refactor(session-broker): split broker into reusable runtime-neutral … #213

Job	Run time
Terminal smoke tests	38s
Verify prebuilt npm package (macos-latest)	40s
Build compiled binary	21s
Verify prebuilt npm package (ubuntu-latest)	34s
Verify npm package	39s
Typecheck + tests	2m 13s
	5m 5s

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