Per-Environment Module Exclusion

What: Modules with environment-specific config (Google Tag Manager, error reporting, profiling) use $settings['config_exclude_modules'] in settings.php to exclude from config export/import.

Rationale: Some modules need different config per environment — GTM container ID is different on staging vs production; error reporting verbosity differs in dev. Config sync is one-way: what's in config/sync overwrites the active site. Without exclusion, deploying staging config to production overwrites the prod GTM container with the staging one. config_exclude_modules tells the config system to leave those modules' config alone during import.

When it applies: Modules whose config legitimately differs per environment. NOT a workaround for accidental local-only config drift — that's a separate problem (use drush config:export discipline).

Example:

// settings.php (or a per-environment include like settings.local.php)
$settings['config_exclude_modules'] = [
  'google_tag',           // GTM container ID per env
  'config_inspector',     // dev-only diagnostic module
  'devel',                // dev-only
  'webprofiler',          // dev-only
];

# Verify the exclusion is honored
drush config:status      # excluded modules' config doesn't appear as "different"
drush config:import     # excluded modules' active config is preserved