fix: Reject non-V1 events in KafkaBinding#encode_event

Raise SpecVersionError when encode_event receives an event with a
specversion that does not start with "1", ensuring V0.3 events cannot
be encoded via the Kafka binding.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Daniel Azuma <dazuma@gmail.com>

Author: dazuma

lib/cloud_events/kafka_binding.rb

@@ -209,6 +209,9 @@ def encode_event(event, structured_format: false, key_mapper: :NOT_SET, **format
       if event.is_a?(Event::Opaque)
         return encode_opaque_event(event)
       end
+      unless event.spec_version.start_with?("1")
+        raise(SpecVersionError, "Unrecognized specversion: #{event.spec_version}")
+      end
       if structured_format
         encode_structured_event(event, structured_format, key_mapper, **format_args)
       else

test/test_kafka_binding.rb

@@ -493,6 +493,16 @@
       message = kafka_binding.encode_event(event, key_mapper: nil)
       assert_nil message[:key]
     end
+
+    it "raises SpecVersionError for a V0 event" do
+      v0_event = CloudEvents::Event::V0.new(id: my_id,
+                                            source: my_source_string,
+                                            specversion: "0.3",
+                                            type: my_type)
+      assert_raises CloudEvents::SpecVersionError do
+        kafka_binding.encode_event(v0_event, key_mapper: nil)
+      end
+    end
   end
 
   describe "encode_event structured mode" do