fix: request the CSS width for Retina srcset entries and use it in sizes

[selul]

Related issues: #1111, #1113

With Retina images on, the page profiler's 2x srcset candidates delivered twice their advertised width, and the sizes attribute got a second, doubled condition for the same breakpoint. Both came from the same value: the 2x entry carries its delivered width (for example 824, advertised as 824w) together with dpr: 2, and that width was used both as the URL's w and as the sizes slot.

What changed

• Optml_Tag_Replacer::add_missing_srcset_attributes() — for an entry with dpr > 1, the CSS width is width / dpr:
  • the URL asks for the CSS width with the dpr (w:412/dpr:2), because the CDN multiplies w by dpr. This is the same convention the plugin already uses for its other dpr:2 / 2x sources. The 824w candidate now delivers 824px instead of 1648px (Profiled width candidates can deliver twice their advertised intrinsic width with Retina Quality #1111);
  • the sizes slot is the CSS width, so the 1x and 2x entries give the same condition and array_unique() keeps one (Generated sizes attribute can contain duplicate max-width conditions #1113).

Note

Only sites with Retina images on (off by default) and only profiler-generated 2x candidates are affected. Their URLs change once, so the CDN fetches those variants again. Fixing it in PHP also corrects the profiles already stored (they last up to 7 days), with no JS change.

Not in this PR: when a page already has a sizes attribute, enhance_existing_sizes() sorts the merged conditions by breakpoint descending, so the first max-width condition matches every smaller viewport and the rest are never used. That changes sizes on most profiled pages and deserves its own issue.

Tests

• tests/test-srcset.php: with Retina on, a 2x entry's URL is w:412/dpr:2/h:300 … 824w (no w:824); two breakpoints with 1x and 2x entries give one condition each, (max-width: 480px) 300px, (max-width: 768px) 412px. Both fail on development. Mutations (URL or sizes with the delivered width, height not divided) each fail a test.

QA

1. Turn on Retina images in WP Admin → Optimole → Settings, and keep the page profiler on.

2. Open a page with large content images on a desktop browser, then reload it once the profile is stored.

3. View the source of an image that got a generated srcset.

   Expect: each 2x-sized candidate URL has w:<half the descriptor>/dpr:2 (for example w:412/dpr:2 … 824w), and sizes has one max-width condition per breakpoint.

Verification (head 335e1b4d)

Check	Result
PHPUnit, full suite, PHP 8.4 (WP 7.1.3)	PASS: 366 tests (baseline 364 + 2 new)
tests/test-srcset.php run alone	PASS: 37 tests
New tests on the development source	FAIL (2 of 2)
phpcs, phpstan (build-only include errors excluded locally; CI builds assets first)	PASS

Not proven

• The delivered pixel size against the live CDN (the multiplier is inferred from the plugin's own dpr:2 / 2x usage).

🤖 Generated with Claude Code

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