# Design Decisions — Impeccable Wave

## 1. Motion Token System

### Approach

Define CSS custom properties for motion in `apps/web/src/styles/globals.css`, then reference from components. This is the standard pattern (CSS custom properties) that integrates natively with Tailwind v4's `@theme` directive.

### Token Schema

```css
@theme {
  /* Durations */
  --duration-instant: 0ms;
  --duration-fast: 100ms;
  --duration-normal: 150ms;
  --duration-slow: 200ms;
  --duration-deliberate: 300ms;

  /* Easing curves */
  --ease-enter: cubic-bezier(0.22, 1, 0.36, 1);      /* entrances, button press */
  --ease-move: cubic-bezier(0.25, 1, 0.5, 1);         /* slides, drawers, panels */
  --ease-hover: ease;                                   /* hover states, color transitions */
  --ease-emerge: cubic-bezier(0.165, 0.84, 0.44, 1);  /* modals, popovers scaling in */
  --ease-exit: cubic-bezier(0.4, 0, 0.2, 1);           /* quick dismissals */

  /* Reduced motion override */
  --motion-reduce-transform: none;
  --motion-reduce-opacity: none;
}
```

The `.dark` block or `@media (prefers-reduced-motion: reduce)` overrides `--motion-reduce-*` to `none` and sets duration overrides to `0ms`.

### Usage pattern

```tsx
// Before
className="transition-colors duration-150"

// After
className="transition-colors duration-[var(--duration-fast)] ease-[var(--ease-hover)]"
```

For framer-motion, reference same tokens via JS constants in `lib/motion.ts`.

## 2. Animation Library Choice: framer-motion

### Why framer-motion over alternatives

| Feature | framer-motion | motion (standalone) | CSS-only |
|---------|--------------|---------------------|----------|
| Layout animations | `layout` prop | `layout` prop | ❌ Requires JS |
| AnimatePresence | ✅ | ✅ | ❌ |
| Spring physics | ✅ | ✅ | ❌ (CSS steps approximation) |
| Gesture handling | `drag`, `whileHover`, `whileTap` | Same API | Partial |
| Stagger children | `staggerChildren` variant | Same | ❌ |
| Bundle size | ~30KB gzipped | ~10KB gzipped | 0KB |
| React 18 compat | ✅ 12.x | ✅ 12.x | N/A |

**Decision:** Use `framer-motion` (full-featured). The `motion` standalone package (same API, smaller bundle) is a future migration if bundle size becomes a concern. For this wave, framer-motion's broader ecosystem and established React 18 support are the safe choice.

### Bundle impact

`framer-motion` v12 adds ~30KB gzipped. Route-level code splitting in Phase 5 will offset this by reducing the initial bundle by an estimated 100-200KB (the current bundle includes all 6 page components). Net bundle impact: **~70KB reduction** after code splitting.

## 3. Workspace Pane Animation Strategy

### Current architecture

The workspace grid (`Workspace.tsx`) renders panes from `panes[]` array in a CSS grid. Pane open/close is a state mutation — panes appear/disappear instantly. Reorder is handled by drag (HTML5 native).

### Animated approach

```
┌─────────────────────────────────┐
│         Workspace Grid          │
│  ┌──────────┐ ┌──────────┐     │
│  │ Chat     │ │ Terminal │     │
│  │ (enter:  │ │ (enter:  │     │
│  │  slideL) │ │  slideR) │     │
│  └──────────┘ └──────────┘     │
│  ┌──────────────────────────┐   │
│  │ Coder (enter: slideUp)   │   │
│  └──────────────────────────┘   │
└─────────────────────────────────┘
```

**Key decisions:**
1. **Pane open**: Slide in from the nearest edge (left-pane opens from left, right-pane from right, bottom-pane from bottom) with fade. 200ms `ease-out`.
2. **Pane close**: Quick fade (100ms) — exit should be faster than enter per animation best practices.
3. **Pane reorder**: `layout` prop on each pane wrapper. framer-motion handles the FLIP calculation automatically.
4. **Tab switch**: Content crossfade (150ms). Not a slide — tabs are content replacement, not navigation.
5. **Split pane**: New pane emerges from the split point (scale + fade, `transform-origin` at the split edge).

### Implementation

```tsx
// Workspace.tsx — pane wrapper
<motion.div
  layout
  initial={{ opacity: 0, scale: 0.95 }}
  animate={{ opacity: 1, scale: 1 }}
  exit={{ opacity: 0, scale: 0.95, transition: { duration: 0.1 } }}
  transition={{ type: 'spring', stiffness: 300, damping: 30 }}
>
  <PaneComponent />
</motion.div>
```

`AnimatePresence` wraps the pane grid so exiting panes animate out before DOM removal.

## 4. Message Stagger Entrance

### Approach

Use framer-motion's `staggerChildren` variant on the message list container, with individual item variants for the entrance.

```tsx
const containerVariants = {
  initial: {},
  animate: {
    transition: {
      staggerChildren: 0.03,  // 30ms between messages
    },
  },
};

const messageVariants = {
  initial: { opacity: 0, y: 8 },
  animate: { opacity: 1, y: 0, transition: { duration: 0.2, ease: 'easeOut' } },
};
```

**Edge cases:**
- **New messages during streaming**: Only animate the first appearance of a message. Once visible, subsequent content updates (streaming deltas) should not re-animate. Track via `data-animated` attribute.
- **Scroll-anchored messages**: When the user is scrolled to bottom and a new message arrives, animate it in. When the user has scrolled up, suppress animation to avoid disorientation.
- **Initial load**: All existing (already-loaded) messages appear without animation. Only NEW messages animate in.
- **Reasoning block**: The collapsible reasoning block uses a spring-based height transition instead of the grid-rows CSS trick.

## 5. Keyboard Shortcuts Dialog

### Invocation

`Cmd+/` or `?` in the workspace. A modal overlay triggered via a new keyboard handler in `Session.tsx`.

### Content

Grouped into sections:

```
Navigation         │ Cmd+` Terminal  │ Cmd+T New Terminal
                   │ Cmd+C New Chat  │ Cmd+W Close Pane
                   │ Tab / Shift+Tab │ Cycle panes

Chat               │ Enter Send      │ Shift+Enter Newline
                   │ Cmd+[ 1-9 ]     │ Jump to tab
                   │ @               │ Mention file
                   │ /               │ Slash commands

Terminal           │ Cmd+Shift+C     │ Copy
                   │ Cmd+F           │ Search
                   │ Esc             │ Close search

General            │ Cmd+/           │ This panel
                   │ ?               │ This panel
```

### Data source

Derived from existing keyboard handlers in `Session.tsx` and component files. Centralized into a single `KEYBOARD_SHORTCUTS` constant in `lib/keyboard-shortcuts.ts`.

## 6. Undo Toast System

### Approach

Extend the existing Sonner toast system. Destructive actions call `toast.success(message, { action: { label: 'Undo', onClick: rollback } })`. Each action needs a rollback function.

### Implementation pattern

```typescript
// In component with destructive action
async function deleteChat(chatId: string) {
  const previousMessages = await api.chats.messages.list(chatId); // snapshot
  await api.chats.remove(chatId); // optimistic delete

  toast.success('Chat deleted', {
    action: {
      label: 'Undo',
      onClick: async () => {
        await api.chats.restore(chatId, previousMessages); // rollback
      },
    },
    duration: 5000, // 5s to undo
  });
}
```

### Scope

Start with 3 high-impact undo actions:
1. **Delete chat** — snapshot messages, restore on undo
2. **Archive project** — toggle unarchive
3. **Close pane** — reopen via `closedPaneStack` (already exists)

## 7. Font Pairing Strategy

### Goals
- Distinctive but still technical/developer-appropriate
- Must pair well with JetBrains Mono (code font stays)
- Must support variable weights for the Tailwind v4 font-weight system
- Must be available on Google Fonts (self-hosted via `@fontsource`)

### Candidate pairs

| Pair | Vibe | Google Fonts | Variable |
|------|------|-------------|----------|
| **Instrument Sans** + JetBrains Mono | Modern, geometric, technical | ✅ | ✅ |
| **Public Sans** + JetBrains Mono | Clean, neutral, authoritative | ✅ | ✅ |
| **Satoshi** + JetBrains Mono | Bold, editorial, confident | ❌ (paid) | ✅ |
| **Onest** + JetBrains Mono | Rounded, approachable but tech | ✅ | ✅ |
| **Plus Jakarta Sans** + JetBrains Mono | Refined, slightly warmer | ✅ | ✅ |

**Decision:** Defer final choice to implementation. Replace Inter with chosen font via `@fontsource` import in `main.tsx` + update the `--font-sans` token in `globals.css`.

## 8. Code Splitting Architecture

### Current
```tsx
// App.tsx — static imports, all loaded upfront
import Home from '@/pages/Home'
import Project from '@/pages/Project'
import Session from '@/pages/Session'
import Settings from '@/pages/Settings'
import Analytics from '@/pages/Analytics'
import Results from '@/pages/Results'
```

### Target
```tsx
// App.tsx — dynamic imports with named exports
const Home = lazy(() => import('@/pages/Home'))
const Project = lazy(() => import('@/pages/Project'))
const Session = lazy(() => import('@/pages/Session'))
const Settings = lazy(() => import('@/pages/Settings'))
const Analytics = lazy(() => import('@/pages/Analytics'))
const Results = lazy(() => import('@/pages/Results'))

// Single Suspense boundary wrapping all routes
<Routes>
  <Route path="/" element={<Suspense fallback={<FullPageLoader />}><Home /></Suspense>} />
  ...
</Routes>
```

### Chunk strategy

- **Vendor chunk**: `react`, `react-dom`, `react-router-dom` → stable, infrequently changed
- **UI chunk**: `framer-motion`, `lucide-react`, `react-markdown`, `shiki` → large UI libs
- **Per-page chunks**: Each page component loads on demand

Configured via `vite.config.ts` `build.rollupOptions.output.manualChunks`.

## 9. Empty State Pattern

### Standard template

```tsx
// New reusable component
function EmptyState({ icon, title, description, action }: EmptyStateProps) {
  return (
    <div className="flex flex-col items-center justify-center gap-3 py-16">
      <div className="text-muted-foreground/40">{icon}</div>
      <p className="text-sm font-medium text-foreground">{title}</p>
      {description && (
        <p className="text-xs text-muted-foreground text-center max-w-[240px]">{description}</p>
      )}
      {action && <Button variant="outline" size="sm" onClick={action.onClick}>{action.label}</Button>}
    </div>
  );
}
```

Replace current text-only empty states in `Home.tsx` (no projects), `Project.tsx` (no sessions), and `SessionLandingPage.tsx` (no chats).

## 10. StatusDot Animation Fix

### Current
```tsx
// No transform-origin set — rotation around center creates blur
<span className="absolute top-0 left-1/2 -translate-x-1/2 size-0.5 rounded-full bg-amber-500" />
```

### Target
```tsx
// Explicit transform-origin + motion-safe guard
<span className="absolute top-0 left-1/2 -translate-x-1/2 size-0.5 rounded-full bg-amber-500 motion-safe:animate-spin-slow motion-reduce:hidden" style={{ transformOrigin: 'center 6px' }} />
```

The `size-0.5` dots orbit at 12px diameter. `transform-origin: center 6px` centers rotation at the orbit midpoint.