Expand description
Owns the multi-file working set: a list of paths, a current-index
cursor, and the navigation primitives that the colon-prompt dispatch
consumes (:n, :p, :e, :d, :x, :t).
Does NOT own Source instances long-term — those are constructed on
demand by main::open_source_for_path and dropped on switch, so a
100-file invocation doesn’t mmap 100 files at once.