fix(web): disable single-dollar inline math in remark-math

[heavygee]

Summary

Disables single-dollar inline math in remark-math so prose containing currency amounts no longer collapses into KaTeX output.

$$...$$ block math (on its own line) is unchanged.

Fixes #800.

Problem

remark-math is configured with defaults, which means singleDollarTextMath: true. Any pair of $ characters in a paragraph becomes a math span, so messages like:

The plan is $200/mo and the bill is $80 — total $400 saved.

render with everything between the first and last $ collapsed into a single <span class="katex"> block — whitespace stripped, letters reflowed as italic math symbols, apostrophes turned into prime marks. The text is no longer readable as prose.

Currency mentions are common in chat (pricing discussions, plan comparisons, billing), so the false-positive rate is high enough that day-to-day prose has been hitting it.

Approach

Pass singleDollarTextMath: false to remarkMath in web/src/components/assistant-ui/markdown-text.tsx. This is a single source of truth — MarkdownText, Reasoning, and MarkdownRenderer all import the same MARKDOWN_PLUGINS array, so the fix lands in every markdown surface at once.

Block math $$...$$ continues to render. This matches GitHub-flavored markdown semantics, which only treat $$...$$ (or fenced ```math) as math.

Trade-off vs #237

#237 added KaTeX support and explicitly mentioned single-dollar form $ E= mc^2 $ as desired. This PR partially reverses that — single-dollar inline math goes away. Math-heavy users will need to switch to $$E = mc^2$$ on its own line. The trade-off felt worth it because false positives from currency $ are common in chat prose, while inline math is rare; happy to revisit if maintainers prefer a different policy.

Testing

3 new regression tests in web/src/components/assistant-ui/markdown-text.test.ts drive the unified pipeline end-to-end and assert against the rendered HTML:

• prose with multiple $N amounts → no class="katex", no <math> element, all amounts present as literal text
• the real-world reported paragraph → renders as plain text
• $$E = mc^2$$ block math → still produces a KaTeX block

$ bun run test
Test Files  85 passed (85)
     Tests  739 passed (739)

$ bun run typecheck
$ tsc --noEmit

Related

• Fixes bug(web): currency prose containing two $ signs is rendered as KaTeX math, mangling messages #800
• Partially reverses behavior introduced for 希望能在前端页面加一个latex公式渲染的能力，比如接入mathjax #237

Questions

Open to a different policy if maintainers prefer (e.g. only disable single-dollar when followed by a digit, to keep $ E= mc^2 $ working). Happy to iterate.

[github-actions]

Findings

• [Minor] New test imports undeclared markdown packages — the added regression test now imports unified, remark-parse, remark-rehype, and hast-util-to-html directly, but none of those packages are declared in web/package.json or the root/package manifests (checked repo manifests). The test currently relies on transitive dependencies from other markdown packages, so a valid dependency update can remove or move them and make bun run test:web fail even though this test still compiles conceptually. Evidence: web/src/components/assistant-ui/markdown-text.test.ts:2
  Suggested fix:

  {
      "devDependencies": {
          "hast-util-to-html": "^9.0.5",
          "remark-parse": "^11.0.0",
          "remark-rehype": "^11.1.2",
          "unified": "^11.0.5"
      }
  }

Summary

• Review mode: initial
• One dependency hygiene issue found in the new test. No correctness issue found in the remarkMath option change itself. Residual risk: I could not run the web test locally because bun is not installed in this runner.

Testing

• Not run (automation): bun command not available in runner.

HAPI Bot

[github-actions]

[Minor] This test now imports unified, remark-parse, remark-rehype, and hast-util-to-html directly, but the web package does not declare any of them. That makes bun run test:web depend on transitive dependencies from other markdown packages, so a valid dependency update can break this test without touching it.

Suggested fix:

{
    "devDependencies": {
        "hast-util-to-html": "^9.0.5",
        "remark-parse": "^11.0.0",
        "remark-rehype": "^11.1.2",
        "unified": "^11.0.5"
    }
}