[codex] Use underscored direct subagent tool names #6303

Job	Run time
build-and-check	3m 15s
test-integration-packages/internal	1m 11s
test-integration-packages/billing	1m 4s
test-integration-common	39s
test-integration-sdk	1m 22s
test-integration-cli	55s
test-integration-web	45s
test-common	51s
test-integration-packages/agent-runtime	42s
test-packages/billing	49s
test-packages/agent-runtime	49s
test-.agents	45s
test-web	1m 16s
test-packages/internal	56s
test-cli	56s
test-sdk	45s
	17m 0s

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