Introduce @huggingface/transformers-llguidance

packages/transformers-llguidance/README.md

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+# @huggingface/transformers-llguidance
+
+Experimental constrained-generation helpers for Transformers.js.
+
+This package exports `LlguidanceConstraint`, which turns an llguidance response format into the `logits_processor` and `stopping_criteria` objects accepted by Transformers.js generation.
+
+```js
+import { LlguidanceConstraint } from "@huggingface/transformers-llguidance";
+
+const { logits_processor, stopping_criteria } =
+  await LlguidanceConstraint.fromResponseFormat(tokenizer, {
+    type: "json_schema",
+    json_schema: {
+      type: "object",
+      properties: {
+        answer: { type: "string" },
+      },
+      required: ["answer"],
+      additionalProperties: false,
+    },
+  });
+
+await model.generate({
+  ...inputs,
+  logits_processor,
+  stopping_criteria,
+});
+```
+
+## Regex constraints
+
+Use `type: "regex"` to constrain generation to a regular expression. For example, this only allows ISO-like dates in `YYYY-MM-DD` format:
+
+```js
+import { LlguidanceConstraint } from "@huggingface/transformers-llguidance";
+
+const { logits_processor, stopping_criteria } =
+  await LlguidanceConstraint.fromResponseFormat(tokenizer, {
+    type: "regex",
+    regex: "\\d{4}-\\d{2}-\\d{2}",
+  });
+
+const output = await model.generate({
+  ...inputs,
+  logits_processor,
+  stopping_criteria,
+});
+```

packages/transformers-llguidance/jest.config.mjs

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+/** @type {import('jest').Config} */
+export default {
+  clearMocks: true,
+  collectCoverage: true,
+  coverageDirectory: "coverage",
+  coveragePathIgnorePatterns: ["node_modules", "tests"],
+  coverageProvider: "v8",
+  roots: ["./tests/"],
+  testTimeout: 32000,
+  transform: {},
+};

packages/transformers-llguidance/package.json

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+{
+  "name": "@huggingface/transformers-llguidance",
+  "version": "0.0.0",
+  "description": "llguidance integration helpers for Transformers.js constrained generation",
+  "main": "./dist/index.cjs",
+  "types": "./types/index.d.ts",
+  "type": "module",
+  "exports": {
+    "import": {
+      "types": "./types/index.d.ts",
+      "default": "./dist/index.js"
+    },
+    "require": {
+      "types": "./types/index.d.ts",
+      "default": "./dist/index.cjs"
+    }
+  },
+  "scripts": {
+    "format": "prettier --write . --ignore-path ../../.prettierignore",
+    "format:check": "prettier --check . --ignore-path ../../.prettierignore",
+    "typegen": "tsc --build",
+    "dev": "node scripts/dev.mjs",
+    "build": "node scripts/build.mjs && pnpm typegen",
+    "test": "node --experimental-vm-modules node_modules/jest/bin/jest.js --verbose"
+  },
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/huggingface/transformers.js.git"
+  },
+  "keywords": [
+    "transformers",
+    "transformers.js",
+    "huggingface",
+    "llguidance",
+    "constrained-generation"
+  ],
+  "author": "Hugging Face",
+  "license": "Apache-2.0",
+  "bugs": {
+    "url": "https://github.com/huggingface/transformers.js/issues"
+  },
+  "homepage": "https://github.com/huggingface/transformers.js#readme",
+  "peerDependencies": {
+    "@huggingface/transformers": "^4.2.0"
+  },
+  "devDependencies": {
+    "@huggingface/transformers": "workspace:*",
+    "@types/jest": "^30.0.0",
+    "@types/node": "^24.1.0",
+    "esbuild": "^0.27.2",
+    "jest": "^30.2.0",
+    "typescript": "5.9.3"
+  },
+  "files": [
+    "src",
+    "dist",
+    "types",
+    "README.md",
+    "LICENSE",
+    "!**/*.tsbuildinfo"
+  ],
+  "publishConfig": {
+    "access": "public"
+  },
+  "dependencies": {
+    "llguidance": "^0.1.8"
+  }
+}

packages/transformers-llguidance/scripts/build.mjs

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+import { build } from "esbuild";
+import { rmSync } from "node:fs";
+
+rmSync("dist", { recursive: true, force: true });
+
+const common = {
+  entryPoints: ["src/index.ts"],
+  bundle: true,
+  platform: "neutral",
+  target: "es2022",
+  sourcemap: true,
+  external: ["@huggingface/transformers", "llguidance"],
+};
+
+await Promise.all([
+  build({
+    ...common,
+    format: "esm",
+    outfile: "dist/index.js",
+  }),
+  build({
+    ...common,
+    format: "cjs",
+    outfile: "dist/index.cjs",
+  }),
+]);

packages/transformers-llguidance/scripts/dev.mjs

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+import { context } from "esbuild";
+import { spawn } from "node:child_process";
+import { rmSync } from "node:fs";
+
+rmSync("dist", { recursive: true, force: true });
+rmSync("types", { recursive: true, force: true });
+
+const watchLogger = {
+  name: "watch-logger",
+  setup(build) {
+    let startTime = 0;
+
+    build.onStart(() => {
+      startTime = performance.now();
+      console.log(`[transformers-llguidance] rebuilding ${build.initialOptions.outfile}...`);
+    });
+
+    build.onEnd((result) => {
+      const duration = (performance.now() - startTime).toFixed(2);
+      if (result.errors.length > 0) {
+        console.log(`[transformers-llguidance] rebuild failed in ${duration}ms`);
+      } else {
+        console.log(`[transformers-llguidance] rebuilt ${build.initialOptions.outfile} in ${duration}ms`);
+      }
+    });
+  },
+};
+
+const common = {
+  entryPoints: ["src/index.ts"],
+  bundle: true,
+  platform: "neutral",
+  target: "es2022",
+  sourcemap: true,
+  external: ["@huggingface/transformers", "llguidance"],
+  plugins: [watchLogger],
+};
+
+const contexts = await Promise.all([
+  context({
+    ...common,
+    format: "esm",
+    outfile: "dist/index.js",
+  }),
+  context({
+    ...common,
+    format: "cjs",
+    outfile: "dist/index.cjs",
+  }),
+]);
+
+await Promise.all(contexts.map((ctx) => ctx.watch()));
+
+const tscWatch = spawn("tsc", ["--build", "--watch", "--preserveWatchOutput"], {
+  stdio: "inherit",
+  shell: true,
+});
+
+console.log("Watching @huggingface/transformers-llguidance...");
+
+process.on("SIGINT", async () => {
+  tscWatch.kill();
+  await Promise.all(contexts.map((ctx) => ctx.dispose()));
+  process.exit(0);
+});