Root cause of the recurring 'Illegal option -o pipefail' failures
(ed49b8d resolve-versions; b7197e8 promote-base-latest, run 418):
docker-publish.yml had no workflow-level default shell, so Gitea's
sh/dash default applied and every bash-syntax step had to individually
remember 'shell: bash'.
- docker-publish.yml: add 'defaults: run: shell: bash' — fixes the whole
class; all pre-existing dash steps are POSIX so bash runs them unchanged.
- lint.yml: new workflow, runs on every push/PR (not just release tags):
* scripts/check-workflow-shell.sh — Gitea-accurate guard: fails if any
run: step doesn't resolve to bash. Catches the omit-shell+bash-syntax
case that actionlint MISSES (actionlint models GitHub, where the
default shell is bash, so a shell-less step is assumed bash).
* actionlint + shellcheck — catches explicit 'shell: sh' + bash syntax
(SC3040) and general workflow errors.
Verified locally: guard + actionlint pass current workflows; guard fails
a synthetic omit-shell+pipefail workflow; shellcheck clean.
pi