fix: fail fast when session is not started #3323

Job	Run time
checks / docs	45s
checks / readme-snippets	15s
checks / pre-commit	59s
checks / test (3.11, lowest-direct, windows-latest)	1m 53s
checks / test (3.13, locked, windows-latest)	1m 58s
checks / test (3.13, lowest-direct, windows-latest)	1m 56s
checks / test (3.11, locked, ubuntu-latest)	1m 8s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 21s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 24s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 31s
checks / test (3.10, locked, ubuntu-latest)	1m 27s
checks / test (3.10, locked, windows-latest)	2m 10s
checks / test (3.13, locked, ubuntu-latest)	1m 13s
checks / test (3.10, lowest-direct, windows-latest)	1m 50s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 12s
checks / test (3.12, locked, windows-latest)	1m 49s
checks / test (3.12, locked, ubuntu-latest)	1m 36s
checks / test (3.14, lowest-direct, windows-latest)	1m 44s
checks / test (3.12, lowest-direct, windows-latest)	2m 23s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 15s
checks / test (3.14, locked, ubuntu-latest)	2m 15s
checks / test (3.11, locked, windows-latest)	2m 2s
checks / test (3.14, locked, windows-latest)	2m 59s
all-green	5s
	37m 10s

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