feat(web): add math display modes for chat

[luke2x]

LaTeX in assistant messages currently appears as raw commands in chat. I ran into this in Nightly while studying maths. This adds automatic typesetting and a readable plain-text alternative in the shared web/desktop renderer.

Math display

Choose Settings → Appearance → LaTeX rendering. The preference is saved per device or browser.

Mode	Result
Off	Existing Markdown rendering, including raw TeX commands.
Readable	Plain text with fractions, powers, roots, integral limits, aligned steps, and piecewise conditions.
On (default)	Typeset equations with KaTeX.

Supports \(...\), \[...\], and $$...$$. Single-dollar prices, shell variables, skill mentions, and code keep their existing behavior. Fenced math blocks remain code, including when an unrelated equation appears elsewhere in the same message. Incomplete expressions stay literal until closed, including in lists and blockquotes. Copying equations preserves the TeX; wide display equations scroll inside the message. Native mobile keeps its current renderer.

Performance

Ordinary messages and Off use the existing Markdown pipeline. Math code loads on demand only after the existing Markdown parse finds a delimiter outside code; Readable produces text from semantic MathML, skipping visual HTML generation and the typesetting stylesheet/fonts. A bounded 64-expression cache avoids typesetting unchanged equations again as surrounding text streams. Generated markup uses trust: false, and authored HTML is sanitized first.

Screenshots

The actual three-mode control, with Readable selected:

The same message in all three modes. Click an image for the full-resolution capture.

Off — existing behavior	Readable — plain text	On — typeset math

Also available: original capture before this change, Off selected, and On selected. Evidence is uploaded to GitHub and is not committed in the source diff.

Verification

• 407 tests pass across 9 focused files, covering parsing, chat rendering, streaming, settings contracts/persistence, copying, settings restore, and settings search. Scoped type-aware lint/type checking pass with existing warnings.
• In the isolated app, selected each mode, reloaded to check persistence, and opened the same example. Off kept the existing text, Readable produced plain spans with no KaTeX/MathML DOM, and On rendered all 10 expressions (6 display, 4 inline) with no errors. Examples include definite/improper/double integrals, series, limits, roots, Greek letters, aligned working, and a piecewise function.
• Regression tests also verify that inline, fenced, indented, quoted, and list-contained code never triggers a cold math import in On or Readable, and that ordinary equations still load their renderer.
• On and Readable are each tested with parsed and literal HTML: equations render, heading links scroll without changing the URL, and authored HTML remains sanitized or literal as selected.
• Browser requests confirmed no math modules in Off and no typesetting CSS/fonts in Readable. Regression tests verify one typesetting call across ten streaming updates and separate cached output for Readable/On. Desktop shares this renderer; an Electron package was not built.

Scope and approval

• Scope: explicit math delimiters in the shared web/desktop chat renderer, with On by default and Readable/Off alternatives. Native mobile and single-dollar delimiters are outside this PR.
• Problem discussion: Render LaTeX/math in chat for research workflows (#9641).
• Approval: still pending for this scope. A maintainer previously expressed conditional support for fully opt-in rendering if it stays simple. That comment does not explicitly approve default-On rendering or the three-mode proposal here. Adding the math renderer and changing the default display behavior requires scope approval under CONTRIBUTING.md.

Related proposals: #16724, #14574, #16469, #17217. This proposal includes a Readable mode alongside explicit delimiters and streaming safeguards.

Model: gpt-6.1-sol. Harness: Codex in T3 Code.

[AKolenda]

duplicate PR #16724

[luke2x]

duplicate PR #16724

this adds a display setting too and more, updated the PR to show it now

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-08T20:51:56.136933Z	a58d9a4	Draft marked ready

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Reviewing files that changed from the base of the PR and between 097333a and a893ef2.

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📒 Files selected for processing (6)

• apps/web/package.json
• apps/web/src/components/ChatMarkdown.test.tsx
• apps/web/src/components/ChatMarkdown.tsx
• apps/web/src/index.css
• packages/contracts/src/settings.ts
• packages/shared/package.json

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📝 Walkthrough

📝 Walkthrough

📝 Walkthrough

Walkthrough

Chat Markdown now supports off, readable, and typeset LaTeX modes. Shared parsing recognizes math delimiters, and web rendering uses KaTeX or readable text. Settings, clipboard serialization, styling, tests, and documentation cover these modes.

Changes

Chat math rendering

Layer / File(s)	Summary
LaTeX rendering setting packages/contracts/src/settings.ts, packages/contracts/src/settings.test.ts, apps/web/src/components/settings/SettingsPanels.tsx, apps/web/src/components/settings/settingsSearch.ts, docs/user/appearance.md	The settings contract defines off, readable, and on, with on as the default. Appearance settings provide mode selection and reset behavior. Search and documentation include the setting.
Shared math parsing packages/shared/src/markdownMath.ts, packages/shared/src/markdownMath.test.ts, packages/shared/src/markdownPipeline.ts, packages/shared/package.json, apps/web/src/markdown-incremental.test.tsx	The shared Markdown plugin recognizes dollar and backslash delimiters and assigns inline or display classes. It preserves unfinished input as text in specified cases. Sanitization and parsing tests cover the resulting nodes, including streaming math.
KaTeX and readable rendering apps/web/package.json, apps/web/src/components/chat/markdownMath.ts, apps/web/src/components/chat/markdownMathReadable.ts, apps/web/src/components/chat/markdownMathRendered.ts, apps/web/src/components/chat/useChatMath.ts, apps/web/src/components/chat/useChatMath.test.tsx, apps/web/src/index.css	The web app adds cached KaTeX rendering and a readable-text transformation based on MathML. It loads plugins by mode and adds styles for rendered and readable math. Tests cover lazy plugin loading.
Chat rendering and copy behavior apps/web/src/components/ChatMarkdown.tsx, apps/web/src/markdown-clipboard.ts, apps/web/src/components/ChatMarkdown.test.tsx	ChatMarkdown applies math plugins based on the setting and message text. Clipboard serialization preserves TeX delimiters. Tests cover rendering modes, streaming, MathML output, malformed LaTeX, and copied content.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant ChatMarkdown
  participant useChatMathPlugins
  participant remarkChatMath
  participant KaTeX
  ChatMarkdown->>useChatMathPlugins: pass rendering mode and message text
  useChatMathPlugins->>ChatMarkdown: provide loaded mode-specific plugins
  ChatMarkdown->>remarkChatMath: parse math delimiters
  remarkChatMath->>KaTeX: pass math nodes through the rendering pipeline

Loading

Suggested reviewers: juliusmarminge

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Merge Risk: ⚪ Minimal · up to a893e

The selected math rendering mode is connected to the chat renderer. No actionable merge-blocking issue remains in the supplied evidence.

Security Architecture Review

Security architecture risk: 🔵 Low · up to a893e

Math rendering introduces new processing of message content by default. The inspected paths preserve HTML sanitization, restrict trusted TeX features, and keep failures in the existing Markdown display path. No security regression was established, but the additional rendering dependencies and incomplete broader coverage leave some uncertainty.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — A party able to influence rendered message text can supply expressions to the new math processor in the viewing client. The inspected adapter operates on rendering trees and adds no service credential, tenant authorization, or command-execution capability. This bounds the demonstrated exposure to client rendering and copying, rather than establishing safety for every dependent.

Trust Boundaries and Controls

• observed — The raw-HTML branch parses and sanitizes authored HTML before KaTeX, which is configured with trust false. The literal-HTML branch omits raw HTML parsing. ChatMarkdown continues passing its existing URL transform to ReactMarkdown.
• observed — Readable mode converts generated semantic MathML into text nodes and attaches a TeX clipboard representation. It does not interpret the readable result as authored HTML.

Resilience and Maintainability Implications

• observed — Lazy loads are deduplicated per active mode. Selection checks the current mode, and effect cleanup suppresses late consumer updates after cancellation. Import failure retains the ordinary sanitization policy rather than falling back to an unsanitized renderer.

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🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check		The description provides detailed problem context, implementation scope, verification results, and screenshots. However, it does not use the required Problem and Change section headings, and it explic…	Add explicit Problem and Change sections, and obtain or link explicit maintainer approval for the proposed scope. Update the Scope and approval section with the approval comment before merging.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: adding configurable math display modes for chat.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Full details: Description check

Explanation

The description provides detailed problem context, implementation scope, verification results, and screenshots. However, it does not use the required Problem and Change section headings, and it explicitly states that the required maintainer approval for the default-On, three-mode scope is still pending.

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⚠️ Outside diff range comments (1)

🟡 Minor · Confirm approval for the default-On behavior. · settings.ts:314

packages/contracts/src/settings.ts:314
🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Confirm approval for the default-On behavior.

CONTRIBUTING.md requires explicit maintainer approval for changed product defaults, including defaults exposed through settings. The PR description states that approval for default-On is still pending.

If approval is absent, default this setting to "off" so existing settings do not opt into typesetting.

Suggested fix

-    Schema.withDecodingDefault(Effect.succeed("on" as const)),
+    Schema.withDecodingDefault(Effect.succeed("off" as const)),

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Review comment at @packages/contracts/src/settings.ts at line 314:
Change the decoding default in the setting schema near
`Schema.withDecodingDefault` from `"on"` to `"off"` so existing settings do not
enable typesetting by default.

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Outside diff comments:
Review comments at @packages/contracts/src/settings.ts:
- Line 314: Change the decoding default in the setting schema near
`Schema.withDecodingDefault` from `"on"` to `"off"` so existing settings do not
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Inline comments:
Review comments at @apps/web/src/components/ChatMarkdown.tsx:
- Line 3407: Update the ReactMarkdown configuration alongside the existing
mathPlugins.remark spread to pass the selected mathPlugins.rehype or
mathPlugins.literalRehype transforms, preserving the required sanitization
order. Ensure the mode-specific math transforms from useChatMathPlugins and the
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