Attempt to fix race conditions in 'set_and_wait_rc' by counting telem…

[vlad-scherbich]

Motivation

~25 of 32 system test failures on dd-trace-py main in 2026 stem from dynamic configuration tests. Root cause: a race in set_and_wait_rc—it can match stale app-client-configuration-change telemetry events from a previous RC update and return before the new config is actually applied.

Changes

• set_and_wait_rc: Replace wait_for_telemetry_event(..., clear=True) with telemetry event counting. Snapshot the count of app-client-configuration-change events before setting RC, then poll until the count increases—guaranteeing we match a genuinely new event, not a stale one.
• test_capability_tracing_sample_rules: Increase wait_loops from 100 to 400 (~4s) so the library has enough time to send its first RC request.
• _MAX_RC_EVENT_WAIT_LOOPS: Add module-level constant (400) for the RC event polling loop instead of a magic number.

Files modified: tests/parametric/test_dynamic_configuration.py

Workflow

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2. Work on your PR until the CI passes
3. Mark it as ready for review
   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

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Reviewer checklist

• Anything but tests/ or manifests/ is modified ? I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added, removed or renamed?
  • Get a review from R&P team

[github-actions]

CODEOWNERS have been resolved as:

utils/scripts/list_flaky_system_tests.sh                                @DataDog/system-tests-core
tests/parametric/test_dynamic_configuration.py                          @DataDog/system-tests-core @DataDog/apm-sdk-capabilities
utils/docker_fixtures/_test_agent.py                                    @DataDog/system-tests-core