What

Promotes the browser leg from a single React smoke test to the full unit + connectionConfig suite running inside a real headless Chromium (@vitest/browser + Playwright) — the same coverage test:bun / test:deno / test:cf get. 69 files / 343 tests green locally against production.

pnpm test:browser   # installs Chromium via pretest:browser, then runs the suite

React is gone as requested — the smoke test (tests/runtimes/browser/run.test.tsx) and its seven devDependencies (react, react-dom, @types/react, @types/react-dom, @testing-library/react, @vitejs/plugin-react, vitest-browser-react). Chromium installation moves off the default pretest hook onto pretest:browser, so plain pnpm test no longer downloads a browser.

The one thing the smoke test uniquely covered — the SDK driven with no process global at all, the way a real browser bundle runs — is kept as a dedicated test, since the rest of the suite runs against a process.env shim that would mask a regression there:

// tests/runtimes/browser/noProcessGlobal.test.ts
Reflect.deleteProperty(globalThis, 'process')
const sandbox = await Sandbox.create(template, { apiKey, domain })
await sandbox.files.write('hello.txt', 'Hello World')

Failure screenshots are off (browser.screenshotFailures: false): these tests never render anything, so vitest's default would write a PNG of a blank page per failed test into .vitest-attachments/.

Test bugs the leg surfaced

1. Two assertions were vacuous. commands/kill and pty/kill asserted rejects.toThrowError(ProcessExitError) — but ProcessExitError has never been exported from src. Vite's SSR transform resolves the missing named import to undefined, so toThrowError(undefined) asserted nothing on any runtime; real ESM in the browser turns it into a hard SyntaxError. Now CommandExitError.

2. files/read.test.ts ran three tests twice — a byte-identical duplicated block, provisioning a second real sandbox for each on every runtime leg.

3. A cold-cache-only flake, root-caused. api/http2 and envd/http2 carried dead vi.doUnmock('undici') / vi.doUnmock('../../src/utils') calls from an old refactor (neither file mocks anything any more). The bare 'undici' one made Vite discover and pre-bundle a Node HTTP client mid-run, reloading the browser page under the running suite and breaking whichever file was being collected. Verified: 1-in-4 failure before, three cold-cache runs green after.

Node-only test APIs are replaced with cross-runtime equivalents: node:crypto randomUUID/createHash → WebCrypto, Buffer → TextEncoder/TextDecoder, path.basename → inline.

Two real browser bugs found

Both verified over the wire; neither was fixable in the SDK alone.

Pagination silently truncated — the cursor lives in the x-next-token response header, which the API didn't name in Access-Control-Expose-Headers, so a browser withheld it and every page looked like the last:

const paginator = Sandbox.list({ limit: 10 })
const all = []
while (paginator.hasNext) all.push(...(await paginator.nextItems()))
// Node: all 200 sandboxes.  Browser (before the fix): 10, hasNext === false, no error.

Fixed upstream in infra#3388, so the tests are un-gated here and just need the prod rollout (see the callout above). SDK-293.

SDK-294 — isRunning() threw instead of returning false. A stopped sandbox's 502 came from the edge without CORS headers, so the probe rejected opaquely (running: 204 + ACAO: * / paused: 502 + no ACAO). Because a browser always preflights the SDK's envd requests (they carry E2b-Sandbox-Id/E2b-Sandbox-Port) and a preflight needs an ok status, adding the header to the 502 alone wasn't enough — the OPTIONS path needed a 2xx too. This also silently downgraded the kill-mid-request error from the actionable TimeoutError to a generic SandboxError across 24 call sites.

Fixed upstream in infra#3389, which also fixes the content negotiation the investigation turned up: the proxy chose HTML over JSON by User-Agent sniffing, and browser fetch can't override its UA, so an SDK call from a browser got the HTML error page where it expects JSON (Accept was ignored). Both are un-gated here.

How limitations are handled

No capability flags — nothing is skipped for being a browser. The five tests that read a response from a server the test itself starts in the sandbox now start a CORS-enabled one, via corsHttpServerCmd in tests/setup.ts:

// was: 'python3 -m http.server 8000' — no CORS headers, so a browser hands the
// test an opaque `TypeError: Failed to fetch` instead of the response
await sandbox.commands.run(corsHttpServerCmd(8000), { background: true })

This was originally gated behind a canFetchSandboxServers flag as an inherent browser limitation. It isn't one: the server is the test's own, and a real browser app's server opts into CORS exactly the same way — so the gate was hiding coverage of getHost and the proxy path rather than documenting a wall. Access-Control-Allow-Headers plus do_OPTIONS also covers the traffic-access-token test, whose custom header the browser preflights.

Confirmed on the browser leg (run): of the five tests this un-gates, three now pass — ping server in running sandbox, sandbox works without token, auto-resume wakes paused sandbox on http request. That's the CORS server working end-to-end through the proxy against production. The other two are the two infra#3389 needs anyway: pause and resume a sandbox with http server calls isRunning() on a paused sandbox, and sandbox requires traffic access token reads a proxy-synthesized 403 (which 3389 gives CORS headers) after a preflight that can't carry the token (which 3389 answers on the getDestination error path).

The exclude list is only for genuinely Node-only suites (tests/bundle/** reads dist via node:fs, tests/undici.test.ts resolves packages off process.versions.node) plus the two msw suites, whose msw/node entry pulls in node:http and can't be served to a browser. Porting those needs setupWorker plus a service worker from a public dir — tracked as a follow-up on SDK-292, and worth doing since cancellation is the most runtime-divergent part of this SDK.

CI

New browser matrix leg on ubuntu-22.04, with the Playwright cache moved onto it (no other leg needs Chromium any more). The leg is dropped by node-only staging callers, and it's the only leg whose result depends on the API's CORS headers — the matrix comment now says so, rather than claiming the non-Node legs add no backend signal.

Notes

• No changeset: test-only, matching test(js-sdk): run the template test suite on Bun #1600 and the other recent test(js-sdk) commits.
• vi.stubEnv and delete process.env.X keep working in the browser because the shim aliases process.env to import.meta.env, which is where vitest puts config env and where stubEnv writes. Verified E2B_DEBUG=1 pnpm test:browser correctly skips the debug-gated tests.
• Verification for the CORS server, since a browser-side change like this is easy to get subtly wrong: ran a local instance of the exact generated command and fetched it cross-origin (different port = different origin) from real Chromium — simple GET readable, and a custom-header request survives the preflight. Negative control against a plain python -m http.server reproduces the TypeError: Failed to fetch the browser leg was showing, so the probe is meaningful rather than vacuous. Also checked there's exactly one Access-Control-Allow-Origin header — a duplicate would make browsers reject the response.
• Review feedback addressed in 4c94fca: the pause and resume a sandbox with http server test now carries the canFetchSandboxServers gate too (it fetches its own python -m http.server, so it was a real miss that the isRunning failure happened to mask), and noProcessGlobal.test.ts imports the SDK dynamically inside the test body — a static import is evaluated at collection time, while the process shim is still installed, so it only covered the call path and not module evaluation.
• No new type errors: 22 pre-existing test type errors before and after (the 2 that went away are the ProcessExitError ones this fixes).
• Not addressed, pre-existing, flagged in case you want a follow-up: tests/api/list.test.ts duplicates five tests byte-for-byte (only the three betaPause ones intentionally differ, instance vs static), and files/write.test.ts:130 repeats write file as a strict subset of the test at :6 — together ~7 redundant sandboxes per run per leg. Left alone rather than deleting tests outside this change's scope.

Closes SDK-292

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