The reconciler's startrek subscribe had failed every sweep since 2026-08-19 with "payload is not a JSON object". Not transient: startrek.website (Lemmy 0.19.20, Elestio-packaged nginx) routes to the Lemmy backend only when Accept is byte-for-byte "application/activity+json" or the ld+json profile form — our "activity+json, ld+json; profile=...; q=0.9" list fell through to lemmy-ui and came back as a 200 text/html SPA shell, so every object fetch from that instance (community, Person actors, posts) failed. Send the bare type, which is exactly what Lemmy's activitypub-federation crate, PieFed and Mbin send on their own fetches (verified against source and live against lemmy.world, lemmy.ml, piefed.social, fedia.io, startrek.website). Also name the media type when a 2xx body is non-JSON under a non-JSON Content-Type, so the next content-negotiation miss reads "response is text/html, not JSON" instead of the opaque parser error; mislabelled valid JSON still parses. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>