Both sides added jsonContentType; keep one. The no-entry 502 test kills the
backends outright, since main replays a unanimous 500, and the cached
content-type test moves to /nodes, the only cached path left.
Fact answers must be as current as a backend's own, and X-Cache/Age are
headers PuppetDB never sends.
- serve /facts, /facts/<name>[/<value>] and /fact-names live on every request
- keep the in-memory cache on merged /nodes only
- drop X-Cache and Age everywhere; /healthz still reports cache state
- answer successful queries with PuppetDB's application/json;charset=utf-8
unkin-agent