Ship native ESM to avoid bundling an extra KaTeX copy

[cyanzhong]

Why

The packaging fix in #10 made clean installs work, but routed both import and require to CommonJS. MarkEdit-preview imports KaTeX as ESM, while the plugin then required CommonJS KaTeX, so Vite bundled an additional copy. This fixes that packaging regression without changing the parser.

Changes

• Route import to native dist/index.mjs and require to the existing dist/index.js.
• Supply a matching .d.mts declaration for native ESM TypeScript consumers, preserving the CommonJS types and existing declaration subpath.
• Compile and watch both formats from the same source with correct embedded-source maps. CommonJS runtime and source map remain byte-identical to 1.1.7.
• Add package-entry, type-resolution, source-map, shared KaTeX instance, and fixture-parity checks.
• Document native ESM usage; no version bump or release tag changes.

Validation

• All 71 existing assertions pass.
• All 53 fixtures render identically through ESM and CommonJS.
• Native ESM/CommonJS imports and NodeNext consumer types pass.
• Both entry points render from an extracted npm pack tarball.
• Watch mode updates both runtimes and declarations; repeated compilation passes npm run verify-dist.
• Full MarkEdit-preview builds were run in memory with deployment disabled and the packed ESM entry, without changing Preview files.

Preview entry	JavaScript bytes	Gzip bytes
Installed 1.1.7 CommonJS	5,295,115	1,522,885
Original TypeScript source	5,022,788	1,442,220
Proposed packed ESM	5,022,788	1,442,220

The new bundle removes the additional top-level CommonJS KaTeX module and returns exactly to the original-source bundle size. Mermaid retains its own pre-existing KaTeX dependency.

[Copilot]

Copilot review overview

🟡 Changes recommended

Resolve the package-version inconsistency and add runtime/type assertions against an extracted npm pack tarball.

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Review effort: Lite
Findings: 1

Open (1)

• Revert unintended package version bump in manifests · New

What changed in this PR

Adds native ESM packaging alongside CommonJS to prevent duplicate KaTeX bundling while preserving existing behavior.

Changes:

• Adds conditional ESM/CommonJS exports and ESM declarations.
• Builds both formats with source maps and expanded validation.
• Documents ESM usage and updates generated artifacts.

File	Reviewed changes
types.d.ts	Declaration formatting updates.
test/​package.js	Entry-point, type, source-map, and parity checks.
README.md	Native ESM usage documentation.
package.json	Conditional exports and dual-format build configuration.
package-lock.json	Package metadata synchronization.
dist/​index.mjs.map	Generated ESM source map.
dist/​index.mjs	Generated native ESM runtime.
dist/​index.d.mts	ESM TypeScript declaration.
build/​compile.js	Dual-format compilation and watch support.

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