fix(java): use REPLACE_STUB_ID for unregistered writeReplace classes to prevent cross-JVM ClassNotFoundException

[wakilurislam]

PR Description

Why?

When Fory serializes an unregistered class with writeReplace() returning a different type (e.g., a Hibernate/ByteBuddy proxy), the outer type info writes the proxy class name to the byte stream. On a different JVM where that proxy class doesn't exist, deserialization fails with ClassNotFoundException.

What does this PR do?

Adds an instanceof ReplaceResolveSerializer check in ClassResolver.buildUnregisteredTypeId() to return REPLACE_STUB_ID instead of NAMED_EXT. This writes a compact 1-byte internal type ID without the class name, matching the existing pattern for lambdas (LAMBDA_STUB_ID) and JDK proxies (JDK_PROXY_STUB_ID).

The original NAMED_EXT fallback for serializer == null (before serializer creation) is preserved unchanged.

Changes

ClassResolver.java:

1. buildUnregisteredTypeId() — return REPLACE_STUB_ID when serializer is ReplaceResolveSerializer:

   protected int buildUnregisteredTypeId(Class<?> cls, Serializer<?> serializer) {
-    if (serializer == null && !cls.isEnum() && useReplaceResolveSerializer(cls)) {
-      return Types.NAMED_EXT;
+    if (!cls.isEnum()) {
+      if (serializer instanceof ReplaceResolveSerializer) {
+        return REPLACE_STUB_ID;
+      }
+      if (serializer == null && useReplaceResolveSerializer(cls)) {
+        return Types.NAMED_EXT;
+      }
     }

2. addSerializer() — guard against overwriting typeIdToTypeInfo[REPLACE_STUB_ID]:

+      if (typeId == REPLACE_STUB_ID) {
+        classInfoMap.put(type, typeInfo);
+      } else {
+        updateTypeInfo(type, typeInfo);
+      }

WriteReplaceCrossJvmTest.java (new): 6 test methods × 4 configurations = 24 tests covering cross-JVM proxy, same-JVM regression, same-type replace, round-trip, and nested proxy in DTO.

Related issues

• Fixes [Java] Unregistered writeReplace classes cause ClassNotFoundException on cross-JVM deserialization #3635

AI Contribution Checklist

• Substantial AI assistance was used in this PR: yes

AI Usage Disclosure
- substantial_ai_assistance: yes
- scope: code drafting, tests, design analysis
- affected_files_or_subsystems: java/fory-core ClassResolver.java, WriteReplaceCrossJvmTest.java (new)
- ai_review: two fresh AI reviewers on current HEAD — both found 0 actionable issues.
- human_verification: full fory-core test suite (1820 tests, 0 failures). ObjectStreamSerializerTest (82), URLSerializerTest (9), ReplaceResolveSerializerTest (58) all pass. Cross-JVM test fails without fix (4 failures), passes with fix (24/24).
- performance_verification: N/A — one-time cold-path change only
- provenance_license_confirmation: Apache-2.0 compatible, all original work.

Does this PR introduce any user-facing change?

No public API or binary protocol changes. Wire format changes only for unregistered ReplaceResolveSerializer classes (bug fix — previous format was broken for cross-JVM).

Benchmark

N/A — one-time buildUnregisteredTypeId() call, not per-element.

review_1_with_skill.md
review_2_without_skill.md