wp-build: Add --no-script-debug flag to skip unminified asset generation

[kraftbj]

What problem does this address?

wp-build generates both minified (.min.js) and unminified (.js) assets for every entry point. The unminified copies exist solely for SCRIPT_DEBUG — in normal operation, 100% of them go unused. For plugins shipping via WordPress.org, this doubles (or more) the JavaScript footprint of the build/ directory.

As a concrete example: one project's build/ directory ships ~2.7 MB of unminified JS alongside ~1.2 MB of minified equivalents. The unminified files account for ~61,000 lines of code that serve no purpose in production.

The generated PHP registration templates also assume unminified files are always present on disk:

$extension = defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ? '.js' : '.min.js';

When plugin authors exclude unminified files from their distributions (the natural fix for the size problem), SCRIPT_DEBUG = true causes registered script URLs to point to non-existent files, breaking functionality.

What is your proposed solution?

Add a --no-script-debug flag to wp-build that:

1. Skips generating unminified assets entirely — no .js / .css counterparts to the .min.js / .min.css files, saving build time and disk space.
2. Emits a build-time constant (has_debug_assets) in constants.php so the generated PHP registration templates know whether unminified files exist, rather than relying on runtime file_exists() checks.
3. Updates the PHP registration templates to consult has_debug_assets before choosing the unminified path. When SCRIPT_DEBUG is true but has_debug_assets is false, the templates fall back to the minified file gracefully.

This affects the CLI, the build pipeline, and 4 PHP templates:

• script-registration.php.template
• module-registration.php.template
• routes-registration.php.template
• style-registration.php.template

The pattern in each template becomes:

$extension = '.min.js';
if ( defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG && $build_constants['has_debug_assets'] ) {
    $extension = '.js';
}

Without --no-script-debug, behavior is unchanged — both minified and unminified assets are generated and has_debug_assets is true. With --no-script-debug, only minified assets are generated, has_debug_assets is false, and SCRIPT_DEBUG falls back gracefully.