The alpha.8 backward-compat test in test-manifest-verification.sh was the
second copy that broke both alpha.10 and alpha.11 pipelines. The test fails
because verify-release checks for artifacts (bootstrap/*, mesh firewall unit)
that were added after alpha.8.
Per release-policy.md, tags are immutable — bump to alpha.12.
alpha.10 tag produced a failed release pipeline (test-release-contract.sh
still asserted alpha.9, and run-negative-tests.sh test 5 failed on
cross-version verify-release). Per release-policy.md, published tags are
immutable — errors are fixed in the next tag.
