Migrated from Method backlog

This issue was created from a legacy filesystem backlog card. GitHub Issues are now the live work tracker; repository docs remain Method evidence.

Source backlog: docs/method/backlog/cool-ideas/PROCESS_cycle-packet-markdownlint-gate.md
Original lane: cool-ideas
Original legend: PROCESS
Original priority: medium

Original backlog card

Cycle Packet Markdownlint Gate

This review round caught witness and retro packet issues that a small
markdown lint pass could have surfaced before PR review: unlabeled code
fences, empty placeholder blocks, and wording drift inside committed
artifacts.

Idea: add a bounded markdown validation step for cycle packets and other
generated repo artifacts so contract-level doc issues fail fast instead
of landing as manual review cleanup.

Proposed Contract

Prerequisites

• PROCESS_validate-command.md defines the parent method validate
  surface. This item assumes that contract lands first or in the same
  slice.

• Scope globs:
  markdown rules cover
  docs/design/[0-9][0-9][0-9][0-9]-*/**/*.md and
  docs/method/retro/[0-9][0-9][0-9][0-9]-*/**/*.md.

• Rules:
  MD040 (fenced code blocks need a language),
  MD031 (fenced code blocks need surrounding blank lines), and custom
  packet checks for required frontmatter keys on generated docs.

• Frontmatter checks:
  design docs require title, legend, cycle, and source_backlog;
  top-level retro docs at
  docs/method/retro/[0-9][0-9][0-9][0-9]-*/*.md require title,
  cycle, design_doc, outcome, and drift_check; witness
  artifacts under **/witness/**/*.md are linted for markdown rules
  only unless they later get their own explicit frontmatter contract.

• Integration point:
  this item depends on PROCESS_validate-command.md. The intended
  surface is method validate markdown as a subcommand of the parent
  method validate CLI implemented in src/cli.ts, not a separate
  top-level verb. Implementers should either land both contracts in the
  same slice or wire this markdown gate into the existing validate
  command surface before invoking it locally, from pre-commit, or from
  a CI job such as markdown-contract.

• Pass / fail behavior:
  exit 0 when all scoped files satisfy the bounded rule set; exit
  non-zero when any scoped file violates one of the named rules or
  frontmatter checks, with output that names the file and failing rule.

Non-goals

• Lint every markdown file in the repository.
• Replace broader review judgment on cycle quality with style-only
  checks.