Edit history from formerRepresentations

Pleroma and Akkoma send a post's earlier versions with it. A post PrivaPub first meets after its edits now has its
history, and an edit that carries them brings the versions missed in between; each is read as the post itself is. The
Akkoma scenario checks a post fetched after two edits by an account no persona follows.

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

PrivaPub.Tests/Federation/FormerRepresentationsTests.cs

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+using MongoDB.Entities;
+
+using PrivaPub.Federation.Objects;
+using PrivaPub.Models.Post;
+using PrivaPub.Models.Social;
+using PrivaPub.Tests.Support;
+
+using System.Text.Json.Nodes;
+
+namespace PrivaPub.Tests.Federation
+{
+	// Pleroma's and Akkoma's edited posts carry their earlier versions (formerRepresentations): a post first met after its
+	// edits has its history, and an edit tells the ones missed in between
+	[Trait("Category", "Integration")]
+	public sealed class FormerRepresentationsTests : IAsyncLifetime
+	{
+		Harness _harness;
+
+		public async ValueTask InitializeAsync()
+		{
+			Assert.SkipUnless(MongoFixture.Enabled, MongoFixture.Skip);
+			_harness = await Harness.Start();
+		}
+
+		public async ValueTask DisposeAsync()
+		{
+			if (_harness != default)
+				await _harness.DisposeAsync();
+		}
+
+		static string Origin(RemoteActor actor) => new Uri(actor.Id).GetLeftPart(UriPartial.Authority);
+		static readonly DateTime Start = DateTime.UtcNow.AddHours(-1);
+
+		static JsonObject Version(string text, int minutes) => new()
+		{
+			["type"] = "Note", ["content"] = $"<p>{text}</p>", ["published"] = Start.ToString("O"),
+			["updated"] = minutes == 0 ? default : Start.AddMinutes(minutes).ToString("O")
+		};
+
+		async Task<(RemoteActor Carol, JsonObject Note)> Followed(string text, int minutes, params JsonObject[] former)
+		{
+			var token = TestContext.Current.CancellationToken;
+			var (_, alice) = await _harness.Persona("alice");
+			var carol = new RemoteActor(_harness.Peer, "carol");
+			await DB.Default.SaveAsync(new Following { AvatarId = alice.Id, TargetActorURI = carol.Id, State = FollowState.Accepted }, token);
+			var note = Version(text, minutes);
+			note["id"] = $"{Origin(carol)}/objects/{Guid.NewGuid():N}";
+			note["attributedTo"] = carol.Id;
+			note["to"] = new JsonArray(Addressing.Public);
+			note["cc"] = new JsonArray($"{carol.Id}/followers");
+			if (former.Length > 0)
+				note["formerRepresentations"] = new JsonObject { ["type"] = "OrderedCollection", ["totalItems"] = former.Length, ["orderedItems"] = new JsonArray(former) };
+			return (carol, note);
+		}
+
+		Task Deliver(RemoteActor carol, string type, JsonObject note) => _harness.Deliver(carol, "/human-centipede", new JsonObject
+		{
+			["id"] = $"{Origin(carol)}/activities/{Guid.NewGuid():N}", ["type"] = type, ["actor"] = carol.Id,
+			["to"] = new JsonArray(Addressing.Public), ["object"] = note.DeepClone()
+		});
+
+		Task<Post> Stored(JsonObject note) =>
+			DB.Default.Find<Post>().Match(p => p.ObjectURI == note["id"]!.GetValue<string>()).ExecuteSingleAsync(TestContext.Current.CancellationToken);
+
+		[Fact]
+		public async Task A_post_first_met_after_its_edits_has_its_history()
+		{
+			var (carol, note) = await Followed("third", 40, Version("second", 20), Version("first", 0));
+
+			await Deliver(carol, "Create", note);
+
+			var post = await Stored(note);
+			Assert.Equal(["<p>first</p>", "<p>second</p>"], post.Revisions.Select(r => r.ContentHtml));
+			Assert.Equal("<p>third</p>", post.ContentHtml);
+		}
+
+		[Fact]
+		public async Task An_edit_tells_the_versions_missed_in_between()
+		{
+			var (carol, note) = await Followed("first", 0);
+			await Deliver(carol, "Create", note);
+
+			var edited = (JsonObject)note.DeepClone();
+			edited["content"] = "<p>third</p>";
+			edited["updated"] = Start.AddMinutes(40).ToString("O");
+			edited["formerRepresentations"] = new JsonObject
+			{
+				["type"] = "OrderedCollection", ["totalItems"] = 2, ["orderedItems"] = new JsonArray(Version("second", 20), Version("first", 0))
+			};
+			await Deliver(carol, "Update", edited);
+
+			var post = await Stored(note);
+			Assert.Equal(["<p>first</p>", "<p>second</p>"], post.Revisions.Select(r => r.ContentHtml));
+			Assert.Equal("<p>third</p>", post.ContentHtml);
+		}
+	}
+}