Function domain union syntax falls back to full real-line domain

[dqnykamp]

Summary

<function> domains do not currently support union syntax in attribute text (for example domain="(-4,-1) union (1,4)").

When this syntax is used, parsing fails and the function falls back to an all-real-line domain.

Reproduction

<graph renderer="doenet" name="g">
  <shortDescription>test graph</shortDescription>

  <function domain="(-4,-1) union (1,4)">x^2</function>
</graph>

Actual behavior

• The function appears defined everywhere.
• The function's domain state value appears to be the full real line.
• Warnings include:
  • Insufficient dimensions for domain for function. Domain has 0 intervals but the function has 1 input.
  • Invalid format for domain for function.

Expected behavior

For single-variable functions, union domains should be accepted and enforced, so the function is only defined on (-4,-1) ∪ (1,4).

Source analysis

Two places contribute to the fallback behavior:

1. packages/doenetml-worker-javascript/src/components/IntervalList.js

• breakEmbeddedStringsIntoIntervalPieces rejects non-whitespace tokens at top level, so union causes parse failure.

2. packages/doenetml-worker-javascript/src/components/Function.js

• Domain validation expects one interval per input dimension and only accepts trees with root "interval".
• On mismatch/invalid format, it emits warnings and falls back to infinite domain.

Impact

This issue is in shared function domain state computation (not specific to a single renderer).