Parent tasks

Work bigger than one task hangs its parts on a parent (board #755; a generalization of an epic). It is one tag on the child, parent:#12, so there is no new machinery: a task's children are the tasks that name it.

• One parent, no cycles. parent holds one value, like project. Parents nest: an epic of epics is a parent with a parent.
• A parent is as complete as its least complete child, automatically (owner, 2026-09-30). When a child moves, the store moves the parent in the same commit, attributed to whoever moved the child, and so on up the chain. Least complete is by lane order: inbox, freezer, backlog, ready, in-progress, review, done. A child that ended obsolete or rejected isn't holding anything back, so it doesn't count. When every counting child is done, the parent is done and closes; a new or reopened child reopens it.
• A parent's status isn't set by hand while it has children: the refusal says it follows its parts, and which are holding it back.
• A parent doesn't drag its parts (owner, 2026-10-06): it is organizational first. To move a whole piece of work, move its unfinished parts — virta parts #12 freezer, or the board's offer when you drag a parent — and the parent follows them.
• Progress is derived, never stored: 3/7 is three of seven counting children done.

virta child #12 "The first part"     # files a child of #12 (its project, kind, area, priority)
virta set #40 parent=#12             # makes an existing task a part of #12
virta parent #40 "The epic"          # files a parent for #40, at #40's status
virta parts #12 freezer              # moves #12's unfinished parts; #12 follows
virta list "parent:#12"              # its parts