feat(parser-pipeline): create @endo/parser-pipeline

Babel AST parsing is expensive. When multiple consumers need to analyze or transform the same module source (`@endo/evasive-transform`, `@endo/module-source`, LavaMoat policy inspection), parsing each one independently wastes significant wall-clock time.

This package composes Babel visitor passes from multiple packages into a **single** _parse-traverse-generate_ cycle. It provides two parser factories, which can be provided to `@endo/compartment-mapper` APIs:

- `createComposedParser()`: synchronous, in-process; for the execution path where modules load on-demand
- `createWorkerParser()`: async, worker-pool-backed; for policy generation where hundreds of modules can parse in parallel

Use of these APIs makes both `moduleTransforms` and `syncModuleTransforms` options in `@endo/compartment-mapper` APIs _redundant_;  any desired transforms are best performed within the pipeline (including string-based preprocessing).

Author: boneskull

.changeset/thin-swans-press.md

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+---
+'@endo/parser-pipeline': minor
+---
+
+Create `@endo/parser-pipeline`, which exposes utilities to one-shot AST parsing for `@endo/compartment-mapper` consumers.

packages/parser-pipeline/LICENSE

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packages/parser-pipeline/README.md

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+# @endo/parser-pipeline
+
+Composable Babel visitor pipelines for JavaScript module analysis and transformation. Parses source once, runs multiple visitor passes, and generates code once. Eliminates redundant AST parsing when multiple consumers need to process the same source.
+
+## Example
+
+```javascript
+import fs from 'node:fs';
+import url from 'node:url';
+import { createComposedParser } from '@endo/parser-pipeline';
+import { createModuleSourcePasses } from '@endo/module-source';
+import { createEvasiveTransformPass } from '@endo/evasive-transform';
+import { importLocation } from '@endo/compartment-mapper';
+import { makeReadPowers } from '@endo/compartment-mapper/node-powers.js';
+
+let moduleSourceState;
+
+const parser = createComposedParser(
+  // recordBuilder: constructs the module record from generated code
+  (generatedCode, location) =>
+    moduleSourceState.buildRecord(generatedCode, location),
+  {
+    analyzerFactories: [
+      // Read-only pass: extract imports, exports, reexports
+      (_location, _specifier) => {
+        moduleSourceState = createModuleSourcePasses();
+        return moduleSourceState.analyzerPass;
+      },
+    ],
+    transformFactories: [
+      // Mutating pass: defang SES-forbidden patterns
+      (_location, _specifier) => createEvasiveTransformPass(),
+      // Mutating pass: rewrite ESM to SES-compatible functor
+      (_location, _specifier) => moduleSourceState.transformPass,
+    ],
+  },
+);
+
+// Use as a parserForLanguage entry in @endo/compartment-mapper
+await importLocation(makeReadPowers({ fs, url }), '/path/to/module.js', {
+  parserForLanguage: { mjs: parser },
+});
+```
+
+## Installation
+
+```bash
+yarn add @endo/parser-pipeline
+```
+
+## Usage
+
+This package exports two parser constructors, each returning a `ParserImplementation` or `AsyncParserImplementation` compatible with `@endo/compartment-mapper`'s common `parserForLanguage` option.
+
+### `createComposedParser(recordBuilder, options?): ParserImplementation`
+
+Synchronous, in-process pipeline. Parses each module in the calling thread. Best for the execution path where modules are loaded on-demand (including synchronous dynamic `require()` for CJS).
+
+```javascript
+import { createComposedParser } from '@endo/parser-pipeline';
+
+const parser = createComposedParser(recordBuilder, {
+  analyzerFactories, // read-only visitor factories (run first)
+  transformFactories, // mutating visitor factories (run after analyzers)
+  sourcePreprocessor, // optional string transform before Babel parse
+  onModuleComplete, // optional callback after each module completes
+});
+
+// parser satisfies ParserImplementation with synchronous: true
+```
+
+The `recordBuilder` is a required first argument. It is a synchronous function which receives the generated code and module location. It must return a `FinalStaticModuleType` (e.g., a SES `ModuleSource`-compatible record).
+
+#### Visitor Ordering
+
+1. All `analyzerFactories` run first (read-only traversals)
+2. All `transformFactories` run next (mutating traversals)
+3. Code generation runs once after all visitors complete
+
+Each factory is called once per module with `(location, specifier)` and must return a fresh visitor instance with independent state.
+
+### `createWorkerParser(workerScript, options?): TerminatableAsyncParserImplementation`
+
+Async, worker-pool-backed pipeline. Dispatches each module to a worker thread for parsing. Multiple modules parse in parallel across cores. Useful where modules need up-front analysis prior to execution.
+
+```javascript
+import fs from 'node:fs';
+import url from 'node:url';
+import { createWorkerParser } from '@endo/parser-pipeline';
+import { loadLocation } from '@endo/compartment-mapper';
+import { makeReadPowers } from '@endo/compartment-mapper/node-powers.js';
+
+const parser = createWorkerParser(new URL('./my-worker.js', import.meta.url), {
+  workerData: {
+    /* serializable config for workers */
+  },
+  onModuleComplete, // optional callback with analyzer results
+  maxWorkers: 4, // defaults to os.availableParallelism() - 1
+  idleTimeout: 1000, // ms before idle workers terminate
+});
+
+// parser satisfies AsyncParserImplementation with synchronous: false
+
+// Use as a parserForLanguage entry in @endo/compartment-mapper
+try {
+  await loadLocation(makeReadPowers({ fs, url }), '/path/to/module.js', {
+    parserForLanguage: { mjs: parser },
+  });
+} finally {
+  // parser has a .terminate() method to terminate the worker pool when finished.
+  await parser.terminate();
+}
+```
+
+The worker pool manages dispatch, queueing, and idle termination.
+
+#### Worker Scripts
+
+Worker scripts import their own visitor modules and call `runPipelineInWorker` from `@endo/parser-pipeline/worker-runner.js`:
+
+```javascript
+// my-worker.js
+import { runPipelineInWorker } from '@endo/parser-pipeline/worker-runner.js';
+import { createEvasiveTransformPass } from '@endo/evasive-transform';
+import { createModuleSourcePasses } from '@endo/module-source';
+import { isMainThread, parentPort, workerData } from 'node:worker_threads';
+
+if (!parentPort || isMainThread) {
+  throw new Error('This module must be run as a worker thread');
+}
+
+// runPipelineInWorker registers a listener for messages on parentPort;
+// removePipelineListener removes it, if needed.
+const { removePipelineListener } = runPipelineInWorker(parentPort, {
+  createAnalyzerPasses: (location, specifier) => [
+    // your read-only analysis visitors
+  ],
+  createTransformPasses: (location, specifier) => {
+    const ms = createModuleSourcePasses();
+    return {
+      passes: [createEvasiveTransformPass(), ms.transformPass],
+      analyzerPass: ms.analyzerPass,
+      buildRecord: ms.buildRecord,
+    };
+  },
+  sourcePreprocessor: source => source, // optional
+});
+```
+
+**The worker script depends on the visitor packages.** The parser-pipeline package provides _only_ the pool infrastructure and runner.
+
+## License
+
+Copyright © 2026 Endo Contributors. Licensed under the [Apache-2.0 License](LICENSE).