fix: fail fast when session is not started #2159

Job	Run time
checks / readme-snippets	11s
checks / pre-commit	31s
checks / test (3.13, lowest-direct, windows-latest)	2m 34s
checks / test (3.11, locked, ubuntu-latest)	51s
checks / test (3.14, locked, windows-latest)	3m 19s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 4s
checks / test (3.11, locked, windows-latest)	2m 41s
checks / test (3.13, locked, ubuntu-latest)	50s
checks / test (3.10, lowest-direct, windows-latest)	2m 45s
checks / test (3.10, locked, windows-latest)	2m 17s
checks / test (3.10, lowest-direct, ubuntu-latest)	59s
checks / test (3.12, locked, ubuntu-latest)	56s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 17s
checks / test (3.13, lowest-direct, ubuntu-latest)	54s
checks / test (3.11, lowest-direct, windows-latest)	2m 34s
checks / test (3.13, locked, windows-latest)	2m 24s
checks / test (3.10, locked, ubuntu-latest)	51s
checks / test (3.14, locked, ubuntu-latest)	2m 28s
checks / test (3.12, lowest-direct, windows-latest)	3m 41s
checks / test (3.14, lowest-direct, windows-latest)	2m 35s
checks / test (3.11, lowest-direct, ubuntu-latest)	53s
checks / test (3.12, locked, windows-latest)	3m 53s
all-green	2s
	40m 30s

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