fix(openfeature): isolate invalid flags [backport v2.9]

[leoromanovsky]

Motivation

A malformed flag can reject the complete UFC configuration. This makes unrelated flags return defaults.

Backport the exact merged main commit 6d96ff5424 to release-v2.9.x. A compatibility commit adapts tests to the older evaluator signature.

Changes and Decisions

• Parse and validate flags independently.
• Reject only the malformed flag.
• Keep valid neighboring flags available for evaluation.
• Use the shared FFE fixture corpus.

[datadog-prod-us1-4]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: No data available
• Overall Coverage: 62.04% (+0.03%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 28ec9e5 | Docs | Datadog PR Page | Give us feedback!}

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-08-05 20:59:08

Comparing candidate commit 28ec9e5 in PR branch agent/backport-ufe-invalid-flag-v2.9 with baseline commit f5f7068 in branch release-v2.9.x.

Found 4 performance improvements and 0 performance regressions! Performance is the same for 269 metrics, 2 unstable metrics, 1 flaky benchmarks without significant changes.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:BenchmarkOTLPProtoSize/1000spans

• 🟩 execution_time [-18.230µs; -17.207µs] or [-5.612%; -5.297%]

scenario:BenchmarkOTLPProtoSize/100spans

• 🟩 execution_time [-1.865µs; -1.751µs] or [-5.744%; -5.393%]

scenario:BenchmarkOTLPProtoSize/10spans

• 🟩 execution_time [-232.893ns; -223.907ns] or [-6.941%; -6.673%]

scenario:BenchmarkOTLPProtoSize/1span

• 🟩 execution_time [-28.721ns; -26.739ns] or [-7.076%; -6.588%]

Known flaky benchmarks

These benchmarks are marked as flaky and will not trigger a failure. Modify FLAKY_BENCHMARKS_REGEX to control which benchmarks are marked as flaky.

Known flaky benchmarks without significant changes:

• scenario:BenchmarkOTLPTraceWriterFlush

[darccio]

Approving on behalf of @DataDog/dd-trace-go-guild as the original PR was reviewed and approved.

[darccio]

Failures are unrelated.