I would start with "begin" and then use "end" to denote the beginning and ending of such syntax blocks.

Maybe, at a later stage we could replace this by parentheses.

I think curly braces would be more clear than parentheses. We should use parentheses for grouping operations, like we do in math. No need to re-invent the wheel.

Genius!

That's a great idea, especially for businesses. A common, business-oriented, prompting language, with a simple, well-defined grammar would be great for accountants, businessmen and financiers. They could do their own vibe coding with such a method.