test(ffe): enable .NET EVP flagevaluation egress

[leoromanovsky]

Motivation

.NET needs route-level system-test coverage for flag-evaluation EVP delivery through the Datadog Agent, direct intake, and the serverless sidecar.

Linear: FFL-1492

Changes

• Explicitly install the shared OpenFeature provider and select the agentless configuration source in agentless FFE scenarios.
• Enable the three .NET flag-evaluation egress cases at v3.53.0:
  • Datadog Agent
  • agentless direct intake
  • agentless serverless sidecar
• Keep the remaining .NET flag-evaluation behavior cases marked missing_feature (FFLSDK-28).

Decisions

• Keep provider activation explicit because selecting a configuration source does not install the provider.
• Activate only the three egress cases validated against the branch-built tracer.
• Stack on test(nodejs): validate agentless EVP exposure egress #7602 so the shared direct-intake system-CA binding is reviewed once.

Validation

• ./build.sh dotnet -w poc -- passed against the branch-built tracer package.
• ./format.sh --check -- passed.
• ./run.sh TEST_THE_TEST tests/test_the_test/test_manifest.py -- 32 passed.
• ./run.sh TEST_THE_TEST tests/test_the_test/test_mock_ffe_agentless_backend.py -- 9 passed.
• ./run.sh TEST_THE_TEST -- 438 passed, 1 expected xfail.
• Manifest computation at .NET 3.53.0 confirmed exactly three egress classes enabled and eleven behavior classes disabled.
• Datadog Agent flag-evaluation egress -- 1 passed in 66.95s.
• Agentless direct flag-evaluation egress -- 1 passed in 15.17s; post-restack verification passed in 44.53s.
• Agentless serverless-sidecar flag-evaluation egress -- 1 passed in 15.60s.
• A control run with only the Node-specific CA location timed out after 30s; binding the proxy CA at the system bundle path made direct delivery observable before teardown.

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on your PR until CI passes.
3. Keep test-logic review with the RFC owner; ask the R&P team in #apm-shared-testing for framework or non-obvious harness changes.

Note

FOR SYSTEM-TEST FRAMEWORK OR SCENARIO HELP, USE #apm-shared-testing.

Reviewer checklist

• Test logic has RFC-owner review.
• Any framework or scenario change has R&P review in #apm-shared-testing.

[github-actions]

CODEOWNERS have been resolved as:

manifests/dotnet.yml                                                    @DataDog/system-tests-reviewers
tests/test_the_test/test_mock_ffe_agentless_backend.py                  @DataDog/feature-flagging-and-experimentation-sdk @DataDog/system-tests-core
utils/_context/_scenarios/agentless_endtoend.py                         @DataDog/system-tests-core

[linear-code]

FFL-1492

[datadog-datadog-us1-prod]

🎉 All green!

❄️ No new flaky tests detected

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