[Regression] Auto-scaling for KaTeX block is always enable regardless of @auto-scaling theme metadata

[yhatt]

Version of Marp Tool

Marp Core v3.8.0

Operating System

Other (fill out in the environment field)

Environment

• Node.js version (Marpit / Marp Core/ Marp CLI): v18.17.0

How to reproduce

Put the theme and Markdown into sandbox directory in Marp Core repository:

/* @theme test */

section {
  background: #fff;
}

---
theme: test
math: katex
---

# Auto-scaling for KaTeX <!--fit-->

$$
{1 + \frac{q^2}{(1-q)} + \frac{q^6}{(1-q)(1-q^2)} + \frac{q^{12}}{(1-q)(1-q^2)(1-q^3)} + \frac{q^{20}}{(1-q)(1-q^2)(1-q^3)(1-q^4)} + \frac{q^{30}}{(1-q)(1-q^2)(1-q^3)(1-q^4)(1-q^5)}} + \frac{q^{42}}{(1-q)(1-q^2)(1-q^3)(1-q^4)(1-q^5)(1-q^6)} + \frac{q^{56}}{(1-q)(1-q^2)(1-q^3)(1-q^4)(1-q^5)(1-q^6)(1-q^7)} + \frac{q^{72}}{(1-q)(1-q^2)(1-q^3)(1-q^4)(1-q^5)(1-q^6)(1-q^7)(1-q^8)} + \frac{q^{90}}{(1-q)(1-q^2)(1-q^3)(1-q^4)(1-q^5)(1-q^6)(1-q^7)(1-q^8)(1-q^9)} + \cdots = \prod_{j=0}^{\infty}\frac{1}{(1-q^{5j+2})(1-q^{5j+3})}, \quad\quad \text{for }\lvert q\rvert<1.
$$

And run yarn sandbox.

Expected behavior

Math block should not scale down to fit the slide, because the custom theme is not defined @auto-scaling metadata.

Actual behavior

Math block is scaling down to fit the slide.

Additional information

Reported in https://github.com/orgs/marp-team/discussions/159#discussioncomment-6955411.

This regression has been present since v3.0.0. In that version, the new auto-scaling component was produced, but the auto-scaling metadata was not taken into account.

Other scaling elements such as <!--fit--> are still following @auto-scaling correctly. In above example, <!--fit--> in the heading is just ignored by the theme.