Preserve config defaults safely

When adding or modifying configuration settings, treat default values as part of the public API: do not silently change an existing default (e.g. bumping a parser limit from 1000 to 10000) unless the change is intentional and documented. If a default behavior must change, add a deprecation warning that fires only when the application relies on the implicit default, not when the user has explicitly set that value — track this with an internal flag rather than inferring intent from the chosen value.

// Track whether the user explicitly configured the setting
var usingDefaultExtendedParser = true;

app.set('query parser', function (val) {
  usingDefaultExtendedParser = false; // user made an explicit choice
  return parseExtendedQueryString(val);
});

// Only warn when no explicit choice was made
if (usingDefaultExtendedParser) {
  deprecate('default extended query parser is deprecated, set explicitly to override');
}

Additionally, always read or write configuration through the established accessor functions (app.get() / app.set()) rather than touching the internal settings object directly (e.g. app.settings.etag). Direct property access bypasses validation/defaults handling and was deprecated for this reason — use app.get('etag') instead.</description> </invoke>