v1.46.1

A map inside a map item knows the outer items' writers. R179 replica,
one builder per region inside each of the four groups: a region builder in
group_00 wrote only its own files, but its write-scope gate charged it with
79 render files from builders in the other groups. Its item failed although
the builder passed.

• An outer item's scope now includes what the items of its own inner maps
  write (_item_scopes). The outer map's disjoint check covers them too.
• A nested map gives its items the outer peer scopes as well as its own
  sibling scopes (parent.peer_scopes). A concurrent writer in another
  outer item is then a peer, not this worker's write.
• A nested map without its own fork passes the outer map's fork source to
  its items. Region builders under a forking group map fork the shared
  session; before, they started fresh.
• Test only: the dashboard port test accepts the next free port, not always
  port + 1 (another process held port + 1 on an Ubuntu 3.9 runner).