Bogus sourceType error when using file dependencies

[nex3]

If I load a chain of modules through a file: dependency, esmify throws a ParseError: 'import' and 'export' may appear only with 'sourceType: module' even when all packages declare it. Here's a repro:

$ echo '{"dependencies": {"subpkg": "file:subpkg"},"sourceType":"module"}' > package.json
$ echo 'import "subpkg";' > test.js
$ mkdir subpkg
$ cd subpkg
$ echo '{"name":"subpkg","dependencies":{"immutable":"^4.2.0"},"sourceType":"module","main":"index.js"}' > package.json
$ echo 'import "immutable";' > index.js
$ npm install
$ cd ..
$ npm install --save-dev browserify esmify
$ npx browserify -p esmify test.js --outfile out.js

This produces:

/home/nweiz/goog/pkg/dart/cli_pkg/browser_library_test/build/npm/node_modules/immutable/dist/immutable.es.js:5950
export default Immutable;
^
ParseError: 'import' and 'export' may appear only with 'sourceType: module'

It looks like somehow it's loading the "module" entrypoint for immutable.js but not parsing it as a module. Note that immutable.js works fine with browserify if it's not imported from a subpackage, and that the error still appears even after editing its package.json to also contain "sourceType": "module".

Tested with Node v18.12.1, browserify 17.0.0, esmify 2.1.1, immutable 4.2.4