[Phase 16] Write the SBOM / supply-chain standard (prerequisite of S12) #889

Roadmap · Phase 16 · prerequisite of step S12 · size M · planned in docs/roadmap/phase-16-trust-surface-hardening.md:904-908

Summary

SBOMs appear only as descriptive prose and one command; nothing states what a correct SBOM is or what the supply-chain gates mean. Phase 16 S12 has nothing to be reviewed against until this exists.

What the standard must settle

• The CycloneDX version.
• Component completeness: root exclusion, bom-ref uniqueness, license coverage, dependency graph.
• The retention channel and window.
• The meaning of each check_pip_audit.py severity tier.

Acceptance criteria

• The standard lives under docs/standards/ in the layout documentation.md prescribes and is listed in docs/standards/README.md.
• It answers every point above with a rule a reviewer can check, not a description.
• Phase 16 step S12 can be reviewed against it.

_{Planned in docs/roadmap/phase-16-trust-surface-hardening.md (read at f94595f). Unit IDs (F-W20260729-…) come from the 2026-07-29/30 full-project review; the issue numbers next to them are the October 2026 review's records of the same defects.}