A boost or a favourite given again is sent again

Every boost of a post was announce-{post}, and every favourite like-{post}:
after an Undo, giving it again made the same activity id, which the
delivery queue had already delivered and dropped (and a server that
remembers ids would ignore). Found by decePub's e2e actions against the
pasture, which unboost and boost again. Now each boost and favourite is an
activity of its own, as Mastodon's are, and an Undo names the one it ends;
a concurrent second boost is removed after saving. An edit's Update is
named to the millisecond, a quote approval's to the tick.

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

PrivaPub.Tests/Http/FederationGetTests.cs

@@ -170,7 +170,7 @@ namespace PrivaPub.Tests.Http
 			var announce = items[0];
 			Assert.Equal("Announce", announce["type"]!.GetValue<string>());
 			Assert.Equal(reblog.ObjectURI, announce["id"]!.GetValue<string>());
-			Assert.Equal($"{persona.ActorUri()}/grunts/announce-{boosted.ID}", announce["id"]!.GetValue<string>());
+			Assert.Equal($"{persona.ActorUri()}/grunts/announce-{reblog.ID}", announce["id"]!.GetValue<string>());
 			Assert.Equal(boosted.ObjectURI, announce["object"]!.GetValue<string>());
 			Assert.Equal(persona.ActorUri(), announce["actor"]!.GetValue<string>());
 
@@ -436,7 +436,7 @@ namespace PrivaPub.Tests.Http
 			string Path(string id) => $"/peasants/{persona.UserName}/grunts/{id}";
 
 			var create = await _client.Fetch(Path($"create-{post.ID}"));
-			var announce = await _client.Fetch(Path($"announce-{original.ID}"));
+			var announce = await _client.Fetch(Path($"announce-{reblog.ID}"));
 
 			Assert.Equal(HttpStatusCode.OK, create.Status);
 			Assert.Equal(ActivityJson, create.MediaType);
@@ -451,7 +451,8 @@ namespace PrivaPub.Tests.Http
 
 			foreach (var unknown in new[] { $"create-{followersOnly.ID}", $"create-{Guid.NewGuid():N}"[..31], $"announce-{post.ID}", $"like-{post.ID}", "x" })
 				Assert.Equal(HttpStatusCode.NotFound, (await _client.Fetch(Path(unknown))).Status);
-			Assert.Equal(HttpStatusCode.NotFound, (await _client.Fetch($"/peasants/{friend.UserName}/grunts/announce-{original.ID}")).Status);
+			Assert.Equal(HttpStatusCode.NotFound, (await _client.Fetch(Path($"announce-{original.ID}"))).Status);
+			Assert.Equal(HttpStatusCode.NotFound, (await _client.Fetch($"/peasants/{friend.UserName}/grunts/announce-{reblog.ID}")).Status);
 		}
 
 		[Fact]