GET-017: be get --nosub won't advance a store-backed switch-worktree's ref at all (stuck at its base), forcing fresh-clone salvage to land

Distinct from GET-016 (there the ref advances without the tree; here the ref does not advance at all). In certain store-backed worktrees be get --nosub does NOT fast-forward the local branch ref: this session MEM-041's and MEM-042's worktrees stayed pinned at 5104a855 across repeated be get --nosub, never pulling d857a9cc/91f215a4, while a sibling worktree (MEM-044) advanced normally. The stuck ones carried a 105-byte .be switch file vs MEM-044's 223-byte — pointing at a .be-switch-shape fast-forward gap (the GET-012 cwd-.be disambiguation: absent→worktree, dir→clone, file→switch). .refs.idx was fresh (not the stale-idx trap). Consequence: such worktrees can't update onto trunk in place, the Issues.mkd "update-first" step fails, and MEM-041/042/044 had to be landed by recreating fresh clones at the current tip. See GET, GET-012, GET-016, Issues.

Repro (to pin)

Issues

Planned