Block themes lose all CSS after the first request per worker ($wp_styles / style-engine state not reset)

[luthermonson]

Summary

Block themes render under worker mode — but only the first request each worker
serves gets any CSS. Every later request on that worker prints zero <style> tags.

This is the adapter-side half of ephpm/ephpm#116.
The engine-side crash reported there no longer reproduces (see the ephpm-side
investigation); what remains is WordPress state this adapter has to reset.

Measured (WordPress 6.7.1, Twenty Twenty-Five, worker_count = 1)

	request 1	request 2 on the same worker
/ response size	50704 B	12012 B
inline <style> blocks	21	0

Probing the worker's state right after the first render:

done_count=30                 # $wp_styles->done
global_styles_done=1          # wp_style_is('global-styles', 'done')
queue=30
style_engine_stores=1
  store=block-supports rules=9
unique_id=3                   # wp_unique_id() counter, keeps climbing

Everything lost on request 2: global-styles-inline-css,
core-block-supports-inline-css, wp-block-library-inline-css, and the
per-block wp-block-*-inline-css sheets.

wp_unique_id() climbing is a second-order problem: the markup keeps emitting
fresh wp-container-core-group-is-layout-N / ...-navigation-is-layout-N class
names (observed -16 on one request, -30 on the next) while the CSS defining
them is never printed again — so even a cached stylesheet would not match.

Root cause

Three pieces of WordPress state are per-request in fpm but worker-lifetime here:

• $wp_styles / $wp_scripts — WP_Dependencies::$done and ::$queue
• WP_Style_Engine_CSS_Rules_Store — static store registry (block-supports)
• wp_unique_id()'s static counter

Worker::resetRequestGlobals() resets $wp_query / $wp / $post / the current
user, but not these.

Suggested fix

Reset the dependency + style-engine registries per request, alongside the existing
resetRequestGlobals() work:

• re-instantiate (or clear done/queue/to_do on) $wp_styles and $wp_scripts
• WP_Style_Engine_CSS_Rules_Store::remove_all_stores()
• re-fire the enqueue lifecycle so wp_enqueue_scripts / wp_enqueue_block_assets
  run against the fresh registries

Re-instantiating $wp_styles throws away boot-time wp_register_style()
registrations, so the reset likely has to snapshot the registered set at boot and
restore it per request rather than starting empty.

Repro

e2e/Dockerfile as-is, plus a mu-plugin forcing a block theme:

add_filter('pre_option_template',   fn() => 'twentytwentyfive');
add_filter('pre_option_stylesheet', fn() => 'twentytwentyfive');

Run with EPHPM_PHP__WORKER_COUNT=1 — with the default 3 workers, alternating
requests land on different (still-cold) workers and the loss is invisible.

Acceptance

/ renders byte-comparable CSS on every request of a worker's life, and the e2e
suite can drop its bundled classic theme in favour of a stock block theme.