Revert "ScriptInfo: tweak how reader field is managed"

This reverts commit 09d2e40225d37cc1c21d0707c65ba931a4c012bc.

This change introduced a critical bug in script execution.
Fix bugs in script execution and parameter parsing

The topic branch 'lazy-script-params' was not fully ready to be merged.
This commit fixes problems introduced by that unfinished work.