## Summary
Implements M1 of the draggable panels spec from #608: the `DragManager`
class with core drag mechanics.
Fixes#608 (M1: DragManager core drag mechanics)
## What's New
### `public/drag-manager.js` (~215 lines)
- **State machine:** `IDLE → PENDING → DRAGGING → IDLE`
- **5px dead zone** on `.panel-header` to disambiguate click vs drag —
prevents hijacking corner toggle and close button clicks
- **Pointer events** with `setPointerCapture` for reliable tracking
- **`transform: translate()`** during drag — zero layout reflow
- **Snap-to-edge** on release: 20px threshold snaps to 12px margin
- **Z-index management** — dragged panel comes to front (counter from
1000)
- **`_detachFromCorner()`** — transitions panel from M0 corner CSS to
fixed positioning
- **Escape key** cancels drag and reverts to pre-drag position
- **`restorePositions()`** — applies saved viewport percentages on init
- **`handleResize()`** — clamps dragged panels inside viewport on window
resize
- **`enable()`/`disable()`** — responsive gate control
### `public/live.js` integration
- Instantiates `DragManager` after `initPanelPositions()`
- Registers `liveFeed`, `liveLegend`, `liveNodeDetail` panels
- **Responsive gate:** `matchMedia('(pointer: fine) and (min-width:
768px)')` — disables drag on touch/small screens, reverts to M0 corner
toggle
- **Resize clamping** debounced at 200ms
### `public/live.css` additions
- `cursor: grab/grabbing` on `.panel-header` (desktop only via `@media
(pointer: fine)`)
- `.is-dragging` class: opacity 0.92, elevated box-shadow, `will-change:
transform`, transitions disabled
- `[data-dragged="true"]` disables corner transition animations
- `prefers-reduced-motion` support
### Persistence
- **Format:** `panel-drag-{id}` → `{ xPct, yPct }` (viewport
percentages)
- **Survives resize:** positions recalculated from percentages
- **Corner toggle still works:** clicking corner button after drag
clears drag state (handled by existing M0 code)
## Tests
14 new unit tests in `test-drag-manager.js`:
- State machine transitions (IDLE → PENDING → DRAGGING → IDLE)
- Dead zone enforcement
- Button click guard (no drag on button pointerdown)
- Snap-to-edge behavior
- Position persistence as viewport percentages
- Restore from localStorage
- Resize clamping
- Disable/enable
## Performance
- `transform: translate()` during drag — compositor-only, no layout
reflow
- `will-change: transform` only during active drag (`.is-dragging`),
removed on drop
- `localStorage` write only on `pointerup`, never during `pointermove`
- Resize handler debounced at 200ms
- Single `style.transform` assignment per pointermove frame — negligible
cost
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Co-authored-by: you <you@example.com>
Kpa-clawbot