chore: mark US-033 as complete and update progress log

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

prd.json

@@ -585,7 +585,7 @@
         "Verify in browser using dev-browser skill"
       ],
       "priority": 33,
-      "passes": false,
+      "passes": true,
       "notes": ""
     },
     {

progress.txt

@@ -476,3 +476,18 @@
   - Custom edges go in `src/components/editor/edges/` directory
   - Use amber color scheme for conditional edges to distinguish from regular edges
 ---
+
+## 2026-01-22 - US-033
+- What was implemented: Auto-save to LocalStorage with debounced saves and draft restoration prompt
+- Files changed:
+  - src/app/editor/[projectId]/FlowchartEditor.tsx - added LocalStorage auto-save functionality, draft check on load, and restoration prompt UI
+- **Learnings for future iterations:**
+  - Use lazy useState initializer for draft check to avoid ESLint "setState in effect" warning
+  - LocalStorage key format: `vnwrite-draft-{projectId}` for project-specific drafts
+  - Debounce saves with 1 second delay using useRef for timer tracking
+  - Convert React Flow Node/Edge types back to app types using helper functions (fromReactFlowNodes, fromReactFlowEdges)
+  - React Flow Edge has `sourceHandle: string | null | undefined` but app types use `string | undefined` - use nullish coalescing (`?? undefined`)
+  - Check `typeof window === 'undefined'` in lazy initializer for SSR safety
+  - clearDraft is exported for use in save functionality (US-034) to clear draft after successful database save
+  - JSON.stringify comparison works for flowchart data equality check
+---