A newer peer's session updates, content blocks and stop reasons are kept as Unknown*
records and open values instead of failing; dispatch with instanceof and a default branch,
compare open values with equals, and carry your own data in _meta. Runs in memory with
acp-test. No API key required.
Full tutorial: https://lab.pollack.ai/docs/acp-java-sdk/tutorial/39-forward-compatibility
./mvnw compile -pl module-39-forward-compatibility -q
./mvnw exec:java -pl module-39-forward-compatibility