Environment variables not detected in automatic builds

    "build": {
        "command": "npm run register"
    }

import dotenv from 'dotenv';

dotenv.config({ path: '.dev.vars' });

const token = process.env.DISCORD_TOKEN;
const applicationId = process.env.DISCORD_APPLICATION_ID;

if (!token) {
    throw new Error('The DISCORD_TOKEN environment variable is required.');
}

[custom build] Running: npm run register
[custom build] 
[custom build] > register
[custom build] > node src/register.js
[custom build] 
[custom build] 
[custom build] [[email protected]] injecting env (0) from .dev.vars -- tip: ⚡️ secrets for agents: https://dotenvx.com/as2
[custom build] 
[custom build] file:///opt/buildhome/repo/src/register.js:16
[custom build]     throw new Error('The DISCORD_TOKEN environment variable is required.');
[custom build]           ^
[custom build] 
[custom build] Error: The DISCORD_TOKEN environment variable is required.
[custom build]     at file:///opt/buildhome/repo/src/register.js:16:8
[custom build]     at ModuleJob.run (node:internal/modules/esm/module_job:274:25)
[custom build]     at async onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:644:26)
[custom build]     at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:117:5)
[custom build] 
[custom build] Node.js v22.16.0
[custom build] 

[custom build] Running: npm run register
[custom build] 
[custom build] > register
[custom build] > node src/register.js
[custom build] 
[custom build] 
[custom build] [[email protected]] injecting env (3) from .dev.vars -- tip: :closed_lock_with_key: prevent building .env in docker: https://dotenvx.com/prebuild
[custom build] 
[custom build] Registered all commands