Backport the preloaded FEP-ef61 context to all maintenance branches

[dahlia]

Problem

While processing incoming ActivityPub requests, Fedify attempts to load the following JSON-LD context remotely:

https://w3id.org/fep/ef61

The URL currently redirects to:

https://raw.codeberg.page/fediverse/fep/fep/ef61/fep-ef61.jsonld

When the remote endpoint temporarily returned HTTP 502, Fedify failed to parse the incoming document and aborted inbox request processing.

A shortened version of the log:

ERR fedify·runtime·docloader: Failed to fetch document: 502 'https://raw.codeberg.page/fediverse/fep/fep/ef61/fep-ef61.jsonld'

ERR fedify·federation·http: An error occurred while serving request 'POST' ...
jsonld.InvalidUrl: Dereferencing a URL did not result in a valid JSON-LD object. URL: "https://w3id.org/fep/ef61"

details: {
  code: 'loading remote context failed',
  url: 'https://w3id.org/fep/ef61',
  cause: FetchError: ... HTTP 502
}

This happened repeatedly within a few minutes, so temporary availability problems at the context host can prevent otherwise valid incoming activities from being processed.

Expected behavior

Processing an activity that references the FEP-ef61 context should not depend on the availability of the remote context server.

Existing fix

The FEP-ef61 context is already vendored and registered in the preloaded context loader on main, as part of #830 and #928.

However, the fix is not included in the currently maintained release branches. Could the context-preloading portion of #928 be backported to all of the following branches?

• 2.0-maintenance
• 2.1-maintenance
• 2.2-maintenance
• 2.3-maintenance

This should allow applications on every maintained Fedify release line to process documents referencing https://w3id.org/fep/ef61 without depending on the availability of the remote context server.