[codex] Clarify string tool input errors #6436

Job	Run time
build-and-check	2m 31s
test-integration-packages/billing	1m 4s
test-integration-packages/internal	1m 3s
test-integration-web	52s
test-integration-packages/agent-runtime	40s
test-integration-common	41s
test-integration-cli	45s
test-integration-sdk	1m 24s
test-packages/agent-runtime	53s
test-common	50s
test-.agents	50s
test-packages/internal	48s
test-packages/billing	53s
test-cli	50s
test-sdk	48s
test-web	1m 9s
	16m 1s

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