What Agile concept expresses delivering value in slices rather than in layers/stages?

Outing planning for the next iteration an agile team identifies most of the story points that are expected to be delivered. How should an agile practitioner work with the team to help identity the iteration's remaining scope?

One of the major tools and techniques used in Lean Software Development is Value Stream Mapping. What is the primary purpose of value stream mapping?

An agile coach is facing a dilemma: On one hand, there is a requirement that is vital and will consume all capacity of the team. On the other hand, there are some chore-related tasks that will improve the team's ability to produce results. The team insists on implementing these tasks since they will increase efficiency.
What should the agile coach do?

A visual control used in Lean software development to represent the velocity of business solutions delivered over time is a: