Autoformat Input Rules First Slice

Goal

Create a shared input-rules runtime in @platejs/autoformat that can own both:

• the existing insertText-driven autoformat dispatch
• neighboring non-plain-autoformat input behavior such as math delimiter conversion

without lying that math is just another plain autoformat rule.

Findings

• AutoformatPlugin currently owns a text-only rule loop in AutoformatPlugin.ts.
• math delimiter conversion needs both insertText and insertBreak, which makes it a bad fit for plain text-only autoformat rules but a good fit for a shared autoformat-owned input-rule lane.
• Current editor-behavior law still correctly says math delimiter triggers are outside the plain autoformat family, under source-preserving conversion.
• The right unification target is shared input-rule infrastructure, not a larger AutoformatPlugin rule union pretending Enter promotion is text autoformat.

Recommended First Slice

1. Add shared input-rule types and runner helpers in @platejs/autoformat.
2. Refactor AutoformatPlugin to use the shared insertText input-rule runner.
3. Move math delimiter conversion fully onto AutoformatPlugin through autoformat-owned insertTextRules and insertBreakRules.
4. Keep package boundaries honest:
   • AutoformatPlugin still owns plain block/mark/text autoformat.
   • math keeps only equation node/render/transform ownership.
   • @platejs/autoformat owns the reusable input-rule runtime and the math delimiter input rules.

Verification Target

• package tests for autoformat and math still pass
• package/app build and typecheck pass
• docs expose AutoformatPlugin + autoformatMathInput
• no legacy math trigger plugin names remain

Notes

• If verified code lands in both packages, add a changeset before handoff.

Progress

• Added shared input-rule runners in packages/autoformat/src/lib/inputRules.ts.
• Refactored AutoformatPlugin.ts to dispatch both plain autoformat text rules and autoformat-owned insertText / insertBreak input rules through the shared runtime.
• Added autoformat-owned math delimiter rules in autoformatMathInput.ts.
• Added autoformat runner unit coverage in inputRules.spec.ts.
• Patched architecture notes so the neighboring input-rule lane can live in shared @platejs/autoformat infrastructure without pretending math is plain autoformat.
• Deleted the separate math input plugin surface so math input behavior is fully hosted on autoformat.
• Added package changesets for the new autoformat-owned input-rule surface and the math package breaking change.

Verification

• pnpm --filter @platejs/autoformat test -- inputRules.spec.ts AutoformatPlugin.spec.tsx
• pnpm --filter @platejs/autoformat test -- autoformatMathInput.spec.tsx
• bun test packages/autoformat/src/lib/rules/math/autoformatMathInput.spec.tsx apps/www/src/__tests__/package-integration/math/math-trigger.slow.tsx
• pnpm install
• pnpm brl
• pnpm build
• pnpm turbo typecheck --filter=./packages/autoformat --filter=./packages/math --filter=./packages/code-block --filter=./apps/www
• pnpm lint:fix
• browser verification on http://127.0.0.1:3200/blocks/playground: typing a unique ZZZMathStart $x$ sequence converted to an inline equation node, removed the literal dollar-delimited text, and left KaTeX-backed inline math markup in the editor DOM