[Bug]: JS examples CI still invokes Jest after Vitest migration #918

Expected Behavior

The JS Examples workflow should run the JS SDK's example tests against the Python local runner using the test runner provided by the checked-out JS SDK.

Actual Behavior

The JS SDK installs and builds successfully, but the Python harness exits before any example tests run:

npm error npx canceled due to missing packages and no YES option: ["jest@30.5.2"]
[js-examples] error: jest wrote no results to .../js-examples/jest.json; see its output above
Process completed with exit code 2.

Observed in both:

• PR #917 CI run.
• An earlier run on main, with the same error and JS revision. This predates chore: prepare Python SDK 3.0.2 release #917's version bump and test cleanup.

Steps to Reproduce

1. Use Python SDK checkout db37e61ed0101e092262b7f173c5829d2a35078a, Python 3.14, Node.js 22, and Hatch 1.16.5.

2. Check out aws/aws-durable-execution-sdk-js at a34bf9288ac6a35def7d15283dbbdb111bdcf1f3 in js-sdk/.

3. Run:

   hatch run dev-testing:js-examples --js-dir js-sdk --out /tmp/js-examples

The harness installs and builds the JS packages, then fails when starting Jest.

SDK Version

Python repository commit db37e61ed0101e092262b7f173c5829d2a35078a (Core 3.1.0 / Testing 1.4.1 release preparation). Also reproduced by CI on main at e4bbbcd5fcc74c1b04c40bb34461e9e0978d7494.

Python Version

3.14.10

Is this a regression?

Yes. The workflow previously passed, for example run 41498565642. It follows JS main, so an upstream test-framework change can break a Python run without a Python behavior change.

Additional Context

The JS SDK migrated from Jest to Vitest in aws/aws-durable-execution-sdk-js#1167. At the failing JS revision, the examples package uses vitest.config.ts and NODE_ENV=integration vitest run; Jest and jest.config.integration.js have been removed.

Python's JS examples harness still invokes:

npx --no-install jest --config jest.config.integration.js ...

The workflow checks out JS main by default.

Update the harness to use Vitest's integration configuration, CLI options, and JSON reporter. Preserve test selection, worker limits, expected-failure handling, and failure detection when results are missing or incomplete. Update the harness tests and documentation, and validate the workflow against the migrated JS SDK. Installing Jest alone would not restore the removed configuration or migrated test code.