fix(mailparser): kaputte/truncated Multipart-Mails partiell indexieren statt scheitern

Bei NextPart()-Fehler (EOF, malformed header) wird der bereits geparste Inhalt
zurückgegeben statt der gesamte Parse abgebrochen. parseMultipart() gibt keinen
Fehler mehr zurück — partieller Text/HTML ist besser als gar kein Index-Eintrag.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pkg/mailparser/parser.go

@@ -180,9 +180,9 @@ func Parse(raw []byte) (*ParsedMail, error) {
 
 	if strings.HasPrefix(mediaType, "multipart/") {
 		boundary := params["boundary"]
-		if err := parseMultipart(pm, msg.Body, boundary); err != nil {
-			return nil, fmt.Errorf("mailparser: multipart: %w", err)
-		}
+		// Ignore parse errors — return partial content instead of failing completely.
+		// Malformed/truncated multipart emails still get metadata + whatever parts parsed.
+		parseMultipart(pm, msg.Body, boundary) //nolint:errcheck
 	} else {
 		body, _ := io.ReadAll(msg.Body)
 		decoded := decodeBody(body, msg.Header.Get("Content-Transfer-Encoding"))
@@ -198,15 +198,14 @@ func Parse(raw []byte) (*ParsedMail, error) {
 }
 
 // parseMultipart walks MIME parts and fills text, html, and attachments.
-func parseMultipart(pm *ParsedMail, body io.Reader, boundary string) error {
+// Truncated or malformed parts are skipped — partial content is better than nothing.
+func parseMultipart(pm *ParsedMail, body io.Reader, boundary string) {
 	mr := multipart.NewReader(body, boundary)
 	for {
 		part, err := mr.NextPart()
-		if err == io.EOF {
-			break
-		}
 		if err != nil {
-			return err
+			// io.EOF = normal end; any other error = truncated/malformed — stop here.
+			break
 		}
 
 		ct := part.Header.Get("Content-Type")
@@ -244,9 +243,7 @@ func parseMultipart(pm *ParsedMail, body io.Reader, boundary string) error {
 
 		// Nested multipart
 		if strings.HasPrefix(mediaType, "multipart/") {
-			if err := parseMultipart(pm, bytes.NewReader(decoded), params["boundary"]); err != nil {
-				return err
-			}
+			parseMultipart(pm, bytes.NewReader(decoded), params["boundary"])
 			continue
 		}
 
@@ -257,7 +254,6 @@ func parseMultipart(pm *ParsedMail, body io.Reader, boundary string) error {
 			pm.HTMLBody += string(decoded)
 		}
 	}
-	return nil
 }
 
 // decodeCharset converts data from the declared MIME charset to UTF-8.