bvandeusenandClaude Opus 5
5e72076298
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`cache-from`/`cache-to` on `<image>:buildcache`, `mode=max`, on all three
build steps. Closes the half of the driver change that step 1 left open.
Step 1 measured worse, not better, and that was expected but is worth stating
with numbers. Run 4896, first builds after moving to `docker-container`:
build-web 3m44s (cold baseline 2m23s)
build-ml 3m49s (cold baseline 3m20s)
build-agent 11m12s (cold baseline 9m26s)
The container driver gets a FRESH buildkit instance per job, so it has no
local layer store to fall back on — where the old docker driver at least
reused whatever the runner's dockerd happened to hold. That is why a registry
cache is the only cache this driver can have, and why step 1 on its own is a
regression rather than a win.
`mode=max` so intermediate stages cache too. The agent's two ~150s pip layers
and web's frontend-builder stage are the entire cost, and a min-mode cache
would drop exactly those.
A `:buildcache` tag is not the withdrawn tag scheme returning. Rule 145
narrowed against names NOTHING reads; this one is read by every build that
runs, is one moving ref per image rather than one per build, holds cache blobs
rather than a shippable artifact, and is overwritten in place rather than
accumulating. Closer to `:dev` than to the `:2026.8.28` tags 318 deleted — and
said so in the workflow, so it is not "cleaned up" by a later reader.
Expect the next build to be slower again, once: it is still cold AND now pays
the cache export. The measurement that matters is the one after that.
Scribe #3114.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>