Problem Statement

Currently, default variables like BITBUCKET_BRANCH, BITBUCKET_COMMIT, and others are unavailable when pipelines are triggered by webhooks (e.g., pull request created/updated or push events) during the preparsing phase of Bitbucket Pipelines because these variables are only defined after the pipeline is created. 

This limitation prevents developers from dynamically configuring pipelines based on these default variables during pre-parsing.

Proposed Solution for the Feature Request:

Provide support for default variables (e.g., BITBUCKET_BRANCH, BITBUCKET_COMMIT etc.) during the preparsing phase, even when pipelines are triggered by webhooks (pull requests or push events).

Ensure these variables are initialized earlier in the pipeline lifecycle, so they are accessible during preparsing.