Safer script evaluation #6208

Summary

Implement safer script evaluation by running user-defined scripts in a well-defined, restrictive execution environment.

Proposed Changes

1. Restrictive evaluation environment

Evaluate scripts in a well-defined restrictive environment that only includes access to:

• refs
• Bundled libraries
• state
• queueEvents
• addEvents

2. New script registration interface

Introduce a new interface for script execution: register a script snippet as a function that gets written out to utils/scripts.js. This provides a centralized, inspectable location for all registered script functions.

3. Python-side Var for the execution environment

Create a python-side Var that represents the execution environment, so that script snippets can reference names like refs or addEvents correctly and with proper type awareness.