docs: add SDD specs + user requirements + tests

- .agents/specs/: spec-driven-dev docs for arcrun MVP, auth-recipe,
  credential-primitives-wasm (active refactor), landing-page,
  sdk-and-website, u6u-core-mvp, u6u-platform-evolution.
- .agents/steerings/tech.md: detailed tech stack rationale.
- docs/user_requirements/: long-form requirements incl. credential
  primitives, pages spec, py strategy analysis.
- tests/: end-to-end harness scaffolding.

These are the durable context backing CLAUDE.md's SDD protocol.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.agents/steerings/tech.md

@@ -0,0 +1,62 @@
+# Tech Stack — arcrun
+
+## Runtime & Deployment
+- **Cloudflare Workers** — all backend services deploy as Workers via Wrangler
+- **Cloudflare KV** — workflow definitions, credentials (encrypted), recipes, sessions
+- **Cloudflare R2** — WASM binary storage (`WASM_BUCKET`)
+- **Cloudflare Pages** — frontend deployment (arcrun.dev landing page)
+
+## Languages & Frameworks
+- **TypeScript** — Workers (HTTP routing/orchestration only), CLI, SDKs
+- **TinyGo / AssemblyScript** — all component logic, compiled to WASM (WASI preview1)
+- **Hono** — HTTP framework for all Workers (routing, middleware, OpenAPI)
+- **Zod** — schema validation and OpenAPI spec generation (`@hono/zod-openapi`)
+- **React 19** + **Vite** — frontend (landing page)
+- **Tailwind CSS v4** — styling
+
+## Testing
+- **Vitest** — test runner
+- **@cloudflare/vitest-pool-workers** — Workers-specific test pool for cypher-executor
+
+## Package Management
+- **pnpm** — used in most packages (some use npm)
+
+---
+
+## Common Commands
+
+### Per-service (run from the service directory)
+
+```bash
+# Start local dev server
+pnpm dev          # or: npm run dev
+
+# Deploy to Cloudflare
+pnpm deploy
+
+# Run tests (single pass)
+pnpm test         # runs: vitest run
+```
+
+### WASM Components (TinyGo)
+
+```bash
+# Build a component
+cd registry/components/{name}/
+tinygo build -target=wasi -o main.wasm main.go
+```
+
+### CLI
+
+```bash
+cd cli/
+npm run build
+acr --help
+```
+
+## API Documentation
+Each Worker exposes OpenAPI docs at runtime:
+- `/doc` — OpenAPI JSON spec
+- `/ui` — Swagger UI
+
+Dev base URLs: Cypher Executor → `http://localhost:8788`