ci: experiment with conservative smart system-test selection

[cgcote]

What does this PR do?

Adds a shadow-only system-test selector that recommends scenario groups from changed tracer source paths. The existing tracer_release system-test execution remains unchanged.

The selector narrows only changes isolated to a recognized product area. Shared, mixed, empty, or unclassified changes fail open to tracer_release. Each recommendation is published in the GitHub job summary with a reason per changed file.

Motivation:

Collect evidence for smarter system-test selection without reducing PR coverage or asking developers to trust an enforcement mechanism.

Change log entry

None. This is internal CI tooling.

Additional Notes:

This first shadow experiment validates deterministic selection, reporting, and conservative fallback behavior. It does not skip tests. Runtime coverage can replace or augment the initial source-area evidence after the shadow data establishes the workflow.

How to test the change?

• Ruby syntax checks pass for the selector and its spec.
• The workflow parses as YAML and git diff checks pass.
• Standalone smoke checks cover isolated AppSec, native profiling, and mixed shared changes.
• The repository RSpec task could not run locally because the checkout is missing development gems benchmark-ips and zstd-ruby; CI will run spec/github/system_tests_selector_spec.rb.

[datadog-prod-us1-3]

 

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ℹ️ Info

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🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 90.64% (-0.00%)

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