* fix: isJson assertion fails after res.setBody() with object in node-vm
Objects created inside Node's vm.createContext() have a different Object
constructor than the host realm. When res.setBody() is called with a JS
object from a script, _.cloneDeep preserves the cross-realm prototype,
causing obj.constructor === Object to fail in the isJson assertion.
Replace with Object.prototype.toString.call() which is cross-realm safe.
* fix: register isJson chai assertion in QuickJS test runtime
The bundled chai in QuickJS only exposes { expect, assert } via
requireObject — no Assertion class. Access the prototype through
Object.getPrototypeOf(expect(null)) and use Object.defineProperty
to register the json property directly.
* fix: enable assertion chaining on isJson in QuickJS runtime
The QuickJS isJson property getter was missing `return this`, preventing
chai assertion chaining (e.g. expect(body).to.be.json.and...).
- Added interpolation to setVar method's value field.
- Added playwright test to test the fix.
- Added jest test to test out the fix.
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Playwright - PASS
Jest - PASS
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