[ellenbauer]

Refs #2726

What was wrong

On St Francis Pet Hospital (Squarespace), the phone menu opened but its items sat off screen (translateX(330px)), and every link after "Home" was hidden.

Squarespace draws its phone menu as sliding panels ("folders") of item wrappers:

nav.header-menu-nav-list
  div.header-menu-nav-folder.header-menu-nav-folder--active   (root folder)
    div.header-menu-nav-folder-content > div.header-menu-nav-wrapper
      div.header-menu-nav-item > a   (Home)
      div.header-menu-nav-item > a   (About Us, Services, ...)
  div.header-menu-nav-folder   (the About Us folder, off canvas until opened)

Two generic readings in NavigationPattern broke it:

1. Peer item wrappers were read as a submenu. primaryNavigationAnchor() and collectSubmenuContainers() treat an anchor-only wrapper that follows an item's own anchor as that item's submenu (<div><a>Parent</a><div><a>Child</a></div></div>, from bc29d45). They also applied it when the first anchor came from a sibling wrapper of the same shape. So every div.header-menu-nav-item after "Home" became a child of "Home", and the whole root folder became one closed core/navigation-submenu.
2. Classes of list-level wrappers were carried onto each item. sharedReplacedWrapperClassNames() carries the classes of the wrappers core collapses between an item and its link. Without an li its walk did not stop at the item, so it also took the folder, folder content and wrapper classes, which hold every item. Each item then matched .header-menu-nav-folder{position:absolute;transform:translateX(100%)}. The --active state class that cancels it on the root folder is not shared by every item, so it was dropped.

Either one alone still leaves the items off screen, so both are in this PR, as two scoped changes.

What changed

• An anchor-only wrapper is a submenu only when the parent's anchor is the wrapper's own direct child, which is the documented shape. A wrapper beside a peer wrapper is a peer item.
• replacedAncestorWrapperClassNames() stops at a wrapper that also holds another labelled link, the same way it already stops at an li. The per-item wrapper (div.header-menu-nav-item) still carries its classes.

Tests

• New tests/unit/navigation-peer-item-wrappers.php, 3 assertions: wrapped peers stay flat links, panel classes stay off the items, and the per-item wrapper class is still carried. All 3 fail on trunk and pass here.
• navigation-anchor-cluster-submenu.php (the bc29d45 shapes) still passes.

End to end

Studio imports of the St Francis capture with v0.38.1 (the last base that reads these captures), iPhone user agent at 375, dialog opened through its bound trigger. Quality gate passed on both.

• Base (localhost:8938): all 15 menu items off screen (translateX(330px), every link after Home inside a closed submenu).
• With fix(php-transformer): stack declared block menu items in core flow layout #2742, fix(php-transformer): keep wrapped peer menu items flat and off panel classes #2743 and fix(php-transformer): keep the source panel box on a projected modal dialog #2744 (localhost:8941): Home, About Us, Services, Telemedicine, Careers, Contact Us and Online Pharmacy on screen at x=0, width 375, on a white panel.
• 1280: the desktop folder "About Us" is now flattened into the top row (the base had it as a submenu wrongly labelled "Our Mission & Commitment"). Fixed in fix(php-transformer): read a button that controls a sibling link panel as a submenu #2781.
• composer test (memory_limit -1) passed.

Still open (not in this PR)

• The About Us folder's links now show in the same flat list instead of as a drill-down. In the source they sit in a second panel that a[data-folder-id="/aboutus"] opens. Mapping that panel to a submenu needs the data-folder-id to data-folder link, which is Squarespace vocabulary, so it is left for a separate change.

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