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fix(mobile): typeset \(…\) and \[…\] math when Render math is on - #29739
With Settings → Appearance → Render math on, the mobile app (iOS, iPadOS, Android) shows formulas written as \(…\) and \[…\] as raw TeX, while $…$ and $$…$$ typeset. Web reads all four forms, and docs/user/appearance.md says mobile does too. Reproduced on main at 60aec28 on a Pixel 9 dev client paired to an isolated dev server: a real Claude reply containing the issue's \[A=\begin{pmatrix}1&1\\0&1\end{pmatrix}\], \[\det(A-\lambda I)=0\] and inline \(…\) formulas rendered as [A=\begin{pmatrix}1&1\0&1\end{pmatrix}], in light and dark themes, while the $$…$$ line in the same reply typeset.
Mobile renders Markdown with react-native-enriched-markdown, whose md4c parser only recognises $ as a math delimiter.
Change
markdownWithDollarMath (apps/mobile/src/lib/markdownDocument.ts) rewrites the delimiters of \(…\) and \[…\] formulas to $…$ and $$…$$ before the text reaches md4c. MobileEnrichedMarkdownText applies it only when Render math is on. Formulas are found with the shared markdownMathRanges, the same parser web renders with, so code spans, fences, escapes and citations such as \[1\] are untouched. Only the two delimiter characters at each end are replaced, so the TeX and container prefixes like > stay as written.
A message is left exactly as authored, which is what main shows, in these cases:
md4c would not accept the new $: a formula touching a letter, a digit or CJK text, or touching another formula.
The message contains a literal $ outside a dollar formula, such as a price or $HOME, which md4c would pair with an inserted delimiter.
A linear pre-pass estimates the shared parser would take too long, because unclosed openers make it reread their paragraph or the rest of the message.
The parser's range walk throws on very deeply nested Markdown.
Messages without \( or \[ return before any parsing.
F3: guards. Eligible, punctuated, Unicode-flanked and consecutive-line formulas typeset. Suffixed, CJK-adjacent and touching formulas stay as on main. A reply with a price stays as authored.
F4: Markdown file preview (the file-embed preprocessing path) at app text size 22. It covers frontmatter, HTML, a blockquote, a list, a table, consecutive display lines, a wide fraction and invalid TeX.
F2: Render math off → on on the same thread, without resending. Steps: open Settings → Appearance, turn Render math off, open the thread (source shows), then turn it back on and reopen the thread (math typesets).
Pixel 9 · light, after
iPhone 17 Pro · dark, after
What else changed in the captures (before and after were seeded independently, so these are not frozen-clock comparisons):
Turn timestamps and work durations differ between the two separately seeded fixtures.
The iOS status-bar clock was not frozen.
Math rows are taller, so content below them moves.
Invalid TeX shows md4c's literal fallback, and a very wide fraction clips horizontally at text size 22. That is existing renderer behaviour.
Not verified:
A settled iOS frame after reopening a <details> disclosure. The Android recording passes. The iOS recordings show the reopen only in their last frames, about 0.24 s before the export ends.
Native selection and copy interactions near math.
Pending-question, PR and review-comment hosts (covered by a labelled renderer harness only).
Provider streaming (covered by controlled prop updates only).
A physical iPad: cannot-verify ios-device. The simulator covers the same JS and native parser.
The seed prompts and the F6/F8 harness are not linked: this VM had no file-upload tool. All fixtures are synthetic.
Model and harness: Claude Opus 5.5 (issue lead, implementation, red test, reviewer B) and GPT-6.1 Sol (reviewer A, proof audit, evidence capture), in T3 Code via Claude Code and Codex.
These tests reproduce #29599: \(…\) and \[…\] formulas reach md4c, which
only typesets $ and $$ delimiters, so mobile shows them as raw text.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The native md4c parser only knows $ and $$ delimiters, so replies using
backslash delimiters showed raw TeX on iOS and Android. Rewrite just the
delimiters of formulas the shared math parser (the one web renders with)
finds, leaving code, escapes and container prefixes untouched.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
md4c opens `$` only after a line edge, whitespace or punctuation and closes
it only before one, and merges touching `$` runs. Rewrite a `\(`/`\[`
formula only when its dollar delimiters flank and touch no other `$` or
formula; otherwise leave it as authored. Skip the rewrite when unclosed
delimiters could make the math parser scan more than a fixed budget.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The previous guard charged every `\(`, `\[` and `$` to the end of the
message, so long replies full of closed formulas stayed raw while short
unclosed-delimiter inputs still took up to a second to parse.
The estimate now charges per character, per non-blank line and per
delimiter. A failed opener also pays for how far it sits along its line.
An unclosed `\(`, `\[` or `$$` rereads its paragraph. A `\[` alone on
its line reads to the next line ending in `\]`, and `$$` reads to the
next `$$`. Closed formulas cost nothing extra.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…conversion
Charge a bare \[ fence line and stop inline reads at a backtick in the
parse guard, leave replies whose literal $ md4c would pair with an
inserted delimiter as authored, and fall back to the source when the
range walker overflows.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Macroscope's review found this PR approvable — Mobile Markdown now renders recognized backslash-delimited math when Render math is enabled. The change preserves the existing preference and uses conservative fallbacks without altering stored content.
You can add or adjust custom eligibility rules. Learn more.
No actionable comments were generated in the recent review.
Walkthrough
The mobile markdown path now converts eligible \(...\) and \[...\] formulas to dollar-delimited math when math rendering is enabled. The conversion preserves input when parsing exceeds its budget or formula delimiters fail its checks.
Changes: Mobile math conversion
Layer / File(s)
Summary
Convert and apply math delimiters apps/mobile/src/lib/markdownDocument.ts, apps/mobile/src/native/EnrichedMarkdownText.tsx, apps/mobile/src/lib/markdownDollarMath.test.ts
markdownWithDollarMath checks parse cost and formula boundaries before converting eligible delimiters. The native markdown component applies the conversion when math rendering is enabled. Tests cover conversion and cases where the input remains unchanged.
No merge-blocking issue is established for the mobile math conversion; it is mergeable after normal checks.
Pre-merge checks: 4
Check name
Status
Explanation
Title check
The title clearly and concisely describes the main mobile math-rendering fix and identifies the affected delimiters and setting.
Linked Issues check
Issue #29599 requires formatted inline and display math on mobile when Render math is enabled. markdownWithDollarMath converts eligible \\(…\\) and \\[…\\] delimiters to md4c-supported $ and $$ …
Out of Scope Changes check
The changes stay within issue #29599. They add the mobile math conversion helper, integrate it with the mobile enriched Markdown renderer, and add focused automated tests. The parser guards and preser…
Description check
The description is complete and relevant. It covers the problem, implementation, scope, focused tests, device verification, screenshots, limitations, and agent details. The scope section links issue #…
Full details: Linked Issues check
Explanation
Issue #29599 requires formatted inline and display math on mobile when Render math is enabled. markdownWithDollarMath converts eligible \(…\) and \[…\] delimiters to md4c-supported $ and $$ delimiters. MobileEnrichedMarkdownText applies the conversion only when mathRenderingEnabled is true. The implementation preserves code, citations, escapes, unsafe dollar contexts, and parser-limit cases. The added tests cover the issue reply, matrices, inline math, display math, and guard cases.
Full details: Out of Scope Changes check
Explanation
The changes stay within issue #29599. They add the mobile math conversion helper, integrate it with the mobile enriched Markdown renderer, and add focused automated tests. The parser guards and preservation behavior support safe implementation of the requested mobile rendering fix.
Full details: Description check
Explanation
The description is complete and relevant. It covers the problem, implementation, scope, focused tests, device verification, screenshots, limitations, and agent details. The scope section links issue #29599, but it does not include an explicit maintainer approval comment or explain why approval was not required.
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Thanks @juliusmarminge for the fix and device evidence! #32180 (986a4f56a8) now covers this on main using native support for \(…\) and \[…\] when Render math is enabled, so this workaround is no longer needed.
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bugfixFix PR opened by an issue lead; enters the PR loopsize:L100-499 changed lines (additions + deletions).vouch:trustedPR author is trusted by repo permissions or the VOUCHED list.
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bugfix
Problem
With Settings → Appearance → Render math on, the mobile app (iOS, iPadOS, Android) shows formulas written as
\(…\)and\[…\]as raw TeX, while$…$and$$…$$typeset. Web reads all four forms, anddocs/user/appearance.mdsays mobile does too. Reproduced on main at 60aec28 on a Pixel 9 dev client paired to an isolated dev server: a real Claude reply containing the issue's\[A=\begin{pmatrix}1&1\\0&1\end{pmatrix}\],\[\det(A-\lambda I)=0\]and inline\(…\)formulas rendered as[A=\begin{pmatrix}1&1\0&1\end{pmatrix}], in light and dark themes, while the$$…$$line in the same reply typeset.Mobile renders Markdown with react-native-enriched-markdown, whose md4c parser only recognises
$as a math delimiter.Change
markdownWithDollarMath(apps/mobile/src/lib/markdownDocument.ts) rewrites the delimiters of\(…\)and\[…\]formulas to$…$and$$…$$before the text reaches md4c.MobileEnrichedMarkdownTextapplies it only when Render math is on. Formulas are found with the sharedmarkdownMathRanges, the same parser web renders with, so code spans, fences, escapes and citations such as\[1\]are untouched. Only the two delimiter characters at each end are replaced, so the TeX and container prefixes like>stay as written.A message is left exactly as authored, which is what main shows, in these cases:
$: a formula touching a letter, a digit or CJK text, or touching another formula.$outside a dollar formula, such as a price or$HOME, which md4c would pair with an inserted delimiter.Messages without
\(or\[return before any parsing.Scope and approval
Fixes #29599
Verification
vp test run apps/mobile/src/lib/markdownDollarMath.test.ts: 8 passed.The issue's reply test fails on main. The unflanked, long-reply, literal-dollar and reread tests each failed before the commit that fixed them.
vp run check:changed: format, lint, knip, typecheck (2 packages), tests and React compiler all pass.Device captures below. Environment:
T3CODE_DEV_SEED=0.F1: the issue's reply
F3: guards. Eligible, punctuated, Unicode-flanked and consecutive-line formulas typeset. Suffixed, CJK-adjacent and touching formulas stay as on main. A reply with a price stays as authored.
F4: Markdown file preview (the file-embed preprocessing path) at app text size 22. It covers frontmatter, HTML, a blockquote, a list, a table, consecutive display lines, a wide fraction and invalid TeX.
F9: over the parse budget. A formula followed by 300 unclosed
\[lines stays as authored. The pair has zero changed pixels at threshold zero.F2: Render math off → on on the same thread, without resending. Steps: open Settings → Appearance, turn Render math off, open the thread (source shows), then turn it back on and reopen the thread (math typesets).
What else changed in the captures (before and after were seeded independently, so these are not frozen-clock comparisons):
Not verified:
<details>disclosure. The Android recording passes. The iOS recordings show the reopen only in their last frames, about 0.24 s before the export ends.cannot-verify ios-device. The simulator covers the same JS and native parser.The seed prompts and the F6/F8 harness are not linked: this VM had no file-upload tool. All fixtures are synthetic.
Model and harness: Claude Opus 5.5 (issue lead, implementation, red test, reviewer B) and GPT-6.1 Sol (reviewer A, proof audit, evidence capture), in T3 Code via Claude Code and Codex.
🤖 Generated with Claude Code