fix: fail fast when session is not started #2756

Job	Run time
checks / readme-snippets	11s
checks / pre-commit	48s
checks / test (3.10, locked, ubuntu-latest)	58s
checks / test (3.11, locked, ubuntu-latest)	47s
checks / test (3.10, lowest-direct, windows-latest)	1m 38s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 3s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 0s
checks / test (3.10, locked, windows-latest)	1m 45s
checks / test (3.12, lowest-direct, windows-latest)	1m 24s
checks / test (3.11, locked, windows-latest)	1m 33s
checks / test (3.14, lowest-direct, ubuntu-latest)	56s
checks / test (3.12, locked, windows-latest)	1m 28s
checks / test (3.13, locked, ubuntu-latest)	53s
checks / test (3.14, lowest-direct, windows-latest)	1m 55s
checks / test (3.13, lowest-direct, windows-latest)	1m 48s
checks / test (3.13, locked, windows-latest)	1m 55s
checks / test (3.14, locked, windows-latest)	2m 20s
checks / test (3.14, locked, ubuntu-latest)	2m 1s
checks / test (3.12, locked, ubuntu-latest)	1m 2s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 1s
checks / test (3.11, lowest-direct, windows-latest)	1m 35s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 9s
all-green	3s
	29m 13s

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