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The engine gaps left open after the SDK batch (2026.9.12.2) #1893

Job	Run time
toolchain: musl + llvm	10m 5s
toolchain: gcc (cold self-host)	10m 28s
build + unit tests (linux x86_64, self-host)	12m 13s
examples: the curriculum builds	8m 56s
integration: mcpp builds & runs xlings	9m 24s
	51m 6s