Fix cross-team search from: filter not working (#31277)

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/store/sqlstore/post_store.go

@@ -2079,11 +2079,18 @@ func (s *SqlPostStore) buildSearchPostFilterClause(teamID string, fromUsers []st
 	}
 
 	// Sub-query builder.
-	sb := s.getSubQueryBuilder().Select("Id").From("Users, TeamMembers").Where(
-		sq.And{
-			sq.Eq{"TeamMembers.TeamId": teamID},
-			sq.Expr("Users.Id = TeamMembers.UserId"),
-		})
+	sb := s.getSubQueryBuilder().Select("Id")
+	if teamID == "" {
+		// Cross-team search: don't filter by team membership
+		sb = sb.From("Users")
+	} else {
+		// Team-scoped search: filter by team membership
+		sb = sb.From("Users, TeamMembers").Where(
+			sq.And{
+				sq.Eq{"TeamMembers.TeamId": teamID},
+				sq.Expr("Users.Id = TeamMembers.UserId"),
+			})
+	}
 	sb = s.buildSearchUserFilterClause(fromUsers, false, userByUsername, sb)
 	sb = s.buildSearchUserFilterClause(excludedUsers, true, userByUsername, sb)
 	subQuery, subQueryArgs, err := sb.ToSql()