Typed custom server notifications; warn on unbound client-side drops #3654

Job	Run time
checks / readme-snippets	15s
checks / test (3.12, locked, ubuntu-latest)	1m 43s
checks / test (3.13, locked, ubuntu-latest)	54s
checks / test (3.13, locked, windows-latest)	1m 55s
checks / pre-commit	55s
checks / test (3.12, lowest-direct, windows-latest)	1m 40s
checks / test (3.14, locked, ubuntu-latest)	1m 26s
checks / test (3.14, lowest-direct, windows-latest)	2m 4s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 19s
checks / test (3.13, lowest-direct, windows-latest)	2m 1s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 23s
checks / test (3.14, locked, windows-latest)	1m 58s
checks / docs	1m 3s
checks / test (3.10, locked, windows-latest)	1m 57s
checks / test (3.10, lowest-direct, windows-latest)	1m 47s
checks / test (3.12, locked, windows-latest)	1m 33s
checks / test (3.11, locked, ubuntu-latest)	1m 23s
checks / test (3.10, locked, ubuntu-latest)	1m 31s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 25s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 22s
checks / test (3.11, locked, windows-latest)	1m 55s
checks / test (3.11, lowest-direct, windows-latest)	1m 59s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 27s
all-green	3s
	34m 58s

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