docs(desktop): enhance README with environment setup

packages/desktop/README.md

@@ -4,6 +4,38 @@ Native OpenCode desktop app, built with Tauri v2.
 
 ## Development
 
+### Environment Setup
+
+Before running the desktop app, you must set the `RUST_TARGET` environment variable based on your platform:
+
+**macOS:**
+
+```bash
+# Apple Silicon (M1/M2/M3)
+export RUST_TARGET=aarch64-apple-darwin
+
+# Intel
+export RUST_TARGET=x86_64-apple-darwin
+```
+
+**Windows:**
+
+```bash
+export RUST_TARGET=x86_64-pc-windows-msvc
+```
+
+**Linux:**
+
+```bash
+# x64
+export RUST_TARGET=x86_64-unknown-linux-gnu
+
+# ARM64
+export RUST_TARGET=aarch64-unknown-linux-gnu
+```
+
+### Running the App
+
 From the repo root:
 
 ```bash
@@ -16,17 +48,88 @@ This starts the Vite dev server on http://localhost:1420 and opens the native wi
 If you only want the web dev server (no native shell):
 
 ```bash
+export RUST_TARGET=<your-target>  # Set based on your platform
 bun run --cwd packages/desktop dev
 ```
 
+### Development Scripts
+
+- `bun run --cwd packages/desktop dev` - Start web dev server only
+- `bun run --cwd packages/desktop tauri dev` - Start native desktop app with hot reload
+- `bun run --cwd packages/desktop tauri build` - Build production desktop app
+
 ## Build
 
 To create a production `dist/` and build the native app bundle:
 
 ```bash
+export RUST_TARGET=<your-target>  # Set based on your platform
 bun run --cwd packages/desktop tauri build
 ```
 
+The built app will be available in `src-tauri/target/release/bundle/`.
+
+## Project Structure
+
+- `src/` - React frontend source code
+- `src-tauri/` - Tauri Rust backend configuration
+- `src-tauri/sidecars/` - OpenCode CLI binary for desktop integration
+- `scripts/` - Build and development scripts
+
+## Sidecar Integration
+
+The desktop app includes a sidecar binary that provides CLI functionality within the desktop environment. The binary is automatically built and copied during development.
+
+Supported platforms:
+
+- macOS (Intel and Apple Silicon)
+- Windows (x64)
+- Linux (x64 and ARM64)
+
 ## Prerequisites
 
-Running the desktop app requires additional Tauri dependencies (Rust toolchain, platform-specific libraries). See the [Tauri prerequisites](https://v2.tauri.app/start/prerequisites/) for setup instructions.
+Running the desktop app requires additional Tauri dependencies:
+
+### Required Tools
+
+- **Rust toolchain** - Install from [rustup.rs](https://rustup.rs/)
+- **Platform-specific libraries** - See [Tauri prerequisites](https://v2.tauri.app/start/prerequisites/)
+
+### macOS Dependencies
+
+```bash
+# Install Xcode Command Line Tools
+xcode-select --install
+```
+
+### Linux Dependencies
+
+```bash
+# Ubuntu/Debian
+sudo apt update
+sudo apt install libwebkit2gtk-4.0-dev \
+    build-essential \
+    curl \
+    wget \
+    libssl-dev \
+    libgtk-3-dev \
+    libayatana-appindicator3-dev \
+    librsvg2-dev
+```
+
+### Windows Dependencies
+
+- Microsoft Visual Studio C++ Build Tools
+- WebView2 Runtime (usually included with Windows 10/11)
+
+## Troubleshooting
+
+### "RUST_TARGET not set" Error
+
+Make sure to export the appropriate `RUST_TARGET` environment variable for your platform before running any development commands.
+
+### Build Issues
+
+- Ensure you have the latest Rust toolchain: `rustup update`
+- Clear Tauri cache: `rm -rf packages/desktop/src-tauri/target`
+- Reinstall dependencies: `bun install`