Add harness workflow and Material showcase design system

AGENTS.md

@@ -24,10 +24,44 @@ Sub-agents should use this context policy:
 - Keep shared integration files owned by the main thread whenever possible
 - If a sub-agent needs a shared dependency or a shared export change, have it report that back rather than editing unrelated files
 
+## Harness Workflow
+
+Agents should treat the following files as the default system of record before making non-trivial
+changes:
+
+- `DESIGN.md`
+- `README.md`
+- `CONTRIBUTING.md`
+- `roadmap.md`
+- `packages/ui/src/lib/contracts.ts`
+- `apps/docs/src/component-authoring.stories.tsx`
+- `docs/harness-engineering.md`
+- `docs/orchestration.md`
+
+When work spans multiple surfaces or changes public behavior, start by creating or updating an
+execution plan in `docs/exec-plans/`.
+
+Prefer the narrowest useful harness suite while working:
+
+- `pnpm harness:select`
+- `pnpm harness:validate:changed`
+- `pnpm harness:validate:static`
+- `pnpm harness:validate:component`
+- `pnpm harness:validate:docs`
+- `pnpm harness:validate:docs-smoke`
+- `pnpm harness:validate:consumers`
+- `pnpm harness:validate:pr`
+- `pnpm harness:validate:release`
+
+Every suite writes a JSON report under `.artifacts/harness/`.
+Worktree-backed orchestration runs use `pnpm harness:orch -- <orch command>` and store state under
+`.artifacts/orch/`.
+
 ## Priority
 
 If there is any conflict between older default delegation habits and this file:
 
+- follow `DESIGN.md` for the active visual language and motion direction
 - follow this file for sub-agent model selection
 - follow this file for sub-agent reasoning effort
 - follow this file for context fallback behavior