AOT: mb_detect_encoding() NestedJIT for runtime strings (#34358)

[PurHur]

Summary

• Closes AOT: mb_detect_encoding() refuses runtime strings — LogicException 1-arg NestedJIT (leftover of #3075, ext/mbstring/mbstring.c) #34358 — mb_detect_encoding() thin AOT threw LogicException on runtime haystack or literal encodings-list + strict; only 1-arg string literals folded.
• Add MbDetectEncodingJitHelper + MbDetectEncodingRuntime (peer AOT: mb_scrub() refuses runtime strings — LogicException (leftover of #6050, ext/mbstring/mbstring.c) #34338 mb_scrub) — UTF-8/ASCII/ISO-8859-1/8BIT leaf detect without VmMbstring.
• Extend JitMbDetectEncoding::invoke for runtime string + compile-time encodings/strict; spine-sync helper units.

php-src: ext/mbstring/mbstring.c — PHP_FUNCTION(mb_detect_encoding).

Test plan

• ./script/aot-smoke.sh → 8 passed, 0 failed
• Repro (Zend/VM/AOT match):

  UTF-8
  UTF-8
  ASCII
  

  ./script/docker-exec.sh -- bash -lc 'php bin/vm.php test/repro/aot_mb_detect_encoding_runtime.php'
  ./script/docker-exec.sh -- bash -lc 'php bin/compile.php -o /tmp/det.bin test/repro/aot_mb_detect_encoding_runtime.php && /tmp/det.bin'

• ./script/phpunit.sh --filter MbDetectEncodingRuntimeAotTest → OK (2 tests, 11 assertions)
• php script/check-selfhost-spine-coverage-sync.php → OK (7876/7876)

Not run: full differential sweep, north-star5-verify-fast, compliance suites.

Made with Cursor

[PurHur]

Superseded by #34359 already merged on master — duplicate NestedJIT mb_detect_encoding fix.