fix: fail fast when session is not started #2158

Job	Run time
checks / pre-commit	38s
checks / readme-snippets	12s
checks / test (3.10, lowest-direct, ubuntu-latest)	53s
checks / test (3.11, lowest-direct, ubuntu-latest)	59s
checks / test (3.10, lowest-direct, windows-latest)	3m 34s
checks / test (3.11, locked, windows-latest)	2m 33s
checks / test (3.11, lowest-direct, windows-latest)	2m 55s
checks / test (3.10, locked, ubuntu-latest)	51s
checks / test (3.12, lowest-direct, ubuntu-latest)	59s
checks / test (3.12, locked, ubuntu-latest)	56s
checks / test (3.13, locked, ubuntu-latest)	49s
checks / test (3.13, locked, windows-latest)	2m 32s
checks / test (3.13, lowest-direct, ubuntu-latest)	56s
checks / test (3.11, locked, ubuntu-latest)	51s
checks / test (3.10, locked, windows-latest)	2m 22s
checks / test (3.14, lowest-direct, windows-latest)	2m 28s
checks / test (3.13, lowest-direct, windows-latest)	2m 54s
checks / test (3.12, locked, windows-latest)	3m 27s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 17s
checks / test (3.14, locked, ubuntu-latest)	2m 14s
checks / test (3.12, lowest-direct, windows-latest)	3m 15s
checks / test (3.14, locked, windows-latest)	3m 12s
all-green	5s
	40m 52s

Provide feedback