fix

internal/provider/selectel/selectel.go

@@ -337,10 +337,35 @@ func (c *Client) ApplyChanges(ctx context.Context, creds provider.Credentials, z
 	}
 
 	base := "/zones/" + url.PathEscape(zoneID) + "/rrset"
+	applied := 0
 	for _, d := range cs.Diffs {
 		if d.ReadOnly || d.Kind == diff.InSync {
 			continue
 		}
+		if err := c.applyOne(ctx, base, tok, idByKey, d); err != nil {
+			// Apply is not atomic: name the failing record and how many
+			// diffs already went through, so the operator can see the state.
+			return fmt.Errorf("%s (применено до ошибки: %d): %w", describeDiff(d), applied, err)
+		}
+		applied++
+	}
+	return nil
+}
+
+// describeDiff renders a diff for error messages: "add CNAME mail.x. [value]".
+func describeDiff(d diff.RecordDiff) string {
+	rec := d.Desired
+	if rec == nil {
+		rec = d.Actual
+	}
+	out := fmt.Sprintf("%s %s", d.Kind, d.Key())
+	if rec != nil {
+		out += fmt.Sprintf(" ttl=%d %q", rec.TTL, rec.Values)
+	}
+	return out
+}
+
+func (c *Client) applyOne(ctx context.Context, base, tok string, idByKey map[string]string, d diff.RecordDiff) error {
 	switch d.Kind {
 	case diff.Add:
 		if d.Desired == nil {
@@ -372,7 +397,6 @@ func (c *Client) ApplyChanges(ctx context.Context, creds provider.Credentials, z
 			return err
 		}
 	}
-	}
 	return nil
 }