Track: PHP 8.6 pre-release follow-ups on master (windows artifacts, GA cleanups)

[lisachenko]

Tracking issue for the temporary accommodations #278 made while PHP 8.6 is pre-release (currently 8.6.0beta2 / nightly 8.6.0-dev on CI). Each item self-heals or carries a marker in the code; this issue is the single place to tick them off as the 8.6 release cycle progresses.

Blocked on the PHP release cycle

• include/8.6/windows-x64-{nts,zts} engine definitions — windows.php.net publishes no build or devel pack for snapshot versions, so the windows generation legs currently skip cleanly (tools/generator/generate.php prints ==> SKIPPED, the workflow records generated=false). Once a tagged 8.6 build (RC or GA) is on windows.php.net, run one workflow_dispatch of generate-windows-headers.yml against master — the commit job pushes the artifacts, and CI's presence guards stop warning.
• PHPStan phpVersion — pinned at 80500 in phpstan.dist.neon (with a TODO): PHPStan 2.2.9 still rejects 80600. Bump to 80600 once a PHPStan release accepts it.
• php-cs-fixer unsupported-version allowance — .php-cs-fixer.dist.php sets setUnsupportedPhpVersionAllowed(true) because the fixer caps supported syntax at PHP 8.5. Drop the call once php-cs-fixer lists 8.6 as supported.
• Regenerate all 8.6 artifacts at GA — the committed linux/darwin definitions were generated from 8.6.0beta2 / nightly snapshots. On 8.6.0 GA the header-drift job (docker) and the darwin/windows generation workflows regenerate and diff automatically; expect one refresh commit if engine structures moved between beta2 and GA. composer install also stops needing --ignore-platform-req=php for local development on pre-release builds at that point.

Self-healing fallbacks to retire (optional cleanup after GA)

These keep working after GA (the stable path always wins), so removing them is tidiness, not correctness:

• Docker -rc image fallback — resolveBaseImage() in tools/generator/generate.php plus the digest-resolution steps in ci.yml (header-drift, tests-internal-debug) fall back to php:8.6-rc-cli/-zts while Docker publishes only the -rc family. Consider removing once php:8.6-cli/-zts exist, or keep as permanent resilience for the next minor's pre-release window.
• Nightly php-src source-ref fallback — native generation for X.Y.Z-dev builds fetches the three sliced sources from the PHP-X.Y branch / master instead of a release tag. Generic and harmless to keep; noted here for completeness.
• Windows snapshot skip paths — the two -dev clean-skip exits in tools/generator/generate.php and the generated output gating in generate-windows-headers.yml become dead code paths on tagged builds; same keep-or-remove call as the docker fallback.

Docs to flip at GA

• README support matrix — the 8.6 row is 🚧 in progress with footnote ¹ ("definitions track the latest beta"). Flip to ✅ supported, update the platform list (darwin artifacts already landed via the generation workflow in feat: target PHP 8.6 #278; windows joins with the first item above), and drop the footnote.
• Release/tag — once GA artifacts are in, consider the first tag of the 8.6 line (same motion as Release the 8.4 line (first tag matching the targeted PHP version) #95/Tag an 8.4.1 release so tag-based consumers get the debugger primitives #141 for the 8.4 line).

Refs: #278 (the 8.6 bump), #276 (cascade flow on 8.4), branch 8.5 (took over PHP 8.5 support).