[Bug]: Typing after a selected skill lags, worse on long prompts#30657

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. Open any project whose provider offers skills.
2. In the composer, pick a skill from the $ or / menu so it becomes a chip.
3. Keep typing after the chip, ideally until the prompt is a few hundred characters long.

Expected behavior

Typing after a skill chip costs the same as typing plain text.

Actual behavior

Each keystroke gets slower once a skill is selected, and the gap grows with prompt length.

Median time per keystroke (dev build, e68e19d605, measured in the browser):

A skill chip is serialized as $name. mayContainMath in packages/shared/src/markdownMath.ts treats any $ as possible math, so collectComposerInlineTokens and buildTiptapContent run the full remark + GFM + math parser over the whole prompt. That happens several times per keystroke: cursor conversions in ComposerPromptEditorTiptap and ChatComposer, plus buildDocJson passed as useEditor's content option, which is rebuilt on every render although it is only read on mount. splitPromptIntoComposerSegments goes from 3 µs on plain text to about 250 µs with one $skill.

Impact

Typing visibly lags after selecting a skill, worse on long prompts.

Version or commit

e68e19d605 (main)

Environment

Web, Linux, Chromium-based browser, dev build.