Because artifacts pass through many repositories on the way to the final product, trust is established as a recurring process at each handoff rather than once at the start, and what goes into and comes out of each build step is verified to confirm the expected step was run by the expected component. The trust chain includes the sub-elements, components, workers and attestors involved, and it is renewed through their interactions.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.