codex: add a repo-local workflow-fail-fast skill for CI/publish/readiness changes

[mk3008]

Summary

Add a repo-local skill for CI, workflow, and publish-path changes that pushes reviews toward fail-fast checks and explicit readiness alignment instead of warn-only or late-failing flows.

Background

Recent workflow-related review comments repeatedly converged on the same concerns:

• failure should happen earlier when possible
• readiness checks should match the actual execution path
• warn-only validation is often too weak for release-affecting paths
• a workflow can appear fixed while still failing later in the pipeline

These are recurring review themes and should not depend on manually repeating the same guidance in each PR.

Problem

The current repository guidance does not provide a reusable, repo-local skill for reviewing workflow and publish-path changes with a fail-fast mindset.

As a result, CI and workflow fixes may still allow patterns such as:

• readiness steps that do not match the actual step being protected
• warn-only gates where failure should block
• late-stage failures that could have been stopped earlier
• PR reporting that says a workflow change is fixed without clearly separating repository evidence from supplementary evidence

Proposal

Add a repo-local skill, tentatively named workflow-fail-fast, with the following responsibility:

When a PR changes CI, workflow, publish, or readiness logic, the skill must explicitly check and report:

• whether a warn-only condition should become fail-fast
• whether readiness checks and actual execution steps are aligned
• whether failure can be moved earlier in the workflow
• whether the PR separates repository evidence from supplementary evidence
• whether any remaining non-blocking behavior is intentional and justified

This issue is about review and verification shape, not about forcing one specific workflow implementation.

Expected benefit

• reduce “looks fixed but still fails later” workflow changes
• make release-affecting workflow reviews more consistent
• improve fail-fast behavior for CI and publish-path changes
• reduce repeated reviewer prompts around the same workflow concerns

Definition of done

• a repo-local workflow-fail-fast skill exists
• the skill defines a standard review checklist for CI/workflow/publish/readiness changes
• PRs in this area can reference the skill and produce an explicit fail-fast/readiness report
• workflow reviews become less dependent on repeated custom reviewer guidance