#263 landed on main after this branch's head and asserts that a healthy
assigned attention under blocked posts nothing at all. The #252 echo makes
every blocked issue carry one comment — its parse — so the proxy is false
while the contract behind it is not: probe 66 draws the parse echo and no
attention diagnostic.
Re-spelled the way the same section's other cases already spell it, as the
absence of the attention-malformed marker, plus a companion assertion that
exactly one comment landed. That is strictly tighter than test -f was: this
case now fails if an attention comment appears beside the echo, which the
old form could not detect once any comment existed.
Refs #252
d604abd074