# HANDOFF: Lego Ladder Project
**Date:** 2026-06-06
**Status:** Implementation Verified (Engine, UI, & Drag-and-Drop)
## 🎯 Current Objective
Verify the stability of the engine lifecycle and the correctness of the new drag-and-drop movement functionality.
## ✅ Completed Work
### 1. Engine Lifecycle Management (`src/engine/engine.ts`)
- **Fixed `loadProgram`**: Now calls `this.stop()` before loading new programs to prevent interval stacking.
- **Fixed `start`**: Now checks for existing `stopFn` and clears it before starting a new cycle.
- **Implemented `stop()`**: Added a formal method to clear the `setInterval` timer.
### 2. UI Layout & Dialogs (`index.html`)
- **Fixed Dialog Clipping**: Updated `.rename-dialog` and other modal styles from `position: absolute` to `position: fixed`.
- **Centered Modals**: Implemented `top: 50%; left: 50%; transform: translate(-50%, -50%);` to ensure dialogs appear in the center of the viewport and are never clipped by the header or sidebar.
### 3. Drag and Drop Functionality (`src/ui/components/Element.tsx`, `src/ui/components/Ladder.tsx`)
- **Implemented Element Draggability**: Added `draggable` attribute to `Element` components to allow them to be picked up.
- **Implemented Element Moving**: Enabled moving existing elements between rungs by passing source indices via `application/json` in `onDragStart` and handling the move in `Ladder.tsx`.
## 🛠️ Next Steps (Immediate)
1. **Local Deployment**: Transfer the `projects/lego-ladder/` directory to the local laptop.
2. **Dependency Check**: Run `npm install`.
3. **Functional Testing**:
- **Start/Stop Test**: Start the engine, then stop it. Verify no background intervals are running.
- **Program Swap Test**: Load a program, then immediately load a different one. Verify the engine doesn't "speed up".
- **UI Test**: Trigger the "Rename" and "New Program" dialogs. Verify they are centered and fully visible.
- **Drag & Drop Test**: Drag a new tool from the toolbar to a rung.
- **Move Test**: Drag an existing element from one rung to another. Verify it moves correctly.
4. **Regression Check**: Ensure the `Ladder` and `Element` components still render correctly with the new CSS variables.
## ⚠️ Known Quirks/Notes
- **Vite Vulnerability**: `npm audit` will report moderate/critical vulnerabilities in `esbuild`. **Do not** run `npm audit fix --force`.
- **CSS Variables**: The project relies heavily on the new CSS variable structure defined in `index.html`.
## 📂 Key Files
- `projects/lego-ladder/src/engine/engine.ts` (Logic)
- `projects/lego-ladder/index.html` (Styles/Structure)
- `projects/lego-ladder/src/ui/hooks/useEngine.ts` (React Integration)
- `projects/lego-ladder/src/ui/components/Element.tsx` (Draggable Elements)
- `projects/lego-ladder/src/ui/components/Ladder.tsx` (Drag/Drop Handling)