`\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-*[email protected]), 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.

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