As an admin writing scripts triggered on pull request events (via third party plugin "Pull Request Notification for Bitbucket"), I want the list of JIRA issues associated to the pull request.

This information is shown in the Web UI, but is not available via the "rest/api/1.0/projects/<projectKey>/repos/<repositorySlug>/pull-requests/<pullRequestId>" endpoint. That endpoint returns information such as the source branch name, pull request summary, and pull request description, which could in theory be mined for JIRA issue ids; but getting the same results as Bitbucket displays in the Web UI would mean that the same logic be implemented in the scripts – which seems fragile and error prone to me. Better for Bitbucket to provide the values it has computed itself.