Why does 26 R1 build-tools prevent screens in /src/development/ from building 'includes'?

In a new 26 R1 instance, screens in /src/development using qp-include do not build the included elements.

I’ve spent 4-6 hours racking my brain attempting to figure out what’s wrong. Here it is:

It's a bug in the Acumatica build-tools package — specifically in extractScreenNameFromHTMLFile in utils.js.

The guard clause at line 78 blocks development paths:

function extractScreenNameFromHTMLFile(rootContext, resourcePath) {
    const filePath = resourcePath;
    const fileData = path.parse(filePath);
    const screensPath = path.join(rootContext, SRC_DIR, SCREENS_DIR);
    const screensCustomizationPath = path.join(rootContext, SRC_DIR, SCREENS_CUSTOMIZATION_DIR);
    const systemScreensPath = path.join(rootContext, SRC_DIR, SYSTEM_SCREENS_DIR);
    // ← This guard only allows src/screens, src/customizationScreens, src/systemScreens
    if (!fileData.dir.startsWith(screensPath) && !fileData.dir.startsWith(screensCustomizationPath) && fileData.dir !== systemScreensPath)
        return undefined;

Why should we not be able to build includes in development?