Similar to how the SPACELIFT_COMMIT_BRANCH and SPACELIFT_COMMIT_SHA exist in the plugin execution environment as well as TF_VAR_spacelift_commit_branch / TF_VAR_spacelift_commit_sha, please add a SPACELIFT_COMMIT_MESSAGE / TF_VAR_spacelift_commit_message with the run.commit.message from the VCS webhook when available.