Propagate DB errors from findGmailSource instead of masking as nil

A query failure in GetSourcesByIdentifier was silently converted to
"account not found" with exit code 0. Now findGmailSource returns
an error, and verify propagates it.

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

Author: wesm

cmd/msgvault/cmd/addaccount.go

@@ -145,21 +145,22 @@ Examples:
 
 func findGmailSource(
 	s *store.Store, email string,
-) *store.Source {
+) (*store.Source, error) {
 	sources, err := s.GetSourcesByIdentifier(email)
 	if err != nil {
-		return nil
+		return nil, fmt.Errorf("look up sources for %s: %w", email, err)
 	}
 	for _, src := range sources {
 		if src.SourceType == "gmail" {
-			return src
+			return src, nil
 		}
 	}
-	return nil
+	return nil, nil
 }
 
 func hasGmailSource(s *store.Store, email string) bool {
-	return findGmailSource(s, email) != nil
+	src, _ := findGmailSource(s, email)
+	return src != nil
 }
 
 func init() {

cmd/msgvault/cmd/verify.go

@@ -92,7 +92,10 @@ Examples:
 		// under the identifier from add-account. Filter to Gmail
 		// specifically since the same identifier may exist for
 		// other source types (mbox, imap).
-		source := findGmailSource(s, email)
+		source, err := findGmailSource(s, email)
+		if err != nil {
+			return fmt.Errorf("get source: %w", err)
+		}
 		if source == nil {
 			fmt.Printf("Gmail account %s not found in database.\n", email)
 			fmt.Println("Run 'sync-full' first to populate the archive.")