Deliveries to followers carry a digest of them, per server

Owner decision of 2026-10-06 (FEP-8fcf). A persona's delivery addressed to its followers carries a signed
Collection-Synchronization header naming its followers, its roll-call (…/groupies/roll-call) and the digest of its
accepted followers on the receiving server only. The roll-call answers a signed request with the persona's followers
on the signer's server and nobody else's.

Mastodon gives every Undo{Follow} it sends after reading a roll-call the same id (…#follows//undo), so a second one
looked like a copy: an Undo of a Follow that comes again while the follow it ends exists again is now kept once per
follow.

Checked live (scenarios/followsync.sh): Mastodon drops a follow PrivaPub lost, and undoes one it lost itself.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

PrivaPub/Federation/Controllers/PeasantsController.cs

@@ -143,6 +143,20 @@ namespace PrivaPub.Federation.Controllers
 			return Activity(ActivityPubRenderer.OrderedCollection(local.Followers, (int)count, default));
 		}
 
+		// FEP-8fcf: the persona's followers on the server that signs the request, and nobody else's (FollowersSynchronization)
+		[HttpGet, Route("{actor}/groupies/roll-call")]
+		public async Task<IActionResult> RollCall(string actor, CancellationToken token)
+		{
+			var local = await _localActors.FindByUserName(actor, token);
+			if (local is not { IsFederated: true } || !FollowersSynchronization.Synchronizes(local))
+				return NotFound();
+			var requester = await _fetches.Requester(Request, token);
+			if (requester == default)
+				return StatusCode(StatusCodes.Status401Unauthorized);
+			var there = await FollowersSynchronization.On(local, FollowersSynchronization.Origin(requester.ActorURI), token);
+			return Activity(ActivityPubRenderer.OrderedCollection(FollowersSynchronization.RollCall(local), there.Count, there.Select(f => (JsonNode)f)));
+		}
+
 		[HttpGet, Route("{actor}/stalking")]
 		public async Task<IActionResult> Following(string actor, CancellationToken token)
 		{