build: Bundle vats with vite #763

grypez · 2026-01-22T02:24:30Z

Replace @endo/bundle-source with Vite for vat bundling and @endo/import-bundle with direct Compartment.evaluate() for bundle loading.

Motivation

The Endo bundling tools have complex dependency chains and produce large bundles. Vite provides a simpler, faster bundling pipeline with better tree-shaking and smaller output.

Changes

Bundling

New bundleVat function using Vite's build() API with IIFE output
Custom Rollup plugins for export metadata extraction and comment stripping
CLI commands (bundle, watch) updated to use Vite bundler

Bundle Loading

loadBundle() evaluates bundles via Compartment.evaluate()
Validates moduleFormat, code, exports, and modules properties
Passes endowments and inescapable globals to the compartment

Dependencies

Removed: @endo/bundle-source (except from @metamask/kernel-shims), @endo/import-bundle
Added: vite, acorn (for comment stripping)

Bundle Format

{
  "moduleFormat": "iife",
  "code": "var __vatExports__ = (function() { ... })();",
  "exports": ["buildRootObject"],
  "modules": { "./foo.js": { "renderedExports": [...], "removedExports": [...] } }
}

Migration

Existing bundles using endoZipBase64 format are no longer supported. Regenerate bundles using ocap bundle <entry>.

Closes: #742

Note

High Risk
High risk because it changes the vat bundle format and the security-sensitive code-loading path (replacing @endo/import-bundle with Compartment.evaluate()), which could break existing bundles or alter sandboxing behavior.

Overview
Replaces Endo-based vat bundling/loading with a Vite + IIFE pipeline. The CLI bundle/watch flow now uses a new Vite-based bundleVat builder (plus Rollup plugins to strip comments and capture export metadata) and drops @endo/bundle-source/@endo/init in favor of @metamask/kernel-shims/endoify.

Updates the kernel to consume the new bundle format. VatSupervisor now fetches bundle content as text and loads it via a new loadBundle() helper that validates moduleFormat: "iife" and evaluates the bundle in a SES Compartment, and kernel-utils adds a VatBundle type + isVatBundle guard with tests. Integration/fixture bundles and tests are updated accordingly, and @endo/import-bundle is removed from ocap-kernel dependencies.

^{Written by Cursor Bugbot for commit 4d3ef97. This will update automatically on new commits. Configure here.}

github-actions · 2026-01-22T15:26:31Z

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	88.45% ⬇️ -0.14%	5807 / 6565
🔵	Statements	88.33% ⬇️ -0.14%	5901 / 6680
🔵	Functions	87.44% ⬇️ -0.22%	1512 / 1729
🔵	Branches	84.58% ⬇️ -0.25%	2101 / 2484

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
packages/cli/src/app.ts	0% 🟰 ±0%	0% 🟰 ±0%	0% 🟰 ±0%	0% 🟰 ±0%	15-155
packages/cli/src/commands/bundle.ts	92.3% 🟰 ±0%	50% 🟰 ±0%	100% 🟰 ±0%	92.3% 🟰 ±0%	72
packages/cli/src/commands/watch.ts	100% 🟰 ±0%	100% 🟰 ±0%	100% 🟰 ±0%	100% 🟰 ±0%
packages/cli/src/vite/export-metadata-plugin.ts	0%	0%	0%	0%	19-30
packages/cli/src/vite/strip-comments-plugin.ts	100%	100%	100%	100%
packages/cli/src/vite/vat-bundler.ts	0%	0%	0%	0%	18-54
packages/kernel-utils/src/index.ts	100% 🟰 ±0%	100% 🟰 ±0%	100% 🟰 ±0%	100% 🟰 ±0%
packages/kernel-utils/src/vat-bundle.ts	100%	100%	100%	100%
packages/ocap-kernel/src/vats/VatSupervisor.ts	74.64% 🟰 ±0%	44.82% 🟰 ±0%	58.33% 🟰 ±0%	74.64% 🟰 ±0%	122, 133, 141, 179, 217-221, 232, 241-242, 263-265, 268, 272-274, 309, 326-334
packages/ocap-kernel/src/vats/bundle-loader.ts	100%	100%	100%	100%

Generated in workflow #3446 for commit 4d3ef97 by the Vitest Coverage Report Action

github-actions · 2026-01-22T15:26:32Z

📊 View full HTML coverage report for main

rekmarks

Really nice!

packages/ocap-kernel/src/vats/bundle-loader.ts

packages/cli/README.md

packages/cli/test/integration/serve.test.ts

packages/cli/src/vite/vat-bundler.ts

packages/cli/src/commands/bundle.test.ts

packages/cli/src/vite/strip-comments-plugin.ts

packages/kernel-utils/src/vat-bundle.ts

packages/cli/src/vite/strip-comments-plugin.ts

packages/ocap-kernel/src/vats/bundle-loader.ts

grypez · 2026-01-27T17:59:33Z

We could remove the 'modules' key from the new bundle format. It is included here as a PoC for attaching metadata to the bundles.

grypez · 2026-01-28T17:34:31Z

PR History: #763 · build: Bundle vats with vite

Reviewer	Comments	Status
rekmarks	5/5 ●	re-approval needed
cursor	9/9 ●

Jan 22 · rekmarks · CHANGES_REQUESTED — 5/5 ●

File	Comment	Resolution
`bundle-loader.ts:L9`	Remove Vite-specific naming from type	✓ `99c6775d`
`README.md:L5`	nit: documentation wording	✓ `99c6775d`
`serve.test.ts:L23`	Import VatBundle type, relocate to kernel-utils	✓ `61af648a`
`vat-bundler.ts:L56`	Comment should note import only in comments	✓ #772
`vat-bundler.ts:L8`	Code smell: moduleFormat declared multiple times	✓ `61af648a`

Jan 22 · cursor · COMMENTED — 2/2 ●

File	Comment	Resolution
`vat-bundler.ts:L56`	Import pattern regex may break `.import()` calls	✓ #772
`bundle-loader.ts:L33`	Missing code property validation	✓ `1424d588`

Jan 23 · cursor · COMMENTED — 4/4 ●

File	Comment	Resolution
`bundle.test.ts:L70`	Test uses incorrect moduleFormat 'vite-iife'	✓ `f80313b7`
`strip-comments-plugin.ts:L53`	Regex literals not handled	✓ #772
`strip-comments-plugin.ts:L46`	Template literal expressions not handled	✓ #772
`strip-comments-plugin.ts:L63`	Multi-line comment removal creates syntax errors	✓ #772

Jan 23 · cursor · COMMENTED — 2/2 ●

File	Comment	Resolution
`vat-bundle.ts:L30`	isVatBundle doesn't validate all properties	✓ `db40d34d`
`strip-comments-plugin.ts:L26`	Wrong sourceType for IIFE parsing	✓ `6cd04a3f`

Jan 23 · cursor · COMMENTED — 1/1 ●

File	Comment	Resolution
`bundle-loader.ts:L33`	inescapableGlobalProperties treated as escapable	✗ Rejected

	Resolved ●	Unresolved ○
	14 total	0 total
Fixed	✓ 13
Rejected	✗ 1
Punted	⤳ 0
Void	∅ 0
New		◇ 0
Pending		→ 0
Discussing		⇄ 0
Deferred		↓ 0

packages/cli/src/vite/vat-bundler.ts

packages/cli/src/vite/export-metadata-plugin.ts

packages/ocap-kernel/src/vats/bundle-loader.ts

packages/cli/test/test.bundle

packages/ocap-kernel/src/vats/bundle-loader.ts

packages/cli/src/commands/bundle.test.ts

packages/ocap-kernel/src/vats/bundle-loader.ts

rekmarks

Just a couple of nits!

rekmarks · 2026-01-29T17:15:16Z

packages/kernel-utils/src/vat-bundle.ts

+export const isVatBundle = (value: unknown): value is VatBundle =>
+  isObject(value) &&
+  hasProperty(value, 'moduleFormat') &&
+  value.moduleFormat === 'iife' &&
+  hasProperty(value, 'code') &&
+  typeof value.code === 'string' &&
+  hasProperty(value, 'exports') &&
+  Array.isArray(value.exports) &&
+  hasProperty(value, 'external') &&
+  Array.isArray(value.external);


This should be done with superstruct

rekmarks · 2026-01-29T17:21:18Z

packages/cli/src/vite/vat-bundler.ts

+          stripCommentsPlugin() as unknown as PluginOption,
+          metadataPlugin as unknown as PluginOption,


Odd that we have to cast them here.

Co-authored-by: Erik Marks <[email protected]>

Reuses the acorn parsing dependency from `@ocap/kernel-agents-repl` to authoritatively scrub comments from vat bundles. Refs #770  --- > [!NOTE] > Replaces the comment scrubber with an AST-based implementation to reliably remove comments (including those containing `import(`) from bundled code. > > - Refactors `vite/strip-comments-plugin` to use Acorn (`parse` with `onComment`) and return unchanged code when no comments are found > - Adds unit tests for `strip-comments-plugin` covering single/multi-line comments, strings, regex, templates, and empty input > - Adds `acorn` dependency in `@ocap/cli` and updates `yarn.lock` > > <sup>Written by [Cursor Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit 3a59ba8. This will update automatically on new commits. Configure [here](https://cursor.com/dashboard?tab=bugbot).</sup>

status: substantiated ### Incomplete type guard doesn't validate all VatBundle properties **Medium Severity** The `isVatBundle` type guard asserts that a value is a `VatBundle`, but only validates `moduleFormat` and `code` properties. The `VatBundle` type also requires `exports: string[]` and `modules: Record<...>` properties. Code that uses this type guard will believe it has a complete `VatBundle` after the check, but accessing `.exports` or `.modules` could return `undefined` if an incomplete object passed the check. Location: packages/kernel-utils/src/vat-bundle.ts#L24-L30

status: substantiated ### Missing validation of `code` property in bundle loader **Medium Severity** The `loadBundle` function validates that `moduleFormat` equals `'vite-iife'` but does not validate that `code` exists or is a string before using it in `compartment.evaluate`. If a malformed bundle is loaded (e.g., corrupted file, incompatible version) with correct `moduleFormat` but missing or non-string `code`, the template literal interpolation would produce invalid JavaScript (like `"undefined"` or `"[object Object]"`) leading to confusing evaluation errors or silently returning `undefined` instead of proper exports. Location: packages/ocap-kernel/src/vats/bundle-loader.ts#L29-L33

status: substantiated ### Wrong sourceType for parsing IIFE bundle output **Low Severity** The `stripCommentsPlugin` uses `sourceType: 'module'` to parse vite's IIFE output, but IIFE bundles are scripts, not modules. Module parsing implies strict mode, which rejects certain legacy JavaScript patterns (octal literals, `with` statements, etc.). If bundled dependencies contain non-strict-mode code that wasn't transpiled, `parse()` throws a SyntaxError, preventing comment stripping and causing the build to fail unexpectedly. Location: packages/cli/src/vite/strip-comments-plugin.ts#L21-L26

Add validation that code exists and is a string before calling compartment.evaluate in loadBundle. Co-Authored-By: Claude Opus 4.5 <[email protected]>

Add validation for exports (Array.isArray) and modules (object && !== null) properties in the isVatBundle type guard. Co-Authored-By: Claude Opus 4.5 <[email protected]>

Change sourceType from 'module' to 'script' in stripCommentsPlugin to correctly handle IIFE bundles that may contain non-strict-mode patterns like octal literals and with statements. Co-Authored-By: Claude Opus 4.5 <[email protected]>

Co-Authored-By: Claude Opus 4.5 <[email protected]>

- Remove `export` keyword from BundleMetadata type (only used internally) - Replace modules metadata collection with simple `external: []` field - Update VatBundle type and isVatBundle type guard accordingly - Update vat-bundle tests to use external instead of modules Co-Authored-By: Claude Opus 4.5 <[email protected]>

Update the test bundle fixture to use `external: []` instead of `modules: {}` to match the updated VatBundle type definition. Co-Authored-By: Claude Opus 4.5 <[email protected]>

Use parsed.code directly after validation instead of casting to an intermediate VatBundle type that is only used for its code property. Co-Authored-By: Claude Opus 4.5 <[email protected]>

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Address rekmarks review comments: - Use superstruct for VatBundle type guard instead of manual checks - Import Plugin from vite instead of rollup to remove unnecessary casts Co-Authored-By: Claude Opus 4.5 <[email protected]>

cursor

Cursor Bugbot has reviewed your changes and found 1 potential issue.

packages/ocap-kernel/src/vats/bundle-loader.ts

Tests that loadBundle throws clear validation error for malformed content. Currently fails with TypeError instead of descriptive error message. Co-Authored-By: Claude Opus 4.5 <[email protected]>

Validate that parsed JSON is a non-null object before accessing properties. Prevents TypeError when bundle content is "null" or other non-object JSON. Co-Authored-By: Claude Opus 4.5 <[email protected]>

grypez force-pushed the grypez/bundle-with-vite branch 3 times, most recently from 504110d to 1a13965 Compare January 22, 2026 15:17

grypez marked this pull request as ready for review January 22, 2026 18:29

grypez requested a review from a team as a code owner January 22, 2026 18:29

grypez force-pushed the grypez/bundle-with-vite branch from 1a13965 to b8e02c0 Compare January 22, 2026 18:45

rekmarks requested changes Jan 22, 2026

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rekmarks mentioned this pull request Jan 23, 2026

refactor: Make makeJsonAgent bundleable with @endo/bundle-source #750

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grypez force-pushed the grypez/bundle-with-vite branch from bdc4c89 to 85c60f8 Compare January 23, 2026 19:56

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grypez force-pushed the grypez/bundle-with-vite branch 3 times, most recently from daa5828 to 6cd04a3 Compare January 26, 2026 23:28

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grypez and others added 21 commits January 29, 2026 11:54

respin yarn

d8b0178

fix test mock

dd54c25

Apply some suggestions from code review

7d1ffcd

Co-authored-by: Erik Marks <[email protected]>

address remaining review comments

69039b0

small fixes

46caccd

add isVatBundle to index test

0fa7ea3

fix(2:2): validate code property in loadBundle

ca925e5

Add validation that code exists and is a string before calling compartment.evaluate in loadBundle. Co-Authored-By: Claude Opus 4.5 <[email protected]>

fix(4:1): validate all VatBundle properties in isVatBundle

9ca966b

Add validation for exports (Array.isArray) and modules (object && !== null) properties in the isVatBundle type guard. Co-Authored-By: Claude Opus 4.5 <[email protected]>

fix(5:4): remove redundant assert from loadBundle

0d4fbdf

Co-Authored-By: Claude Opus 4.5 <[email protected]>

fix(5:1): remove unused VatBundle re-export

4f7d795

Co-Authored-By: Claude Opus 4.5 <[email protected]>

fix: update test.bundle fixture to use external field

c4ba419

Update the test bundle fixture to use `external: []` instead of `modules: {}` to match the updated VatBundle type definition. Co-Authored-By: Claude Opus 4.5 <[email protected]>

fix(6:2): remove unnecessary VatBundle type cast

685b9af

Use parsed.code directly after validation instead of casting to an intermediate VatBundle type that is only used for its code property. Co-Authored-By: Claude Opus 4.5 <[email protected]>

fix(7:1): use external field in test bundle mocks

2082e18

Co-Authored-By: Claude Opus 4.5 <[email protected]>

fix(7:2): remove unnecessary export from LoadBundleOptions

831a2dc

Co-Authored-By: Claude Opus 4.5 <[email protected]>

grypez force-pushed the grypez/bundle-with-vite branch from d511472 to c0cf139 Compare January 29, 2026 17:56

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grypez and others added 2 commits January 29, 2026 12:21

repro(8:1): add tests for null/non-object bundle content

acce346

Tests that loadBundle throws clear validation error for malformed content. Currently fails with TypeError instead of descriptive error message. Co-Authored-By: Claude Opus 4.5 <[email protected]>

fix(8:1): add null check validation to loadBundle

4d3ef97

Validate that parsed JSON is a non-null object before accessing properties. Prevents TypeError when bundle content is "null" or other non-object JSON. Co-Authored-By: Claude Opus 4.5 <[email protected]>

rekmarks approved these changes Jan 29, 2026

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Merged via the queue into main with commit fa7d847 Jan 29, 2026
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grypez deleted the grypez/bundle-with-vite branch January 29, 2026 18:49

		stripCommentsPlugin() as unknown as PluginOption,
		metadataPlugin as unknown as PluginOption,

build: Bundle vats with vite #763

build: Bundle vats with vite #763

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grypez commented Jan 22, 2026 • edited by cursor bot Loading Uh oh! There was an error while loading. Please reload this page.

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Motivation

Changes

Bundling

Bundle Loading

Dependencies

Bundle Format

Migration

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grypez commented Jan 27, 2026

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grypez commented Jan 28, 2026

PR History: #763 · build: Bundle vats with vite

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grypez commented Jan 22, 2026 •

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