doc-diagnostic

The diagnostic and canon skill. Owns three things:

1. The alternatives catalog -- what to write when a user impulse should not be an ADR. Full catalog: references/alternatives-catalog.md.
2. The ADR canon -- templates, status lifecycle, numbering, required fields, immutability rules. (In this file.)
3. The audit procedure -- folder-level KEEP / MERGE / REWRITE / DELETE / MOVE / BACKFILL-ADR classification used by /doc-audit. Full procedure: references/audit-procedure.md.

Use this skill when routing a doc request, picking a template, naming a status, or auditing an existing doc set. The drafting / discovery / critique skills consume the canon defined here; they do not redefine it.

The four-question diagnostic (run before recommending any doc)

The canonical four-question check. The doc-expert agent and every other skill in this plugin reference this section rather than restate it. Before agreeing to produce any document, run all four. If any answer is "no" or "unclear," the doc should not be written yet.

1. Purpose -- one sentence stating what question this doc answers for a reader who already knows the system exists.
2. Audience -- a specific reader in a specific situation. ("Future maintainers" is not an audience; "an on-call engineer at 03:00 with a P1" is.)
3. Owner -- a named human accountable for keeping it true. No owner → drift within months.
4. Update trigger -- a concrete event that causes the doc to be revisited or superseded. No trigger → fossil-in-waiting.