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ci: cancel superseded PR runs and restore from the remote build cache #574
Description
Lean CI spends runner time on runs nobody needs, and starts cold more often than necessary.
- Superseded PR runs. Today a PR often had two concurrent runs for the same head (retarget plus push), and runs for already-merged PRs kept going. Add a
concurrencygroup tolean_action_ci.ymlthat cancels in-progress runs for the same pull request. Never cancelpushruns onmain:check_abstract_ci.pygates PDF publication on the exact-sourcemainrun, andmainuploads the remote cache. Never cancelmerge_groupruns: the merge queue now requiresci-checks. - Cold starts. CI restores
.lakeonly from the GitHub Actions cache, which is over its 10 GB limit and evicts per-ref copies. After a cslib pin bump, every run started beforemainsaved a fresh cache took 30–50 minutes.mainalready uploads complete build outputs to the remote cache, so having CI fetch them before building should make most PR and merge-queue runs warm.
Constraints: keep correctness and trust unchanged. Lean CI still builds and tests (restored outputs are reused only where Lake's traces match), and the trust note in scripts/cache/README.md must be updated honestly. Reads are anonymous and need no secrets. Changes must be no-ops when the remote cache misses.
Done when: a PR run demonstrates the restore (a warm build from the remote cache, with log evidence), superseded PR runs cancel while main and merge_group runs are unaffected, and the README trust section is accurate. Before/after timing comes from real runs.
Follows #539 and Samuel's request to pursue build efficiencies that don't hurt users, developers or results.
Activity
SamuelSchlesinger commentedon Oct 23, 2026
Claimed by worker
worker-claude-574-c4b0c164(Claude Code, Opus 5.5), delegated bycoordinator-claude-c4b0c164-20261023. Scope: the issue as written (PR-only concurrency cancellation inlean_action_ci.yml, remote-cache restore before the build, README trust note, before/after timing from real runs). Branch:ci/remote-cache-restore-574. Status: active.ci: cancel superseded PR runs and restore from the remote build cache
doc(cache): describe CI's reuse of the remote cache in the trust note
SamuelSchlesinger commentedon Oct 23, 2026
worker-claude-574-c4b0c164: active. Draft PR #582 is open; the concurrency stanza cancelled its superseded run as intended. Next: controlled timing runs (workflow_dispatch on throwawayexp/574-*branches that never save to the Actions cache), then the PR write-up.doc(cache): state CI's download sizes and why it skips current modules
SamuelSchlesinger commentedon Oct 23, 2026
worker-claude-574-c4b0c164: awaiting review in #582 (headfeae8d6d, CI green). The PR description has the controlled timings: a cold start takes 4.7 min with the remote cache and 47.4 min without; a stale.laketakes 3.0 or 3.8 min versus 13.3 min. It also has the concurrency demonstration, the trust note, limitations and a reply to each review point. The throwawayexp/574-*branches stay until review.ci: cancel superseded PR runs and restore from the remote build cache
doc(cache): describe CI's reuse of the remote cache in the trust note
doc(cache): state CI's download sizes and why it skips current modules