DevEx: Builtin capability matrix (VM / JIT / AOT per function)

[PurHur]

Problem

Contributors cannot tell if array_merge is VM-only, JIT, or AOT without reading ext/standard/*.php and catching LogicException messages. README (#48) is prose-only.

Goal

Generated docs/capabilities.md (or JSON) from ext/standard/Module.php + JIT class presence + compliance test tags.

Implementation plan

1. Script script/capability-matrix.php scans:
   • Internal classes with jit() method
   • Files throwing not implemented for JIT
   • PHPT dirs: compliance, fixtures/aot
2. Output markdown table: Function | VM | JIT | AOT | Notes
3. CI check: drift fails if new builtin missing from matrix.
4. Link from README and 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 roadmap.

Acceptance criteria

• Matrix covers all functions in Module.php
• CI fails when new ext/standard/foo.php not listed

Links

• Docs: Rewrite README feature list to match current compiler (2026) #48 README rewrite (embed matrix link)