Most of these exist because they are the specific ways this kind of app normally goes wrong.

Dart

Never use AlertDialog, showDialog, or an unstyled showModalBottomSheet. Every confirmation, form, picker, and menu is an LdBottomSheet.

Never use SnackBar. Toasts are LdToast, which renders through an Overlay outside the page's own tree and therefore wraps its content in Material(type: MaterialType.transparency). Skip that and text inside throws "No Material widget found". This is a common miss and it is handled once, in the component, so no caller has to remember.

Never render nothing for an empty list, or a bare "No items". Every empty list is LdEmptyState.

Never write Text('Error: $e'), and never let Flutter's red screen show. Every failure is LdErrorState with a retry bound to the call that actually failed, and ErrorWidget.builder is overridden globally for the ones nobody anticipated.

Never hardcode a font family or call GoogleFonts.* inside a widget. Every text style resolves from Theme.of(context).textTheme at build time. A component that hardcodes its own font silently keeps using the wrong language's face forever, because nothing about a locale change ever touches it.

Never import dio, drift, or web_socket_channel from a page or a widget.

Never put business logic in a build method.

Riverpod

Watch narrow, not wide. A build that watches several providers at the top of a large widget rebuilds all of it on any change, which is the single biggest performance mistake available here.
Use select where only one field matters.
Side effects go in ref.listen, never as a consequence of a .watch used for rendering.
flutter_hooks for state that belongs to the widget, not the app. Reaching for a provider for local UI state is the same mistake in the other direction.
RepaintBoundary around anything that redraws on its own.

Go

gofmt and go vet clean. Both run in CI.
Errors are values with context: wrap with %w and a sentence.
Every mutating handler resolves the caller's role against the node. There is no client that gets a shortcut.
No access returns 404, not 403.
Anything reaching the filesystem goes through pathsafe.
The helper never builds a shell command. Fixed argument lists only.

Copy

Plain, direct English. Natural Arabic, checked against the glossary rather than translated from scratch. No filler and no marketing voice: say what the thing does.