Add libdatadog FFI Reason enum support to OpenFeature binding

* Add DEFAULT and DISABLED constants to AssignmentReason module
* Update error handling to use specific assignment reasons:
  - DEFAULT_ALLOCATION_NULL errors → AssignmentReason::DEFAULT
- FLAG_DISABLED errors → AssignmentReason::DISABLED
- Other errors → AssignmentReason::ERROR
* Align Ruby binding with libdatadog's complete FFI Reason enum
* Maintain backward compatibility with existing constants
* All 31 internal evaluator tests continue passing

Author: sameerank

lib/datadog/open_feature/binding/assignment_reason.rb

@@ -4,10 +4,14 @@ module Datadog
   module OpenFeature
     module Binding
       # Assignment reasons returned in ResolutionDetails
+      # Aligned with libdatadog FFI Reason enum
       module AssignmentReason
         TARGETING_MATCH = 'TARGETING_MATCH'
         SPLIT = 'SPLIT'
         STATIC = 'STATIC'
+        DEFAULT = 'DEFAULT'      # For DefaultAllocationNull cases (matches libdatadog FFI Reason::Default)
+        DISABLED = 'DISABLED'    # For FlagDisabled cases  
+        ERROR = 'ERROR'
       end
     end
   end

lib/datadog/open_feature/binding/internal_evaluator.rb

@@ -150,7 +150,7 @@ def create_success_result(value, variant, allocation_key, variation_type, do_log
             variant: variant,
             error_code: nil,  # nil for successful cases (so "if result.error_code" works correctly)
             error_message: '',  # Empty string for Ok cases (matches libdatadog FFI)
-            reason: convert_reason_to_symbol(reason),
+            reason: reason,
             allocation_key: allocation_key,
             do_log: do_log,
             flag_metadata: {
@@ -170,11 +170,14 @@ def create_error_result(error_code, error_message)
                                 ERROR_CODE_MAPPING[error_code] || :general
                               end
 
-          # Determine reason based on error type
-          reason = if [Ext::DEFAULT_ALLOCATION_NULL, Ext::FLAG_DISABLED].include?(error_code)
-                     :static # These are expected conditions, not errors
+          # Determine reason based on error type - aligned with libdatadog FFI Reason enum
+          reason = case error_code
+                   when Ext::DEFAULT_ALLOCATION_NULL
+                     AssignmentReason::DEFAULT
+                   when Ext::FLAG_DISABLED
+                     AssignmentReason::DISABLED
                    else
-                     :error
+                     AssignmentReason::ERROR
                    end
 
           ResolutionDetails.new(
@@ -511,25 +514,6 @@ def convert_variation_type_for_output(variation_type)
           VARIATION_TYPE_MAPPING[variation_type] || variation_type.to_s.downcase
         end
 
-        def convert_reason_to_symbol(reason)
-          # Convert assignment reasons to string format matching libdatadog Reason enum
-          case reason
-          when AssignmentReason::STATIC
-            'STATIC'
-          when AssignmentReason::TARGETING_MATCH
-            'TARGETING_MATCH'
-          when AssignmentReason::SPLIT
-            'SPLIT'
-          when 'ERROR'
-            'ERROR'
-          when 'DEFAULT'
-            'DEFAULT'
-          when 'DISABLED'
-            'DISABLED'
-          else
-            reason.to_s if reason
-          end
-        end
 
       end
     end