fix: Reject CloudEvents 0.3 in KafkaBinding structured mode decode

The binary decode path already raised SpecVersionError for non-1.x spec
versions, but structured mode would accept and return a V0 event. Now
decode_structured_content checks the decoded event's spec_version and
raises SpecVersionError if it does not start with "1".

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

@@ -281,7 +281,13 @@ def decode_structured_content(message, content_type, allow_opaque, **format_args
                                             content_type: content_type,
                                             data_decoder: @data_decoders,
                                             **format_args)
-      return result[:event] if result
+      if result
+        event = result[:event]
+        if event && !event.spec_version.start_with?("1")
+          raise(SpecVersionError, "Unrecognized specversion: #{event.spec_version}")
+        end
+        return event
+      end
       return Event::Opaque.new(content, content_type) if allow_opaque
       raise(UnsupportedFormatError, "Unknown cloudevents content type: #{content_type}")
     end

test/test_kafka_binding.rb

@@ -350,6 +350,25 @@
       end
     end
 
+    it "raises SpecVersionError for structured event with specversion 0.3" do
+      v03_hash = {
+        "data" => "hello",
+        "id" => my_id,
+        "source" => my_source_string,
+        "specversion" => "0.3",
+        "type" => my_type,
+      }
+      v03_struct = JSON.dump(v03_hash)
+      message = {
+        key: nil,
+        value: v03_struct,
+        headers: { "content-type" => "application/cloudevents+json" },
+      }
+      assert_raises CloudEvents::SpecVersionError do
+        kafka_binding.decode_event(message, reverse_key_mapper: nil)
+      end
+    end
+
     it "raises FormatSyntaxError for malformed JSON" do
       message = {
         key: nil,