The PATH-stubbed gh gains a `.http-error` mode: the response body goes
to STDOUT, the reason to stderr, the status non-zero. The existing
`.error` sentinel produces empty stdout, which is the *safe* path — an
empty label set either way — and is why this class was never caught.
The three must-fail-before cases, plus the 200-`null` path a status
check alone leaves open, the suppressed-marker duplicate, the D6 tail's
count and numbers, and the crash handler proven distinct from a skip.
Refs #247
865d5bd1df