ci: a yq failure in select-e2e's index pipelines is invisible and reads as intended full-suite conservatism #3650

Summary

In hack/select-e2e.sh, the ownership and reverse-dependency indexes are built as OWNERS=$(build_owners_index | sort -u) and REVERSE=$(build_reverse_deps | sort -u), where both functions are a single yq invocation over $SOURCES_DIR/*.yaml. If yq fails, for any reason from a missing binary to a malformed PackageSource, the pipeline's exit status is sort's, so set -e never fires and the script continues with an empty index. Nothing in the output distinguishes "yq broke" from "no owners matched".

Why it matters

The failure is safe in direction but invisible in nature: with empty indexes every changed path falls through to escalation, so the practical result is a full suite run on every PR. Selection quietly stops doing its job, CI cost jumps, and because the symptom is "full suite selected", it reads as intended conservatism rather than a broken tool. Nobody gets a signal to fix anything.

Fix shape

Check the yq halves explicitly: capture each function's output first, test the exit status, and on failure print one loud line naming yq as the broken component before falling back to the full suite. The direction of the fallback is already right; the missing piece is the sentence that says the fallback happened and why.