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/Federation/Outbox/DeliveryService.cs

@@ -258,7 +258,11 @@ namespace PrivaPub.Federation.Outbox
 					_logger.LogInformation("Delivery to {Inbox} refused with {Status}", payload.Inbox, status);
 					return JobOutcome.Dead($"{status} {response.ReasonPhrase}");
 				}
-				await _breaker.Failed(job.Host, $"{status}", token);
+				// a gateway's 502, 503 or 504 says the server behind it is down, which counts against the host; any other 5xx
+				// says the server is up and failed on this activity (Smithereen's 500 on a document its JSON-LD reader
+				// refused), retried on its own while the host's other deliveries go on
+				if (status is 502 or 503 or 504)
+					await _breaker.Failed(job.Host, $"{status}", token);
 				return JobOutcome.Retry($"{status} {response.ReasonPhrase}");
 			}
 			catch (BlockedDestinationException ex)