After further investigation, it appears that ":/foo" indeed resolves to the commit with message "foobar" (in the above example) if the commits are not all created at the same time: e.g., by adding `sleep 1` between the commit commands, or exporting `GIT_AUTHOR_DATE`.
This leaves only the question of why :/<text> references don't resolve to commits reachable only from HEAD, and whether this is the best behavior.
