Bug(expr): round(x, ndigits) returns float for ndigits <= 0, contradicting RFC 0006's own signature table

[uberware]

Summary

RFC 0006's signature table for round states it returns int when ndigits <= 0, and gives
round(1234.5, -1) → 1230 as its example. The implementation returns 1230.0 :: float.

Versions

• openjd-model 0.11.1 and 0.11.2 from PyPI (both bundle openjd-expr 0.2.1)
• openjd-rs main at 1a89f3a — still reproduces

Reproduction

from openjd.expr import parse_expression
r = parse_expression("round(1234.5, -1)").evaluate_with_metrics()
print(str(r.value), str(r.value.type))   # -> 1230.0 float

Expected vs actual

Expression	Expected (RFC 0006)	Actual
round(1234.5, -1)	1230 :: int	1230.0 :: float

Why this is a bug

The spec's own signature table declares the int return for ndigits <= 0 and works this
exact input. (Python's built-in round returns a float here, so this looks like Python
behavior standing in where the spec deliberately diverges from Python.)