Adapt PowerShell parser to structural projections

[Aaronontheweb]

Summary

• replace the legacy flat PowerShell splitter with a recursive structural coordinator for statements, pipelines, and current-scope parenthesized groups
• retain full structure for isolated child-host wrappers and current-scope Invoke-Expression wrappers while preserving exact compatibility-leaf identity
• make dynamic host controls, hidden executable expressions, redirects, and dynamic identities explicitly incomplete
• promote call-operator script blocks to the locked v0.3 fail-closed behavior and update its curated corpus manifest
• update SPEC, OpenSpec, and the implementation plan

Security posture

Only exact static host control prefixes are decoded. Dynamic or quoted controls, --%, -Command -, -CommandWithArgs/-cwa, computed Invoke-Expression, dynamic identities, redirects, and undiscovered execution remain incomplete or fail closed. Direct structural depth is rejected before recursive descent.

Validation

• Release build: 0 warnings, 0 errors
• Full test suite: 1,224/1,224
• Headers: pass
• dotnet format: pass
• OpenSpec strict validation: pass
• Slopwatch: 0 findings
• adversarial review: GO