader {
+    pub fn new(plugin_dir: PathBuf) -> Self {
+        Self { plugin_dir }
+    }
+
+    pub fn scan_and_load(&self) -> anyhow::Result<()> {
+        // TODO: scan plugin_dir, load each file
+        Ok(())
+    }
+
+    fn load(&self, _path: &Path) -> anyhow::Result<()> {
+        // TODO: detect format, dispatch to wasm/dylib/static loader
+        Ok(())
+    }
+}
--- a/src/plugin/mod.rs
+++ b/src/plugin/mod.rs
@@ -0,0 +1,4 @@
+pub mod loader;
+pub mod panic;
+pub mod surface;
+pub mod translator;
--- a/src/plugin/panic.rs
+++ b/src/plugin/panic.rs
@@ -0,0 +1,14 @@
+/// Isolates panics from external plugins so they don't crash the runtime.
+pub fn catch_plugin_panic<F, R>(plugin_id: &str, f: F) -> Option<R>
+where
+    F: FnOnce() -> R + std::panic::UnwindSafe,
+{
+    match std::panic::catch_unwind(f) {
+        Ok(result) => Some(result),
+        Err(_) => {
+            eprintln!("Plugin {} panicked! Unloading.", plugin_id);
+            // TODO: unload plugin, render fallback
+            None
+        }
+    }
+}
--- a/src/plugin/surface.rs
+++ b/src/plugin/surface.rs
@@ -0,0 +1,35 @@
+/// Cell grid for external plugin rendering.
+/// Runtime allocates, plugin borrows during render() call.
+#[repr(C)]
+pub struct EjSurface {
+    pub width: u16,
+    pub height: u16,
+    pub cells: *mut EjCell,
+}
+
+#[derive(Clone, Copy)]
+#[repr(C)]
+pub struct EjCell {
+    pub ch: u32,
+    pub style: EjStyleId,
+}
+
+pub type EjStyleId = u32;
+
+impl EjSurface {
+    pub fn new(width: u16, height: u16) -> Self {
+        let count = (width * height) as usize;
+        let cells = vec![EjCell { ch: 0, style: 0 }; count].into_boxed_slice();
+        let ptr = Box::into_raw(cells) as *mut EjCell;
+        Self { width, height, cells: ptr }
+    }
+}
+
+impl Drop for EjSurface {
+    fn drop(&mut self) {
+        unsafe {
+            let count = (self.width * self.height) as usize;
+            let _ = Vec::from_raw_parts(self.cells, count, count);
+        }
+    }
+}
--- a/src/plugin/translator.rs
+++ b/src/plugin/translator.rs
@@ -0,0 +1,13 @@
+/// Translates C-ABI calls to Rust trait objects.
+/// Wraps external plugins into Runtime-compatible types.
+pub struct Translator;
+
+impl Translator {
+    pub fn new() -> Self {
+        Self
+    }
+
+    // TODO: wrap EjProviderVTable into Box<dyn PanelProvider>
+    // TODO: wrap EjTool into Box<dyn Tool>
+    // TODO: cell grid → Buffer blitting
+}
--- a/src/runtime/ctx.rs
+++ b/src/runtime/ctx.rs
@@ -0,0 +1,9 @@
+//! ProviderCtx has been removed in favor of the Command pattern.
+//! Providers return Commands from handle_event() instead of calling
+//! into the system via a context trait.
+
+/// Shared services available to all providers.
+pub trait RuntimeServices {
+    // TODO: fn config(&self) -> &Config;
+    // TODO: fn db(&self) -> &DbHandle;
+}
--- a/src/runtime/lifecycle.rs
+++ b/src/runtime/lifecycle.rs
@@ -0,0 +1,12 @@
+/// Manages provider lifecycle: init, hide, show, shutdown.
+pub struct LifecycleManager;
+
+impl LifecycleManager {
+    pub fn new() -> Self {
+        Self
+    }
+
+    // TODO: track active provider instances per panel
+    // TODO: handle keep_alive_on_hide semantics
+    // TODO: atomic unload (shutdown all providers from a plugin)
+}
--- a/src/runtime/mod.rs
+++ b/src/runtime/mod.rs
@@ -0,0 +1,9 @@
+pub mod ctx;
+pub mod lifecycle;
+pub mod registry;
+pub mod traits;
+
+pub use ctx::RuntimeServices;
+pub use lifecycle::LifecycleManager;
+pub use registry::{ModuleRegistry, RegisteredProvider};
+pub use traits::*;
--- a/src/runtime/registry.rs
+++ b/src/runtime/registry.rs
@@ -0,0 +1,134 @@
+use std::collections::HashMap;
+
+use ratatui::{buffer::Buffer, layout::Rect};
+use super::traits::*;
+
+/// Central registry for all module contributions.
+pub struct ModuleRegistry {
+    pub panel_providers: HashMap<String, RegisteredProvider>,
+    pub tools: HashMap<String, Box<dyn Tool>>,
+    pub menu_items: Vec<Box<dyn MenuItem>>,
+    pub status_widgets: Vec<Box<dyn StatusWidget>>,
+}
+
+pub struct RegisteredProvider {
+    pub desc: ProviderDesc,
+    pub factory: ProviderFactory,
+    pub instance: Option<Box<dyn PanelProvider>>,
+}
+
+impl Default for ModuleRegistry {
+    fn default() -> Self {
+        Self {
+            panel_providers: HashMap::new(),
+            tools: HashMap::new(),
+            menu_items: Vec::new(),
+            status_widgets: Vec::new(),
+        }
+    }
+}
+
+impl ModuleRegistry {
+    /// Get all providers registered for a given panel type.
+    pub fn providers_for_panel(&self, panel: PanelType) -> Vec<&RegisteredProvider> {
+        self.panel_providers
+            .values()
+            .filter(|rp| rp.desc.panel == panel)
+            .collect()
+    }
+
+    /// Get a mutable registered provider by id.
+    pub fn provider_mut(&mut self, id: &str) -> Option<&mut RegisteredProvider> {
+        self.panel_providers.get_mut(id)
+    }
+
+    /// Instantiate a provider by id if not already created.
+    pub fn ensure_instance(&mut self, id: &str) -> Option<&mut Box<dyn PanelProvider>> {
+        let rp = self.panel_providers.get_mut(id)?;
+        if rp.instance.is_none() {
+            let factory = std::mem::replace(&mut rp.factory, Box::new(|| panic!("factory consumed")));
+            let mut instance = (factory)();
+            instance.init();
+            rp.instance = Some(instance);
+        }
+        rp.instance.as_mut()
+    }
+
+    /// Find the best provider for a source on a given panel.
+    /// Returns (provider_id, score). Score 0 means no match.
+    pub fn find_best_provider(
+        &self,
+        panel: PanelType,
+        source: &Source,
+        mime_hint: Option<&str>,
+    ) -> Option<(String, i32)> {
+        let mut best: Option<(String, i32)> = None;
+        for rp in self.providers_for_panel(panel) {
+            let score = if let Some(inst) = &rp.instance {
+                inst.can_open(source, mime_hint)
+            } else {
+                // We can't call can_open without an instance.
+                // Fallback: use a static heuristic based on desc/capabilities.
+                // For now, assume all registered providers on this panel
+                // might handle generic sources at a low score.
+                // A real implementation could store a static scorer.
+                0
+            };
+            if score > 0 {
+                if best.as_ref().map(|(_, s)| score > *s).unwrap_or(true) {
+                    best = Some((rp.desc.id.clone(), score));
+                }
+            }
+        }
+        best
+    }
+
+    /// Shutdown all provider instances.
+    pub fn shutdown_all(&mut self) {
+        for rp in self.panel_providers.values_mut() {
+            if let Some(mut inst) = rp.instance.take() {
+                inst.shutdown();
+            }
+        }
+    }
+}
+
+impl Registrar for ModuleRegistry {
+    fn register_provider(
+        &mut self,
+        desc: ProviderDesc,
+        factory: ProviderFactory,
+    ) {
+        let id = desc.id.clone();
+        self.panel_providers.insert(
+            id,
+            RegisteredProvider {
+                desc,
+                factory,
+                instance: None,
+            },
+        );
+    }
+
+    fn register_tool(&mut self, desc: ToolDesc, handler: Box<dyn Tool>) {
+        self.tools.insert(desc.name.clone(), handler);
+    }
+
+    fn register_menu_item(
+        &mut self,
+        desc: MenuItemDesc,
+        handler: Box<dyn Fn() + Send>,
+    ) {
+        // TODO: wrap handler into a MenuItem trait object
+        let _ = (desc, handler);
+    }
+
+    fn register_status_widget(
+        &mut self,
+        desc: StatusWidgetDesc,
+        render: Box<dyn Fn(Rect, &mut Buffer) + Send>,
+    ) {
+        // TODO: wrap render into a StatusWidget trait object
+        let _ = (desc, render);
+    }
+}
--- a/src/runtime/traits.rs
+++ b/src/runtime/traits.rs
@@ -0,0 +1,333 @@
+use ratatui::{buffer::Buffer, layout::Rect};
+use std::collections::HashMap;
+use std::path::PathBuf;
+
+// ---------------------------------------------------------------------------
+// Plugin
+// ---------------------------------------------------------------------------
+
+/// A plugin registers its contributions during bootstrap.
+pub trait Plugin: Send {
+    fn bootstrap(registrar: &mut dyn Registrar);
+}
+
+// ---------------------------------------------------------------------------
+// Source — what is being presented/launched
+// ---------------------------------------------------------------------------
+
+/// Where the content comes from.
+#[derive(Clone, Debug)]
+pub enum Source {
+    /// Local file or directory.
+    File { path: PathBuf },
+
+    /// Network resource.
+    Url { url: String },
+
+    /// In-memory blob.
+    Memory { name: String, data: Vec<u8> },
+}
+
+impl Source {
+    /// Guess MIME type from path extension or content.
+    pub fn mime_hint(&self) -> Option<String> {
+        match self {
+            Source::File { path } => {
+                let ext = path.extension()?.to_str()?;
+                match ext {
+                    "rs" => Some("text/rust".into()),
+                    "toml" => Some("text/toml".into()),
+                    "md" => Some("text/markdown".into()),
+                    "json" => Some("application/json".into()),
+                    "sh" | "bash" => Some("text/x-shellscript".into()),
+                    "py" => Some("text/x-python".into()),
+                    "js" => Some("text/javascript".into()),
+                    "ts" => Some("text/typescript".into()),
+                    "txt" => Some("text/plain".into()),
+                    _ => Some("text/plain".into()),
+                }
+            }
+            Source::Url { url } => {
+                if url.ends_with(".md") {
+                    Some("text/markdown".into())
+                } else {
+                    None
+                }
+            }
+            Source::Memory { name, .. } => {
+                if name.ends_with(".json") {
+                    Some("application/json".into())
+                } else {
+                    Some("text/plain".into())
+                }
+            }
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Command — what a Provider wants the system to do
+// ---------------------------------------------------------------------------
+
+/// Actions a Provider can request from the system.
+#[derive(Clone, Debug)]
+pub enum Command {
+    /// Present content in a panel. The system asks providers on that panel
+    /// who can handle this source, and picks the highest scorer.
+    Present {
+        panel: PanelType,
+        source: Source,
+        mime_hint: Option<String>,
+    },
+
+    /// Launch a tool/session in a panel by id. Not a bid — direct dispatch.
+    Launch {
+        panel: PanelType,
+        tool_id: String,
+        params: serde_json::Value,
+    },
+
+    /// Switch focus to a panel.
+    FocusPanel(PanelType),
+
+    /// Show a transient message in the status bar.
+    ShowMessage { msg: String, level: MessageLevel },
+}
+
+// ---------------------------------------------------------------------------
+// PanelProvider
+// ---------------------------------------------------------------------------
+
+/// Renders content into a panel (Sidebar, Main, or Agent).
+pub trait PanelProvider: Send {
+    /// Downcast to Any for runtime type checking.
+    fn as_any(&self) -> &dyn std::any::Any {
+        panic!("as_any not implemented")
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
+        panic!("as_any_mut not implemented")
+    }
+
+    /// Unique id of this provider instance.
+    fn id(&self) -> &str;
+
+    /// Called once after the provider instance is created.
+    fn init(&mut self) {}
+
+    /// Called every frame to render content into the given area.
+    fn render(&mut self, area: Rect, buf: &mut Buffer);
+
+    /// Called when this provider's panel has focus and receives input.
+    /// Returns handled-or-not plus any commands to dispatch.
+    fn handle_event(&mut self, event: crossterm::event::Event) -> (EventResult, Vec<Command>);
+
+    /// Called when focus enters or leaves this provider's panel.
+    fn focus_changed(&mut self, focused: bool);
+
+    /// Called when the provider is about to be hidden (but not destroyed).
+    fn hide(&mut self);
+
+    /// Called when the provider becomes visible again.
+    fn show(&mut self);
+
+    /// Called before the provider instance is destroyed.
+    fn shutdown(&mut self);
+
+    /// Score how well this provider can handle the given source.
+    /// Return 0 = cannot handle. Higher = better match.
+    fn can_open(&self, _source: &Source, _mime_hint: Option<&str>) -> i32 {
+        0
+    }
+
+    /// Whether to keep this provider alive when hidden.
+    fn keep_alive_on_hide(&self) -> bool {
+        false
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Tool
+// ---------------------------------------------------------------------------
+
+/// Callable by Agents via LLM function calling.
+pub trait Tool: Send {
+    fn name(&self) -> &str;
+    fn description(&self) -> &str;
+    fn schema(&self) -> ToolSchema;
+    fn execute(&self, input: ToolInput) -> ToolOutput;
+}
+
+// ---------------------------------------------------------------------------
+// Menubar / StatusWidget
+// ---------------------------------------------------------------------------
+
+/// Menubar entry.
+pub trait MenuItem: Send {
+    fn id(&self) -> &str;
+    fn label(&self) -> &str;
+    fn parent(&self) -> Option<&str>;
+    fn shortcut(&self) -> Option<&str>;
+    fn invoke(&self);
+}
+
+/// Status bar widget.
+pub trait StatusWidget: Send {
+    fn id(&self) -> &str;
+    fn position(&self) -> StatusPosition;
+    fn render(&self, area: Rect, buf: &mut Buffer);
+}
+
+// ---------------------------------------------------------------------------
+// Registrar
+// ---------------------------------------------------------------------------
+
+/// Registration interface exposed during Plugin::bootstrap.
+pub trait Registrar {
+    fn register_provider(
+        &mut self,
+        desc: ProviderDesc,
+        factory: ProviderFactory,
+    );
+
+    fn register_tool(&mut self, desc: ToolDesc, handler: Box<dyn Tool>);
+
+    fn register_menu_item(
+        &mut self,
+        desc: MenuItemDesc,
+        handler: Box<dyn Fn() + Send>,
+    );
+
+    fn register_status_widget(
+        &mut self,
+        desc: StatusWidgetDesc,
+        render: Box<dyn Fn(Rect, &mut Buffer) + Send>,
+    );
+}
+
+// ---------------------------------------------------------------------------
+// Supporting types
+// ---------------------------------------------------------------------------
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum EventResult {
+    /// Event was handled, stop propagation.
+    Consumed,
+    /// Event was not handled, pass to next handler.
+    PassThrough,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub enum PanelType {
+    Sidebar,
+    Main,
+    Agent,
+}
+
+#[derive(Clone, Debug)]
+pub struct ProviderDesc {
+    pub id: String,
+    pub name: String,
+    pub panel: PanelType,
+    pub capabilities: Vec<Capability>,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Capability {
+    Render,
+    HandleEvent,
+    HandleDrag,
+    AsyncRender,
+}
+
+pub type ProviderFactory =
+    Box<dyn FnOnce() -> Box<dyn PanelProvider> + Send>;
+
+#[derive(Clone, Debug)]
+pub struct ToolDesc {
+    pub name: String,
+    pub description: String,
+    pub parameters: Vec<ToolParameter>,
+}
+
+#[derive(Clone, Debug)]
+pub struct ToolParameter {
+    pub name: String,
+    pub param_type: ParamType,
+    pub required: bool,
+    pub description: String,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum ParamType {
+    String,
+    Number,
+    Boolean,
+    Enum(Vec<String>),
+}
+
+#[derive(Clone, Debug)]
+pub struct ToolInput {
+    pub args: HashMap<String, serde_json::Value>,
+}
+
+#[derive(Clone, Debug)]
+pub struct ToolOutput {
+    pub success: bool,
+    pub content: String,
+    pub metadata: Option<serde_json::Value>,
+}
+
+impl ToolOutput {
+    pub fn ok(content: impl Into<String>) -> Self {
+        Self {
+            success: true,
+            content: content.into(),
+            metadata: None,
+        }
+    }
+
+    pub fn err(content: impl Into<String>) -> Self {
+        Self {
+            success: false,
+            content: content.into(),
+            metadata: None,
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct ToolSchema {
+    // TODO: JSON Schema for LLM function calling
+}
+
+#[derive(Clone, Debug)]
+pub struct MenuItemDesc {
+    pub id: String,
+    pub label: String,
+    pub parent: Option<String>,
+    pub shortcut: Option<String>,
+    pub order: i32,
+}
+
+#[derive(Clone, Debug)]
+pub struct StatusWidgetDesc {
+    pub id: String,
+    pub position: StatusPosition,
+    pub min_width: u16,
+    pub order: i32,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum StatusPosition {
+    Left,
+    Right,
+    Center,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum MessageLevel {
+    Info,
+    Warn,
+    Error,
+}
--- a/src/ui/focus.rs
+++ b/src/ui/focus.rs
@@ -0,0 +1,33 @@
+use crate::runtime::PanelType;
+
+/// Manages focus state across panels and widgets.
+pub struct FocusManager {
+    pub panel: PanelType,
+    pub menubar_active: bool,
+}
+
+impl Default for FocusManager {
+    fn default() -> Self {
+        Self {
+            panel: PanelType::Main,
+            menubar_active: false,
+        }
+    }
+}
+
+impl FocusManager {
+    pub fn focus_panel(&mut self, panel: PanelType) {
+        self.panel = panel;
+        self.menubar_active = false;
+    }
+
+    pub fn focus_menubar(&mut self) {
+        self.menubar_active = true;
+    }
+
+    pub fn is_menubar_focused(&self) -> bool {
+        self.menubar_active
+    }
+
+    // TODO: handle Tab cycling within panel widgets
+}
--- a/src/ui/layout.rs
+++ b/src/ui/layout.rs
@@ -0,0 +1,46 @@
+use ratatui::layout::{Constraint, Direction, Layout, Rect};
+
+/// Manages panel proportions and handles drag-to-resize.
+pub struct LayoutManager {
+    sidebar_ratio: f32, // 0.0 ~ 1.0
+    agent_ratio: f32,   // 0.0 ~ 1.0
+}
+
+impl Default for LayoutManager {
+    fn default() -> Self {
+        Self {
+            sidebar_ratio: 0.20,
+            agent_ratio: 0.28,
+        }
+    }
+}
+
+impl LayoutManager {
+    pub fn compute(&self, area: Rect) -> Panels {
+        let main_ratio = 1.0 - self.sidebar_ratio - self.agent_ratio;
+
+        let horizontal = Layout::default()
+            .direction(Direction::Horizontal)
+            .constraints([
+                Constraint::Percentage((self.sidebar_ratio * 100.0) as u16),
+                Constraint::Percentage((main_ratio * 100.0) as u16),
+                Constraint::Percentage((self.agent_ratio * 100.0) as u16),
+            ])
+            .split(area);
+
+        Panels {
+            sidebar: horizontal[0],
+            main: horizontal[1],
+            agent: horizontal[2],
+        }
+    }
+
+    // TODO: persist ratios to config
+    // TODO: handle mouse drag on splitters
+}
+
+pub struct Panels {
+    pub sidebar: Rect,
+    pub main: Rect,
+    pub agent: Rect,
+}
--- a/src/ui/menubar.rs
+++ b/src/ui/menubar.rs
@@ -0,0 +1,186 @@
+use crossterm::event::{Event, KeyCode, KeyModifiers};
+use ratatui::{
+    buffer::Buffer,
+    layout::Rect,
+    style::{Color, Modifier, Style},
+    text::{Line, Span},
+    widgets::{Paragraph, Widget},
+};
+
+/// Renders the top menubar with Alt+ shortcuts and tracks active state.
+pub struct Menubar {
+    items: Vec<MenuEntry>,
+    active_index: Option<usize>,
+    active_submenu: Option<usize>,
+}
+
+struct MenuEntry {
+    label: String,
+    shortcut: char,
+    submenu: Vec<String>,
+}
+
+impl Default for Menubar {
+    fn default() -> Self {
+        Self {
+            items: vec![
+                MenuEntry {
+                    label: "File".into(),
+                    shortcut: 'F',
+                    submenu: vec!["New File".into(), "Open...".into(), "Save".into(), "Save All".into(), "Exit".into()],
+                },
+                MenuEntry {
+                    label: "Edit".into(),
+                    shortcut: 'E',
+                    submenu: vec!["Undo".into(), "Redo".into(), "Cut".into(), "Copy".into(), "Paste".into()],
+                },
+                MenuEntry {
+                    label: "View".into(),
+                    shortcut: 'V',
+                    submenu: vec!["Sidebar".into(), "Terminal".into(), "Zoom In".into(), "Zoom Out".into()],
+                },
+                MenuEntry {
+                    label: "Agent".into(),
+                    shortcut: 'A',
+                    submenu: vec!["Run".into(), "Stop".into(), "Settings...".into()],
+                },
+                MenuEntry {
+                    label: "Help".into(),
+                    shortcut: 'H',
+                    submenu: vec!["Documentation".into(), "Shortcuts".into(), "About".into()],
+                },
+            ],
+            active_index: None,
+            active_submenu: None,
+        }
+    }
+}
+
+impl Menubar {
+    /// Handle menubar-specific key events. Returns true if consumed.
+    pub fn handle_event(&mut self, event: &Event) -> bool {
+        if let Event::Key(key) = event {
+            // Alt+letter to open menu
+            if key.modifiers.contains(KeyModifiers::ALT) {
+                if let KeyCode::Char(c) = key.code {
+                    let upper = c.to_ascii_uppercase();
+                    if let Some(idx) = self.items.iter().position(|e| e.shortcut == upper) {
+                        self.active_index = Some(idx);
+                        self.active_submenu = Some(0);
+                        return true;
+                    }
+                }
+            }
+
+            // Menu navigation when active
+            if self.active_index.is_some() {
+                match key.code {
+                    KeyCode::Esc => {
+                        self.active_index = None;
+                        self.active_submenu = None;
+                        return true;
+                    }
+                    KeyCode::Left => {
+                        if let Some(idx) = self.active_index {
+                            self.active_index = Some(idx.saturating_sub(1));
+                            self.active_submenu = Some(0);
+                        }
+                        return true;
+                    }
+                    KeyCode::Right => {
+                        if let Some(idx) = self.active_index {
+                            self.active_index = Some((idx + 1).min(self.items.len() - 1));
+                            self.active_submenu = Some(0);
+                        }
+                        return true;
+                    }
+                    KeyCode::Up => {
+                        if let Some(sub) = self.active_submenu {
+                            self.active_submenu = Some(sub.saturating_sub(1));
+                        }
+                        return true;
+                    }
+                    KeyCode::Down => {
+                        if let Some(idx) = self.active_index {
+                            let max = self.items[idx].submenu.len().saturating_sub(1);
+                            if let Some(sub) = self.active_submenu {
+                                self.active_submenu = Some((sub + 1).min(max));
+                            }
+                        }
+                        return true;
+                    }
+                    KeyCode::Enter => {
+                        // TODO: invoke menu action
+                        self.active_index = None;
+                        self.active_submenu = None;
+                        return true;
+                    }
+                    _ => {}
+                }
+            }
+        }
+        false
+    }
+
+    pub fn is_active(&self) -> bool {
+        self.active_index.is_some()
+    }
+
+    pub fn deactivate(&mut self) {
+        self.active_index = None;
+        self.active_submenu = None;
+    }
+}
+
+impl Widget for &Menubar {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        let spans: Vec<Span> = self
+            .items
+            .iter()
+            .enumerate()
+            .flat_map(|(i, entry)| {
+                let is_active = self.active_index == Some(i);
+                let mut chars = entry.label.chars();
+                let first = chars.next().unwrap();
+
+                let first_style = if is_active {
+                    Style::default()
+                        .fg(Color::Black)
+                        .bg(Color::White)
+                        .add_modifier(Modifier::UNDERLINED)
+                        .add_modifier(Modifier::BOLD)
+                } else {
+                    Style::default()
+                        .fg(Color::Rgb(204, 204, 204))
+                        .add_modifier(Modifier::UNDERLINED)
+                        .add_modifier(Modifier::BOLD)
+                };
+                let rest_style = if is_active {
+                    Style::default()
+                        .fg(Color::Black)
+                        .bg(Color::White)
+                } else {
+                    Style::default().fg(Color::Rgb(204, 204, 204))
+                };
+
+                let parts = vec![
+                    Span::raw("  "),
+                    Span::styled(first.to_string(), first_style),
+                    Span::styled(chars.as_str().to_string(), rest_style),
+                ];
+
+                // Render submenu if active
+                if is_active {
+                    // We can't render a dropdown in the same line as the menubar
+                    // For now just highlight the active item
+                }
+
+                parts
+            })
+            .collect();
+
+        Paragraph::new(Line::from(spans))
+            .style(Style::default().bg(Color::Rgb(45, 45, 45)))
+            .render(area, buf);
+    }
+}
--- a/src/ui/mod.rs
+++ b/src/ui/mod.rs
@@ -0,0 +1,9 @@
+pub mod focus;
+pub mod layout;
+pub mod menubar;
+pub mod router;
+pub mod scheduler;
+pub mod splash;
+pub mod statusbar;
+
+pub use layout::LayoutManager;
--- a/src/ui/router.rs
+++ b/src/ui/router.rs
@@ -0,0 +1,20 @@
+use crossterm::event::Event;
+
+/// Routes input events through the 3-layer system:
+/// 1. System emergency shortcuts
+/// 2. Focused PanelProvider
+/// 3. Global shortcuts / Menubar
+pub struct EventRouter;
+
+impl EventRouter {
+    pub fn new() -> Self {
+        Self
+    }
+
+    pub fn route(&mut self, event: Event) {
+        // TODO: Layer 1 — system shortcuts (Ctrl+C, Ctrl+Q)
+        // TODO: Layer 2 — focused provider
+        // TODO: Layer 3 — global shortcuts / menubar
+        let _ = event;
+    }
+}
--- a/src/ui/scheduler.rs
+++ b/src/ui/scheduler.rs
@@ -0,0 +1,30 @@
+use ratatui::{backend::Backend, Frame, Terminal};
+
+/// Schedules and executes the per-frame render.
+pub struct RenderScheduler;
+
+impl RenderScheduler {
+    pub fn new() -> Self {
+        Self
+    }
+
+    pub fn render<B: Backend>(&mut self, terminal: &mut Terminal<B>) {
+        terminal
+            .draw(|frame| {
+                self.render_frame(frame);
+            })
+            .expect("render failed");
+    }
+
+    fn render_frame(&self, frame: &mut Frame) {
+        let _area = frame.area();
+        // TODO:
+        // 1. Draw splash if active
+        // 2. Otherwise draw main UI:
+        //    a. Menubar
+        //    b. Sidebar Provider
+        //    c. Main Panel Provider
+        //    d. Agent Panel Provider
+        //    e. Status Bar
+    }
+}
--- a/src/ui/splash.rs
+++ b/src/ui/splash.rs
@@ -0,0 +1,78 @@
+use ratatui::{
+    buffer::Buffer,
+    layout::{Alignment, Constraint, Direction, Layout, Rect},
+    style::{Color, Modifier, Style},
+    text::Line,
+    widgets::{Paragraph, Widget},
+};
+
+/// Splash screen shown on startup.
+pub struct SplashScreen;
+
+impl Widget for &SplashScreen {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        // Background
+        for y in area.top()..area.bottom() {
+            for x in area.left()..area.right() {
+                buf[(x, y)].set_bg(Color::Rgb(20, 18, 15));
+            }
+        }
+
+        let vertical = Layout::default()
+            .direction(Direction::Vertical)
+            .constraints([
+                Constraint::Percentage(20),
+                Constraint::Length(8),
+                Constraint::Length(1),
+                Constraint::Length(1),
+                Constraint::Length(1),
+                Constraint::Length(1),
+                Constraint::Min(0),
+            ])
+            .split(area);
+
+        // ASCII art dog
+        let dog = Paragraph::new(vec![
+            Line::from("                         ████████                         "),
+            Line::from("                      ████░░░░░░████                      "),
+            Line::from("                    ████░░░░░░░░░░████                    "),
+            Line::from("                   ████░░░▓▓▓▓▓▓░░░████                   "),
+            Line::from("                  ████░░░▓░░░░░░▓░░░████                  "),
+            Line::from("                  ███░░░░▓░░▓▓░░▓░░░░███                  "),
+            Line::from("                  ███░░░░░▓░░░░░▓░░░░░███                 "),
+            Line::from("                   ███░░░░░▓▓▓▓▓▓░░░░░███                 "),
+        ])
+        .alignment(Alignment::Center)
+        .style(Style::default().fg(Color::Rgb(210, 170, 90)));
+        dog.render(vertical[1], buf);
+
+        // Title
+        let title = Paragraph::new("EVERJOY")
+            .alignment(Alignment::Center)
+            .style(
+                Style::default()
+                    .fg(Color::Rgb(210, 170, 90))
+                    .add_modifier(Modifier::BOLD)
+                    .add_modifier(Modifier::UNDERLINED),
+            );
+        title.render(vertical[2], buf);
+
+        // Subtitle
+        let subtitle = Paragraph::new("An AI-native TUI workflow")
+            .alignment(Alignment::Center)
+            .style(Style::default().fg(Color::Rgb(150, 140, 130)).add_modifier(Modifier::ITALIC));
+        subtitle.render(vertical[3], buf);
+
+        // Version
+        let version = Paragraph::new("v0.1.0 — for Hoshu Chiu & Everjoy Chiu 🐕")
+            .alignment(Alignment::Center)
+            .style(Style::default().fg(Color::Rgb(120, 110, 100)));
+        version.render(vertical[4], buf);
+
+        // Hint
+        let hint = Paragraph::new("◀  Press any key to start  ▶")
+            .alignment(Alignment::Center)
+            .style(Style::default().fg(Color::Rgb(180, 180, 180)).add_modifier(Modifier::BOLD));
+        hint.render(vertical[5], buf);
+    }
+}
--- a/src/ui/statusbar.rs
+++ b/src/ui/statusbar.rs
@@ -0,0 +1,65 @@
+use ratatui::{
+    buffer::Buffer,
+    layout::Rect,
+    style::{Color, Style},
+    text::{Line, Span},
+    widgets::{Paragraph, Widget},
+};
+
+/// Dynamic status bar showing editor state, focus, and agent status.
+pub struct StatusBar {
+    pub filename: String,
+    pub file_type: String,
+    pub encoding: String,
+    pub cursor_line: usize,
+    pub cursor_col: usize,
+    pub agent_status: String,
+    pub focused_panel: String,
+    pub message: Option<(String, Color)>,
+}
+
+impl Default for StatusBar {
+    fn default() -> Self {
+        Self {
+            filename: "main.rs".into(),
+            file_type: "Rust".into(),
+            encoding: "UTF-8".into(),
+            cursor_line: 1,
+            cursor_col: 1,
+            agent_status: "idle".into(),
+            focused_panel: "Main".into(),
+            message: None,
+        }
+    }
+}
+
+impl Widget for &StatusBar {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        let left = format!(
+            "  {}  |  {}  |  {}  |  Ln {}, Col {}  ",
+            self.filename, self.file_type, self.encoding, self.cursor_line, self.cursor_col
+        );
+        let right = format!("  [{}]  |  {}  ", self.agent_status, self.focused_panel);
+
+        let left_width = left.len() as u16;
+        let right_width = right.len() as u16;
+        let mid_width = area.width.saturating_sub(left_width + right_width);
+
+        let mid = if let Some((msg, color)) = &self.message {
+            let padded = format!(" {:^width$} ", msg, width = mid_width as usize);
+            Span::styled(padded, Style::default().fg(*color).add_modifier(ratatui::style::Modifier::BOLD))
+        } else {
+            Span::raw(" ".repeat(mid_width as usize))
+        };
+
+        let line = Line::from(vec![
+            Span::styled(left, Style::default().fg(Color::Rgb(204, 204, 204))),
+            mid,
+            Span::styled(right, Style::default().fg(Color::Rgb(204, 204, 204))),
+        ]);
+
+        Paragraph::new(line)
+            .style(Style::default().bg(Color::Rgb(30, 60, 90)))
+            .render(area, buf);
+    }
+}