What’s the big idea? After scrolling and clicking I’m not sure what this gets me. What’s the durability guarantee? Is this at-least-once, at-most-once, or thoug

What’s the big idea? After scrolling and clicking I’m not sure what this gets me. What’s the durability guarantee? Is this at-least-once, at-most-once, or thoughts-and-prayers message delivery? What happens when a node crashes?