setup: WSL installer picks Windows Bun and produces a non-working binary / Node launcher

[li-xiu-qi]

Problem

On WSL, if the user has installed Bun from Windows (e.g. via npm i -g bun on Windows), the bun executable appears first on PATH as /mnt/c/.../bun. scripts/setup.sh currently runs command -v bun, finds this Windows binary, and then:

1. Calls pnpm build:bin, which invokes the Windows Bun to compile dist/bin/step. The resulting binary is a Windows PE executable that cannot run in WSL, or fails with DLL / loader errors.
2. If no Bun is found at all, it installs the Node-based launcher. OpenTUI packages (@opentui/core, @opentui/react) rely on Bun-specific module resolution (bun: protocol imports and extensionless subpath imports), so step voice fails on Node with errors like:
   • Cannot find module 'react-reconciler/constants'
   • Only URLs with a scheme in: file, data, and node are supported by the default ESM loader. Received protocol 'bun:'

Environment

• step-realtime-cli version: 1.0.0
• OS: WSL (Ubuntu on Windows)
• which bun returns a path under /mnt/c/...
• A Linux-native Bun is installed at e.g. ~/.bun/bin/bun

Expected behavior

bash scripts/setup.sh should build / install a launcher that works on WSL. It should prefer a Linux-native Bun over a Windows Bun and, when available, install the native Bun binary launcher.

Actual behavior

Setup either builds a broken Windows binary or falls back to a Node launcher that cannot run OpenTUI.

Root cause

scripts/setup.sh resolves Bun unconditionally via command -v bun. It does not distinguish Windows (/mnt/) and Linux-native executables, and it does not honor STEP_BUN_BIN.

Related

• build: bundled OpenTUI chunk is empty, step fails with createLocalTuiClientApp not exported #25 (build chunk issue)
• runtime: OpenTUI dependencies fail on standard Node.js after build fix #29 (Node.js runtime incompatibility with OpenTUI)
• fix(build): emit OpenTUI runtime chunk and build agent-sdk #28 (PR fixing build: bundled OpenTUI chunk is empty, step fails with createLocalTuiClientApp not exported #25)