Forwarded activities are believed as far as their origin vouches

A thread's server passes on what happens in it, signed with its own key: Mastodon forwards the replies to its
accounts' posts and their deletions, Friendica every activity in its threads. PrivaPub answered them 401, which also
tells a sender its signature failed. Now they get 202 and nothing in them is believed: a forwarded Create or Update is
taken as its object reads at the actor's origin, a Delete of a public or unlisted copy once that origin answers 404 or
410 (RemoteActorService.IsGone; FederationHttp remembers the status of a refusal), anything else is let go, and our own
activities coming back are ignored. A forwarded copy has its own dedupe key, so one that failed never hides the
author's own delivery.

A reply in the thread of someone followed here is kept, as Mastodon keeps them. Mastodon delivers a reply to the
followers of the account it answers; PrivaPub dropped those as unaddressed, which the pasture showed: the outsider's
reply its Mastodon scenario said was never delivered had been, and was thrown away.

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

PrivaPub/Infrastructure/Http/FederationHttp.cs

@@ -23,6 +23,7 @@ namespace PrivaPub.Infrastructure.Http
 	{
 		bool IsAllowed(Uri target);
 		Task<FetchedJson> GetJson(string url, string accept, Action<HttpRequestMessage> sign, CancellationToken token);
+		Task<(int Status, FetchedJson Json)> GetJsonStatus(string url, string accept, Action<HttpRequestMessage> sign, CancellationToken token);
 		bool FailedTemporarily(string url);
 		Task<(Uri FinalUri, string Html)> GetPage(string url, CancellationToken token);
 		Task<HttpResponseMessage> OpenMedia(string url, System.Net.Http.Headers.RangeHeaderValue range, CancellationToken token);
@@ -295,6 +296,24 @@ namespace PrivaPub.Infrastructure.Http
 			}
 		}
 
+		// the document and the status its origin answered with (a refusal remembered from the last five minutes keeps its
+		// status; 0 when it never answered)
+		public async Task<(int Status, FetchedJson Json)> GetJsonStatus(string url, string accept, Action<HttpRequestMessage> sign, CancellationToken token)
+		{
+			if (Uri.TryCreate(url, UriKind.Absolute, out var target) && _cache.TryGetValue(NegativeKey(target), out Refusal remembered))
+				return (remembered.Status, default);
+			var exchange = new Exchange(url, HttpScope.Purpose ?? "object");
+			try
+			{
+				var json = await GetJson(url, accept, sign, exchange, token);
+				return (exchange.Status ?? 0, json);
+			}
+			finally
+			{
+				Record(exchange);
+			}
+		}
+
 		async Task<FetchedJson> GetJson(string url, string accept, Action<HttpRequestMessage> sign, Exchange exchange, CancellationToken token)
 		{
 			if (!Uri.TryCreate(url, UriKind.Absolute, out var target) || !IsAllowed(target))
@@ -367,7 +386,7 @@ namespace PrivaPub.Infrastructure.Http
 		}
 
 		public bool FailedTemporarily(string url) =>
-			Uri.TryCreate(url, UriKind.Absolute, out var target) && _cache.TryGetValue(NegativeKey(target), out bool transient) && transient;
+			Uri.TryCreate(url, UriKind.Absolute, out var target) && _cache.TryGetValue(NegativeKey(target), out Refusal refusal) && refusal.Transient;
 
 		public async Task<(byte[] Bytes, string ContentType)> GetMedia(string url, long maxBytes, CancellationToken token)
 		{
@@ -610,13 +629,15 @@ namespace PrivaPub.Infrastructure.Http
 
 		static string NegativeKey(Uri target) => "federation-http:refused:" + target.AbsoluteUri;
 
+		sealed record Refusal(bool Transient, int Status);
+
 		FetchedJson Refuse(string negativeKey, string url, string reason, Exchange exchange, string code, bool transient = false)
 		{
 			if (transient)
 				exchange.Failed(code);
 			else
 				exchange.Refused(code);
-			_cache.Set(negativeKey, transient, NegativeCacheLifetime);
+			_cache.Set(negativeKey, new Refusal(transient, exchange.Status ?? 0), NegativeCacheLifetime);
 			_logger.LogInformation("GET {Url} refused: {Reason}", url, reason);
 			return default;
 		}