fix(php-transformer): recognize paragraph-labelled menus inside custom-element hosts

[chubes4]

Problem

A horizontal desktop menu whose item labels are wrapped in <p> inside the anchors was imported as escaped HTML in a companion block attribute. The Site Editor could edit the mobile core/navigation only.

After that menu became a real core/navigation, its items started at the container's leading edge (x=580) instead of the source/baseline position (x=733).

Root cause

Builders wrap an ordinary <nav> in a presentation-only custom element. That host is not a menu, but at depth it is captured as a generated companion, so paragraph-wrapped labels never become core/navigation-link blocks.

Once the landmark is recognized, the generated list is a flex container. It inherits an ancestor column and wraps, and core's default packing is flex-start. The source list is a block of inline items packed with text-align: right (or a row flex list packed with justify-content). That declaration was dropped, so the items started at the box edge. Setting layout.justifyContent alone does not fix it: on a wrapping column, justification packs the cross axis.

Fix

Before companion capture, if a custom element's only element child is a <nav> the existing navigation recognizer claims, lower that landmark to core/navigation and keep host id/class/style on a layout shell. No platform selectors.

Carry the list's horizontal packing onto the navigation as layout.justifyContent, and project flex-direction: row plus the matching justify-content onto that navigation's container only, scoped to the source list's own classes so other menus are unchanged.

Both viewport menus remain separate core/navigation blocks. Shared wp_navigation binding is #2246.

Regression test

php tests/unit/paragraph-label-desktop-menu.php

Fails before (unfixed host recognition, git stash of the recognition fix):

FAIL: shallow layout wrapper materializes the paragraph-labelled menu as core/navigation
FAIL: deep layout wrapper materializes the paragraph-labelled menu as core/navigation
Paragraph-label desktop menu: 8 failed, 3 passed

Fails before the packing projection (recognition present, projection stashed):

FAIL: shallow layout wrapper keeps the list text-align packing as navigation justification
FAIL: deep layout wrapper keeps the list text-align packing as navigation justification
Paragraph-label desktop menu: 2 failed, 11 passed

Fails before the scoped container rule (unscoped projection stashed):

FAIL: shallow layout wrapper projects the list packing onto that navigation container only
FAIL: deep layout wrapper projects the list packing onto that navigation container only
Paragraph-label desktop menu: 2 failed, 13 passed

Passes after:

Paragraph-label desktop menu passed: 15 assertions

Also passed: php tests/unit/navigation-layout-default.php, php tests/unit/navigation-vertical-orientation.php, php tests/unit/navigation-hidden-menu-hoist.php, php tests/unit/custom-block-generator.php.

Verification

Rebased onto trunk after #2243. Fresh import with SSI origin/main (9c83decd, v1.17.23) paired to this HEAD (9e35ea27e).

Desktop item x, source/baseline/fix. The #2243 baseline renders the preserved source list (text-align: right, inline-block items) and matches the source position called out in review.

viewport	item	source/baseline	previous fix	this fix
1440	Home	733	580	733
1440	Blog	1002	—	1002
1440	Shop	1051	—	1051
1440	Events	1103	—	1103
1440	Contact	1164	—	1164
768	Home	61	—	61

All measured desktop item deltas vs baseline are 0px. One visible header. First link y=45 at 1440 and 768.

At 390 the desktop menu stays hidden. Opening the mobile menu shows the same item positions as the baseline (Home x=138, Shop x=139, Contact x=134).

Saving a desktop navigation-link label from Blog to Journal (the same block-attribute write the Site Editor performs) renders Journal at x=1002, y=45. The mobile block is a separate core/navigation and is unchanged. Shared entity binding remains #2246.

Fixes #2244

AI disclosure: implemented by xAI Grok 4.7 via OpenCode (opencode run), orchestrated and reviewed by Claude (Anthropic).

[chubes4]

Review: regression test verified in the cook report; requesting changes before merge — desktop menu items shift left (x=580 vs 733 in the baseline/source). Please rebase on trunk (#2243 merged) and restore item geometry. Shared desktop/mobile menu entity tracked separately in #2246.

AI disclosure: review by Claude (Anthropic) via OpenCode.