fix(gateway): guard indexed message access for noUncheckedIndexedAccess #39

Job	Run time
build (agentos-server, packages/agentos-server/Dockerfile)	28s
build (computeragent-server, examples/Dockerfile.harness, examples/computeragent-server.ts, harness)	4m 48s
build (harness-server, examples/Dockerfile.harness, examples/harness-server.ts, harness)	5m 13s
build (agentos-spa, agentos/Dockerfile, spa)	1m 2s
	11m 31s

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