feat(editor): a formula reads as markup around operands

[PathGao]

Two changes to how a formula looks in the editor, one in the theme and one in the extractor. Stacked on nothing — #686 is merged and this sits on master.

What was wrong

math.marker and math both resolved to the code role, so the split the semantic layer exists to make was invisible: the $ and the formula were the same green. And the body was one flat span, so \frac and the a it applies to arrived identical.

source	before	after
$…$, $$…$$	same green as the body	markup blue, like ## and >
formula body	green, upright	green, italic
\frac, \alpha, \,, \\	body green	markup blue
{, }, _, ^, +, =	body green	body green, deliberately

Why those choices

A control sequence is markup. \frac is to a and b what ## is to a title, so it takes the marker modifier and lands on the rule that already exists. No new legend entry, no new palette colour.

Braces and scripts stay with the operands. They are markup too, and marking them was the first thing I tried: \frac{\sqrt{\pi}}{2} comes out almost entirely blue, with \pi and 2 the only green left, and the command names stop standing out. VS Code's md-math grammar ends up in the same place from the other direction — it scopes braces and operators, and the default themes give those scopes no colour at all.

The body is italic. The one thing about a formula a colour cannot say. TeX typesets variables italic, so the source and the rendered output agree at a glance. Obsidian pairs the italic with a monospace family; ITokenThemeRule has no fontFamily and Monaco's mtkN class is a per-style index rather than a per-construct one, so only half of that is reachable from a theme.

The body is covered with no gaps. A requirement, not tidiness: a range no semantic token claims keeps the Monarch grammar's colour, and the grammar has never heard of $. It reads the two underscores in x_i + y_j as an emphasis run and italicises the middle of the formula — the defect Zettlr#276 describes. the_formula_body_is_covered_whole is the test that holds it.

comrak's own math extension is off in markdown_options, so math_spans is the only thing that claims these ranges and nothing competes with the finer spans.

Cost

Two dense inline formulas on every one of 500 lines — a document far past anything real:

	spans	median parse
before	3000	3.40 ms
after	12000	4.44 ms

Prose is unchanged at 1.3 ms, and one parse is still cached per model version.

Tests

semantic.rs — a control sequence carrying the marker modifier, including the single-character \,; braces and scripts staying with the operands; the body covered with no gaps.

editorTheme.test.ts — the delimiters resolving to the same colour as every other marker and not to the body's, the body keeping the code colour, and the italic being spelled out.

Verification

npm run check         809 files, 0 errors, 0 warnings
npm test              948 pass
npm run test:vitest   376 pass
cargo test            160 pass
cargo fmt --check     clean
cargo clippy          -D warnings, clean

🤖 Generated with Claude Code