Preventing aggregation pipeline to access courses inside skills

To maintain service boundaries and ensure proper separation of concerns within our microservice architecture, direct aggregation lookups ($lookup) from the skills context into the courses collection must be avoided.

    const documents = await this.model.aggregate<SkillCourseAggregateDocument>([
      {
        $lookup: {
          from: 'courses',
          let: { skillName: '$name' },
          pipeline: [
            {
              $match: {
                $expr: {
                  $in: ['$$skillName', '$skills'],
                },
              },
            },
            { $match: queryFilter },
          ],
          as: 'courses',
        },
      },
    ]);

…creates a tight coupling between the skills(inside global microservice)and

courses domains by assuming internal schema knowledge and exposing cross-context joins. This breaks the principle of encapsulation and introduces hidden dependencies that make services harder to evolve independently.