Add convergent recovery and exact staging cleanup

crates/remora-attempt/tests/mutations.rs

@@ -573,7 +573,7 @@ async fn failure_disposition_retries_with_budget_and_becomes_terminal_when_exhau
         &harness.pool,
         &first.attempt_id,
         FailureRecord {
-            class: RuntimeFailureClass::TransientTarget,
+            class: RuntimeFailureClass::TransientTarget.into(),
             disposition: FailureDisposition::Retryable,
         },
     )
@@ -623,7 +623,7 @@ async fn failure_disposition_retries_with_budget_and_becomes_terminal_when_exhau
     assert_eq!(
         exhausted.failure,
         Some(FailureRecord {
-            class: RuntimeFailureClass::Internal,
+            class: RuntimeFailureClass::Internal.into(),
             disposition: FailureDisposition::Retryable,
         })
     );