fix: support stdin scripts and preserve JS IIFE returns

[Lhy099]

Summary

• Allow browser-harness to execute scripts from stdin/heredoc when no -c flag is provided
• Preserve existing -c behavior without reading stdin
• Make helpers.js() retry IIFE wrapping only after an Illegal return statement error, so valid IIFEs keep their return value

---

Summary by cubic

Adds stdin/heredoc script support to browser-harness when no -c is provided. Tightens helpers.js() to only auto-wrap on "Illegal return statement" when it’s a SyntaxError, preserving valid IIFE return values.

• New Features

  • browser-harness executes code from stdin when run with no args.
  • -c behavior is unchanged and never reads stdin.
  • Prints a concise usage message for invalid or empty input.

• Bug Fixes

  • helpers.js() retries with an IIFE only when "Illegal return statement" is a SyntaxError; runtime Error messages are not retried.
  • Valid IIFEs are evaluated as-is and keep their return value; simple expressions still pass through.

^{Written for commit 9b9fb48. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 4 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="helpers.py">

<violation number="1" location="helpers.py:213">
P2: Broad string matching for retry can re-run side-effectful JS when unrelated runtime errors include "Illegal return statement".</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review, or fix all with cubic.}