• This PR contains AI-generated code, but I have carefully reviewed it myself. Otherwise, my PR may be closed.

Description

Add a new exe format that compiles TypeScript into a standalone Node.js Single Executable Application (SEA) using the node --build-sea API.

CLI usage:

# Produces ./index executable (named after entry key)
tsdown ./src/index.ts --format exe

# Custom output name — produces ./hello (or hello.exe on Windows)
tsdown ./src/index.ts --format exe -o hello

Config file:

export default defineConfig({
  entry: ['src/cli.ts'],
  format: 'exe',
  outFile: 'myapp',
  exe: {
    useCodeCache: true,   // default: true
    useSnapshot: false,    // default: false
  },
})

Key behaviors:

• Requires Node.js >= 25.5.0 (for node --build-sea support)
• Single entry point only — multiple entries are rejected at config validation time
• outDir is only used as a staging directory for intermediate JS output and is cleaned up after the build; the final binary is output to the project root (cwd)
• Output name resolution: --out-file / outFile > first entry key > "app" fallback; .exe extension auto-appended on Windows
• Several options are force-overridden for exe: dts: false, sourcemap: false, exports: false, publint: false, attw: false, unbundle: false, report: false, and all dependencies are force-bundled
• Watch mode is disabled (logs a warning and builds once)
• Code splitting is disabled (codeSplitting: false) — SEA only supports a single script as its entry, so dynamic import() calls must be inlined into the bundle rather than emitted as separate chunks
• macOS: automatic ad-hoc codesigning via codesign --sign - (warns on failure)
• CJS legacy warning is suppressed — since exe is internally mapped to cjs for Rolldown, the usual CJS deprecation warning would be misleading
• formatBytes now auto-scales to MB for large outputs (exe binaries embed the Node.js runtime)
• Experimental — emits a warning on every build

Linked Issues

Additional context

The exe format is internally normalized to cjs — Rolldown bundles everything into a single CJS file, then node --build-sea produces the final standalone binary as a post-build step.