The substring check `"return " in expression` incorrectly matched
expressions that already contained an IIFE with an internal return,
causing double-wrapping and a silent None result. Guard with
`not expression.strip().startswith("(")` so pre-wrapped expressions
pass through unchanged.
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Agents naturally write js() calls with top-level `return`, which is a
syntax error in Runtime.evaluate. js() now detects `return ` and wraps
the expression in an IIFE so both styles work without callers needing
to know the CDP constraint.
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Sarath S Menon