Fix thread-local leak on self-reference and circular dependency

Move begin/ensure to wrap the early return path so the thread-local
evaluating set is always cleaned up, even when a circular dependency
or self-reference triggers the early return. Added tests to verify.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jnunemaker

lib/flipper/expressions/feature_enabled.rb

@@ -13,11 +13,11 @@ def self.call(feature_name, context:)
         # Track the current feature so A -> B -> A is caught
         added_current = evaluating.add?(current_feature)
 
-        # Circular dependency: return false to break the cycle
-        return false if evaluating.include?(feature_name)
-
-        evaluating.add(feature_name)
         begin
+          # Circular dependency: return false to break the cycle
+          return false if evaluating.include?(feature_name)
+
+          evaluating.add(feature_name)
           actor = context[:actor]
           if actor
             Flipper.enabled?(feature_name, actor)

spec/flipper_integration_spec.rb

@@ -653,6 +653,23 @@
       evaluating = Thread.current[:flipper_evaluating_features]
       expect(evaluating.nil? || evaluating.empty?).to be(true)
     end
+
+    it "cleans up thread-local state after self-reference" do
+      feature.enable Flipper.feature_enabled(:search)
+
+      feature.enabled?
+      evaluating = Thread.current[:flipper_evaluating_features]
+      expect(evaluating.nil? || evaluating.empty?).to be(true)
+    end
+
+    it "cleans up thread-local state after circular dependency" do
+      feature.enable Flipper.feature_enabled(:other)
+      flipper[:other].enable Flipper.feature_enabled(:search)
+
+      feature.enabled?
+      evaluating = Thread.current[:flipper_evaluating_features]
+      expect(evaluating.nil? || evaluating.empty?).to be(true)
+    end
   end
 
   context "for FeatureDisabled" do