Bug: empty scripts fail before normal execution

[nholthaus]

Problem

Running an empty script file currently fails before normal execution begins instead of handling the file gracefully. This makes the runtime brittle for a simple edge case.

Specification

Handle empty script files safely.

Acceptance criteria:

• Running an empty script file does not crash.
• The runtime either exits cleanly without work or emits a single explicit user-facing error.
• Existing behavior for non-empty scripts is preserved.
• Comment-only or whitespace-only scripts are handled consistently.

Motivation

This improves runtime robustness and covers an edge case that should not require special handling by script authors.