fix(mui): render Breadcrumb links as MUI Link so styling applies

[adem-loghmari]

PR Checklist

• The commit message follows our guidelines
• Related issue(s) linked
• Tests for the changes have been added
• Docs have been added / updated (not needed, no public API change)
• Changesets have been added

What is the current behavior?

In @refinedev/mui's Breadcrumb, the internal LinkRouter helper is typed to accept MUI LinkProps (sx, underline, color, variant) but renders them onto a bare native <span>:

const LinkRouter = (props: LinkProps & { to?: string }) => {
  const { to, children, ...restProps } = props;
  return (
    <Link to={to || ""}>
      <span {...restProps}>{children}</span>
    </Link>
  );
};

Because <span> is a plain DOM element, none of the MUI styling props do anything, they just get dumped onto the node as invalid HTML attributes. Visible impact: breadcrumb links aren't flex-aligned with their icons, get no hover underline, don't inherit color, and don't get the intended typography size.

This is a regression from the v5 migration (#6945), commit 5d63adac08. Before that, LinkRouter rendered MUI's actual Link. When the legacy-router plumbing was removed in favor of useLink(), the component was rewritten to wrap a <span> but the props were never re-wired to a MUI component. The file still carried an unused import { Link as MuiLink } from "@mui/material" from that incomplete change.

fixes #7462

What is the new behavior?

LinkRouter now renders a real MUI Link, using the router's link component as the underlying element:

<MuiLink component={Link} to={to || ""} {...restProps}>
  {children}
</MuiLink>

This matches the existing pattern used by refine's MUI buttons (component={LinkComponent}), so the styling props (sx, underline, color, variant) are consumed by MUI while client-side routing through to is preserved. The previously-dead MuiLink import is now used.

Notes for reviewers

The shared breadcrumbTests suite (packages/ui-tests) only checks structure (text, href, icon), so this slipped through untested. I added a MUI-specific test in packages/mui/src/components/breadcrumb/index.spec.tsx asserting the rendered link carries the MuiLink-root class and that no styling props leak into the DOM. Verified the test fails on the old <span> implementation and passes with the fix.

[changeset-bot]

🦋 Changeset detected

Latest commit: 59d42c0

The changes in this PR will be included in the next version bump.

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Name	Type
@refinedev/mui	Patch

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