feat(ffe): add runtime-backed PHP feature flag evaluation

[leoromanovsky]

Motivation

This PR adds real server-side PHP feature flag evaluation backed by Remote Config and the libdatadog native evaluator. PHP 7 gets a Datadog API, PHP 8 can use the optional OpenFeature bridge, and both paths use the same live runtime evaluator.

This is intentionally the evaluation layer only. Exposure delivery, exposure caching, and evaluation metrics land in the later hook, exposure, and metrics PRs.

Shared planning doc: https://docs.google.com/document/d/1NvMfTpZWLBlFmEFNjdnlMyeVpy5l7KD8qujGFco6w2w/edit?tab=t.0

Decisions

• Production clients/providers read only from the live Remote Config-backed native runtime.
• The root package remains PHP 7 installable; the OpenFeature SDK is used only in PHP 8 test/app environments and is not a root dependency.
• productionRuntime=false remains a temporary guardrail while the hook, exposure delivery, and evaluation metrics layers are incomplete. The final production-ready PHP FFE stack should not ship with that warning enabled.
• The PHP/OpenFeature bridge passes a targeting key plus flat primitive attributes (bool, int, float, string) into the native evaluator. Nested arrays, objects, and null attribute values are dropped at the boundary.
• DDTrace\Testing\ffe_load_config exists only for local/canonical fixture tests.

Where this PR fits in the stack

This is the bottom layer of the 4-PR stack. #3909 adds the shared hook, while #3910 (EVP exposures) and #3911 (OTLP metrics) build on top of that hook.

Where this PR fits in the target system

This PR contributes the in-PHP evaluation surface: UserCode -> OpenFeature Client (PHP 8) / DDTrace FeatureFlags Client (PHP 7 + 8), the DDTrace OpenFeature DataDogProvider, the NativeEvaluator FFI bridge into libdatadog, and the Remote Config client for the FFE_FLAGS product.

Changes

• Imports the libdatadog FFE evaluator path and keeps PHP user-facing APIs as thin adapters over the native runtime.
• Wires PHP 7-safe DDTrace\FeatureFlags evaluation through live Remote Config.
• Adds a PHP 8-only DDTrace\OpenFeature provider bridge.
• Adds the canonical DataDog/ffe-system-test-data submodule and a native-runtime PHPT loop over ufc-config.json and evaluation-cases/*.json.

Not Included

• Exposure writer, exposure cache, or EVP forwarding.
• Exposure flush/dedup tests.
• Flag-evaluation metric emission.

Validation

• php vendor/bin/phpunit --config phpunit.xml tests/api/Unit/FeatureFlags tests/OpenFeature/DataDogProviderTest.php: 29 tests / 87 assertions.
• make test_featureflags: 8 tests / 29 assertions.
• MAX_TEST_PARALLELISM=1 TESTS=tests/ext/ffe/native_bridge_evaluate.phpt make test_c: 1/1 passed.
• MAX_TEST_PARALLELISM=1 TESTS=tests/ext/ffe/system_test_data_evaluate.phpt make test_c: 1/1 passed.
• make test_internal_api_randomized: passed.

Dogfooding Validation

See DataDog/ffe-dogfooding#68.

Ran the PHP 7 and PHP 8 servers locally; observed correct evaluations.

[datadog-datadog-prod-us1-2]

🎉 All green!

🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 60.70% (-0.03%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 782f622 | Docs | Datadog PR Page | Give us feedback!}

[datadog-datadog-prod-us1-2]

 

✨ Fix all issues with BitsAI

⚠️ Warnings

🚦 1 Pipeline job failed

DataDog/apm-reliability/dd-trace-php | check-big-regressions     

🔧 Fix in code (Fix with Cursor).

Regression Check failed. Metric 'MetricName.EXECUTION_TIME' in scenarios has regressions larger than threshold. Received exit code 5.

ℹ️ Info

No other issues found (see more)

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 60.74% (+0.00%)

Useful? React with 👍 / 👎

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 4cf261d | Docs | Datadog PR Page | Give us feedback!}

[pr-commenter]

Benchmarks [ tracer ]

Benchmark execution time: 2026-05-28 02:35:37

Comparing candidate commit 4cf261d in PR branch leo.romanovsky/milestone-1-runtime-evaluation with baseline commit 6b5659e in branch master.

Found 1 performance improvements and 4 performance regressions! Performance is the same for 188 metrics, 1 unstable metrics.

scenario:BM_TeaSapiSpindown

• 🟥 execution_time [+12.479µs; +30.485µs] or [+2.404%; +5.873%]

scenario:ContextPropagationBench/benchInject128Bit-opcache

• 🟥 execution_time [+676.492ns; +735.508ns] or [+39.841%; +43.316%]

scenario:ContextPropagationBench/benchInject64Bit-opcache

• 🟥 execution_time [+684.991ns; +767.009ns] or [+29.938%; +33.523%]

scenario:LogsInjectionBench/benchLogsInfoBaseline-opcache

• 🟥 execution_time [+99.822ns; +176.178ns] or [+5.937%; +10.478%]

scenario:LogsInjectionBench/benchLogsNullBaseline-opcache

• 🟩 execution_time [-1.271µs; -1.151µs] or [-5.806%; -5.254%]

[chatgpt-codex-connector]

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[leoromanovsky]

Feedback from @bwoebi addressed; retest with local build against ffe-dogfooding server with satisfactory results.