`\blacksquare` (and other AMS geometric symbols) with the Gyre Pagella CHTML font they get inline `font-style: italic` and are slanted by the browser

Summary

\blacksquare (U+25FC), \square/\Box (U+25FB), \lozenge/\Diamond (U+25CA), \blacklozenge, \blacktriangle, \bigstar, \checkmark, \maltese, and ~25 more AMS "miscellaneous symbol" macros are registered in the TeX input's AMSsymbols-mathchar0mi character map. mathchar0mi creates an <mi> token whose default mathvariant is italic. The CHTML (and SVG) output therefore renders these geometric symbols with italic styling:

• with the Gyre-Pagella dynamic CHTML font, the glyph node carries the inline style font-family: MJX-GP-ZERO, serif; font-style: italic;, and the browser synthesizes an oblique slant for U+25FC — the black square is visibly tilted;
• the serialized MathML is semantically wrong too: <mi>◼</mi> (italic identifier) instead of an upright ordinary symbol.

In LaTeX (amssymb), \blacksquare is \DeclareMathSymbol{\blacksquare}{\mathord}{AMSa}{"04} — a mathord, upright.

Environment

• MathJax 4.1.3
• TeX input (input/tex), ams package enabled
• CHTML output, Gyre-Pagella font (@mathjax/mathjax-pagella-font), dynamic font mode

Minimal reproduction

browser-repro.html

Observed

CHTML wraps the glyph in an italic identifier element:

<mjx-container ...><mjx-math ...><mjx-mi data-latex="\blacksquare"><mjx-c class="mjx-c25FC">◼</mjx-c></mjx-mi></mjx-math></mjx-container>

MathML:

<mi data-latex="\blacksquare">&#x25FC;</mi>

With the Gyre-Pagella font (dynamic CHTML mode), the glyph node's inline style is:

font-family: MJX-GP-ZERO, serif; font-style: italic;

and the rendered \blacksquare is visibly slanted (browser-synthesized oblique), exactly like an italic math identifier. Compare with the base-package symbol \triangle, which renders <mi mathvariant="normal">&#x25B3;</mi> (upright).

Expected

• \blacksquare renders upright — no font-style: italic, no synthetic slant.
• The serialized MathML should be an upright ordinary symbol (e.g. <mi mathvariant="normal"> or an mo with no operator spacing), matching LaTeX's \mathord class.

Coverage

Scanned eleven v4 font packages (@mathjax/mathjax-*-font@4.1.3), every variant file. "✓" = the codepoint exists in at least one variant (usually the normal variant, from which italic inherits via the prototype chain — the glyph then comes from the math font and is upright); "✗" = absent from the entire package → CHTML falls back to font-style: italic; font-family: <prefix>-ZERO, serif → browser-synthesized slant.

The eleven fonts collapse into four identical-coverage groups:

• A — TeX / new-cm (default) / modern / STIX2: best coverage, only the universal 4 missing.
• B — Asana: adds \diagup, \diagdown.
• C — Fira: misses the geometric set plus \checkmark, \maltese.
• D — Pagella / Bonum / DejaVu / Schola / Termes (Gyre family + DejaVu): misses the geometric set plus \blacktriangle, \blacktriangledown.

command	U+	A: TeX / new-cm / modern / STIX2	B: Asana	C: Fira	D: Pagella / Bonum / DejaVu / Schola / Termes
\blacksquare	25FC	✓	✓	✗	✗
\square/\Box	25FB	✓	✓	✗	✗
\lozenge/\Diamond	25CA	✓	✓	✓	✓
\blacklozenge	29EB	✓	✓	✗	✗
\blacktriangle	25B4	✓	✓	✓	✗
\blacktriangledown	25BE	✓	✓	✓	✗
\bigstar	2605	✓	✓	✗	✗
\checkmark	2713	✓	✓	✗	✓
\maltese	2720	✓	✓	✗	✓
\hslash	210F	✓	✓	✓	✓
\sphericalangle	2222	✓	✓	✓	✓
\measuredangle	2221	✓	✓	✓	✓
\nexists	2204	✓	✓	✓	✓
\complement	2201	✓	✓	✓	✓
\mho	2127	✓	✓	✓	✓
\Finv	2132	✓	✓	✗	✗
\Game	2141	✓	✓	✗	✗
\diagup	2571	✓	✗	✗	✗
\diagdown	2572	✓	✗	✗	✗
\yen	00A5	✗	✗	✗	✗
\circledR	00AE	✗	✗	✗	✗
\beth/\gimel/\daleth (letter-like)	2136–38	✓	✓	✓	✓
\digamma, \varkappa (letter-like)	03DD/03F0	✗	✗	✗	✗

Missing counts per group (of the 26 affected entries): A = 4 (\yen, \circledR, \digamma, \varkappa) · B = 6 · C = 14 · D = 14.

Start with the TeX input's AMSsymbols-mathchar0mi character map and compare the affected macros with the base-package \triangle registration. Use browser-repro.html to inspect the generated CHTML and serialized MathML for the affected symbols across the listed font packages. Done means the symbols are registered as upright ordinary symbols and no longer receive synthetic italic styling.