Set a custom entry file for Metro dev server in React Native build - react-native

Question

I'm writing some scripts that do custom React Native builds for unit testing and such, specifying a custom entry file for the react-native-xcode.sh script using the ENTRY_FILE env variable. This is super useful and great. I'm able to do release builds no problem, and they work just fine, so basically I can build a RN app from any entry file at will. However, when I try a Debug variant build, metro doesn't seem to know about my special custom entry file, and gives me this error:
None of these files exist:
* index(.native|.ios.js|.native.js|.js|.ios.json|.native.json|.json|.ios.ts|.native.ts|.ts|.ios.tsx|.native.tsx|.tsx)
* index/index(.native|.ios.js|.native.js|.js|.ios.json|.native.json|.json|.ios.ts|.native.ts|.ts|.ios.tsx|.native.tsx|.tsx)
at ModuleResolver.resolveDependency (/Users/justin/dev/enmesh/testutilsnative/node_modules/metro/src/node-haste/DependencyGraph/ModuleResolution.js:165:15)
at ResolutionRequest.resolveDependency (/Users/justin/dev/enmesh/testutilsnative/node_modules/metro/src/node-haste/DependencyGraph/ResolutionRequest.js:52:18)
at DependencyGraph.resolveDependency (/Users/justin/dev/enmesh/testutilsnative/node_modules/metro/src/node-haste/DependencyGraph.js:285:16)
at /Users/justin/dev/enmesh/testutilsnative/node_modules/metro/src/lib/transformHelpers.js:267:42
at Server.<anonymous> (/Users/justin/dev/enmesh/testutilsnative/node_modules/metro/src/Server.js:841:41)
at Generator.next (<anonymous>)
at asyncGeneratorStep (/Users/justin/dev/enmesh/testutilsnative/node_modules/metro/src/Server.js:99:24)
at _next (/Users/justin/dev/enmesh/testutilsnative/node_modules/metro/src/Server.js:119:9)
at processTicksAndRejections (internal/process/task_queues.js:97:5)
IN RESOLVER
Error: Unable to resolve module `./index` from ``:
Does anyone know how I can get the Debug build of the app to interface properly with the Metro development server, so I can debug my app builds better? Any guidance here would be greatly appreciated!
Metro is just getting launched automatically by the xcodebuild process, which I'm calling like this:
const args = {
simulator: device,
configuration: variant,
scheme,
projectPath: xcodeProjectPath,
device: undefined,
uuid: undefined,
packager: true,
verbose: true,
port: 8081,
terminal: undefined,
};
const xcodebuildSpawnOptionsArgs: any = {
...args,
cwd: folder,
env: {
PLATFORM: 'ios',
ENTRY_FILE: builtEntryFilePath,
},
};
const buildProcess = spawn(
'xcodebuild',
xcodebuildArgs,
getProcessOptions(xcodebuildSpawnOptionsArgs),
);