tags.pub's activitypub-bot (activitystrea.ms parser) rejects any activity
body containing the https://w3id.org/identity/v1 JSON-LD context with
400 Invalid request body. Fedify 2.0 adds this context via LD Signatures
(RsaSignature2017) on all outbound activities.
Workaround: lib/direct-follow.js sends Follow/Undo(Follow) with a minimal
body (no LD Sig, no proof) using draft-cavage HTTP Signatures, scoped only
to tags.pub via DIRECT_FOLLOW_HOSTS set.
Also removes [federation-diag] inbox POST logging (no longer needed).
Upstream: https://github.com/social-web-foundation/tags.pub/issues/10
