CI fails only after cache restore: what to compare before deleting the cache

When CI fails only after cache restore, compare the cache key, dependency graph, generated files, and install mode before deleting the cache.

Deleting the cache may make the build green, but it can also erase the evidence. A cache-related failure usually means that the restored state no longer matches the current repository assumptions. The mismatch might be a package manager version change, lockfile update, generated client change, compiler cache, browser binary, test fixture, or build artifact that was valid for an older commit.

Start with the cache key. Does it include the lockfile hash, runtime version, operating system, and package manager version? If the key is too broad, a job may restore dependencies created for a different graph. If the key is too narrow, the team may be rebuilding constantly without noticing.

Next, compare a run with cache and a run without cache. Keep the install command and commit fixed. Save the first failing line from both runs. If the no-cache run passes, inspect what the cache restored: dependency directory, compiled output, test database, browser download, or tool-specific folder.

The fix should be specific. Change the cache key, remove one generated folder from restore, pin the tool version, or add a clean step before build. A blanket cache delete is acceptable as a recovery action, but the durable fix should explain why the cache became unsafe.

CI fails only after cache restore: what to compare before deleting the cache

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