Analyze Start-Job child process regions

[Aaronontheweb]

Summary

• analyze Start-Job initialization before main while preserving authored region order
• model the isolated child-process boundary and prevent child state from contaminating host continuation
• apply exact independently rooted working directories, while relative, dynamic, glob, and non-filesystem forms remain Unknown
• preserve inline-value provenance and fail closed for alternate -PSVersion, FilePath, RunAs32, and other unsupported body models

This is the Start-Job sub-slice of OpenSpec task 7.5c; the broader task remains open for Parallel, remote Invoke-Command, and pinned ThreadJob work.

Verification

• dotnet build -c Release — 0 warnings/errors
• dotnet test -c Release --no-build — 2,187 passed
• pwsh ./scripts/Add-FileHeaders.ps1 -Verify
• slopwatch analyze -d . --no-baseline --fail-on warning — 0 issues
• openspec validate v0-3-structured-shell-analysis --strict
• adversarial review GO for staged SHA-256 a9d86c314fff5ac8ca619f93a92ecca7bbf0b52e94139ff9ac9c947430fe6e28