app-shell/sidebar-nav-item.a11y

Keyboard

Every row is a real control: a <a href> when it has a route, otherwise a <button> (NavGo). Tab reaches them in reading order, Enter follows, Space activates the button form.
The split parent is two separate tab stops — body then chevron — so folding is reachable without a pointer.
The group divider is a <button aria-expanded>; Enter folds and unfolds its block.
The rail toggle in the footer is a button with aria-expanded and an aria-label that says what it will do.
There is no roving focus and no arrow-key movement inside the nav; it is a list of links, which is what the ARIA authoring practices ask for.

The active row carries aria-current="page" — that is the programmatic truth; the .active class is only paint.
In the rail the label is hidden with CSS, so each row carries title and aria-label with the same text — the accessible name never disappears with the label.
Fold state is on the control that folds (aria-expanded on .as-grp, .as-row-chev, .as-sub-chev).
The mobile hamburger in the top bar owns aria-expanded and aria-controls="as-side-nav", so the off-canvas sidebar is announced as its target.
The colour tile .sg and the wand are decorative; the label carries the meaning.

app-shell.css declares no focus style of its own and — importantly — does not switch the outline off: the rows are <button>/<a>, so they take the foundation ring from ds.css (outline: 2px solid var(--accent); outline-offset: 1px on :focus-visible).
Folding a group does not move focus; the chevron keeps it.
The nav scrolls inside a scroll area; a focused row below the fold is scrolled into view by the browser.

Computed from packages/ui/src/tokens/tokens.css:

Row label --ink-700 on the sidebar surface = 12.55:1 light, 11.29:1 dark.
Active row --ink-900 on --active-surface — above 12:1 in both themes; the active state is carried by both fill and weight of colour, not by colour alone.
Row icon --ink-500 — mid-tone, above the 3:1 non-text minimum in light theme.
Count pill: .acrm-pill.blue / .amber ink on their tint, both above 4.5:1 (the same pills used across the app).
Focus ring --accent = 4.44:1 light, 3.83:1 dark — passes the 3:1 non-text minimum.

The active state is a fill plus a colour change; there is no shape or icon difference, so a user who cannot see the fill relies on aria-current alone (which is correct, but the visual redundancy is thin).
No disabled style exists for a row that permissions have made unavailable — such rows are removed from the model instead of being shown greyed out.
The rail hides labels below 56px of width; users who need the text must expand the sidebar, there is no tooltip on hover for the rail rows beyond the native title.
There is no skeleton for the navigation while modules and segments load — the nav simply renders fewer rows until the data arrives.