[codex] overhaul Freebuff premium sessions #475

Job	Run time
build-and-smoke-freebuff-windows	3m 30s
build-freebuff	1m 21s
e2e-slash-commands	1m 2s
e2e-startup	1m 17s
e2e-version	1m 3s
e2e-code-edit	1m 7s
e2e-terminal-command	51s
e2e-agent-startup	2m 29s
e2e-help-command	1m 17s
e2e-ads-behavior	1m 13s
	15m 10s

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