Add harness workflow and Material showcase design system

CONTRIBUTING.md

@@ -8,19 +8,23 @@ discipline instead of introducing parallel patterns.
 
 Read the current contract and docs baseline first:
 
+- `DESIGN.md`
 - `roadmap.md`
 - `packages/ui/src/lib/contracts.ts`
 - `apps/docs/src/component-authoring.stories.tsx`
+- `docs/harness-engineering.md`
+- `docs/orchestration.md` when the work may be split across agents
 
 Then inspect the closest existing component before adding a new one.
 
 ## Default workflow
 
-1. Confirm the component or change fits the current system layers.
-2. Reuse the existing contract helpers, slot names, state naming, and variant conventions.
-3. Add or update Storybook stories so behavior is reviewable.
-4. Add or update tests before treating the component as done.
-5. Run the relevant validation commands locally.
+1. Create or update an execution plan in `docs/exec-plans/` when the change is non-trivial.
+2. Confirm the component or change fits the current system layers.
+3. Reuse the existing contract helpers, slot names, state naming, and variant conventions.
+4. Add or update Storybook stories so behavior is reviewable.
+5. Add or update tests before treating the component as done.
+6. Run the relevant validation commands locally.
 
 ## Authoring rules
 
@@ -107,6 +111,17 @@ pnpm typecheck
 pnpm test
 ```
 
+Harness shortcuts:
+
+```bash
+pnpm harness:select
+pnpm harness:validate:static
+pnpm harness:validate:changed
+pnpm harness:validate:component
+pnpm harness:validate:docs
+pnpm harness:validate:consumers
+```
+
 Docs and smoke checks:
 
 ```bash
@@ -115,6 +130,13 @@ pnpm build:docs
 pnpm test:e2e:smoke
 ```
 
+Broader gates:
+
+```bash
+pnpm harness:validate:pr
+pnpm harness:validate:release
+```
+
 ## Practical repo guidance
 
 - Keep shared integration points small. If you only need a new component, avoid unrelated changes.