docs: ship an agent reference in the package, plus a Claude Code skill

.claude/skills/engine-design-system/SKILL.md

@@ -0,0 +1,26 @@
+---
+name: engine-design-system
+description: Rules and component reference for the Engine design system (@engineio/ui). Use when building or reviewing any Engine surface — Svelte components, styles, tokens, colour, type, spacing, the brand marks — or when choosing a Button/Badge/Alert variant, adding a component variant, or picking a colour.
+---
+
+Read `node_modules/@engineio/ui/AGENTS.md` before writing UI. It ships with the
+package, so it matches the installed version — do not rely on memory of these
+rules, and do not copy them into a repo where they will go stale.
+
+If that file is absent the package is not installed here; say so rather than
+guessing at the system.
+
+Non-negotiable, and worth having in mind before you read further:
+
+- Three brand colours: Off Black `#0E0E0E`, Pure White `#FFFFFF`, Magenta
+  `#FF006A`. One accent per surface.
+- Never a hex literal or a Tailwind stock colour. Use a token. CI fails on both.
+- `success` / `warning` / `danger` are FUNCTIONAL. They report state, never
+  category, and never decoration.
+- Ink on any status or accent fill is Off Black. White fails AA on all three.
+- No emoji. No gradients. No light theme. No `dark:` variants.
+- Add a variant by `tv({ extend: … })` in the product, never by forking a
+  component or upstreaming a product-only variant.
+
+For anything the file does not cover, choose the quieter and more mechanical
+option, and flag the gap rather than inventing a rule.

AGENTS.md

@@ -0,0 +1,138 @@
+# @engineio/ui — agent reference
+
+The Engine design system. This file ships inside the package, so it arrives in
+`node_modules/@engineio/ui/AGENTS.md` and versions with the code — point at it
+rather than copying its contents into a repo, or the copy goes stale.
+
+Authoritative source: `docs/brand/ENGINE-DESIGN-SYSTEM.md` and
+`ENGINE-BRAND.md` in the `engineio/engine` repo. Where this file and those
+disagree, **they win and this is a bug**.
+
+## Setup
+
+```css
+@import "tailwindcss";
+@import "@engineio/ui/styles";
+@source "../../../node_modules/@engineio/ui/dist";
+```
+
+**The `@source` line is not optional and its absence is silent.** Tailwind 4
+does not scan `node_modules`, so without it the utility classes the components
+are written against are never generated. The tokens still land and any class
+that also appears in local source still works, so you get a half-styled app
+that reads like a component bug. Path is relative to the CSS file declaring it.
+
+## Importing
+
+```svelte
+import { Button, Card, CardHeader } from "@engineio/ui"
+import { Button } from "@engineio/ui/components/ui/button/index.js"
+import * as Card from "@engineio/ui/components/ui/card/index.js"
+import { EngineWordmark } from "@engineio/ui/components/brand/index.js"
+```
+
+Root barrel exports flat prefixed names (`CardHeader`). Subpath modules export
+`Root`/`Header`/`Content`, so `import * as Card` works. Both `/index.js` and the
+bare subpath resolve.
+
+## Components
+
+Alert, Badge, Button, Card, Checkbox, Dialog, Input, Label, Popover, Progress,
+RadioGroup, Select, Separator, Skeleton, Switch, Table, Tabs, Textarea, Tooltip.
+Marks: `EngineWordmark`, `EngineIcon`.
+
+Not shipped, on purpose: `sonner`, `form`, `data-table`, `drawer`, `resizable`,
+`carousel`, `chart`. Copy from the engine repo if needed.
+
+| Component | Variants |
+| --- | --- |
+| Button | `default` `inverse` `outline` `ghost` `secondary` `link` `icon` `destructive` `success`; sizes `sm` `default` `lg` `icon` `icon-sm` `icon-lg` |
+| Badge | `default` `secondary` `outline` `partner` `success` `warning` `danger` `destructive` |
+| Alert | `default` `success` `warning` `danger` `destructive`; optional `onDismiss` |
+| Marks | `variant="primary"` (white) or `"secondary"` (Off Black) |
+
+There is **one** chip. Badge absorbed Tag — a soft tinted chip, not a solid
+pill. There is no `Tag` export and no `solid` badge variant: an opaque fill can
+only be correct on one surface, and badge fills are translucent so they read on
+the page, on a card and on a table tile alike.
+
+## Tokens
+
+Use these names; never a literal.
+
+```
+colour     --color-background #0E0E0E   --color-foreground #FFFFFF
+           --color-primary #FF006A      --color-primary-press #D60059
+           --color-primary-300 #FF5C9B  (ink on a magenta tint)
+           --color-primary-tint-12 / -24
+           --color-card #161616         --color-popover #1C1C1C
+           --color-grey-950 … --color-grey-050   (the only greys)
+           --color-partner-yellow #FFDD00        (reserved, not in use)
+status     --color-success #00C46A  --color-warning #FFB020  --color-danger #FF3B30
+           each with -foreground (always Off Black) and -tint-12
+           --color-destructive aliases danger
+radii      --radius-tag 6  --radius-field 10  --radius-card-inner 10
+           --radius-media 14  --radius-card 18  --radius-frame 26
+           --radius-control 999
+motion     --ease-brand  --ease-brand-out  --ease-brand-accelerate
+           140ms controls · 220ms surfaces · 360–640ms reveals
+type       --font-brand (Proxima Nova) --font-mono (JetBrains Mono, see gaps)
+depth      --shadow-panel  --shadow-modal   (product chrome and modals only)
+utility    `field` — the shared input skin, incl. the focus ring
+```
+
+## Rules
+
+- **Three brand colours**: Off Black, Pure White, Magenta. One accent per
+  surface, never two.
+- **Status colour is functional.** `success`/`warning`/`danger` report state.
+  Never use them as a categorical palette — `success` for "slots" because green
+  looked right spends the only signal they carry.
+- **No off-palette colour.** Not Tailwind's stock ramps, not a hex literal. CI
+  fails on both.
+- **Retired and unavailable**: Originals Orange `#FF6200`, Sportsbook Blue
+  `#00CCFF`. No accents, no charts, no status.
+- **Ink on any status or accent fill is Off Black.** White fails AA on all three.
+- **Magenta text**: never below 15px bold. Use `--color-primary-300` on a tint.
+- No gradients. No light theme. No `dark:` variants — the dark palette is the
+  only palette. No drop shadows on brand surfaces. No coloured borders, and no
+  coloured left-edge accent to signal category or ownership.
+- Radii by role, and the outer frame is always larger than the inner panel.
+- Borders are 1px hairline or 1.5px container rule. Nothing else.
+- **No emoji, anywhere.** Only `×` for close and `✱` for footnotes.
+- Voice: declarative, British/AU spelling, headlines end in a full stop.
+- Icons: Lucide, 2px stroke, `currentColor`.
+
+## Extending
+
+Do not fork a component to add a variant, and do not upstream a product-only
+variant. Every variant map is exported:
+
+```ts
+import { buttonVariants } from "@engineio/ui"
+import { tv } from "tailwind-variants"
+
+export const appButtonVariants = tv({
+  extend: buttonVariants,
+  variants: { variant: { drawer: "w-full justify-start rounded-none …" } },
+})
+```
+
+Brand rules stay in the package; product variants stay in the product. Every
+primitive also passes `class` through `cn`, so `<Button class="w-full" />` works
+without `!important`.
+
+## Known gaps
+
+State these rather than working around them silently.
+
+1. **No categorical palette.** A per-topic hue set is an unmade brand decision.
+2. **Two deviations from the brand document**, both deliberate: Badge is one
+   component where §6 specifies two, and Alert signals state with a coloured
+   left-edge bar which §11 prohibits for *category or ownership* — state is a
+   narrower reading, not an exemption.
+3. **JetBrains Mono is not loaded.** `--font-mono` falls back to the platform
+   monospace, so every mono surface is off-brand until the binary ships.
+4. **Proxima Nova is commercially licensed** and ships inside this package.
+5. **Engine Integration's accent is unsettled** — build Integration in magenta;
+   `--color-partner-yellow` exists but is not in use.

README.md

@@ -121,6 +121,35 @@ engine repo into your product if you need them. `sonner` was excluded because
 toasts need success and error colours that did not exist; now that they do, it
 is a candidate for the next release.
 
+## Using it with AI agents
+
+The package ships `AGENTS.md`, so it lands at
+`node_modules/@engineio/ui/AGENTS.md` and **versions with the code**. Point at
+that path from a consuming repo rather than copying the rules in — a copy in
+someone's `CLAUDE.md` silently goes stale on the next version bump, and stale
+brand rules are worse than none.
+
+In a consumer's `AGENTS.md` or `CLAUDE.md`:
+
+```md
+UI is built on `@engineio/ui`. Read `node_modules/@engineio/ui/AGENTS.md`
+before writing or reviewing any UI.
+```
+
+For Claude Code specifically, copy the skill instead — it loads only when
+relevant, so the reference costs nothing until a UI task actually needs it:
+
+```bash
+mkdir -p .claude/skills
+cp -R node_modules/@engineio/ui/../../../ui/.claude/skills/engine-design-system \
+  .claude/skills/   # or from a checkout of engineio/ui
+```
+
+Skills have to live in `.claude/skills/`, `~/.claude/skills/` or a plugin —
+Claude Code does not load them from `node_modules` — which is why the substance
+lives in `AGENTS.md` and the skill is a thin pointer to it. That way the copied
+file has nothing in it that can rot.
+
 ## Development
 
 ```bash

package.json

@@ -16,6 +16,7 @@
   },
   "files": [
     "dist",
+    "AGENTS.md",
     "!dist/**/*.test.*",
     "!dist/**/*.spec.*"
   ],