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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.163

Workflow Script Static Validation via AST

What

Workflow scripts are now parsed with the Acorn JavaScript parser (including the acorn-walk tree traversal library) for accurate static validation before execution.

Details
  • 'with' statements are rejected: SyntaxError: 'with' statements are not supported in workflow scripts.
  • 'await using' declarations are rejected: SyntaxError: 'await using' declarations are not supported in workflow scripts.
  • Identifiers starting with the internal prefix are rejected: SyntaxError: Identifier '<name>' is reserved.
  • import() expressions are disallowed.
  • The AST-based approach replaces simpler regex-based checks and properly handles edge cases like await inside async arrow functions with expression bodies.
Evidence

Error messages (search for "'with' statements are not supported in workflow scripts." and "'await using' declarations are not supported in workflow scripts.")

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.163 →