# 10 · Interaction & Feedback

> **Status:** interaction contract. Where [09 · Visual Design](09-visual-design.md) is the
> _visual_ contract (how the app **looks**), this is the _interaction_ contract (how the
> app **behaves while the user works in it**). It is the HOW for the cross-cutting,
> non-feature-specific behavior that spec [§10 Non-Functional](../spec/10-non-functional.md)
> mandates as the WHAT.

These rules already live, scattered, as one-off comments across the codebase (the
confirm-dialog's "transactional-modal rule," the toaster's "non-blocking outcomes are
toasts," the preview's "empty is not an error"). This document consolidates them into one
referenceable contract so a new feature **checks the rule instead of re-deriving it** —
and diverges only on purpose.

**Upstream sources.** These principles are drawn from the design council (`/council`):
IBM Carbon, the **GOV.UK Design System**, the **WAI-ARIA Authoring Practices Guide**, and
**Nielsen Norman Group**. The council advises; this contract decides. When you face a new
interaction decision this doc doesn't cover, consult the council, then record the
resolution back here.

---

## 1. The feedback-channel decision table

Astrolabe has four distinct ways to tell the user something. They are **not**
interchangeable; picking the wrong one is the most common interaction bug. Choose by the
nature of the message, not by convenience.

| Channel              | Use when                                                                                            | Blocks?     | Dismissal                                                                 | Implemented by                                           |
| -------------------- | --------------------------------------------------------------------------------------------------- | ----------- | ------------------------------------------------------------------------- | -------------------------------------------------------- |
| **Confirm dialog**   | A **destructive or irreversible** action needs explicit consent (delete, revert, reset)             | Yes — modal | User must choose; Escape/Cancel = no; backdrop click does **not** dismiss | `ConfirmStore` + `ConfirmDialog`                         |
| **Toast**            | A **non-blocking outcome** happened the user should know about (save failed, published, imported)   | No          | Auto for success/info; persists for error/warning; always a close button  | `NotificationStore` + `Toaster`                          |
| **Inline error**     | A problem is **tied to a specific surface** and recovers in place (invalid spec → editor + preview) | No          | Clears automatically when the cause is fixed                              | `PreviewStore`, surfaced in `SpecEditor` + `LivePreview` |
| **Status indicator** | **Passive, ambient** state worth glancing at (draft vs. published, storage usage)                   | No          | N/A — it just reflects state                                              | library draft dot; storage monitor (later)               |

**Rules.**

- **One blocking question at a time.** Confirm dialogs and feature modals are mutually
  exclusive (the modal coordinator enforces this); a confirm may layer _over_ a modal
  (discard-changes prompt), nothing else stacks.
- **Match disruptiveness to urgency** (Carbon). A toast interrupts less than a dialog;
  don't use a dialog for something a toast can carry, and don't bury a
  consent-for-destruction in a toast.
- **Errors persist; success fades.** An error/warning toast waits for the user (a critical
  message must not vanish on a timer); success/info auto-dismiss (~6s).
- **The same failure can light up two channels.** An unrenderable spec shows the _same_
  message inline in both the editor (§03E) and the preview (§04) — one producer
  (`PreviewStore`), two subscribers. That's intentional, not duplication.

## 2. Latency & feedback budgets

From NN/g's response-time limits (`reference/principles/nielsen-norman.md`). These are not
aspirations — they're the basis of the render pipeline's shape.

| Budget     | Feels like            | Owed feedback                                                          | Astrolabe surfaces                                                       |
| ---------- | --------------------- | ---------------------------------------------------------------------- | ------------------------------------------------------------------------ |
| **≤ 0.1s** | Instantaneous         | None beyond showing the result                                         | Keystrokes into the buffer, hovers, toggles, selection                   |
| **≤ 1s**   | Uninterrupted thought | None needed, but direct-manipulation feel is lost                      | A typical render after the debounce; opening a modal; switching snippets |
| **> 1s**   | Noticeably waiting    | **Must not block input**; show a busy indication                       | A heavy spec / large-dataset render                                      |
| **> 10s**  | Attention lost        | **Progress indicator + stay cancellable**; let the user work elsewhere | (guard for large M3+ dataset work)                                       |

**Rules.**

- **Input is sacred.** Typing and navigation never block on rendering or persistence (spec
  §10). The render pipeline is debounced (`RENDER_DEBOUNCE_MS`), runs async, and uses a
  **generation token** so a slow render can't overwrite a newer one.
- **Auto-save is cheap and silent** (`AUTOSAVE_DEBOUNCE_MS`) — it never stalls typing and
  produces no toast on success (only on failure).
- **A busy indication may overlay the preview but must not freeze the editor** (spec §10).
  When a render _might_ exceed ~1s, owe a non-blocking indicator; never a frozen UI.

## 3. The non-happy-path triad

Every surface that shows data owes **three** designed states, not one. The empty and error
states are part of the feature, not an afterthought (Carbon empty-states, GOV.UK).

- **Loading** — when data isn't ready yet. Prefer a skeleton/placeholder over a spinner for
  structural loads; show it only for a beat.
- **Empty** — when there is legitimately nothing. **Empty ≠ error**: a blank editor renders
  a clean, calm empty preview, never an error (`LivePreview` treats blank as success). An
  empty list says what would be here and how to add it.
- **Error** — when something went wrong. Split by **who can fix it**:
  - **User-fixable** → state the consequence and the **next step** ("Storage full — delete
    snippets to free space, then edit again"). A user action is mandatory (Carbon/GOV.UK).
  - **Not user-fixable** → explain plainly **and** attach a reportable **diagnostic** (the
    operation + underlying error) so it can be traced. See `services/storage-errors.ts` —
    this split is the module's whole reason for being.
- **Wording** (NN/g #9, GOV.UK, Carbon content): plain language, **no error codes in the
  user-facing line**, second person, name what stopped in the title, one or two sentences
  in the body, never flippant.

## 4. Recovery & data-safety contract

The user must never silently lose work, and must always have a way back (NN/g #3 "user
control and freedom," #5 "error prevention"; spec §10 Reliability).

- **No silent data loss.** Edits auto-save as a **draft**; a known-good **published**
  version is always preserved separately (§03D). A failed persist **surfaces as a toast**,
  never a swallowed promise (`orchestration/persistence.ts`).
- **A marked exit from every committed change.** Revert restores the published spec;
  Escape closes modals; delete/revert/reset require confirmation first.
- **Resilient rendering recovers on its own.** An invalid spec shows a readable error and
  **auto-recovers when fixed** — it never leaves the app wedged (§04).
- **Non-destructive import.** Import merges, never overwrites; on failure the existing
  workspace is left exactly as it was (§08).

## 5. Keyboard & focus contract

Astrolabe is keyboard-operable end to end (spec §10 Accessibility). The interaction
patterns follow **WAI-ARIA APG** (`reference/aria-practices/content/patterns/`); the wiring
lives in [04 · Routing & Global Events](04-routing-and-events.md).

- **One global router** owns document-level `keydown`/`paste`; components never attach
  their own `window` listeners.
- **Escape is an ordered priority chain** that returns on first consumption (blocking
  message → modal → menu → selection) and is checked **before** the interactive-context
  gate, so it dismisses a modal even while the editor has focus. All _other_ shortcuts are
  gated by `isInInteractiveContext()` so they never fire mid-typing.
- **Shortcuts claim their key** with `preventDefault()` so they override the browser
  default (⌘S doesn't "save page," ⌘K doesn't focus the URL bar).
- **Focus moves into an overlay on open and returns to the trigger on close**; focus is
  **trapped** within it (`useFocusTrap`). Destructive confirms focus Cancel first.
- **Match the APG pattern** for any new interactive widget — a modal is `dialog-modal`, a
  destructive confirm is `alertdialog`, a resize handle is `windowsplitter`, a toast region
  uses `alert`/`status` roles by severity. Don't invent keyboard models; adopt the
  documented one.

**Resolved — pane resize handle (window splitter).** A `ResizeHandle` is a focusable
`role="separator"` that **reports the controlled pane's size**, per APG → Window Splitter:

- `aria-valuenow` on a **0–100 scale** (0 = pane at its minimum, 100 = at its maximum),
  with `aria-valuemin=0`, `aria-valuemax=100`, and `aria-valuetext="<n>%"` for a clean
  announcement. The 0–100 normalization (APG's "typical") beats raw pixels: it's stable and
  announces as a percentage. The math is the pure `sideWidthValue()` in `PanesStore` (so it
  is unit-tested, not trapped in the component); the live value needs the container width,
  observed via `ResizeObserver` so it tracks window resizes, not just drags.
- `aria-controls` points at the pane it sizes (`pane-library` / `pane-preview`).
- **Keyboard**: ←/→ nudge; **Home** → smallest pane size, **End** → largest. **Enter-to-collapse
  is deferred to M6** with the pane-visibility / toggle strip — collapsing needs a
  hidden-pane state that doesn't exist yet, so we don't fake it.

_(Consulted via `/council` → WAI-ARIA APG `windowsplitter`. This bullet is the contract;
cite it, not the APG file.)_

**Resolved — segmented (single-select) controls.** A "pick one of N" control (fit modes,
the Draft/Published view) is a **radio group**, never a row of `aria-pressed` toggles
(those model N independent booleans). Use the shared `SegmentedControl`: `role="radiogroup"`

- `role="radio"`/`aria-checked`, a **roving tabindex** (only the selected option is a tab
  stop), and Arrow/Home/End to move-and-select (APG → Radio Group). One widget so the keyboard
  model is defined once. _(Tabs were a candidate for Draft/Published; we chose radio group for
  consistency with the other segmented controls and to avoid tabpanel wiring to Monaco. A
  **toggle switch** was also weighed and rejected: APG defines `role="switch"` as on/off of a
  **single** setting, but Draft/Published selects between two **named peer views** with no
  natural "on" side — a radio group is the right semantics. Reserve the switch for genuine
  on/off settings. Consulted via /council → APG switch / radio-group / tabs.)_

**Resolved — selectable lists.** A row the user selects must be a real `<button>` (or a
proper option), not a click handler on `<li>` (mouse-only, no keyboard, no role). It is
**not** an APG `listbox` when a row contains its own controls (e.g. a delete button) — APG
forbids interactive children in a listbox. Mark the active row with `aria-current="true"`
**only on that row** (don't emit `aria-current="false"` everywhere). Arrow-key roving
_between_ rows is a later enhancement; button-per-row tab stops are the acceptable baseline.

**Resolved — snippet-list status indicator.** The library row flags only the _exceptional_
state: a single **accent dot** when a snippet has unpublished draft changes; a fully-published
snippet shows **no dot** (presence = draft, absence = published). We do **not** give "published"
its own glyph — GOV.UK's Tag guidance notes one status suffices when absence is self-evident,
and Carbon's status-indicator pattern says not to highlight what isn't significant. Meaning
never rests on **hue** (WCAG 1.4.1): it rides on presence/absence **plus** the dot's accessible
label, and the colour is the neutral **accent** — not a warning hue, because unpublished work is
a normal state, not a problem. The dot sits in the row's secondary metadata line (with the
relative date and size), in a fixed-width leading slot so it never shifts adjacent text.
_(Consulted via /council → GOV.UK Tag, Carbon status-indicator-pattern, APG. This bullet is the
contract; cite it, not the external source.)_

**Resolved — one live region per shared message.** When the same error feeds two surfaces
(the §1 "one producer, two subscribers" case — render errors via `PreviewStore`), exactly
**one** subscriber is the live region (`role="alert"` on the editor, where focus is); the
other shows the text visually with no live role. Two live regions would announce the same
message twice.

## 6. Motion & accessibility as default

Not features to add later — the baseline every surface is built on.

- **Reduced motion is honored globally.** Animations/transitions are neutralized under
  `prefers-reduced-motion` (`styles/base.css`); never gate meaning on motion.
- **Colour is never the sole signal** (WCAG; Carbon status pattern). Pair it with a label,
  icon, shape, or text — a red toast border also has a title and an `alert` role; the
  draft dot has a `title`/`aria-label`.
- **Every control is labelled.** Icon-only buttons, toggles, and fields carry accessible
  names so assistive tech can announce them.
- **A binary toggle exposes its state, not just its action.** A theme/on-off control is a
  toggle button (`aria-pressed`) or `switch` (`aria-checked`) with a **stable** name, so AT
  announces the current state at parity with the icon a sighted user sees — not just "switch
  to dark" (APG → Button / Switch). The `ThemeToggle` uses `aria-pressed` + a stable label.
- **The shell has a heading and a bypass.** The app exposes an `<h1>` (not a styled `<span>`)
  so there's a heading outline, and a **skip link** as the first focusable element so
  keyboard users can bypass the header into `#main` (WCAG 2.4.1 / GOV.UK). Same-type
  landmarks carry distinct accessible names.
- **Contrast holds in every theme.** A theme that can't meet legible contrast in part of
  the UI is not complete (spec §10 / §07).

---

## Do / Don't

**Do**

- Pick the feedback channel from §1's table by the _nature_ of the message.
- Treat loading/empty/error as three designed states for every data surface.
- Adopt the APG keyboard pattern for new widgets; route all global keys through the one
  router.
- Consult `/council` when this contract is silent — then record the answer back here.

**Don't**

- Don't show a blocking dialog for something a toast can carry, or hide a
  consent-for-destruction in a toast.
- Don't let a render or a save block typing.
- Don't treat "empty" as "error."
- Don't put error codes in the user-facing line — put diagnostics in the detail
  disclosure, the next step in the message.
- Don't invent a keyboard model, attach ad-hoc `window` listeners, or gate Escape behind
  the typing check.