${}{"val"} pattern in add {prop: ${}{"val"}} uses two consecutive brace
groups: empty ${} followed by {"val"} for the actual expression. The prior
fix called parse-expr when already at the brace-close of the empty group,
returning nil. New fix: detect empty ${} (brace-open then brace-close),
skip the close, then read the actual value from the following {…} block.
Also handles non-empty ${expr} directly as before.
Suite hs-upstream-add: 17/19 → 18/19. Smoke 0-195: 174/195 → 175/195.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
giles
5a76a04010