Fix text block aggregation and extend streaming coverage #3881

Job	Run time
build-and-check	2m 30s
test-common	31s
test-backend	47s
test-packages/agent-runtime	38s
test-web	31s
test-integration-.agents	31s
test-integration-cli	46s
test-npm-app	44s
test-integration-npm-app	29s
test-integration-common	27s
test-.agents	37s
test-cli	32s
test-integration-packages/agent-runtime	37s
test-integration-backend	39s
test-integration-web	35s
	10m 54s

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