Our @context stays JSON-LD 1.0, and a 500 no longer takes a host out

The proof term added with integrity proofs had a @graph container, which only JSON-LD 1.1 knows: Smithereen's reader
refused every document carrying our context with a 500. Those 500s, retried, then put Smithereen's host in quarantine
for an hour, and every delivery to it waited. Proofs are canonicalised as JSON (JCS), so the term loses nothing as a
plain id; a test keeps every term within 1.0. Only an unreachable host, a timeout or a gateway's 502, 503 or 504 now
counts against a host: a 500 is the server failing on that one activity, retried on its own.

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

PrivaPub.Tests/Federation/ContextTests.cs

@@ -0,0 +1,32 @@
+using PrivaPub.Federation.Rendering;
+
+using System.Text.Json.Nodes;
+
+namespace PrivaPub.Tests.Federation
+{
+	// The @context on everything we send. Readers that expand JSON-LD 1.0 (Smithereen) refuse a whole document over one
+	// term only 1.1 knows, so every term stays within 1.0
+	public class ContextTests
+	{
+		static readonly string[] Containers10 = ["@list", "@set", "@index", "@language"];
+		static readonly string[] Keywords11 = ["@version", "@protected", "@propagate", "@import", "@nest", "@prefix", "@context", "@direction", "@json"];
+
+		[Fact]
+		public void Every_term_is_json_ld_1_0()
+		{
+			var terms = ActivityPubRenderer.Context().OfType<JsonObject>().Single();
+
+			foreach (var (name, definition) in terms)
+			{
+				if (definition is not JsonObject term)
+					continue;
+				if (term["@container"] is JsonValue container)
+					Assert.True(Containers10.Contains(container.GetValue<string>()), $"{name}: @container {container} is JSON-LD 1.1");
+				Assert.True(term["@container"] is null or JsonValue, $"{name}: an array of containers is JSON-LD 1.1");
+				Assert.DoesNotContain(term.Select(p => p.Key), Keywords11.Contains);
+				Assert.NotEqual("@json", term["@type"]?.GetValue<string>());
+			}
+			Assert.DoesNotContain(terms.Select(p => p.Key), Keywords11.Contains);
+		}
+	}
+}

PrivaPub.Tests/Federation/JobHandlerTests.cs

@@ -666,6 +666,27 @@ namespace PrivaPub.Tests.Federation
 			Assert.StartsWith("500", broken.Error);
 		}
 
+		// a server that fails on one activity is up: its 500s are that delivery's to retry, and only a gateway's 502, 503 or
+		// 504 counts towards taking the host out (Smithereen's 500s on documents it could not read once held every delivery
+		// to it back for an hour)
+		[Fact]
+		public async Task Only_a_gateways_failures_take_the_host_out()
+		{
+			var (_, alice) = await _harness.Persona("alice");
+			_harness.Peer.Answer("/broken/inbox", 500);
+			_harness.Peer.Answer("/gateway/inbox", 502);
+
+			for (var i = 0; i < HostCircuitBreaker.Threshold; i++)
+				await Attempt(alice, _harness.Peer.A + "/broken/inbox");
+			var stillTried = await Attempt(alice, _harness.Peer.A + "/broken/inbox");
+			for (var i = 0; i < HostCircuitBreaker.Threshold; i++)
+				await Attempt(alice, _harness.Peer.A + "/gateway/inbox");
+			var heldBack = await Attempt(alice, _harness.Peer.A + "/broken/inbox");
+
+			Assert.Equal((JobResult.Retry, "500"), (stillTried.Result, stillTried.Error[..3]));
+			Assert.Equal((JobResult.Defer, "the host is unavailable"), (heldBack.Result, heldBack.Error));
+		}
+
 		// Mastodon's 422 for two first contacts racing to create one account, and its 409 for a held lock, are retried a
 		// few times; the third refusal is final like any other
 		[Fact]