`vp run`: scripts get a non-blocking stdin (EAGAIN) when `run` tasks in vite.config.ts use constants

Start by tracing vp run startup and how it loads vite.config.ts and starts the task process; the report points to ensureBlockingStdio() in dist/bin.js as related context. Reproduce with the supplied project, comparing the constant reference and string literal configurations, then inspect where stdin becomes non-blocking. Done means both configurations keep the probe waiting for input and the interactive update prompt accepts input.

Describe the bug

On macOS, interactive prompts started with vp run exit without waiting for input when a task in the run block of vite.config.ts references a constant.

With Bun as the package manager, vp run up, where up is vp update --interactive --latest, prints the package list and exits with Selected 0 packages to update before any key is pressed. Running vp update --interactive --latest directly, or bun run up, waits for input.

A blocking read of stdin shows the cause: the script started by vp run gets a stdin in non-blocking mode. probe.mjs calls readSync(0), and under vp run that call fails right away with EAGAIN. I have not identified what sets O_NONBLOCK.

Neither vp run probe nor vp run up invokes the hello task defined in the run block. Changing its command from a constant reference to the same string literal changes whether these scripts wait for input:

vite.config.ts	vp run probe
no run block	waits for input, then prints stdin is blocking
run: { tasks: { hello: { command: 'echo hello' } } }	waits for input, then prints stdin is blocking
const command = 'echo hello' and run: { tasks: { hello: { command } } }	prints stdin is non-blocking: EAGAIN immediately, without waiting for input

After vp exits, stdin returns to blocking mode.

I found this through vp run deps:update in a project whose run tasks spread shared constants into cache.input. There it happened with vite-plus 1.2.0 and 1.3.0. I tested the reproduction below with 1.3.0.

Possibly related: #2173 added ensureBlockingStdio(), which vite-plus 1.3.0 calls at startup in dist/bin.js. This case still happens on 1.3.0. I have not established whether the two share a cause.

Reproduction

https://github.com/everton-dgn/vp-run-stdin-nonblock

Steps to reproduce

Open a terminal in the reproduction directory. Run the commands below with stdin connected to the terminal, without piping or redirecting input.

1. bun install
2. vp run probe
   • Expected: it prints Waiting for one byte on stdin. Press Enter. and waits. After Enter, it prints stdin is blocking.
   • Actual: it prints stdin is non-blocking: EAGAIN without waiting.
3. vp run up
   • Expected: the package selection list waits for input.
   • Actual: the list is drawn and then replaced right away by Selected 0 packages to update and No packages selected for update.
4. Controls. Run node probe.mjs and press Enter; it prints stdin is blocking. Then run vp update --interactive --latest and bun run up separately. Each one waits at the package selection list. Cancel each list with Ctrl+C, without updating any package.
5. Run cp vite.config.literal.ts vite.config.ts. This writes the same task with the command as a string literal. Repeat steps 2 and 3: both commands now wait for input.

Besides bun.lock and a README with these steps, the repository has these files:

package.json

{
  "name": "vp-run-stdin-nonblock",
  "private": true,
  "type": "module",
  "packageManager": "[email protected]",
  "scripts": {
    "probe": "node probe.mjs",
    "up": "vp update --interactive --latest"
  },
  "dependencies": {
    "is-number": "6.0.0"
  },
  "devDependencies": {
    "vite-plus": "1.3.0"
  }
}

probe.mjs

import { readSync } from 'node:fs'

console.log('Waiting for one byte on stdin. Press Enter.')
try {
  readSync(0, Buffer.alloc(1))
  console.log('stdin is blocking')
} catch (error) {
  console.log(`stdin is non-blocking: ${error.code}`)
}

vite.config.ts, the version that fails:

import { defineConfig } from 'vite-plus'

const command = 'echo hello'

export default defineConfig({
  run: {
    tasks: {
      hello: { command }
    }
  }
})

vite.config.literal.ts, the version that works when copied over vite.config.ts:

import { defineConfig } from 'vite-plus'

export default defineConfig({
  run: {
    tasks: {
      hello: { command: 'echo hello' }
    }
  }
})

System Info

$ vp env current
Node.js:
  Version    24.22.0
  Source     lts
  Installed  true
  Mode       managed

Package Manager:
  Name       bun
  Version    1.4.3
  Source     packageManager
  Installed  true
  Mode       managed

$ vp --version
vp v1.3.0

Local vite-plus:
  vite-plus  v1.3.0

Tools:
  vite             v8.3.4
  rolldown         v1.2.14
  vitest           v5.0.5
  oxfmt            v0.73.0
  oxlint           v1.88.0
  oxlint-tsgolint  v7.0.2004
  tsdown           v0.23.1

Environment:
  Package manager  bun v1.4.3
  Node.js          v24.22.0

macOS 27.0.1 (arm64). I removed the local paths from the vp env current output.

Used Package Manager

bun

Logs

vp run probe, with the failing vite.config.ts. It printed the last line without waiting for Enter:

$ node probe.mjs ⊘ cache disabled
Waiting for one byte on stdin. Press Enter.
stdin is non-blocking: EAGAIN

vp run up, with the failing vite.config.ts and no key pressed. ANSI escape codes are removed:

$ vp update --interactive --latest ⊘ cache disabled
bun update --interactive v1.4.3 (c6da4a4d3)
? Select packages to update - …
  dependencies   Current  Target  Latest
  ❯ □ is-number  6.0.0    6.0.0   7.0.0
✓ Selected 0 packages to update
! No packages selected for update

Validations

• Read the Contributing Guidelines.
• Check that there isn't already an issue for the same bug.
• Confirm this is a Vite+ issue and not an upstream issue (Vite, Vitest, tsdown, Rolldown, or Oxc).
• The provided reproduction is a minimal reproducible example.