The E2E suites, the Windows E2E jobs, the Docker image build and the Nix
flake check took about 120 of the ~140 larger-runner minutes each PR push
spent, and fired on nearly every PR. The 32-core pool backed up behind
them.
On a pull request each slow lane now runs only when the diff touches the
suite, its harness, or the code it guards (classify_changes.py
_E2E_LANES, _DOCKER_PATHS, _NIX_LANE_PATHS), or when the PR carries the
run-e2e label. Every push to main still runs all of them, and a release
run still forces every lane on.
Adding run-e2e reruns the head commit's CI, Docker and Nix runs; detect
reads the live labels because a rerun replays the original event.
Replayed over the last 200 merged PRs, the modelled 32-core cost of one
push drops from about 120 to about 10 runner-minutes.
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