…spec (#9078)

The Bluebird specs set global.Promise = Bluebird in beforeEach and restored it
only in afterEach, holding the mutation across the awaited span round-trip. Under
load the subprocess span arrives late, and the shared assertion helper only
rejects once a payload has already errored, so the spec hangs to mocha's 5 s
timeout while leftover async keeps global.Promise flipped, corrupting context for
every later spec in the file.

1. The instrumentation only reads global.Promise synchronously, when the wrapped
   method runs. Scope the swap to that window via withBluebird() and restore it in
   a finally before any await.
2. assert.strictEqual(promise.constructor, Bluebird) asserts a property that
   depends on module-load order and the call-time global, not on any contract the
   instrumentation makes; it held locally and on Node 18 but saw the native
   constructor on Node 20. Assert the real contract instead: the promisified call
   resolves with the expected stdout and still produces the span.
3. Await the span expectation and the subprocess completion together in one
   Promise.all per spec, so a late or failed span cannot float onto the shared
   agent and match a later spec's expectation.

Drive-by fix:

* Drop the dead `delete require.cache[require.resolve('util')]` (util is a builtin).
* Replace the try/catch rejection check with assert.rejects.

…spec (#9078)

The Bluebird specs set global.Promise = Bluebird in beforeEach and restored it
only in afterEach, holding the mutation across the awaited span round-trip. Under
load the subprocess span arrives late, and the shared assertion helper only
rejects once a payload has already errored, so the spec hangs to mocha's 5 s
timeout while leftover async keeps global.Promise flipped, corrupting context for
every later spec in the file.

1. The instrumentation only reads global.Promise synchronously, when the wrapped
   method runs. Scope the swap to that window via withBluebird() and restore it in
   a finally before any await.
2. assert.strictEqual(promise.constructor, Bluebird) asserts a property that
   depends on module-load order and the call-time global, not on any contract the
   instrumentation makes; it held locally and on Node 18 but saw the native
   constructor on Node 20. Assert the real contract instead: the promisified call
   resolves with the expected stdout and still produces the span.
3. Await the span expectation and the subprocess completion together in one
   Promise.all per spec, so a late or failed span cannot float onto the shared
   agent and match a later spec's expectation.

Drive-by fix:

* Drop the dead `delete require.cache[require.resolve('util')]` (util is a builtin).
* Replace the try/catch rejection check with assert.rejects.

…spec (#9078)

The Bluebird specs set global.Promise = Bluebird in beforeEach and restored it
only in afterEach, holding the mutation across the awaited span round-trip. Under
load the subprocess span arrives late, and the shared assertion helper only
rejects once a payload has already errored, so the spec hangs to mocha's 5 s
timeout while leftover async keeps global.Promise flipped, corrupting context for
every later spec in the file.

1. The instrumentation only reads global.Promise synchronously, when the wrapped
   method runs. Scope the swap to that window via withBluebird() and restore it in
   a finally before any await.
2. assert.strictEqual(promise.constructor, Bluebird) asserts a property that
   depends on module-load order and the call-time global, not on any contract the
   instrumentation makes; it held locally and on Node 18 but saw the native
   constructor on Node 20. Assert the real contract instead: the promisified call
   resolves with the expected stdout and still produces the span.
3. Await the span expectation and the subprocess completion together in one
   Promise.all per spec, so a late or failed span cannot float onto the shared
   agent and match a later spec's expectation.

Drive-by fix:

* Drop the dead `delete require.cache[require.resolve('util')]` (util is a builtin).
* Replace the try/catch rejection check with assert.rejects.