fix: preserve diagnostic context in backend test assertions

crates/workspace-server/src/hosts.rs

@@ -8866,7 +8866,14 @@ mod tests {
             })
             .await
             .expect_err("closed session must reject local operation without another request");
-        assert!(matches!(error, WorkdirError::Unavailable(_)));
+        assert!(matches!(
+            error.classification_source(),
+            WorkdirError::Unavailable(_)
+        ));
+        assert_eq!(
+            error.failure_reason(),
+            Some(workdir::WorkdirFailureReason::SessionClosed)
+        );
         server.join().expect("mock remote server finished");
     }
 

crates/workspace-server/src/server.rs

@@ -37791,9 +37791,13 @@ mod tests {
                     )))
                     .unwrap();
             }
+            let error = write
+                .await
+                .unwrap()
+                .expect_err("mismatched or lost mutation response must remain outcome-unknown");
             assert!(matches!(
-                write.await.unwrap(),
-                Err(workdir::WorkdirError::OutcomeUnknown(_))
+                error.classification_source(),
+                workdir::WorkdirError::OutcomeUnknown(_)
             ));
         }
     }