move main-prompt to agent-runtime #3971

Job	Run time
build-and-check	2m 40s
test-npm-app	33s
test-cli	35s
test-common	34s
test-.agents	29s
test-packages/agent-runtime	42s
test-integration-.agents	30s
test-backend	33s
test-web	34s
test-integration-common	32s
test-integration-cli	29s
test-integration-backend	56s
test-integration-web	29s
test-integration-npm-app	35s
test-integration-packages/agent-runtime	29s
	10m 40s

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