fix: fail fast when session is not started #3413

Job	Run time
checks / pre-commit	55s
checks / readme-snippets	12s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 26s
checks / test (3.11, lowest-direct, windows-latest)	1m 51s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 27s
checks / test (3.14, lowest-direct, windows-latest)	1m 38s
checks / test (3.13, lowest-direct, windows-latest)	2m 1s
checks / test (3.12, locked, windows-latest)	1m 55s
checks / test (3.12, lowest-direct, windows-latest)	2m 27s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 29s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 14s
checks / test (3.10, locked, ubuntu-latest)	1m 33s
checks / test (3.13, locked, windows-latest)	1m 50s
checks / test (3.12, locked, ubuntu-latest)	1m 37s
checks / test (3.14, locked, ubuntu-latest)	2m 26s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 26s
checks / test (3.11, locked, windows-latest)	2m 10s
checks / test (3.10, locked, windows-latest)	2m 35s
checks / test (3.11, locked, ubuntu-latest)	1m 23s
checks / docs	42s
checks / test (3.10, lowest-direct, windows-latest)	1m 57s
checks / test (3.13, locked, ubuntu-latest)	1m 18s
checks / test (3.14, locked, windows-latest)	2m 40s
all-green	5s
	38m 17s

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