Thinker gpt: don't inherit system prompt + tools #6017

Job	Run time
build-and-check	3m 5s
test-integration-packages/internal	1m 7s
test-integration-packages/billing	1m 7s
test-integration-sdk	1m 30s
test-integration-cli	46s
test-integration-common	42s
test-integration-packages/agent-runtime	44s
test-integration-web	49s
test-packages/billing	51s
test-packages/agent-runtime	46s
test-packages/internal	57s
test-cli	53s
test-.agents	43s
test-web	52s
test-common	47s
test-sdk	47s
	16m 26s

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