# Broadcast Configuration Fallback Design

## Goal

Keep Laravel web requests working when Pusher is selected but its required credentials are missing, so sale and transaction detail modals can open instead of receiving a startup 500 response.

## Design

`BroadcastServiceProvider` will validate the configured default broadcaster during boot. When the selected connection is `pusher` and its key, secret, or application ID is blank, the provider will change the runtime default to Laravel's `null` broadcaster before registering broadcast routes and channels. A complete Pusher configuration remains unchanged.

The fallback is runtime-only. It does not edit `.env`, require database changes, or remove broadcast channel definitions. A unit test will cover both incomplete and complete Pusher configurations.

## Error Handling and Verification

The fallback prevents the broadcaster constructor from receiving null credentials. Verification will boot the provider under both configurations, compile Laravel configuration and views, and run the complete test suite.