Variance declarations + a compliance self-check (repokit lint)

[PBNZ]

Retrospective finding — refs #10.

Context

Repos drift from the standard file set silently, and each deviation is discoverable only by
reading that repo end-to-end — or not at all. Observed (anonymised):

• Canonical agent file present, loader shim missing — the file the tooling reads doesn't
  exist, so the canonical one may never load.
• ADR directory absent, replaced by a root-level decisions file — the substitution is only
  partially documented (one aspect of the deviation recorded, the rest not).
• Changelog living at a nested path that the repo's own agent file never names.
• One repo replaces the checkpoint with a README-status contract — documented and honoured. This
  is the good case, and it proves variants are fine when declared.
• Retro-adopted repos snap to clean conventions at the adoption commit, but nothing marks the
  pre-standard history as exempt, so any future audit re-flags it forever.

The standard tolerates variants by design (ceremony scales by tier); what's missing is the rule
that a variant must be declared, and a cheap machine check that the declared structure
actually exists.

Proposal

1. Variance-declaration rule: any deviation from the tier's file set (substitute file,
   relocated file, omitted component) must have a row in the START-HERE map saying what replaces
   what. Undeclared deviation = non-compliance; declared deviation = a variant.
2. Self-check script (scripts/ + optional CI), checking mechanically:
   • canonical agent file + thin shim both present, shim actually imports the canonical file;
   • every START-HERE row's path resolves to an existing file/dir;
   • changelog exists at the declared location;
   • ADR dir (or declared substitute) exists;
   • resume-state artifact (or declared substitute) exists — ties into the resume-state issue.
3. Adoption marker: a one-line convention for retro-adopted repos (e.g. noted in the agent
   file or the adoption commit) defining the compliance horizon, so audits stop re-flagging
   pre-standard history.

Tasks

• Add the variance-declaration rule to the standard's core doc.
• Implement the self-check script; ship as part of the scaffold, retrofittable.
• Document the adoption-marker convention.

Acceptance criteria

• Every deviation in a compliant repo is visible from the START-HERE map alone.
• The self-check passes on a fresh scaffold, fails on each of the drift cases above, and runs in
  seconds locally.

— 🤖 Claude, on behalf of @PBNZ

[PBNZ]

Triage: accepted.

Landed on PR #18 (commits 5c267dc + a5bce08): the variance-declaration rule in the-standard.md (any deviation gets a START-HERE row; undeclared = non-compliance, declared = variant), the adoption-marker convention for retro-adopted repos (one line under the START-HERE map defining the compliance horizon), and scripts/repokit-check.ps1 as a core-tier template — checks shim imports canonical file, every START-HERE path resolves, changelog/ADR/resume-state present or declared. /new-repo stamps and runs it; this repo's CI runs it against itself plus a smoke test proving it fails on each drift case from the retrospective. Runs in ~2 s locally.

— 🤖 Claude, on behalf of @PBNZ

[PBNZ]

Verified on main (f7ab31c): variance-declaration rule + adoption marker in the-standard.md; repokit-check.ps1 stamped at Core, dogfooded green in this repo's CI, smoke test proves it fails on each drift case. Closing on @PBNZ's instruction.

— 🤖 Claude, on behalf of @PBNZ