Address review feedback: use generated RPC types, allow null copilotHome, strengthen test assertions #258

Job	Run time
Java SDK Tests	5m 17s
Smoke Test / Build SDK and run smoke test (JDK 17)	0s
Smoke Test / Build SDK and run smoke test (JDK 25)	-8s
Java SDK Tests	4m 37s
Smoke Test / Build SDK and run smoke test (JDK 17)	-628s
Smoke Test / Build SDK and run smoke test (JDK 25)	-628s
	-670s

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