Preload Lemmy's JSON-LD context

Bundle Lemmy's JSON-LD context in vocab-runtime and register it as a
preloaded context for the default document loader.  This lets Fedify parse
Lemmy-originated activities without application-specific document loader
workarounds for the context URL's non-JSON-LD response headers.

Update the changelog for the next vocab-runtime release.

Fixes #714

Assisted-by: Codex:gpt-5.4

Author: dahlia

CHANGES.md

@@ -8,6 +8,15 @@ Version 2.0.14
 
 To be released.
 
+### @fedify/vocab-runtime
+
+ -  Added <https://join-lemmy.org/context.json> to preloaded JSON-LD contexts.
+    Lemmy serves this context as `application/json` without a JSON-LD context
+    `Link` header, which caused the default document loader to reject
+    Lemmy-originated activities before application handlers could run.  [[#714]]
+
+[#714]: https://github.com/fedify-dev/fedify/issues/714
+
 
 Version 2.0.13
 --------------

packages/vocab-runtime/src/contexts.ts

@@ -2,6 +2,8 @@
 // https://github.com/fedify-dev/fedify/issues/74
 // cSpell: disable
 
+import joinLemmyContext from "./contexts/join-lemmy.json" with { type: "json" };
+
 const preloadedContexts: Record<string, unknown> = {
   "https://www.w3.org/ns/activitystreams": {
     "@context": {
@@ -4315,6 +4317,15 @@ const preloadedContexts: Record<string, unknown> = {
     },
   },
 
+  // Lemmy's context document is served as application/json without the JSON-LD
+  // context Link header.  The default document loader treats that as a regular
+  // JSON response instead of a JSON-LD context, so every Lemmy activity that
+  // references this URL fails before application handlers run.  We ship a
+  // built-in copy here so Fedify can parse Lemmy-originated activities without
+  // application-level document loader workarounds.
+  // See: https://github.com/fedify-dev/fedify/issues/714
+  "https://join-lemmy.org/context.json": joinLemmyContext,
+
   // Mastodon's "toot:" namespace.  The URL http://joinmastodon.org/ns has
   // *never* served a real JSON-LD context document—Mastodon has always inlined
   // these term definitions directly in every outgoing @context array.  However,

packages/vocab-runtime/src/contexts/join-lemmy.json

@@ -0,0 +1,33 @@
+{
+  "@context": [
+    "https://w3id.org/security/v1",
+    {
+      "as": "https://www.w3.org/ns/activitystreams#",
+      "lemmy": "https://join-lemmy.org/ns#",
+      "litepub": "http://litepub.social/ns#",
+      "pt": "https://joinpeertube.org/ns#",
+      "sc": "http://schema.org/",
+      "mastodon": "http://joinmastodon.org/ns#",
+      "ChatMessage": "litepub:ChatMessage",
+      "commentsEnabled": "pt:commentsEnabled",
+      "sensitive": "as:sensitive",
+      "matrixUserId": "lemmy:matrixUserId",
+      "postingRestrictedToMods": "lemmy:postingRestrictedToMods",
+      "removeData": "lemmy:removeData",
+      "stickied": "lemmy:stickied",
+      "moderators": {
+        "@type": "@id",
+        "@id": "lemmy:moderators"
+      },
+      "expires": "as:endTime",
+      "distinguished": "lemmy:distinguished",
+      "language": "sc:inLanguage",
+      "identifier": "sc:identifier",
+      "Hashtag": "as:Hashtag",
+      "featured": {
+        "@type": "@id",
+        "@id": "mastodon:featured"
+      }
+    }
+  ]
+}