feat(ffe): add native exposure lifecycle

[leoromanovsky]

Motivation

This is PR J in the PHP OpenFeature/FFE stack. PR I wires Remote Config config delivery into the native evaluator; this slice adds native exposure buffering and lifecycle delivery so successful logged evaluations can be drained through the tracer sidecar.

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

Reference implementation: #3630
Libdatadog dependency: DataDog/libdatadog#2026

Changes

• Import ddog_sidecar_send_ffe_exposures from the libdatadog submodule and use it from ext/sidecar.c instead of implementing EVP sidecar forwarding in dd-trace-php.
• Add native FFE exposure state in Rust with LRU deduplication, a capped batch buffer, service/env/version context, flush/free helpers, and fork reset.
• Add PHP extension functions for enqueueing, flushing, setting exposure context, and resetting native exposure state.
• Add NativeExposureWriter and make Client::create() use it by default when the extension functions are available.
• Flush native exposure batches during request shutdown and sidecar shutdown, and reset copied exposure state after fork.
• Add CODEOWNERS coverage for the libdatadog submodule and PHPT coverage for buffer drain/dedup and fork reset behavior.

Decisions

• dd-trace-php owns only the PHP-facing event shaping and native lifecycle buffer; libdatadog owns the sidecar EVP proxy forwarding API.
• NativeExposureWriter::flush() is intentionally a no-op because production delivery is owned by extension lifecycle hooks. Calling the test-only native flush function from userland would drain without forwarding to the sidecar.
• The client still emits the transitional warning and reports productionRuntime => false until the remaining metrics and end-to-end activation slices land.
• This PR depends on the libdatadog FFE sidecar forwarding PR landing before this submodule pointer can merge.

Validation

• git diff --check
• find src/api/FeatureFlags tests/api/Unit/FeatureFlags -name '*.php' -print0 | xargs -0 -n1 php -n -l
• php -n -l tests/ext/ffe/flush_drains_buffer.phpt && php -n -l tests/ext/ffe/fork_resets_dedup.phpt && php -n -l ext/ddtrace.stub.php
• vendor/bin/phpcs -s src/api/FeatureFlags tests/api/Unit/FeatureFlags
• php -n vendor/bin/phpunit --config=phpunit.xml tests/api/Unit/FeatureFlags
• vendor/bin/phpunit --config=phpunit.xml tests/api/Unit/FeatureFlags
• RUSTC_BOOTSTRAP=1 cargo check -p ddtrace-php
• RUSTC_BOOTSTRAP=1 cargo test -p ddtrace-php exposure_flush_drains_buffer_and_keeps_context
• EXTRA_CFLAGS="-I$(brew --prefix pcre2)/include" EXTRA_LDFLAGS="-L$(brew --prefix pcre2)/lib" make -j"$(sysctl -n hw.ncpu)"
• php -n -d extension=tmp/build_extension/modules/ddtrace.so -m | rg -i '^ddtrace$'
• make test_c TESTS=tests/ext/ffe/flush_drains_buffer.phpt
• make test_c TESTS=tests/ext/ffe/fork_resets_dedup.phpt
• make test_c TESTS=tests/ext/ffe/native_bridge_evaluate.phpt
• make test_c TESTS=tests/ext/ffe/remote_config_lifecycle.phpt skipped locally because request-replayer is unavailable outside the Datadog dev environment.

[datadog-prod-us1-6]

 

✨ Fix all issues with BitsAI

⚠️ Warnings

🚦 35 Pipeline jobs failed

DataDog/apm-reliability/dd-trace-php | ASAN test_c: [7.4, arm64]     

🔧 Fix in code (Fix with Cursor).

Memory leak detected in _dd_new_stack at coms.c:195. Aborted execution due to leak sanitizer.

🧪 1 Test failed

tmp/build_extension/tests/ext/ffe/fork_resets_dedup.phpt (FFE: fork handler resets exposure dedup in child) from PHP.tmp.build_extension.tests.ext.ffe   (Fix with Cursor)

004+ 
005+ =================================================================
006+ ==3927==ERROR: LeakSanitizer: detected memory leaks
007+ 
008+ Direct leak of 40 byte(s) in 1 object(s) allocated from:
009+     #0 0xe450b1a2c5cc in calloc (/usr/lib/llvm-19/lib/clang/19/lib/linux/libclang_rt.asan-aarch64.so+0x10c5cc) (BuildId: 01d185df05089232d2f28e13a020257065e55def)
010+     #1 0xe450a7dab934 in _dd_new_stack tmp/build_extension/ext/coms.c:195:35
011+     #2 0xe450a7dab6e0 in ddtrace_coms_minit tmp/build_extension/ext/coms.c:239:35
012+     #3 0xe450a7d8ea18 in dd_activate_once tmp/build_extension/ext/ddtrace.c:485:13
013+     #4 0xe450ae1f701c in __pthread_once_slow nptl/pthread_once.c:116:7
...

DataDog/apm-reliability/dd-trace-php | API unit tests: [7.0]     

🔧 Fix in code (Fix with Cursor).

1 failed test in ClientTest.php: expected 'Datadog-backed PHP feature flag evaluation is not fully enabled yet.' but got 'Datadog-backed PHP feature flag evaluation is not fully production-ready yet.'

DataDog/apm-reliability/dd-trace-php | API unit tests: [7.1]     

🔧 Fix in code (Fix with Cursor).

1 failed test in ClientTest.php: Failed asserting that two strings are identical at line 107.

View all 35 failed jobs.

ℹ️ Info

No other issues found (see more)

❄️ No new flaky tests detected

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

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[pr-commenter]

Benchmarks [ tracer ]

Benchmark execution time: 2026-05-22 02:45:01

Comparing candidate commit 9c7dcaf in PR branch leo.romanovsky/pr-j-exposure-lifecycle with baseline commit cae2759 in branch leo.romanovsky/pr-i-remote-config-lifecycle.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 191 metrics, 2 unstable metrics.

scenario:MessagePackSerializationBench/benchMessagePackSerialization-opcache

• 🟩 execution_time [-8.737µs; -7.163µs] or [-7.993%; -6.553%]