Focus a Block

A post can be the focus from the app. Any other file, or one section of it, only by typing #focus into it. Here a section heading's right-click menu gains Focus Section and Focus File. Click a section heading in the panel to open its menu, and pick one: the file on the right shows what's written.

Proposed

Two items lead a section heading's right-click menu: Focus Section and Focus File, then the menu as now (New Round… on a test file, Add Task Here, Squash Done). When the section or file is the focus, the item reads Remove Focus.
Focus Section writes #focus at the end of the heading's line, as you'd type it. It works on any heading the app shows as a section, ## or ###.
Focus File writes a bare #focus line at the top of the file's body, the same write a post's Focus makes (0.102.0).
The card shows the block, not one task: its title (the heading, or the file's title or name), "project · file · N open", and "Next: …", the first open task, which opens at its line. No box, as with a file today. A heading focus typed by hand reads the same way, replacing today's one-task-at-a-time card for a #focus heading.
It ends with its last open task. The tick that leaves no open task also takes the #focus out, one ⌘Z, as a file's line does now. For a test file, that's every test run.
It joins the queue. If the project already has a focus, the usual Focus Now · Focus Next ask comes first, as for a task.
Not in this cut: a project's whole group, which has no heading in a file to tag.

Open questions

Take Focus Section and Focus File as proposed? (yes, or say what to change)
Should a section focus show on the card as the block ("Round 12 · 4 open · Next: …"), also for a #focus heading you type by hand? (yes/no; recommended yes. Today a focused heading shows one of its tasks at a time.)
Should the last tick take #focus off the heading, as it does for a file? (yes/no; recommended yes)