[meutex]

Problem

Chat math rendering falls back to raw TeX whenever a formula contains an unescaped %, a character models routinely emit in labels such as \text{3.18% dividend yield}. TeX treats % as a comment, so KaTeX rejects the formula, and MathTypeset swaps in the source fallback that was built for unfinished streaming formulas — so a finished message is stuck showing raw \[ ... \] TeX forever.

Change

MathTypeset.typeset() keeps its first katex.renderToString attempt exactly as before (throwOnError: true, same options). Only when that throws does it retry once with every unescaped % escaped to \% (tex.replace(/(^|[^\\])%/g, "$1\\%")), and it still falls back to the raw source only if the retry also throws. Already-escaped \% is left alone, and a formula with nothing to escape (no %, or only already-escaped ones) is not re-parsed. The cache key stays ${display?'display':'inline'}:${tex} and the repaired html is stored under the authored formula's key, so the repair is parsed at most once; failures still cache "". The data-markdown-copy payload and source fallback markup are unchanged.

Scope and approval

PR against meutex/t3code (this fork), triaged from the upstream report pingdotgg#29493. This qualifies under CONTRIBUTING.md's "very small, focused fix for an obvious bug" exception: one production file (apps/web/src/components/chat/MathTypeset.tsx) plus its existing browser test, fixing a single character that otherwise leaves a finished equation permanently raw. Desktop inherits the fix because it wraps apps/web. The mobile native renderer (apps/mobile / RaTeX) is out of scope and needs a separate check.

Verification

• Failing test first: with the source fix temporarily reverted, typesets a display equation whose label has an unescaped percent fails on the raw \[ ... \] source (AssertionError: expected '\[\nR_e=\underbrace{...9.18\%...' to contain '9.18%'). With the fix it passes.
• Focused test, run from apps/web: vp test run src/components/chat/MarkdownMath.browser.test.tsx — 2 passed (1 existing + 1 new).
• vp run check:changed: format ✓, lint ✓ (0 warnings / 0 errors), knip ✓, typecheck (2 packages) ✓, test (1 file) ✓, react compiler ✓.
• Not checked: repo-wide suites (vp check, vp run -r test, vp run -r typecheck are reserved for CI per AGENTS.md), the mobile RaTeX path, and before/after screenshots (the sandbox cannot capture browser screenshots).

Forge (meutex[bot]) — the model and harness that did the work.

Closes #1793641966

[meutex]

PR ready: #1 — fix(web): equations with an unescaped percent now typeset.

MathTypeset.typeset() now retries once with unescaped % escaped to \% when the first KaTeX parse throws, so the report's \text{3.18% dividend yield} equation typesets instead of showing raw \[ ... \] source. Already-parsing formulas are untouched, and genuinely broken/mid-stream formulas still show the source as before.

Verified: new regression test fails on the raw source with the fix reverted, then passes (vp test run src/components/chat/MarkdownMath.browser.test.tsx → 2 passed); vp run check:changed passes (format, lint, knip, typecheck, test, react compiler).

[meutex]

No security findings introduced by #1 (2 file(s) reviewed).

Reviewed 2 changed file(s), 70 changed lines.
Scanners: semgrep, gitleaks, sentrux.
Reviewed against secure-code-review.

Code quality (Sentrux): 1633 → 1633

No findings at or above MEDIUM.

Full report in Meutex