[cdmren]

The Example workflow's ubuntu jobs have failed on every run since 2026-11-09 with collect2: fatal error: cannot find 'ld' (last pass: 2026-11-06). Between those runs ubuntu-latest moved from ubuntu-24.04 to ubuntu-26.04, while the cache keys carry no OS version, so a ~/.stack saved on 24.04 is restored onto 26.04 (exact key hits in the failing logs).

This bumps cache-prefix to v2/ for the test job and sets it for test-stack-yamls, which had none, so both stop restoring the 24.04 caches. It is a hypothesis test: if the ubuntu jobs pass here, stale caches were the cause. If they still fail, the cause is the 26.04 image itself.

Not verified: that the restored GHC is what points at the missing linker.

— by Claude

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