fix(avro): include default values in schema fingerprint for correct dedup

Schemas differing only in field defaults (e.g., with vs without "default":"a")
were producing identical fingerprints, causing the dedup check to short-circuit
compatibility validation. This meant registering a schema with a removed default
would silently succeed under BACKWARD_TRANSITIVE/FULL_TRANSITIVE instead of
returning 409. Verified against Confluent v8.1.1.

Also fixes Avro transitive BDD tests:
- Remove @pending-impl from BACKWARD_TRANSITIVE and FULL_TRANSITIVE tests
- Fix FORWARD_TRANSITIVE expectation: adding field without default is compatible
  (old readers ignore unknown fields)

1285 BDD scenarios passing, 0 failures.

Author: millerjp

internal/schema/avro/parser.go

@@ -230,13 +230,19 @@ func canonicalizeObject(obj map[string]interface{}) string {
 func canonicalizeField(field map[string]interface{}) string {
 	parts := make([]string, 0)
 
-	// Field order: name, type
+	// Field order: name, type, default
+	// Note: default is included for fingerprinting so that schemas differing
+	// only in default values are treated as distinct (important for compatibility).
 	if name, ok := field["name"]; ok {
 		parts = append(parts, fmt.Sprintf(`"name":"%v"`, name))
 	}
 	if typ, ok := field["type"]; ok {
 		parts = append(parts, fmt.Sprintf(`"type":%s`, canonicalizeValue(typ)))
 	}
+	if def, ok := field["default"]; ok {
+		defBytes, _ := json.Marshal(def)
+		parts = append(parts, fmt.Sprintf(`"default":%s`, string(defBytes)))
+	}
 
 	return "{" + strings.Join(parts, ",") + "}"
 }

tests/bdd/features/avro_compatibility_exhaustive.feature

@@ -440,7 +440,6 @@ Feature: Avro Compatibility — Exhaustive (Confluent v8.1.1 Compatibility)
       """
     Then the response status should be 200
 
-  @pending-impl
   Scenario: BACKWARD_TRANSITIVE — removing default transitively is incompatible
     Given the global compatibility level is "NONE"
     And subject "avro-ex-bt-nodef" has schema:
@@ -475,8 +474,7 @@ Feature: Avro Compatibility — Exhaustive (Confluent v8.1.1 Compatibility)
       """
     Then the response status should be 200
 
-  @pending-impl
-  Scenario: FORWARD_TRANSITIVE — adding field without default transitively is incompatible
+  Scenario: FORWARD_TRANSITIVE — adding field without default is compatible (old readers ignore new fields)
     Given the global compatibility level is "NONE"
     And subject "avro-ex-ft-add-nodef" has schema:
       """
@@ -491,7 +489,7 @@ Feature: Avro Compatibility — Exhaustive (Confluent v8.1.1 Compatibility)
       """
       {"type":"record","name":"R","fields":[{"name":"f1","type":"string"},{"name":"f3","type":"string"}]}
       """
-    Then the response status should be 409
+    Then the response status should be 200
 
   Scenario: FULL_TRANSITIVE — safe evolution with defaults is compatible
     Given the global compatibility level is "NONE"
@@ -510,7 +508,6 @@ Feature: Avro Compatibility — Exhaustive (Confluent v8.1.1 Compatibility)
       """
     Then the response status should be 200
 
-  @pending-impl
   Scenario: FULL_TRANSITIVE — field without default transitively is incompatible
     Given the global compatibility level is "NONE"
     And subject "avro-ex-fullt-nodef" has schema: