I don't know who Jackson Mallet is in this context as there's not much information given. He could be an ordinary person with an interesting story, or maybe a local figure.
If we consider a common understanding, 'shaft' can refer to different things like a long, narrow part or a passage. In some novels, if there is a description of a shaft as black, it might be for creating a certain atmosphere, perhaps a sense of mystery or gloom. However, again, without knowing the particular novel, it's just speculation.
Since I don't have more details about the 'putter boy story', it could also be a story where the 'putter boy' is not related to golf at all. Maybe in a small village, there is a boy nicknamed 'putter' because he is always fidgeting or 'puttering' around. He could have adventures around the village, helping people, getting into minor scrapes, and learning important life lessons along the way.
Shaft visual novel could be a term for a visual novel that has some connection to Shaft. Shaft has created many visually striking anime series. In the context of a visual novel, it might imply a certain aesthetic quality similar to what Shaft brings to its anime works, like detailed character designs and elaborate backgrounds.
However, if it's a different kind of 'putter boy story' where 'putter' has another meaning, like a boy who is always busy with small tasks or 'puttering' around. The main plot could be about his daily life in a community. He might be known for his helpful nature, always fixing small things or running errands for the elderly. One day, a big problem arises in the village, like a flood or a fire, and the 'putter boy' uses his knowledge of the area and his quick - thinking skills to help everyone out. His actions then change the way the community views him, from just a busybody to a hero.