fix: fail fast when session is not started #2587

Job	Run time
checks / readme-snippets	15s
checks / pre-commit	32s
checks / test (3.10, locked, ubuntu-latest)	57s
checks / test (3.10, lowest-direct, ubuntu-latest)	55s
checks / test (3.11, locked, windows-latest)	1m 14s
checks / test (3.11, lowest-direct, ubuntu-latest)	51s
checks / test (3.13, locked, ubuntu-latest)	46s
checks / test (3.12, locked, windows-latest)	1m 29s
checks / test (3.11, locked, ubuntu-latest)	54s
checks / test (3.12, locked, ubuntu-latest)	57s
checks / test (3.14, lowest-direct, ubuntu-latest)	51s
checks / test (3.10, lowest-direct, windows-latest)	1m 18s
checks / test (3.13, lowest-direct, windows-latest)	1m 33s
checks / test (3.13, lowest-direct, ubuntu-latest)	54s
checks / test (3.13, locked, windows-latest)	1m 18s
checks / test (3.11, lowest-direct, windows-latest)	1m 18s
checks / test (3.10, locked, windows-latest)	1m 24s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 0s
checks / test (3.14, locked, windows-latest)	2m 19s
checks / test (3.14, locked, ubuntu-latest)	1m 55s
checks / test (3.14, lowest-direct, windows-latest)	1m 29s
checks / test (3.12, lowest-direct, windows-latest)	1m 20s
all-green	3s
	25m 32s

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