feat: add SvelteKit demo app foundation

.gitignore

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 dist
 tmp
 out-tsc
+.svelte-kit
 
 # dependencies
 node_modules

PHASE_0_FOUNDATION.md

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+# Phase 0: Foundation
+
+**Branch:** `feat-demo-0-foundation`
+
+**Goal:** Create fresh SvelteKit app, integrate with Nx and pnpm workspace, verify it builds successfully.
+
+**Success Criteria:**
+- ✅ `apps/demo/` exists with SvelteKit app
+- ✅ `pnpm nx build demo` completes successfully
+- ✅ `pnpm nx dev demo` starts dev server
+- ✅ Dependencies installed via pnpm workspace
+- ✅ Cloudflare adapter configured
+- ✅ No build errors or warnings
+
+---
+
+## Tasks
+
+### 1. Create Fresh SvelteKit App
+
+```bash
+pnpm create svelte@latest apps/demo --template skeleton --types typescript
+```
+Select: TypeScript ✓, ESLint ✓, Prettier ✓, Skip testing tools
+
+### 2. Configure Nx Integration
+
+Create `apps/demo/project.json` with standard Nx configuration:
+- Define targets: `dev`, `build`, `preview`
+- Set executor to `nx:run-commands` for each
+- Point commands to Vite (e.g., `vite dev`, `vite build`)
+- Add build output path: `{projectRoot}/build`
+
+### 3. Add Core Dependencies
+
+```bash
+cd apps/demo
+
+# Add Cloudflare adapter for deployment
+pnpm add -D @sveltejs/adapter-cloudflare
+
+# Add Tailwind CSS for styling (automated setup)
+npx svelte-add@latest tailwindcss
+
+# Add Supabase for backend
+pnpm add @supabase/supabase-js
+
+# Install all dependencies
+pnpm install
+```
+
+### 4. Update Package Configuration
+
+Edit `apps/demo/package.json` to set the package name:
+- Change `"name"` to `"@pgflow/demo"`
+- Add `"private": true`
+
+**Note:** `@pgflow/client`, `@xyflow/svelte`, and `shiki` will be added in later phases as needed.
+
+### 5. Configure Cloudflare Adapter
+
+Update `apps/demo/svelte.config.js`:
+- Import `@sveltejs/adapter-cloudflare` instead of adapter-auto
+- Set in config: `kit: { adapter: adapter() }`
+
+### 6. Test Build
+
+```bash
+# From monorepo root
+pnpm nx build demo
+
+# Verify build output exists
+ls apps/demo/build
+```
+
+### 7. Test Dev Server
+
+```bash
+# From monorepo root
+pnpm nx dev demo
+
+# Open http://localhost:5173/
+# Verify page loads without console errors
+```
+
+---
+
+## Validation Checklist
+
+- [ ] `apps/demo/` exists with `project.json`
+- [ ] `package.json` name is `@pgflow/demo`
+- [ ] Cloudflare adapter configured in `svelte.config.js`
+- [ ] Tailwind CSS working (check for `app.css` with `@tailwind` directives)
+- [ ] `pnpm nx build demo` succeeds, creates `apps/demo/build/`
+- [ ] `pnpm nx dev demo` starts, http://localhost:5173/ loads
+- [ ] No TypeScript or console errors
+
+---
+
+## Troubleshooting
+
+- **`pnpm create svelte` fails:** Check Node.js version (≥18), network connection
+- **`svelte-add tailwindcss` fails:** Run manually: `pnpm add -D tailwindcss postcss autoprefixer`
+- **Nx doesn't recognize demo:** Verify `apps/demo/project.json` exists, run `pnpm nx show projects`
+- **Build fails:** Check Cloudflare adapter installed: `pnpm list @sveltejs/adapter-cloudflare`
+- **Dev server won't start:** Check port 5173 available (`lsof -i :5173`), try `--port 5174`
+
+---
+
+## Next Phase
+
+Proceed to **Phase 1: Vertical Slice** for end-to-end flow execution with minimal UI. Create branch `feat-demo-1-vertical-slice`.

PHASE_1_VERTICAL_SLICE.md

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+# Phase 1: Vertical Slice
+
+**Branch:** `feat-demo-1-vertical-slice`
+
+**Goal:** Implement minimal end-to-end flow execution - from UI button click through Edge Function to real-time status updates. Validates entire integration stack with **client-side auth only**.
+
+**Success Criteria:**
+- ✅ Supabase initialized in demo app
+- ✅ Client-side anonymous auth working
+- ✅ Edge Function with 1-step test flow executes
+- ✅ pgflow packages vendored correctly
+- ✅ pgflow client connects from UI
+- ✅ Button click starts flow
+- ✅ Status updates in real-time
+- ✅ No console errors
+
+**Philosophy:** Build the thinnest possible slice through the entire stack. UI will be ugly - that's fine. Goal is to prove integration works. **No server-side auth needed - demo is public!**
+
+---
+
+## Tasks
+
+### 1. Add pgflow Client Dependency
+
+Edit `apps/demo/package.json` - add `"@pgflow/client": "workspace:*"` to dependencies:
+
+```bash
+pnpm install
+```
+
+### 2. Initialize Supabase
+
+```bash
+cd apps/demo && supabase init && cd ../..
+```
+
+---
+
+### 3. Configure Supabase for pgflow
+
+Edit `apps/demo/supabase/config.toml` - add `"pgflow"` to `[api]` schemas:
+
+```toml
+schemas = ["public", "pgflow"]
+```
+
+---
+
+### 4. Copy Vendoring Script
+
+```bash
+mkdir -p apps/demo/scripts
+cp examples/playground/scripts/sync-edge-deps.sh apps/demo/scripts/
+chmod +x apps/demo/scripts/sync-edge-deps.sh
+```
+
+### 5. Update Vendoring Script Paths
+
+Edit `apps/demo/scripts/sync-edge-deps.sh` - replace `PLAYGROUND_DIR` with `DEMO_DIR`:
+
+```bash
+DEMO_DIR="$(dirname "$SCRIPT_DIR")"
+VENDOR_DIR="$DEMO_DIR/supabase/functions/_vendor"
+```
+
+---
+
+### 6. Add Nx Target for Vendoring
+
+Edit `apps/demo/project.json` - add `sync-edge-deps` target:
+
+```json
+"sync-edge-deps": {
+  "executor": "nx:run-commands",
+  "dependsOn": ["core:build", "dsl:build"],
+  "options": { "command": "./scripts/sync-edge-deps.sh", "cwd": "apps/demo" }
+}
+```
+
+### 7. Build Dependencies and Vendor
+
+```bash
+pnpm nx build core dsl
+pnpm nx sync-edge-deps demo  # Verify: ls apps/demo/supabase/functions/_vendor/@pgflow/
+```
+
+---
+
+### 8. Create Test Flow Definition
+
+Create `apps/demo/supabase/functions/_flows/test-flow.ts`:
+- Import Flow from `@pgflow/dsl`
+- Create simple 1-step flow with slug 'test-flow'
+- Handler returns: `Hello, ${input.run.message}!`
+- Note: Access run input via `input.run.*` pattern
+
+### 9. Create Edge Function Worker
+
+Create `apps/demo/supabase/functions/demo-worker/index.ts`:
+```typescript
+import { EdgeWorker } from '@pgflow/edge-worker';
+import TestFlow from '../_flows/test-flow.ts';
+
+EdgeWorker.start(TestFlow);
+```
+**This 3-line pattern is critical - it's how all pgflow workers are set up!**
+
+### 10. Test Edge Function Locally
+
+```bash
+cd apps/demo
+supabase start  # Then in another terminal:
+supabase functions serve demo-worker
+```
+
+### 11. Create Client-Side Supabase Configuration
+
+Create `apps/demo/src/lib/supabase.ts`:
+- Create Supabase client with URL and anon key (use env vars or local defaults)
+- Create PgflowClient wrapping the Supabase client
+- Export both for use in components
+- **Key point:** Pure client-side - no server hooks, no cookies!
+
+---
+
+### 12. Create Minimal Test UI
+
+Replace `apps/demo/src/routes/+page.svelte` with basic test interface.
+
+**Key patterns to implement:**
+- Anonymous auth: `await supabase.auth.signInAnonymously()` in onMount
+- Start flow: `pgflow.startFlow('test-flow', { message: 'World' })`
+- Listen to events: `run.on('*', (event) => { ... })`
+- Svelte 5 state: `let status = $state<string>('idle')`
+- Display status updates and output
+
+**Remember:** Use `onclick={handler}` not `on:click` (Svelte 5 syntax)
+
+---
+
+### 13. Start Dev Server
+
+```bash
+pnpm nx dev demo  # Ensure supabase start running
+```
+
+### 14. Test End-to-End
+
+Open http://localhost:5173/, click button, verify:
+- Status: `idle` → `starting...` → `running` → `completed`
+- Output shows `"Hello, World!"`
+- Console shows event stream
+
+---
+
+## Validation Checklist
+
+- [ ] Supabase initialized, pgflow packages vendored
+- [ ] Test flow + worker created
+- [ ] Anonymous auth working (check Network tab for auth.signInAnonymously)
+- [ ] `supabase start` and `functions serve demo-worker` running
+- [ ] Dev server starts, button click starts flow
+- [ ] Status updates real-time, output appears, no console errors
+
+---
+
+## Troubleshooting
+
+- **Vendoring fails:** Check `ls pkgs/core/dist`, rebuild with `pnpm nx build core dsl`
+- **Edge Function won't start:** Check `supabase status`, verify vendored files exist
+- **Anonymous auth fails:** Check browser console, ensure Supabase anon key is valid
+- **Flow doesn't start:** Check browser console - Supabase connection, pgflow schema in config.toml, flow slug matches
+- **No real-time updates:** Check Realtime enabled, Edge Function logs, Svelte `$state` reactivity
+- **TypeScript errors:** Verify Svelte 5 syntax (`$state`, `onclick`)
+- **Auth issues:** Remember - this is all client-side! No server hooks needed
+
+**Rollback:** Mock pgflow client to debug Edge Function separately
+
+**Common issues:**
+- `workspace:*` not resolving → `pnpm install --force`
+- Port in use → `lsof -i :54321`, kill process
+- Import paths wrong → Re-run `pnpm nx sync-edge-deps demo`
+
+---
+
+## Next Phase
+
+Proceed to **Phase 2: Article Flow** for 4-step flow and state management. Create branch `feat-demo-2-article-flow`.