Rollup multi file output name

[rgrif]

I am trying to rollup a number of js files and output to a single file with given name. I have the following rollup.config.js which works fine. The output file is built into the build folder, but it has the name multi-entry.js.

import { createBasicConfig } from '@open-wc/building-rollup';
import dynamicImportVars from '@rollup/plugin-dynamic-import-vars';
import merge from 'deepmerge';
import multi from '@rollup/plugin-multi-entry';

const baseConfig = createBasicConfig({
    developmentMode: false,
    outputDir: "build"
});

export default merge(baseConfig, {
    input: ['src/*.js'],
    plugins: [
        multi(),
        dynamicImportVars(),
    ],
});

I have tried many variations such as:

const baseConfig = createBasicConfig({
    developmentMode: false,
    output: "build/bundle.js"
});

This creates multi-entry.js in dist folder.

const baseConfig = createBasicConfig({
    developmentMode: false,
    entryFileName: "bundle.js"
});

This creates multi-entry.js in build folder.

const baseConfig = createBasicConfig({
    developmentMode: false,
    outputDir: "build",
    output: {entryFileNames: "bundle.js"}
});

This creates multi-entry.js in build folder.

Any pointers?