Under bash with set -euo pipefail, source <(cmd) process substitution
doesn't reliably set variables in the caller's scope. The variables
stay empty and -u (nounset) crashes the script. eval "$(cmd)" works
correctly in both bash and zsh.
Fixes: gstack-review-read, gstack-review-log, gstack-slug comment,
gen-skill-docs.ts resolver functions, and regression tests.
e877d3d870