Regression: `Isolate.resolvePackageUri` returns `null` when using resident frontend compiler

[exaby73]

Not sure when this regressed, but running a program with dart run -r causes Isolate.resolvePackageUri and Isolate.resolvePackageUriSync to always return null

To reproduce

pubspec.yaml

name: test_project
description: A sample command-line application.
version: 1.0.0

environment:
  sdk: ^3.10.0

dependencies:
  path: ^1.9.0

bin/test_project.dart

import 'dart:isolate';

Future<void> main() async {
  print(await Isolate.resolvePackageUri(Uri.parse('package:path/')));
}

Expected output

$ dart run
file:///Users/exaby73/.pub-cache/hosted/pub.dev/path-1.9.1/lib/

$ dart run -r
file:///Users/exaby73/.pub-cache/hosted/pub.dev/path-1.9.1/lib/

Actual output

$ dart run
file:///Users/exaby73/.pub-cache/hosted/pub.dev/path-1.9.1/lib/

$ dart run -r
null

Version info

$ dart --version
Dart SDK version: 3.10.0 (stable) (Thu Nov 6 05:24:55 2025 -0800) on "macos_arm64"

[ykmnkmi]

Did it work before? Isolate.resolvePackageUri uses Isolate.packageConfig, which is the path to the package_config.json file located in the .dart_tool folder. Add --packages=.\.dart_tool\package_config.json to the dart run command. #51064.

[exaby73]

Yes the following works:

$ dart run -r --packages=./.dart_tool/package_config.json
file:///Users/exaby73/.pub-cache-3.10.0/hosted/pub.dev/path-1.9.1/lib/

And yes it used to work with -r. I believe this is a regression in 3.10

[exaby73]

I just tested it with 3.9.2, and it correctly resolves. This is a confirmed regression in 3.10

[mraleph]

cc @aam @bkonyi

[aam]

this seems to have regressed with ab44b20