---
description: Do not duplicate parent navigation with a Back control when breadcrumbs exist
globs: {components,lib,src}/**/*.{tsx,ts}
alwaysApply: false
appliesTo: [react]
---

# Exxat DS — breadcrumbs and back navigation

## MUST NOT

When a page uses **`SiteHeader`** with **`breadcrumbs`** (a visible trail such as Patterns → Library → current title), **do not** add a **“Back to …”** link or button in the page body that goes to the same parent as the breadcrumb segment. Breadcrumbs already provide hierarchy and one-click navigation up the tree.

**Do not** put the **current page title** in `breadcrumbs` when you also pass `title` to **`SiteHeader`**. `PageBreadcrumbTrail` appends `currentPage={title}` automatically. Duplicating the leaf (e.g. Components → Toggle Switch → Toggle Switch) breaks the trail.

## MAY

- Rely on **`SiteHeader`** breadcrumbs only for returning to parent routes.
- Use a **single** explicit back affordance on flows that **omit** breadcrumbs by design (e.g. full-screen step, modal route) where product copy requires it.

## SiteHeader breadcrumb overflow

The trail collapses **on room, not on count**. `PageBreadcrumbTrail` measures the row it was given (`useRowFitLadder`) and shows every segment that fits; a trail with space for four crumbs shows four. When the row runs short, middle segments move into a **More** control (`BreadcrumbEllipsis` + `DropdownMenu`) **shallowest first**, so the root and the immediate parent are the last ancestors standing, and the current page truncates only after that.

**MUST NOT** reintroduce a crumb-count threshold (`items.length > 2`), a breakpoint (`hidden md:flex`), or a per-variant collapse rule. Those hide parents on wide screens that had room for them, which is the defect this replaced.

Two things the measurement depends on, so do not remove them without replacing the signal:

- The leaf keeps a **min-width floor** while an ancestor could still step aside. Ancestors do not shrink, so without the floor a tight row squeezes the leaf and never reports overflow at all.
- The list stays **`flex-nowrap`**. A wrapping trail always fits, and pays for the extra crumbs with a second line.

Do **not** wrap breadcrumbs in **`HorizontalScrollRegion`** — that pattern stays for tab/chip rows (**`.cursor/rules/exxat-horizontal-scroll.mdc`**).

## See also

- `components/site-header.tsx`
- `components/page-breadcrumb-trail.tsx`
- `components/templates/primary-page-template.tsx`