Graceful SSE drain on session manager shutdown #1366

Job	Run time
checks / pre-commit	39s
checks / readme-snippets	13s
checks / test (3.13, lowest-direct, windows-latest)	2m 30s
checks / test (3.11, locked, ubuntu-latest)	51s
checks / test (3.10, lowest-direct, windows-latest)	2m 31s
checks / test (3.11, lowest-direct, ubuntu-latest)	59s
checks / test (3.12, lowest-direct, windows-latest)	3m 57s
checks / test (3.14, locked, windows-latest)	3m 8s
checks / test (3.13, lowest-direct, ubuntu-latest)	54s
checks / test (3.13, locked, windows-latest)	2m 23s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 6s
checks / test (3.11, locked, windows-latest)	3m 38s
checks / test (3.13, locked, ubuntu-latest)	51s
checks / test (3.14, locked, ubuntu-latest)	2m 27s
checks / test (3.12, locked, ubuntu-latest)	57s
checks / test (3.12, lowest-direct, ubuntu-latest)	58s
checks / test (3.11, lowest-direct, windows-latest)	2m 41s
checks / test (3.10, locked, windows-latest)	2m 12s
checks / test (3.12, locked, windows-latest)	3m 14s
checks / test (3.14, lowest-direct, windows-latest)	3m 45s
checks / test (3.10, locked, ubuntu-latest)	50s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 0s
all-green	4s
	41m 48s

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