A menu that cannot be opened, or does not say it is open
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Rule · bucket: mechanical · severity: warning · detector: menu-state · since: v0.10.0
Section: Things to avoid
Group: States and interaction

Forbidden:
  The nav links hidden at phone width (`display: none` in a `max-width` query, or by default until a `min-width` one), and a Menu button with no `aria-expanded` — or no button at all

Instead:
  The button that shows the links records it: `aria-expanded="false"` while closed, `"true"` while open, and its visible label or icon changes to **Close** while the menu is open. In `editorial`, `<details>` with `<summary>Menu</summary>` inside the `<nav>` does all of this with no script (`P-14`).

A Menu button that does nothing looks finished in every screenshot. On a phone it is the only way to the rest of the site, so the reader who taps it and sees nothing change has nowhere to go. A button that opens the menu without `aria-expanded` is the same failure for a screen reader: it announces "Menu, button" before and after, and the reader never learns anything happened.
`jig check` catches the hidden navigation with no recorded open state anywhere in the project. It cannot tell whether the button actually opens the menu — `critique` operates it on a render at 360px: tap it, and the links appear, `aria-expanded` changes, and the label or icon reads as close.