test(ffe): enforce dependent flag RC capability contract

docs/understand/scenarios/parametric.md

@@ -308,3 +308,38 @@ def test_stuff(test_library):
 [2]: https://docs.pytest.org/en/6.2.x/usage.html#specifying-tests-selecting-tests
 [3]: https://github.com/roydahan/xunit-viewer
 [4]: ../../utils/build/docker/cpp/parametric/CMakeLists.txt
+
+### Dependent flags over Remote Configuration
+
+`tests/parametric/test_ffe/test_dependent_flags_rc.py` checks the wire contract for
+server SDKs using Agent RC. The supported-build test requires bit 50 on every
+observed request subscribing to `FFE_FLAGS`, before any dependent configuration
+is delivered and after configuration updates. It verifies prerequisite variant
+keys rather than flag values, using configuration delivered exclusively by RC.
+The test agent models capability-gated delivery; this does not validate production
+backend targeting.
+
+Use the [custom tracer build instructions](../../execute/binaries.md) to select
+the SDK and native library under test. With an unreleased supported build, force
+the positive class so a missing-feature manifest cannot turn a regression into
+an expected failure:
+
+```sh
+TEST_LIBRARY=python ./run.sh PARAMETRIC \
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC \
+  -F tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC
+```
+
+For a build known to lack dependent-flag support, select and force
+`Test_FFE_Without_Dependent_Flags_RC` instead. It must receive and evaluate an
+ordinary RC flag while advertising no bit 50. No RC traffic is a failure, not
+proof that an unsupported build is safe. Python 4.16.0 is the explicit legacy
+baseline in the manifest; other legacy/native combinations can use `-F`.
+
+Enable the positive class in each SDK's manifest when its dependent-flag support
+ships, alongside the evaluation suite. All SDKs retain missing-feature declarations
+until a release containing dependent-flag support is confirmed. Python's
+implementation is tracked in [dd-trace-py #21346](https://github.com/DataDog/dd-trace-py/pull/21346);
+use the forced positive class to test that build before enabling a release threshold.
+For Ruby, verify the loaded native package as well as the SDK version. Do not infer
+expected support from whether the SDK happens to advertise bit 50.

manifests/cpp.yml

@@ -187,6 +187,8 @@ manifest:
   tests/parametric/test_extract_behavior.py::Test_ExtractBehavior_Restart::test_baggage: missing_feature (Automatic baggage propagation is not implemented)
   tests/parametric/test_extract_behavior.py::Test_ExtractBehavior_Restart_With_Extract_First::test_baggage: missing_feature (Automatic baggage propagation is not implemented)
   tests/parametric/test_ffe/test_configuration_sources.py: irrelevant (cpp is not in scope for v1 agentless server SDK configuration-source coverage)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC: missing_feature (Dependent flag support must be enabled with the SDK release)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Without_Dependent_Flags_RC: irrelevant (Requires a known legacy build without dependent flag support)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation: missing_feature
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Split_Features: incomplete_test_app (Split-feature hook capture is currently implemented only in the Java parametric client)
   tests/parametric/test_ffe/test_exposure_hooks.py: incomplete_test_app (Exposure hook observations are not implemented)

manifests/dotnet.yml

@@ -1218,6 +1218,8 @@ manifest:
   :  # TODO: a lower version might be supported
     - declaration: bug (FFL-3325)
       component_version: <3.55.0
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC: missing_feature (Dependent flag support must be enabled with the SDK release)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Without_Dependent_Flags_RC: irrelevant (Requires a known legacy build without dependent flag support)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation: '>=3.36.0'  # Modified by easy win activation script
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation::test_ffe_dependent_flags: missing_feature (FFL-1694)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation::test_ffe_flag_evaluation: missing_feature  # Created by easy win activation script

manifests/golang.yml

@@ -2185,6 +2185,8 @@ manifest:
   tests/parametric/test_extract_behavior.py::Test_ExtractBehavior_Restart: incomplete_test_app (The parametric test app does not emit restart span links or preserve baggage)
   tests/parametric/test_extract_behavior.py::Test_ExtractBehavior_Restart_With_Extract_First: missing_feature (DD_TRACE_PROPAGATION_EXTRACT_FIRST=true is unsupported; dd-trace-go panics when extraction fails)
   tests/parametric/test_ffe/test_configuration_sources.py: v2.11.0-dev  # Easy win for all weblogs and version 2.10.1
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC: missing_feature (Dependent flag support must be enabled with the SDK release)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Without_Dependent_Flags_RC: irrelevant (Requires a known legacy build without dependent flag support)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation: v2.5.0-dev
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation::test_ffe_dependent_flags: missing_feature (FFL-1694)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Split_Features: incomplete_test_app (Split-feature hook capture is currently implemented only in the Java parametric client)

manifests/java.yml

@@ -4266,6 +4266,8 @@ manifest:
   ? tests/parametric/test_ffe/test_configuration_sources.py::Test_Feature_Flag_Configuration_Source_Selection::test_stable_true_preserves_default_agentless
   : v1.65.0
   tests/parametric/test_ffe/test_configuration_sources.py::Test_Feature_Flag_Configuration_Source_Warm_State_Preservation: v1.65.0
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC: missing_feature (Dependent flag support must be enabled with the SDK release)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Without_Dependent_Flags_RC: irrelevant (Requires a known legacy build without dependent flag support)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation: v1.56.0
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation::test_ffe_dependent_flags: missing_feature (FFL-1694)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Split_Features: v1.69.0-SNAPSHOT

manifests/nodejs.yml

@@ -2700,6 +2700,8 @@ manifest:
   tests/parametric/test_extract_behavior.py::Test_ExtractBehavior_Restart_With_Extract_First: *ref_5_47_0
   tests/parametric/test_extract_behavior.py::Test_ExtractBehavior_Restart_With_Extract_First::test_baggage: *ref_5_56_0
   tests/parametric/test_ffe/test_configuration_sources.py: *ref_6_8_0
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC: missing_feature (Dependent flag support must be enabled with the SDK release)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Without_Dependent_Flags_RC: irrelevant (Requires a known legacy build without dependent flag support)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation: *ref_5_75_0
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation::test_ffe_dependent_flags: missing_feature (FFL-1694)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Split_Features: incomplete_test_app (Split-feature hook capture is currently implemented only in the Java parametric client)

manifests/php.yml

@@ -1649,6 +1649,8 @@ manifest:
   ? tests/parametric/test_ffe/test_configuration_sources.py::Test_Feature_Flag_Configuration_Source_Selection::test_stable_true_preserves_default_agentless
   : missing_feature (FFL-2705 tracks PHP agentless configuration-source implementation; FFL-2731 tracks system-tests configuration-source contract)
   tests/parametric/test_ffe/test_configuration_sources.py::Test_Feature_Flag_Configuration_Source_Warm_State_Preservation: missing_feature (FFL-2705 tracks PHP agentless configuration-source implementation; FFL-2731 tracks system-tests configuration-source contract)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC: missing_feature (Dependent flag support must be enabled with the SDK release)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Without_Dependent_Flags_RC: irrelevant (Requires a known legacy build without dependent flag support)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation: v1.21.0-dev
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation::test_ffe_dependent_flags: missing_feature (FFL-1694)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Split_Features: incomplete_test_app (Split-feature hook capture is currently implemented only in the Java parametric client)

manifests/python.yml

@@ -3153,6 +3153,10 @@ manifest:
   tests/parametric/test_extract_behavior.py::Test_ExtractBehavior_Restart: v2.20.0
   tests/parametric/test_extract_behavior.py::Test_ExtractBehavior_Restart_With_Extract_First: v2.20.0
   tests/parametric/test_ffe/test_configuration_sources.py: v4.14.0-dev
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC: missing_feature (Dependent flag support must be enabled with the SDK release; dd-trace-py PR 21346)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Without_Dependent_Flags_RC:
+    - declaration: irrelevant (Legacy coverage is pinned to Python 4.16.0)
+      component_version: '<4.16.0 || >4.16.0'
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation: v4.0.0
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation::test_ffe_dependent_flags: missing_feature (FFL-1694)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Split_Features: incomplete_test_app (Split-feature hook capture is currently implemented only in the Java parametric client)

manifests/ruby.yml

@@ -2711,6 +2711,8 @@ manifest:
   tests/parametric/test_extract_behavior.py::Test_ExtractBehavior_Restart: incomplete_test_app (The parametric test app does not emit restart span links or preserve baggage)
   tests/parametric/test_extract_behavior.py::Test_ExtractBehavior_Restart_With_Extract_First: incomplete_test_app (The parametric test app does not emit restart span links or preserve baggage)
   tests/parametric/test_ffe/test_configuration_sources.py: v2.46.0-dev
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC: missing_feature (Dependent flag support must be enabled with the SDK release)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Without_Dependent_Flags_RC: irrelevant (Requires a known legacy build without dependent flag support)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation: v2.23.0
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation::test_ffe_dependent_flags: missing_feature (FFL-1694)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Split_Features: incomplete_test_app (Split-feature hook capture is currently implemented only in the Java parametric client)

manifests/rust.yml

@@ -299,6 +299,8 @@ manifest:
   tests/parametric/test_dynamic_configuration.py::Test_DynamicConfigSdkConfiguration::test_sdk_config_profiling_enabled: missing_feature (SDK_CONFIGURATION capability not yet implemented)
   tests/parametric/test_extract_behavior.py: '>=0.4.1-dev'
   tests/parametric/test_ffe/test_configuration_sources.py: irrelevant (rust is not in scope for v1 agentless server SDK configuration-source coverage)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Dependent_Flags_RC: missing_feature (Dependent flag support must be enabled with the SDK release)
+  tests/parametric/test_ffe/test_dependent_flags_rc.py::Test_FFE_Without_Dependent_Flags_RC: irrelevant (Requires a known legacy build without dependent flag support)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation: '>=0.5.3-dev+fd1307f'  # TODO: a lower version might be supported
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation::test_ffe_dependent_flags: missing_feature (FFL-1694)
   tests/parametric/test_ffe/test_dynamic_evaluation.py::Test_Feature_Flag_Dynamic_Evaluation::test_ffe_flag_evaluation: missing_feature

tests/parametric/test_ffe/test_dependent_flags_rc.py

@@ -0,0 +1,123 @@
+"""Dependent-flag capability and evaluation contract on the Agent RC transport.
+
+Supported and legacy builds have separate manifest-controlled expectations. Never
+infer support from the advertised bit: doing so would hide a missing-bit regression.
+"""
+
+import time
+from typing import Any
+
+from tests.parametric.conftest import APMLibrary
+from tests.parametric.test_ffe.utils import (
+    assert_dependent_flag_capability,
+    deliver,
+    ffe_requests,
+    observe_polls,
+    start_and_deliver,
+)
+from utils import features, pytest, scenarios
+from utils.docker_fixtures import TestAgentAPI
+
+ENV = {
+    "DD_EXPERIMENTAL_FLAGGING_PROVIDER_ENABLED": "true",
+    "DD_FEATURE_FLAGS_ENABLED": "true",
+    "DD_FEATURE_FLAGS_CONFIGURATION_SOURCE": "remote_config",
+    "DD_REMOTE_CONFIG_POLL_INTERVAL_SECONDS": "0.2",
+}
+
+
+def _config(*, parent_variant: str, dependent: bool) -> dict[str, Any]:
+    parent = {
+        "key": "parent",
+        "enabled": True,
+        "variationType": "STRING",
+        # The selected variant key deliberately differs from its value.
+        "variations": {
+            "approved": {"key": "approved", "value": "not-the-variant-key"},
+            "rejected": {"key": "rejected", "value": "approved"},
+        },
+        "allocations": [
+            {"key": "parent-default", "splits": [{"variationKey": parent_variant, "shards": []}], "doLog": False}
+        ],
+    }
+    flags = {"parent": parent}
+    if dependent:
+        flags["child"] = {
+            "key": "child",
+            "enabled": True,
+            "variationType": "STRING",
+            "variations": {key: {"key": key, "value": key} for key in ("matched", "unmatched")},
+            "allocations": [
+                {
+                    "key": "prerequisite",
+                    "rules": [
+                        {
+                            "conditions": [
+                                {"flagEvaluation": {"key": "parent"}, "operator": "ONE_OF", "value": ["approved"]}
+                            ]
+                        }
+                    ],
+                    "splits": [{"variationKey": "matched", "shards": []}],
+                    "doLog": False,
+                },
+                {"key": "fallback", "splits": [{"variationKey": "unmatched", "shards": []}], "doLog": False},
+            ],
+        }
+    return {"createdAt": "2026-11-03T00:00:00Z", "format": "SERVER", "environment": {"name": "test"}, "flags": flags}
+
+
+def _assert_value(test_library: APMLibrary, flag: str, value: str) -> None:
+    deadline = time.monotonic() + 5
+    while True:
+        result = test_library.ffe_evaluate(
+            flag=flag,
+            variation_type="STRING",
+            default_value="caller-default",
+            targeting_key="subject",
+        )
+        if result.get("value") == value and result.get("errorCode") in (None, ""):
+            return
+        assert time.monotonic() < deadline, result
+        time.sleep(0.1)
+
+
+@scenarios.parametric
+@features.feature_flags_dynamic_evaluation
+class Test_FFE_Dependent_Flags_RC:
+    @pytest.mark.parametrize("library_env", [ENV])
+    def test_capability_and_gated_delivery(self, test_agent: TestAgentAPI, test_library: APMLibrary) -> None:
+        """Advertise before delivery, evaluate variant keys, and retain the bit after updates."""
+        start_and_deliver(
+            test_agent,
+            test_library,
+            config_id="dependent-flags",
+            payload=_config(parent_variant="approved", dependent=True),
+            supported=True,
+        )
+        _assert_value(test_library, "child", "matched")
+        previous_count = len(ffe_requests(test_agent))
+        observe_polls(test_agent, supported=True, minimum=previous_count + 2)
+
+        assert_dependent_flag_capability(ffe_requests(test_agent), supported=True)
+        deliver(test_agent, config_id="dependent-flags", payload=_config(parent_variant="rejected", dependent=True))
+        _assert_value(test_library, "child", "unmatched")
+        previous_count = len(ffe_requests(test_agent))
+        observe_polls(test_agent, supported=True, minimum=previous_count + 2)
+
+
+@scenarios.parametric
+@features.feature_flags_dynamic_evaluation
+class Test_FFE_Without_Dependent_Flags_RC:
+    @pytest.mark.parametrize("library_env", [ENV])
+    def test_legacy_build_does_not_advertise(self, test_agent: TestAgentAPI, test_library: APMLibrary) -> None:
+        """A known legacy build receives ordinary flags and never advertises bit 50."""
+        start_and_deliver(
+            test_agent,
+            test_library,
+            config_id="ordinary-flags",
+            payload=_config(parent_variant="approved", dependent=False),
+            supported=False,
+        )
+        _assert_value(test_library, "parent", "not-the-variant-key")
+        previous_count = len(ffe_requests(test_agent))
+        observe_polls(test_agent, supported=False, minimum=previous_count + 2)