Context windows fixes and features (#10975) #433

Job	Run time
test-stable (linux, 3.12, 12.1, stable)	1s
test-stable (linux, 3.10, 12.1, stable)	1s
test-stable (linux, 3.11, 12.1, stable)	1s
test-unix-nightly (linux, 3.11, 12.1, nightly)	1s
	4s

Provide feedback