Function createReaction

createReaction(
    sourcePattern: string,
    targetAction: string,
    options?: ReactionOptions,
): Reaction
createReaction — declarative cross-chamber dispatch rules. Explicit edges between domain modules.
Parameters
- sourcePattern: string
- targetAction: string
- options: ReactionOptions = {}
Returns Reaction
Example
```
createReaction('cartAdd', 'inventoryCheck', {
  when: (cmd, result) => result.ok,
  map:  (cmd) => ({ itemId: cmd.payload.itemId }),
}).install(bus);
```
- Defined in utilities.ts:189