Preserve joined rendering error evidence

reporter.go

@@ -3,6 +3,7 @@ package commandkit
 import (
 	"errors"
 	"io"
+	"reflect"
 	"strings"
 	"sync"
 
@@ -475,13 +476,46 @@ func finishRenderLocked(state *reportingState, destination reportingDestination,
 }
 
 func recordRendererErrorLocked(state *reportingState, destination reportingDestination, renderErr, writeErr error) error {
-	if renderErr == nil || (writeErr != nil && errors.Is(renderErr, writeErr)) {
+	if renderErr == nil || (writeErr != nil && propagatesOnlyWriteError(renderErr, writeErr)) {
 		return nil
 	}
 	state.recordRenderErrorLocked(destination, renderErr)
 	return renderErr
 }
 
+// A joined callback error may contain both a writer failure and independent
+// rendering evidence. Walk each branch once rather than discarding the entire
+// error merely because errors.Is finds the writer failure somewhere in it.
+func propagatesOnlyWriteError(err, writeErr error) bool {
+	for err != nil {
+		if reflect.TypeOf(err).Comparable() && err == writeErr {
+			return true
+		}
+		switch wrapped := err.(type) {
+		case interface{ Unwrap() []error }:
+			found := false
+			for _, child := range wrapped.Unwrap() {
+				if child != nil {
+					found = true
+					if !propagatesOnlyWriteError(child, writeErr) {
+						return false
+					}
+				}
+			}
+			if found {
+				return true
+			}
+		case interface{ Unwrap() error }:
+			if child := wrapped.Unwrap(); child != nil {
+				err = child
+				continue
+			}
+		}
+		return errors.Is(err, writeErr)
+	}
+	return false
+}
+
 func combineOperationErrors(renderErr, writeErr error) error {
 	switch {
 	case renderErr == nil: