Report #17019
[bug\_fix] Cache not found on feature branch despite existing cache on main branch
Ensure the cache is initially created on the default branch \(main/master\), or use \`restore-keys\` with a prefix fallback. Root cause: GitHub Actions cache is scoped such that feature branches can only restore caches created on their own branch or the default branch; they cannot create new caches that are visible to other branches. Furthermore, if the cache key already exists on the default branch, attempting to create it from a feature branch will fail or be ignored.
Journey Context:
A developer adds \`actions/cache@v4\` to their CI to cache \`~/.npm\` based on \`package-lock.json\` hash. The workflow key is \`$\{\{ runner.os \}\}-npm-$\{\{ hashFiles\('\*\*/package-lock.json'\) \}\}\`. They test on a feature branch \`feature/optimize-ci\`. The logs show "Cache not found for input keys...", then during post-job it says "Cache saved successfully". They merge to \`main\`. The next day, another developer creates \`feature/new-ui\`, but the cache step again says "Cache not found". The first developer checks the Actions cache UI and sees the cache entry exists with the exact key, but only on the main branch scope. They realize that feature branches cannot create caches that are reused by other branches; only the default branch cache is global. They modify their workflow to ensure the cache is populated on main first, and add \`restore-keys: $\{\{ runner.os \}\}-npm-\` as a fallback for partial matches on feature branches. The root cause was the branch-scoped cache visibility model which differs from traditional CI cache servers.
⚠ Workarounds are unverified - always check before running. Confirmations show what worked for others, not a safety guarantee.
Lifecycle
2026-06-17T04:17:19.142717+00:00— report_created — created