feat(designbook): technology-neutral IR + stack-adapter pipeline (WHYNOT-WP-0002 T01-T06)

Author the design language once in the canonical React designbook and project it
one-way onto each stack: React -> designbook/ -> ir/ -> adapters/<stack>/.

Phase 0 — contracts & governance (T01-T03):
- ir/SCHEMA.md + ir/schema/{component,tokens}.schema.json — neutral IR contract
  (W3C DTCG tokens; React prop -> HTML attribute mapping; non-portable props flagged).
- adapters/ADAPTER_CONTRACT.md — inputs, drift-report + parity-result shapes,
  idempotency rules, CI exit codes (0 ok / 2 usage / 3 drift / 4 parity / 5 internal).
- .claude/rules/designbook-propagation.md + DesignSystemIntroduction.md §5.1 —
  one-way directionality + drift-resolution workflow.

T04 — canonical React designbook + the missing pull tool:
- The bundled /design-sync skill only PUSHES repo->cloud; it cannot populate
  designbook/. Added scripts/designbook_pull.py + `make designbook-pull`, which drives
  the local claude binary headless (acceptEdits) so DesignSync fetch+write runs in a
  subprocess (contents never hit the orchestrator's context). Pulled 44 files;
  excludes the _whynot-design-seed/ self-copy. Corrected the docs that wrongly called
  /design-sync the pull.

T05 — IR extractor (scripts/ir-extract.mjs + `make ir`):
- ir/tokens.json (80 tokens, DTCG, var() -> {ref} alias resolution); ir/components/*.json
  (10 contracts parsed from .jsx signatures: enum/boolean/number inference, prop->attr
  map, style/callback marked non-portable); ir/exemplars/*.

T06 — Lit token adapter (adapters/lit/ + `make adapt-lit`):
- Full-gen tokens into src/styles/colors_and_type.css :root (marker-bounded, idempotent
  no-op on re-run; hand-authored type CSS preserved).

NOTE: token regen synced Lit to canonical React — fonts IBM Plex -> system stacks and 8
status tokens added. This is a VISUAL change: review and run `pnpm test:visual:update`
before merge. Remaining: T07 scaffold+drift, T08 parity, T09 runbook, T10 2nd-adapter.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

DesignSystemIntroduction.md

@@ -217,6 +217,59 @@ The end-to-end flow for a single design change:
 
 The whole loop, warm, takes minutes. **Automation works only because every step has a deterministic check** — visual regression on both sides, semver, changelogs. Skip those and the pipeline is a slow manual process with extra tools.
 
+### 5.1 The IR pivot — technology-neutral propagation (WHYNOT-WP-0002)
+
+Claude Design's `/design-sync` produces a **React-bound** designbook. To keep the
+language portable across UI stacks (Lit today, others later) without forking it
+per stack, an **intermediate representation (IR)** sits between the atelier and
+each stack's source:
+
+```
+Claude Design (React)  ──/design-sync──▶  designbook/  ──make ir──▶  ir/  ──make adapt-lit──▶  src/ (Lit)
+   canonical authoring        React mirror      neutral blueprint        per-stack adapter
+```
+
+**Directionality is one-way: React → IR → stacks.**
+
+- The **React designbook in Claude Design is canonical.** The shared language is
+  authored there; nothing downstream is the source of truth.
+- `ir/` is the **committed, diffable blueprint** (tokens in W3C DTCG format,
+  per-component contracts, reference exemplars). Only the extractor writes it —
+  never hand-edit `ir/tokens.json`, `ir/components/`, or `ir/exemplars/`. See
+  `ir/SCHEMA.md`.
+- Each stack has an **adapter** (`adapters/<stack>/`, contract in
+  `adapters/ADAPTER_CONTRACT.md`). Adapters are **scaffold + drift-detect**:
+  tokens fully generated, new components stubbed, changed components reported as
+  **drift** — the hand-authored source is never overwritten. Lit is the reference
+  adapter.
+- **Lit-side changes do not flow back automatically.** A change to the shared
+  language must be made in Claude Design (React) and re-propagated through the IR.
+  A Lit→React back-edit that bypasses Claude Design is a governance violation: it
+  silently desyncs the canonical source from the implementation.
+
+**Drift resolution workflow.** When `make adapt-lit` reports drift
+(`adapters/lit/drift/<Name>.md`, exit code `3`):
+
+1. **Triage** — read the drift report. Each issue is one of: prop missing,
+   attribute mismatch, variant added/removed, prop removed, or a **non-portable
+   prop** (a React object/render-prop/callback that has no clean attribute).
+2. **Decide the direction.** If the IR is right and Lit is stale, a human adjusts
+   the Lit element's contract/behaviour to match. If the *language itself* should
+   change, that edit goes to Claude Design (React) and re-propagates — not into Lit.
+3. **Behaviour is filled by a human**, guided by the stub's `TODO` and the drift
+   report. The adapter never authors behaviour.
+4. **Close** — re-run `make adapt-lit` until drift clears, then `make parity-lit`
+   (exit `0`) confirms contract + visual parity. A drift report is "closed" when
+   the next extract+adapt produces no issues for that component.
+
+This **extends** the five-hop pipeline above rather than replacing it: hops 3–5
+(tag → publish → consumer) are unchanged; the IR pivot is inserted between the
+atelier and the Lit source so the same change can later be projected onto a second
+stack without re-authoring it. The full operational sequence is the
+`make designbook-refresh` runbook (WHYNOT-WP-0002 Phase 5). Governance for this
+flow is restated as an enforceable rule in
+`.claude/rules/designbook-propagation.md`.
+
 ---
 
 ## 6. Versioning discipline