The error originates from Vitest when used with jsdom. See vitest-dev/vitest#7906 for more details. This issue is fixed in vitest-dev/vitest#8390, but not yet released.

- Fix elevenlabs transcription test snapshot for Node 24 File serialization
- Allow Node 24 test matrix to fail until jsdom/vitest compat is resolved

Node 24 introduces a stricter AbortSignal instanceof check in native
fetch that rejects jsdom's AbortSignal. This is fixed in vitest 3.2.4+
(vitest-dev/vitest#8390) but requires a vitest major version upgrade.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

- see vitest-dev/vitest#8390 (comment) for path details
- I was running node 22 locally hence I didn't see this issues until CI ran

## Summary

Adds Node.js 24 to the CI test matrix and fixes all build/test
incompatibilities.

Closes #13357

## Changes

### CI & config
- Adds Node.js 24 to `.github/workflows/ci.yml` test matrix
- Adds `^24.0.0` to root `package.json` engines field

### SvelteKit example build fix
- Updates `@sveltejs/adapter-vercel` from v5 to v6 and `@sveltejs/kit`
to v2.55+ in `examples/sveltekit-openai` — adapter-vercel v5 only
supported Node 18/20/22, v6 adds Node 24

### Vitest v2 → v4 upgrade
Node 24 ships with undici v7, which enforces strict `AbortSignal`
instanceof checks in `fetch()`. The jsdom environment in vitest v2/v3
replaces the global `AbortController`/`AbortSignal` with its own
polyfill, and Node 24's native fetch rejects these with `"Expected
signal to be an instance of AbortSignal"`. Vitest v4 stops overriding
these globals
([vitest-dev/vitest#8390](vitest-dev/vitest#8390)),
fixing the incompatibility.

#### Test adaptations required by vitest v4

**`vi.fn()` arrow functions can no longer be used as constructors** —
vitest v4 wraps mock functions differently, so arrow-function mocks fail
with `TypeError: is not a constructor` when called with `new`. Fixed by
changing arrow functions to `function` expressions in mock
implementations:
-
`packages/amazon-bedrock/src/bedrock-event-stream-response-handler.test.ts`
- `packages/baseten/src/baseten-provider.unit.test.ts`
- `packages/gateway/src/gateway-provider.test.ts`
-
`packages/google-vertex/src/google-vertex-auth-google-auth-library.test.ts`

**`toStrictEqual(expect.objectContaining(...))` is stricter** — vitest
v4 now requires that `undefined` properties on the actual object (e.g.
`metadata: undefined`) also appear in the expected pattern. Since these
tests intentionally do partial matching, changed to
`toEqual(expect.objectContaining(...))`:
- `packages/angular/src/lib/chat.ng.test.ts`
- `packages/svelte/src/chat.svelte.test.ts`

**`toThrowError` with an Error object checks all properties** —
previously only checked `message`, now checks every property. The
anthropic overloaded-error test compared `requestBodyValues: {}` against
the full request body. Changed to try/catch with individual property
assertions:
- `packages/anthropic/src/anthropic-messages-language-model.test.ts`

**`test.workspace` renamed to `test.projects`**:
- `packages/svelte/vite.config.ts`

### Other test fixes
- `packages/openai` and `packages/elevenlabs`: Made `File` object
snapshot tests Node version-agnostic (Node 24 serializes additional
`Symbol(state)` on File objects)
- `packages/mcp`: Fixed race condition in SSE reconnect test where
`server.calls[2]` was accessed before the fire-and-forget
`openInboundSse()` completed — added `vi.waitFor()`
- Pinned `tinyexec` to 1.0.2 via pnpm overrides (1.0.3 has broken
package exports on npm)

### Backports 

- v6: #13440
- v5: #13441

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>