Explain invocation presentation failures

reporter.go

@@ -281,6 +281,9 @@ func (r *Reporter) finalize(outcome Outcome, completion func(*Reporter)) Outcome
 
 	state.mu.Lock()
 	if presentationFailedLocked(state) {
+		if outcome.Status == 0 && !hasExplanation(outcome.Explanation) {
+			outcome.Explanation.Message = presentationFailureMessage(state)
+		}
 		outcome = applyPresentationFailure(outcome)
 	}
 	if outcome.Status != 0 {
@@ -328,18 +331,38 @@ func applyPresentationFailure(outcome Outcome) Outcome {
 }
 
 func ensureFallbackExplanation(outcome Outcome) Outcome {
-	if outcome.Explanation.Message != "" {
+	if hasExplanation(outcome.Explanation) {
 		return outcome
 	}
-	for _, detail := range outcome.Explanation.Details {
-		if detail != nil {
-			return outcome
-		}
-	}
 	outcome.Explanation = Explanation{Message: "Command failed."}
 	return outcome
 }
 
+func hasExplanation(explanation Explanation) bool {
+	if explanation.Message != "" {
+		return true
+	}
+	for _, detail := range explanation.Details {
+		if detail != nil {
+			return true
+		}
+	}
+	return false
+}
+
+func presentationFailureMessage(state *reportingState) string {
+	switch {
+	case state.output.renderError != nil:
+		return "Unable to render command output."
+	case state.output.writeError != nil:
+		return "Unable to deliver command output."
+	case state.diagnostics.renderError != nil:
+		return "Unable to render invocation diagnostics."
+	default:
+		return "Unable to deliver invocation diagnostics."
+	}
+}
+
 func renderTerminalLocked(state *reportingState, explanation Explanation) error {
 	destination := state.destination(destinationDiagnostics)
 	destination.submitted = true