test: Wire FDv1 Fallback Directive contract-test capability

The contract harness now treats the FDv1 Fallback Synchronizer as a
distinct field on the data system (DataSystem.FDv1Fallback) rather than
deriving it from the FDv2 synchronizer chain, and gates the directive
subtests on a new fdv1-fallback capability.

Wire the test service to match:
  - declare the fdv1-fallback capability
  - accept the new dataSystem.fdv1Fallback config field
  - build the FDv1 fallback synchronizer from that field directly,
    instead of inferring it from the last polling synchronizer

Also bump the contract-tests pin from v3.0.0-alpha.4 to v3.0.0-alpha.6
so the harness ships the new directive subtests.

Author: keelerm84

.github/actions/check/action.yml

@@ -51,4 +51,4 @@ runs:
         test_service_port: 9000
         enable_persistence_tests: true
         token: ${{ inputs.token }}
-        version: v3.0.0-alpha.4
+        version: v3.0.0-alpha.6

contract-tests/client_entity.rb

@@ -42,9 +42,14 @@ def initialize(log, config)
       if sync_configs && !sync_configs.empty?
         synchronizer_builders = sync_configs.map { |sync_config| build_synchronizer_builder(sync_config) }.compact
         data_system.synchronizers(synchronizer_builders) unless synchronizer_builders.empty?
+      end
 
-        fallback_builder = build_fdv1_fallback_builder(sync_configs)
-        data_system.fdv1_compatible_synchronizer(fallback_builder)
+      # The FDv1 Fallback Synchronizer is wired directly from a top-level
+      # dataSystem.fdv1Fallback config block -- the test harness no longer
+      # infers it from the FDv2 synchronizer chain.
+      fdv1_fallback_config = data_system_config[:fdv1Fallback]
+      if fdv1_fallback_config
+        data_system.fdv1_compatible_synchronizer(build_fdv1_fallback_builder(fdv1_fallback_config))
       end
 
       if data_system_config[:payloadFilter]
@@ -342,21 +347,17 @@ def close
   end
 
   #
-  # Builds an FDv1 fallback polling data source builder using the first available polling config.
+  # Builds an FDv1 fallback polling data source builder from the dedicated
+  # `dataSystem.fdv1Fallback` config block. This block has the same shape as
+  # a polling config (`baseUri`, `pollIntervalMs`).
   #
-  # @param sync_configs [Array<Hash>] Array of synchronizer configurations
+  # @param fdv1_fallback_config [Hash] The FDv1 fallback configuration
   # @return [Object] Returns the configured FDv1 fallback builder
   #
-  private def build_fdv1_fallback_builder(sync_configs)
+  private def build_fdv1_fallback_builder(fdv1_fallback_config)
     builder = LaunchDarkly::DataSystem.fdv1_fallback_ds_builder
-
-    # Use the first available polling config for the fallback base_uri
-    polling_config = sync_configs.lazy.map { |c| c[:polling] }.detect { |p| p }
-    if polling_config
-      builder.base_uri(polling_config[:baseUri]) if polling_config[:baseUri]
-      builder.poll_interval(polling_config[:pollIntervalMs] / 1_000.0) if polling_config[:pollIntervalMs]
-    end
-
+    builder.base_uri(fdv1_fallback_config[:baseUri]) if fdv1_fallback_config[:baseUri]
+    builder.poll_interval(fdv1_fallback_config[:pollIntervalMs] / 1_000.0) if fdv1_fallback_config[:pollIntervalMs]
     builder
   end
 

contract-tests/service.rb

@@ -53,6 +53,7 @@
       'persistent-data-store-redis',
       'flag-change-listeners',
       'flag-value-change-listeners',
+      'fdv1-fallback',
     ],
   }.to_json
 end