Add nda signature middleware

Signed-off-by: Émile Ré <emile@getprobo.com>

pkg/esign/errors.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2025 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package esign
+
+import "errors"
+
+var (
+	ErrElectronicSignatureNotFound = errors.New("electronic signature not found")
+)

pkg/esign/service.go

@@ -17,6 +17,7 @@ package esign
 import (
 	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"strings"
 	"time"
@@ -338,6 +339,10 @@ func (s *Service) GetSignatureByID(ctx context.Context, id gid.GID) (*coredata.E
 		ctx,
 		func(conn pg.Conn) error {
 			if err := signature.LoadByID(ctx, conn, scope, id); err != nil {
+				if errors.Is(err, coredata.ErrResourceNotFound) {
+					return ErrElectronicSignatureNotFound
+				}
+
 				return fmt.Errorf("cannot load electronic signature: %w", err)
 			}