fix: preserve result recovery decode and filesystem causes

internal/agent/recovery_logging_test.go

@@ -86,6 +86,34 @@ func TestRecoveryLogsGrantCauseIdentityAndPersistedBackoff(t *testing.T) {
 	}
 }
 
+func TestResultJournalLogsOriginalDecodeCause(t *testing.T) {
+	out := captureRecoveryLogs(t)
+	j := ResultJournal{Root: privateRecoveryRoot(t)}
+	entry := ResultEntry{SourceEventID: "corrupt-result-event", DispatcherID: "11111111-1111-4111-8111-111111111111", TenantID: 1, Payload: []byte(`{"recording":{}}`)}
+	if err := j.SaveReady(entry); err != nil {
+		t.Fatal(err)
+	}
+	path, err := j.path(entry.SourceEventID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = os.WriteFile(path, []byte("{"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	err = j.Recover(context.Background(), func(context.Context, ResultEntry) error { return nil })
+	if err == nil || !strings.Contains(err.Error(), "unexpected end of JSON input") {
+		t.Fatalf("original decode reason was hidden: %v", err)
+	}
+	for _, part := range []string{"decode_original_result", "unexpected end of JSON input", "event_digest"} {
+		if !strings.Contains(out.String(), part) {
+			t.Fatalf("missing %s: %s", part, out.String())
+		}
+	}
+	if _, err = os.Stat(path); err != nil {
+		t.Fatal("corrupt original file must remain", err)
+	}
+}
+
 func TestResultJournalLogsIndividualCauseAndOriginalIdentity(t *testing.T) {
 	out := captureRecoveryLogs(t)
 	j := ResultJournal{Root: privateRecoveryRoot(t)}

internal/agent/result_journal.go

@@ -223,8 +223,12 @@ func (j ResultJournal) RecoverWithEnd(ctx context.Context, confirmEnd, report fu
 			continue
 		}
 		info, err := os.Lstat(path)
-		if err != nil || !info.Mode().IsRegular() || info.Mode().Perm()&0077 != 0 || info.Size() > 1<<20 {
-			block("validate_result_file", errors.New("private result file is invalid"))
+		if err != nil {
+			block("stat_result_file", err)
+			continue
+		}
+		if !info.Mode().IsRegular() || info.Mode().Perm()&0077 != 0 || info.Size() > 1<<20 {
+			block("validate_result_file", fmt.Errorf("private result file is invalid: mode=%s size=%d", info.Mode(), info.Size()))
 			continue
 		}
 		data, err := os.ReadFile(path)
@@ -236,7 +240,7 @@ func (j ResultJournal) RecoverWithEnd(ctx context.Context, confirmEnd, report fu
 			SourceEventID string `json:"source_event_id"`
 		}
 		if err := json.Unmarshal(data, &id); err != nil {
-			block("decode_original_result", errors.New("invalid private result journal"))
+			block("decode_original_result", fmt.Errorf("invalid private result journal: %w", err))
 			continue
 		}
 		entry, originalPath, err := j.load(id.SourceEventID)