---
name: <SLUG>-interaction-design
description: Interaction design for the <PROJECT NAME> project. State surfaces (modal vs inline vs drawer vs full-page), motion philosophy, input modes (touch/mouse/keyboard), breakpoints, i18n posture, empty/loading/error/offline state postures, time formatting, keyboard policy, optimistic-update strategy, gesture handling, and focus management. Load and apply whenever building UI behavior — modals, forms, navigation, transitions, gestures, error handling, async states, focus management, or any decision about how the interface responds. Pairs with <SLUG>-design-system.
---

# <PROJECT NAME> interaction design

> **Status: <draft | reviewed | locked>**
> Generated by Composer's `ui-system` phase. Re-running that phase
> updates this skill (with confirmation on overwrite).

## How to use this skill

When building UI *behavior* — anything beyond static styling — read
this skill first. Don't invent new state-surface patterns, motion
durations, or empty-state postures. They're declared once here and
reused everywhere. For visual tokens (color, type, spacing), see the
paired `<SLUG>-design-system` skill.

If a screen needs a pattern that isn't declared here, propose it in
this skill before writing the code — not the other way around.

## Input modes

| Mode | Status | Notes |
|---|---|---|
| Touch    | <primary | supported | not supported> | <…> |
| Mouse    | <…> | <…> |
| Keyboard | supported (always — a11y baseline) | full keyboard navigation required |
| Voice    | <typically not supported in v1> | — |
| Switch / assistive | <…> | — |

**Primary**: <which> — design defaults assume this mode.

## State surfaces

One pattern per action class. Used everywhere. If a screen needs a
deviation, document it inline as an exception with a reason.

| Action class | Pattern | Notes |
|---|---|---|
| Quick edit (single field) | <inline edit | popover | drawer> | — |
| Multi-field create | <drawer | modal | full-page route> | — |
| Multi-field edit | <drawer | modal | full-page route> | usually same as create |
| Confirm destructive | modal | always — non-negotiable |
| Settings / configuration | full-page route | — |
| Top-level navigation | <sidebar | tab bar | header nav> | — |
| Detail-from-list | <full route | side panel | drawer> | — |
| Filtering / sorting | <inline controls | popover | drawer> | — |
| Search | <header search | command palette | dedicated page> | — |

## Motion

- **Posture**: <minimal | restrained | expressive>
- **Default duration / easing**: see design-system tokens (`motion.duration.default`, `motion.easing.standard`)

### Animation triggers

| Trigger | Animated? | Duration / easing |
|---|---|---|
| Page / route transitions | <yes | no | conditional> | <token> |
| List item enter / exit | <…> | <token> |
| Modal / drawer open / close | <…> | <token> |
| State changes (toggle, expand) | <…> | <token> |
| Loading → loaded transitions | <…> | <token> |
| Hover / focus state changes | <…> | <token — usually `fast`> |

### Reduced motion

`prefers-reduced-motion: reduce` is **always honored**. Fallback strategy:
- Replace transitions with instant state changes.
- Replace fades with instant show/hide.
- Replace slides with crossfades or instant.
- Keep hover/focus state changes (these are essential signals, not motion).

## Breakpoints

| Breakpoint | Range | Purpose |
|---|---|---|
| Phone   | < <px> | <…> |
| Tablet  | <px> – <px> | <…> |
| Desktop | ≥ <px> | <…> |
| (Large desktop) | ≥ <px> | optional |

- **Primary design target**: <mobile-first | desktop-first | fluid>
- **Fluid scale ranges** *(if used)*: <…>
- See `tokens.ts` `breakpoint` for px values.

## i18n

- **Locales at launch**: <list>
- **RTL support**: <yes | no | planned for vN>
- **Pluralization**: <ICU MessageFormat | library | manual>
- **String length budget**: assume +30% over English for de/fr translations
- **Date / number formatting**: `Intl.DateTimeFormat` / `Intl.NumberFormat` (locale-aware)
- **Locale switching mechanism**: <…>

## State postures

One declared posture per state, used everywhere. Per-screen variation
is an exception that needs justification, not a default.

### Empty
- **Visual**: <icon + heading + body + CTA | heading + body | heading only>
- **Tone**: <encouraging | neutral | matter-of-fact>
- **CTA**: <present always | present when actionable | never>
- **Copy length**: keep to 1–2 sentences; the state itself communicates

### Loading
- **Default pattern**: <skeleton | spinner | blocking>
- **By action class**:
  - List / card containers: <usually skeleton>
  - Inline buttons: <usually spinner-in-button>
  - Page-level: <skeleton or blocking>
- **Threshold for showing loading at all**: <ms — usually 200–300ms>

### Error
- **Surface by class**:
  - Recoverable inline (validation): inline beneath the field
  - Recoverable async (network): toast with retry
  - Unrecoverable (system): dialog
- **Recovery affordances**: <retry | clear path forward | report>
- **Copy tone**: plain language, name what happened, name what to do next
- **Copy length**: 1–2 sentences max
- **Never** show stack traces, error codes without explanation, or "An error occurred" without specifics

### Offline
- **Behavior**: <full subset works | banner only | "go online to continue">
- **Indicator**: <persistent banner | transient toast | none>
- **Sync semantics**: <queue + flush on reconnect | fail loudly | not in v1>
- **Conflict resolution on reconnect**: <see Optimistic updates below>

## Time formatting

- **Relative time** for events within: <threshold — e.g., < 7 days>
  - Pattern: "<3 hours ago>", "<yesterday>", "<last Tuesday>"
- **Absolute time** otherwise:
  - Pattern: <`Intl.DateTimeFormat` locale-aware | explicit format>
  - Example: <e.g., "Apr 28, 2026 4:30 PM">
- **Date-only vs date+time**: show time when it matters (events, logs); date-only for ages, anniversaries, milestones
- **Time zones**: <user-local | fixed | configurable>
- **Tooltip / hover**: relative-time displays should show absolute on hover

## Keyboard

- **Global shortcuts**: <list, or "none in v1">
- **Within-modal**:
  - `Esc` closes (always)
  - Focus trapped while open
  - Focus restored to trigger element on close
- **Tab order**: declared per-flow as relevant; focus visible always (per design-system)
- **Forms**:
  - `Enter` submits *(or Cmd+Enter for multi-line forms)*
  - `Esc` cancels destructive actions only
- **Lists / menus**:
  - Arrow-key navigation: <yes | no in v1>
  - `Home` / `End`: <yes | no>
  - Type-ahead select: <yes | no>

## Optimistic updates & error recovery

- **Default posture**: <optimistic with rollback | pessimistic | mixed>
- **Optimistic by default**: most actions feel fast; rollback on failure
- **Pessimistic by default**: destructive actions, money flows, anything irreversible
- **Mixed strategy** *(if applicable)*:
  - Optimistic for: <action classes>
  - Pessimistic for: <action classes>

### Rollback strategy

- **UI on failure**: <toast + revert | silent revert | dialog>
- **Retry affordance**: <inline retry button | toast button | none>
- **Stale data detection**: <ETag | timestamp | version>

### Conflict resolution

- **Strategy**: <last-write-wins | show conflict UI | append both | platform-specific>
- **User-visible signaling**: <…>

## Gestures (touch only)

<!-- Skip / remove this section if input model doesn't include touch. -->

- **Swipe actions on rows**: <yes (which actions, which directions) | no>
- **Long-press menu**: <yes | no>
- **Pull-to-refresh**: <yes (where) | no>
- **Pinch-to-zoom**: <yes (where — usually images, maps) | no>
- **Edge-swipe back navigation**: <platform default | overridden>

## Focus management

- **After modal close**: restore focus to trigger element (always)
- **After route change**: <heading focus | container focus | no change>
- **After form error**: focus first error field (always)
- **After successful action that closes UI**: restore to a sensible parent
- **On initial page load**: <do not auto-focus | focus main heading | focus primary CTA>
- **Focus visibility**: always visible per design-system tokens; no `outline: none` without a replacement

## Notification patterns

- **Toasts**: <use cases — confirmations, async results>
  - Position: <top-right | bottom-center | platform-default>
  - Duration: <ms — usually 4000–6000>
  - Dismissible: yes
  - Stacking: <max N | replace>
- **Inline notifications / banners**: <use cases — status, warnings, persistent state>
- **Dialogs**: <use cases — confirmation, error, blocking decisions>
- **Badge counts**: <where shown, how cleared>

## Selection & multi-select

- **Single select**: <pattern>
- **Multi-select**:
  - **Trigger**: <long-press (touch), checkbox always visible, shift-click range, etc.>
  - **Action bar**: <sticky bottom | top | inline>
  - **Bulk action limits**: <none | N items max>
- **Select-all**: <yes (where) | no>

## Drag & drop

- **Use cases**: <reordering | moving between lists | upload | none>
- **Affordance**: <handle-only | row-anywhere | platform-default>
- **Touch support**: <yes (long-press to lift) | desktop-only | none>
- **Live preview**: <yes | no>

## TBD on return

<!-- Anything skipped or deferred during the ui-system interview. -->

- <TBD: ...>