Describe the bug
When a workflow uses a Composite Action, if several steps of the Composite Action send some content to the $GITHUB_STEP_SUMMARY, only the content from the latest step is shown in the job summary.

However, if the steps are defined inside the Workflow and not in a Composite Action, the Job Summary displays the content from all the steps.

My use case is the following one: many repositories of the organization use a shared Composite Actions that performs multiple CI-related operations. We would like each step of the Composite Action to report the outcome (e.g. human-readable junit report, compliance checks, deployments, etc.) in Markdown so that they get displayed in the Job Summary page.

To Reproduce
Since the repositories where we faced the issue are private, I've created a public repository on my account to reproduce and document the bug https://github.com/aramirez-es/test-actions-job-summary

As a summary:

• Create a workflow that uses a composite action (see the entrypoint-composite.yml)
• Build a Composite Actions with several steps that send content to the $GITHUB_STEP_SUMMARY (see the action.yml)
• Run the workflow (example)

Expected behavior
The Job Summary displays the content from all the steps in a Composite Action.

Runner Version and Platform

I tested in self-hosted runners (Linux) and Github runners (ubuntu-latest)

What's not working?

No errors but the the actual behaviour does not match with the expected one. According to the official docs,

When a job finishes, the summaries for all steps in a job are grouped together into a single job summary and are shown on the workflow run summary page.

But this is not true when the steps are inside a Composite Action. For the sake of comparison, I created another workflow that inlined all the steps from the Composite Actions, you can see how the Job Summary pages are different

• Workflow with Composite action
• Workflow with inlined steps

Job Log Output

N/A

Runner and Worker's Diagnostic Logs

N/A