[PerfectSlayer]

What Does This Do

Ports the OpenFeature smoke tests from Groovy/Spock to the JUnit 5 smoke test framework, and adds the two framework features they need:

• MockAgentBackend.evpProxy() captures the requests the tracer sends through the event platform proxy, and the mock agent /info advertises the proxy and its allowed headers, like the Groovy smoke base.
• SmokeServerApp.terminate(timeout, unit) stops the app with a termination signal, so a test can assert what it flushes at exit.

The tests run against the in-process mock agent: the dd-apm-test-agent (pinned v1.64.1, and current master) neither proxies the flag evaluation events nor advertises the event platform proxy headers. The scenarios and assertions are unchanged.

Smoke test framework (dd-smoke-tests)

• EvpProxy: query facade over the captured proxy requests (path, headers, body), filtered by intake path, with waitForRequest.
• MockAgentBackend: captures /evp_proxy/v2/ requests, clears them between tests, advertises /evp_proxy/v2/ and evp_proxy_allowed_headers in /info.
• AgentBackend.mockAgent() returns the MockAgentBackend type, to reach its specific surfaces.
• SmokeServerApp.terminate(): completes the test scope diagnostics, sends the termination signal without closing the app output streams (Java 9+), so its shutdown logs stay captured, and waits for the exit. The per-test liveness check accepts a terminated app; a later test fails with an explicit message.
• Polling.waitForFirst: shared by RemoteConfig.waitForRequest and EvpProxy.waitForRequest.
• AbstractSmokeTest.groovy: removes the Remote Config poll capture the deleted Groovy tests were the last users of.
• docs/how_to_smoke_test.md: documents both features.

OpenFeature smoke tests (dd-smoke-tests/openfeature)

• AbstractOpenFeatureSmokeTest: exposures first (exposure cache), then one parameterized test per system tests evaluation case, ordered with @Order instead of @Stepwise.
• OpenFeatureProviderSmokeTest: captures the tracer first Remote Configuration poll in @BeforeAll, before the per-test backend reset, to keep checking it asks for FFE_FLAGS.
• OpenFeatureAgentlessSmokeTest, OpenFeatureStandaloneSmokeTest, OpenFeatureMalformedRemoteConfigSmokeTest: same scenarios as before.
• AbstractOpenFeatureShutdownSmokeTest and its two variants: use terminate() instead of destroying the process.
• OpenFeatureFixtures: the flag configuration, the CDN fixture, the evaluation cases and the app builder.
• Json: keeps numbers as written, as the evaluation cases tell integers from decimals, which the application maps to different types.

Motivation

Moves the OpenFeature smoke tests to the Java smoke test framework (APMLP-1512).

Stack

The full change is in #12709. It was split into this stack to ease the review.

1. Resolve Feature Flags enablement from instrumenter config #12845 (merged)
2. Add dd-openfeature SDK flag configuration and evaluation core #12840 (merged)
3. Add dd-openfeature SDK settings and configuration delivery #12841 (merged)
4. Add dd-openfeature SDK exposure and flag evaluation pipelines #12842 (merged)
5. Add dd-openfeature SDK OpenFeature provider #12843 (merged)
6. Port master Feature Flags changes to the dd-openfeature SDK #12957 (merged)
7. Add the agent bridge for the dd-openfeature SDK #12975 (merged)
8. Connect the dd-openfeature SDK to the agent #12844 (merged)
9. Keep released dd-openfeature SDKs working with the agent #12976 (merged)
10. Resolve the Feature Flags settings like the SDK #12977 (merged)
11. Restore the agent Feature Flags behaviors through the bridge #12978
12. Add agentless and standalone OpenFeature smoke tests #12846
13. Port the OpenFeature smoke tests to JUnit #13106 👈 this PR

Jira ticket: APMLP-1512

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