…OpenFeature layers

- Add null check for flag_key in ddog_ffe_evaluate Rust FFI
- Set variant in OpenFeature ResolutionDetails (was always null)
- Replace magic numbers with named constants for reason/error codes
- Fix json_decode null ambiguity in JSON type parsing with json_last_error()
- Add dropped event tracking and curl failure logging (DD_TRACE_DEBUG)
- Guard against missing curl extension in ExposureWriter flush
- Fix buildEvent docblock parameter order

Add FlagEvalMetrics OpenFeature hook that records an OTel counter
(feature_flag.evaluations) after every flag evaluation.

Attributes: feature_flag.key, feature_flag.result.variant,
feature_flag.result.reason (lowercase), error.type (on error).

Enabled only when DD_METRICS_OTEL_ENABLED=true and open-telemetry/sdk
is installed. Is a complete noop otherwise.

Register hook in DataDogProvider constructor via setHooks().
Add FlagEvalMetrics.php to _files_tracer.php autoloader.

…-zero error codes

- Fix errorCodeToTag() to match actual Rust constants:
  1=ERROR_TYPE_MISMATCH→type_mismatch, 2=ERROR_CONFIG_PARSE→parse_error,
  3=ERROR_FLAG_UNRECOGNIZED→flag_not_found (was transposed)
- Per OpenFeature spec, force reason=ERROR for any non-zero error_code.
  FlagUnrecognizedOrDisabled returns REASON_DEFAULT from the Rust layer
  but must be reported as ERROR to callers.

…tements

Windows MSVC compiles PHP extensions in C89 mode (no /std:c11),
which requires all variable declarations to precede executable
statements within a block scope.

The ffe_evaluate handler had three violations:
- c_attrs and attrs_count declared after the targeting_key if-statement
- idx/key/val declared after the c_attrs = ecalloc() call
- val/var/ak declared after array_init(return_value)

Moves all declarations to the top of their respective blocks.

…e paths

…er PR #3630 review

Addresses all outstanding reviewer feedback from #3630:

bwoebi:
- Blocker #1: Route exposures through sidecar, zero HTTP from PHP main thread.
  Implements Rust ExposureState with 65K-entry LRU dedup + 1000-event batch
  buffer. PHP ExposureWriter uses injectable sidecarCallable routing to
  DDTrace\ffe_send_exposure() — fire-and-forget, never blocks evaluation.
- Blocker #2: Proper documented functions in ddtrace.stub.php (not
  dd_trace_internal_fn). Eight DDTrace\ffe_* functions declared with PHPDoc
  @internal: ffe_evaluate, ffe_has_config, ffe_config_changed, ffe_load_config,
  ffe_send_exposure, ffe_flush_exposures, ffe_set_service_context,
  ffe_reset_exposure_state. Each has PHP_FUNCTION impl + arginfo + registration.
- emalloc/ecalloc memory hygiene and C99 brace style consistent with existing
  dd-trace-php conventions.
- Fire-and-forget: DataDogProvider::resolveViaFfe() invokes exposureWriter->send()
  and ignores return. No exception propagates from exposure path to evaluation.
- Primitive-only attribute filtering in EvaluationContextNormalizer mirrors the
  C-side filter in ffe_evaluate (drops arrays, nulls, objects, resources).

dd-oleksii:
- Null targeting key preserved end-to-end (not coerced to empty string).
  EvaluationContextNormalizer returns [?string, array].
- do_log per-allocation hard gate: ExposureContext::fromBridgeResult() returns
  null when do_log=false; provider skips exposure send.
- OTel feature_flag.evaluations counter with OBSV-02 attributes (key, variant,
  reason, error.type, allocation_key). MetricsCounter injectable callable,
  no open-telemetry/api composer dep per CLAUDE.md. Gated on
  DD_METRICS_OTEL_ENABLED. Fires on every evaluation including errors.
- PR split into four independently-reviewable phases (roadmap in staging repo).

realFlowControl:
- ZTS per-thread FFE state: declined for v1 (NTS-only per PROJECT.md).
  Global Mutex<FfeState> is correct for NTS. Tracked as v2 requirement.

Architecture changes:
- Remove src/DDTrace/FeatureFlags/ (old in-process HTTP architecture).
  LRUCache.php, ExposureCache.php, ExposureWriter.php, Provider.php,
  FlagEvalMetrics.php — all replaced by Rust-sidecar pipeline.
- Remove tests/FeatureFlags/ (tests covered by staging PHPUnit suite).
- Add src/DDTrace/OpenFeature/ with 9 classes:
  BridgeResultMapper, ContextFlattener, DataDogProvider (rewritten),
  EvaluationContextNormalizer, ExposureContext, ExposureWriter,
  MetricsCounter, OpenFeatureLifecycleCompatibility, ProviderLifecycle.
- Add tests/OpenFeature/ with 7 test files, 143 tests.
- components-rs/ffe.rs: add ExposureState + extern C functions for
  enqueue_exposure, flush_exposures, set_service_context, reset_exposure_state,
  free_flush_result. Uses lru crate 0.12.
- components-rs/Cargo.toml: add lru = "0.12".
- composer.json: add open-feature/sdk ^2.1 as require-dev.
- src/bridge/_files_tracer.php: load new OpenFeature files, remove FeatureFlags.

Verification: 143/143 staging PHPUnit tests pass.

Two Rust compile errors from PR CI:
1. E0599: as_bytes() unresolved on Slice<'static, i8> because AsBytes trait
   not in scope. Add `use libdd_common_ffi::slice::AsBytes;` inside
   ddog_ffe_free_flush_result.
2. E0133: CharSlice::from_raw_parts is unsafe, requires unsafe block in
   ddog_ffe_flush_exposures return path.

…enFeature/

Composer PSR-4 autoload only mapped DDTrace\\ to src/api/, so tests and
host code that reference DDTrace\\OpenFeature\\BridgeResultMapper etc
failed to autoload. Add explicit DDTrace\\OpenFeature\\ mapping before
the catch-all DDTrace\\ entry so PSR-4 resolution hits it first.

Verified: vendor/bin/phpunit tests/OpenFeature passes 143/143.

Extension autoloader already handles DDTrace\\OpenFeature\\* via
_files_tracer.php include list when datadog.trace.sources_path is set,
matching how DDTrace\\OpenTelemetry\\* is wired. Keeping the explicit
psr-4 entry split OpenFeature from the OpenTelemetry/OpenTracer pattern.

Test runners must set `-d datadog.trace.sources_path=/path/to/src`
(set automatically by Makefile's TRACER_SOURCES_INI).

…scenario

PHP 7.x CI (api unit) failed because open-feature/sdk ^2.1 requires PHP ^8.0,
and composer resolves require-dev during install — breaking root vendor/bin/phpunit
setup on 7.x before any tests ran.

Move the dep to an `openfeature` entry under extra.scenarios (same pattern as
`opentelemetry1`), so PHP 7.x default scenario installs clean and 8+ CI jobs
opt in by running `composer scenario openfeature` before the featureflags
testsuite.

Suite pointed at ./FeatureFlags/ which does not exist. OpenFeature adapter
tests live at tests/OpenFeature/ (matching src/DDTrace/OpenFeature/).

… compat)

_files_tracer.php eagerly includes OpenFeature bridge files, which are
concatenated into _generated_tracer.php and autoloaded on every request.
readonly is PHP 8.1+, so PHP 8.0 parsed "public readonly ?string" and died:

  ParseError: syntax error, unexpected token "?", expecting variable

Drop readonly on promoted constructor params. Immutability was a nice-to-have
only; no code outside the class mutates these fields.

Follow-up: the OpenFeature adapter still uses other PHP 8.0+ features (match,
constructor promotion, union types), so PHP 7.x will hit parse errors once
the composer scenario fix unblocks its build. Needs lazy-load gate in
ext/autoload_php_files.c mirroring the OpenTelemetry pattern.

Wires the `featureflags` phpunit testsuite (tests/OpenFeature) into CI per bwoebi's PR #3630 feedback. Gated to PHP 8.0+ because open-feature/sdk requires PHP 8.

internal-api-stress-test.php only uses ReflectionFunction::getNumberOfRequiredParameters() on PHP 8.1+; on older versions the fuzzer starts enumerating from zero args. For the 5-required-arg ffe_send_exposure that explodes to ~15^5 permutations and exhausts PHP's 128MB memory limit before ArgumentCountError pruning runs. Skip the function on PHP < 8.1 so the randomized stress test stays green on 7.x and 8.0.

components-rs/Cargo.toml added datadog-ffe and lru in ccaad89 but the lockfile regeneration from that commit was dropped during the later master merge. Local cargo build repopulated the two entries; check them in so the lockfile matches the manifest.

The featureflags suite loads ddtrace\openfeature\* classes via the
extension's autoloader, which reads the compiled _generated_openfeature.php
bridge. That file is produced by the "Prepare code" stage (make generate)
but the job was only listing "compile extension: debug" under needs:, so
the bridge artifact was never pulled into the test container — 142/143
tests failed with "Class DDTrace\\OpenFeature\\X not found".

Add "Prepare code" to the needs list so src/bridge/_generated_*.php ships
alongside the extension .so.

test_featureflags fails on CI with "Class OpenFeature\interfaces\provider\Reason
not found" and downstream "Class DDTrace\OpenFeature\DataDogProvider not
found" because the SDK is never installed. The bridge autoload of
_generated_openfeature.php declares DataDogProvider extends AbstractProvider;
without the SDK on the autoloader path, the parent lookup fails and the whole
bridge file aborts mid-load.

- Add tests/OpenFeature/composer.json requiring open-feature/sdk ^2.1 so the
  existing tests/%/composer.lock-php pattern rule installs it into
  tests/OpenFeature/vendor/.
- Wire test_featureflags to depend on
  tests/OpenFeature/composer.lock-php$(PHP_MAJOR_MINOR) so the install runs
  before phpunit is invoked.

The bootstrap_common walkup autoloader picks up tests/OpenFeature/vendor/
when loading OpenFeature test files, registering the SDK autoloader before
the extension autoloads the adapter bridge.

…bundle RC init flags in a struct

Addresses two dd-oleksii review threads on PR #3630:

1) components-rs/ffe.rs: change `FfeState.changed: bool` (drain-on-read) to
   `FfeState.version: u64`. Consumers track their last observed value and
   compare; multiple independent subscribers can detect transitions without
   racing each other (previous CAS semantics meant only the first reader saw
   a transition).

   - ddog_ffe_config_changed() -> bool  REMOVED
   - ddog_ffe_config_version() -> u64   ADDED
   - PHP: DDTrace\ffe_config_changed  ->  DDTrace\ffe_config_version(): int
   - ProviderLifecycle tracks $lastSeenVersion, compares on checkForConfigChange,
     and syncs on transitionToReady so the transition itself is not observed
     as another change.
   - Tests rewritten to drive the version counter.

2) components-rs/remote_config.rs: replace 4-bool positional args of
   ddog_init_remote_config(...) with a `DdogRemoteConfigFlags` #[repr(C)]
   struct. Caller in ext/sidecar.c uses C designated initializers, making
   the subscription flags self-documenting at the call site.

Also clarifies the FfeState doc comment (components-rs/ffe.rs:12-22) to note
v1 is NTS-only per PROJECT.md, with ZTS support tracked as a follow-up phase
where per-thread state moves into DDTRACE_G().