Preserve joined rendering error evidence

docs/roadmap/remediation.md

@@ -1,6 +1,6 @@
 # Invocation reporting audit remediation
 
-Status: remediation in progress; 1 of 7 findings complete.
+Status: remediation in progress; 2 of 7 findings complete.
 
 ## Review scope
 
@@ -132,7 +132,12 @@ correctly detects missing artifacts or invalid selections.
 
 ## 2. Retain independent rendering errors joined with write errors
 
-Priority: P2. Status: open.
+Priority: P2. Status: complete.
+
+- [x] Completed: joined callback errors retain independent rendering evidence,
+  while plain and wrapped sink errors remain write failures. Output and detail
+  regressions pass, including joined destination errors.
+  Validation: `GOTOOLCHAIN=local go test ./...` in the repository root.
 
 ### Finding and evidence