Font, licence, and the metrics half of Tier 3.
The bundled font is Latin Modern Math under the GUST Font License, added as
fonts/GUST-FONT-LICENSE.txt — deliberately a separate file from fonts/OFL.txt,
which covers JetBrains Mono only. GFL is LPPL-derived, not the SIL OFL; the
framing's F6 corrected that error and this is the discharge. At 733,736 bytes
the font is now the largest embedded asset in the repository.
ttf-parser is declared with default-features = false and only
"opentype-layout". Verified differentially: the ttf-parser feature set from
`cargo tree -e features` is byte-identical with and without this dependency
line, so the declaration widens nothing and forces no rebuild of the font
chain.
That check also corrected acceptance 17, which asserted `std` would be absent.
It is not — fontdb already enables it via `std = ["ttf-parser/std"]`, upstream
and independent of us. As written the criterion would have failed a correct
implementation, so it is now stated as the differential property that actually
matters.
MathConstants reads only what the Q#MS2 subset needs — axis height, script
scale percent, the two script shifts, and fraction rule thickness. Reading
more would be speculative: constants for deferred constructs have no consumer
to validate them, which is the Q#LX5 discipline applied to metrics. A font
with no MATH table is a typed error rather than plausible-looking zeros, so a
bundled-font regression cannot be silent (Q#MS7).
math_italic implements TeX's convention as the framing's table states it:
ASCII letters and lowercase Greek italic, uppercase Greek upright, digits and
operators unchanged, with U+210E for `h` because the 1D4xx run has a hole
there and arithmetic would land on a reserved codepoint.
Five tests, all against the real embedded bytes rather than fixtures, since B5
is the bet that would sink Tier 3 if false. One goes beyond the framing: every
italic mapping must resolve to a glyph the bundled font actually has, because
a mapping that produced tofu would be worse than the roman fallback it
replaces.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Four findings, one of them a real gap.
R2-2 is the substantive one. Rev 2's math-italic fix stopped at ASCII, which
reintroduced the same defect one symbol over: the parser resolves \alpha to
U+03B1, so $\alpha x$ would have drawn an upright alpha beside an italic x —
mixed styles inside a single expression, with the Greek seed map being the
slice's second flagship case after x^2. The mapping now follows TeX's actual
convention and states it as a table: ASCII letters and lowercase Greek in math
italic (U+1D434 and U+1D6FC runs, with the U+210E hole for h), uppercase Greek
deliberately upright, digits and operators unchanged. Acceptance 13 gains
$\alpha$ and $\Gamma$ cases so the uniformity is pinned rather than assumed.
R2-1 was self-inflicted: rev 2's Q#MS3 rewrite added a corrected copy of the
tree-sitter paragraph without deleting the original, leaving the stale rev-1
text immediately below the new one. Removed.
R2-4 sharpens Q#MS11 from "covers" to "intersects". For selections the
distinction is vacuous, but a search match can genuinely half-overlap a span —
searching "2$ af" in "before $x^2$ after" matches from inside the span to
outside it — and the whole-rectangle rule must apply there too, since the box
has no interior byte map to place a partial wash against.
R2-3 moves the follow-up section after prior art; the sections now run 0
through 9 in order.
Acceptance 12 also absorbs a round-2 non-finding: the reviewer's arithmetic
puts \frac{a}{b} near 0.85 and suggests \frac{x^2}{y} also clears the 0.6
floor, so the fallback case has to be computed against the real font rather
than guessed — otherwise the fallback half of the test surprise-passes by
rendering. The criterion now says so and asks for the computed scale to be
pinned.
Framing only; no implementation, no runtime code.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Nine findings, two of them decisions the implementation could not have
proceeded without, one a compliance error. Two rev-1 claims were wrong rather
than imprecise and are withdrawn where they occur.
F1, the fraction height budget, was hidden inside "a box that would exceed the
line" without saying width or height. Lines cannot grow — metrics are uniform
at 16 px over a 22 px line — and a textstyle fraction does not fit. Q#MS10 now
picks fit-to-line scaling with a 0.6x floor and source fallback below it,
records why overdraw and line growth were rejected, and states the honest
consequence: v0 shrinks nested math uniformly where TeX would use style
levels. B6 makes the floor falsifiable against the flagship case.
F3 was a genuine contradiction: acceptance 10 demanded source-width boxes
while Q#MS4 implied layout-chosen width, and that gap IS the caret-toggle
reflow question. Resolved for layout-chosen, because pinning to source width
leaves every fraction sitting in a large permanent gap, whereas reflow is
transient and tied to a deliberate caret move. Acceptance 10 is rewritten to
bound it rather than forbid it.
F2 withdrew the zero-glyph strut: a RichChunk's only width is its text, so the
mechanism is the SourceTab precedent — projected spacer text, width quantized
to whole advances. B1 is restated against the mechanism that exists.
F5 would have bitten real prose immediately: the rev-1 rule renders "prices
are $5 and $6 today" as math. Pandoc currency guards adopted, spans confined
to one line, both in acceptance.
F6 is factual and a licence matter. Latin Modern Math is the GUST Font
License, not OFL, and is 733,736 bytes rather than ~200 KB — verified against
a local TeX Live copy. The bundled licence file must say GFL, and this becomes
the largest embedded asset in the repo. The parent framing carries the same
error; correcting it is recorded as a follow-up rather than done here, since
the parent is already merged.
F4 names the new shaping-invalidation edge as the #120 trap class, including
that suppression must read the effective caret or flap during optimistic
typing. F7 puts math italic in scope, without which the flagship case renders
a roman x. F8 clarifies that glyph IDs are still resolved internally and that
drawing must pin Attrs to the math family. F9 closes the smaller gaps: the
detection hook wording, an overlay rule for selections and washes, degradation
of deferred display syntax, and folding Char/Symbol.
Framing only; no implementation, no runtime code.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
The obvious next unit was Tier 2 (parser) plus Tier 3 (layout). This framing
rejects that for the arc's own reason: the substrate lane's Q#LX5 refused to
land the parser ahead of layout because MathNode's shape is only validated by
a consumer, and that argument does not stop at Tier 2. MathBox is only
validated once a renderer consumes it, so Tiers 2+3 with no Tier 4 reproduce
the same objection one layer up.
The unit is therefore thin and vertical: characters, sub/superscript and
fractions, detected, parsed, laid out against a real OpenType MATH table, and
drawn — with breadth deferred to follow-on work against an API that has been
exercised rather than only designed.
The scout also found a load-bearing error in the parent's integration table.
It places math_parse.rs and math_layout.rs in the core crate, which cannot
work: pmacs-gpu depends only on pmacs-protocol and never on pmacs, so a
core-crate parser is unreachable from the frontend that renders it, and
ttf-parser reaches only pmacs-gpu. Both also contradict the parent's own
"instance never learns a pixel" contract and its "pure frontend
responsibility in v0" protocol section. Q#MS1 moves both modules into
pmacs-gpu.
Two decisions buy the slice most of its simplicity. Rendering is suppressed
whenever the caret is inside a span, which makes editing-shows-source and
moving-away-renders mutually exclusive states and removes the
caret-inside-math problem rather than approximating it. And layout positions
characters rather than glyph IDs, which is sufficient for this subset and
explicitly does not generalise: glyph variants are what stretchy fences and
big operators need, and both are deferred.
Acceptance puts every claim that something reaches the screen on real pixels
through the existing headless render seam, because a layout engine wired to
nothing would pass any weaker test.
Framing only; no implementation, no runtime code.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Levi Neuwirth