docs(devsecops): add Policy as Code section

[s1ns3nz0]

What does this PR change?

Adds a new policy-as-code section under DevSecOps, covering how a policy engine is applied
across the CI/CD pipeline and what NIST SP 800-204D requires of it.

Four pages under docs/pages/devsecops/policy-as-code/:

• Overview — what a policy engine decides, the two evaluation modes (pipeline artifacts vs.
  platform configuration), and the four places SP 800-204D names a policy enforcement engine
• Policy in the CI Pipeline — commit, merge, and build gates
• Policy in Release and Runtime — publishing identity, deployment gates, drift detection
• Governing the Policy Set — which violations block, who may override, where thresholds come
  from, and how rules are owned and retired

The existing DevSecOps pages document which controls to enable. These pages cover the decision
layer above them: what the engine evaluates, what evidence each stage produces, and which
decisions a person is allowed to override. Every control referenced here links out to the page
that documents it rather than restating it — continuous-integration-continuous-deployment,
repository-hardening, security-testing, code-signing, and the isolation/ pages.

Background

This follows a series I recently wrote on NIST SP 800-204D and CI/CD supply chain security:
https://miata.cloud/tags/cicd-security/

The standard's coverage here follows that series. The policy-decision material — rule
classification, threshold derivation, exception handling, and ownership — is new and specific to
this contribution.

On AI assistance

I am not a native English speaker, and I used AI assistance heavily for the English prose. The
structure, scope, and technical decisions are mine, and I verified every claim against its
source:

• NIST SP 800-204D section 5 and Appendix A, read directly rather than summarized. The page
  states that the standard names a policy enforcement engine and names OPA as an example, not
  that it mandates either — section 5.1.1 uses "techniques such as," and 5.1.2 uses "(e.g., Open
  Policy Agent (OPA))"
• CVE-2025-30066 (tj-actions/changed-files), against the NVD entry
• The Ledger Connect Kit timeline, against Ledger's own incident report
• All Rego examples validated against OPA 1.4.2, including the expiring-exception behaviour that
  the governance page's argument depends on

Flagging this because the contributing guidelines draw a line at content entirely generated by
AI. I do not believe this crosses it, but I would rather say so up front than have it surface in
review.

Notes for reviewers

Rego is fenced as python. The site's Shiki bundle has no Rego grammar, and an unrecognized
language fails the build. Python is the closest available approximation and highlights Rego
reasonably. There is a note to that effect at the bottom of the overview page. Happy to switch to
an unhighlighted fence if you would prefer accuracy over readability here.

Folder rather than a single page. The material ran past 1,500 lines. Following the structure
of devsecops/isolation/, it is split into four pages of 257–526 lines each, which is within the
range of existing DevSecOps pages.

Normalization standard. Rebased onto develop and applied the standard from #561 and the
sentence-case rule from #595: Further reading instead of Further Reading & Tools, and
What this framework covers for the overview's page map. pnpm run validate:content --path docs/pages/devsecops/policy-as-code reports 4 passed, 0 failed.

One validator issue worth flagging. utils/validate-content.cjs extracts headings without
stripping fenced code blocks, so a line-start # comment inside a code block parses as an H1.
Any ### that follows is then reported as heading_level_skip. This fired on two of these
pages because Rego uses # for comments. I worked around it by moving the comments into the
surrounding prose, but the same thing will hit any page with Python, Ruby, shell, or YAML
comments at line start. The fix is a one-line change: run stripCode(body) before headings().
Happy to open a separate PR for that if useful.

Verification

• pnpm run docs:build passes
• pnpm run validate:content --path docs/pages/devsecops/policy-as-code: 4 passed, 0 failed
• cspell clean (added Rekor to wordlist.txt)
• markdownlint-cli2 reports 0 issues across all four pages
• All internal links resolve to existing files
• Rego examples re-validated against OPA 1.4.2 after the comment changes

Type of change

• New content
• Edit to existing content
• Outline / structure change
• Typo or formatting fix
• Tooling / config

If applicable

• Editing existing content: tagged the current contributors from the attribution list
• Framework has a steward: asked them to review
• Outline change: updated vocs.config.ts with the dev: true parameter
• Want community feedback: shared this PR in our Discord

[github-actions]

Sidebar Configuration Reminder

This PR includes added, renamed, or removed documentation files:

• docs/pages/devsecops/policy-as-code/ci-pipeline.mdx (added)
• docs/pages/devsecops/policy-as-code/governance.mdx (added)
• docs/pages/devsecops/policy-as-code/index.mdx (added)
• docs/pages/devsecops/policy-as-code/overview.mdx (added)
• docs/pages/devsecops/policy-as-code/release-and-runtime.mdx (added)

Please ensure that:

• The sidebar in vocs.config.ts has been updated to include these files
• New content has the dev: true parameter so it's marked as under development
• Sidebar links match the file paths - use the preview deployment to verify

See Contributing Guide – Sidebar & Navigation for more details.

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