PHLEGM v6 - Final End-User Install Handoff Fix - 2026-10-04

Problem
- The external bootstrap correctly resolved Install-and-Compile.json upstreamInstallRelative from the freshly extracted project root.
- The shared Compiler UI received that exact absolute final-install path and used it for lifecycle cleanup, but did not forward it to the child build process.
- The build matrix therefore recomputed the destination from its own filesystem context. The UI and the build could disagree about where ../../PHLEGM/ meant, so a successful matrix could fail to update the intended sibling live install.
- An earlier checkpoint also used its comment in the extracted outer Developer carrier name; comments belong only in the ZIP filename, never in the canonical carrier directory.

Fix
- Compiler-UI.json now declares lifecycle.finalInstall.buildArgumentSwitch = -FinalInstallPath.
- The shared Compiler-UI.ps1 appends that switch and its already-resolved absolute path to every child build invocation.
- Build-PHLEGM-v6.ps1 accepts -FinalInstallPath and uses it as the single clone destination. Direct/manual build invocations may omit it and retain the data-driven upstreamInstallRelative fallback from the Developer carrier root (the parent of the inner PHLEGM working directory).
- Invoke-PHLEGMEndUserClone no longer re-resolves the manifest path internally.
- The non-destructive matrix merge is unchanged: all passing End-User payloads are union-staged and conflict-checked before the live destination is touched; colliding files are replaced, new files are added, and destination-only content is retained.
- Every merged file is now SHA-256 verified after Copy-Item. A missing or mismatched destination file fails the build instead of silently reporting a successful clone.
- Build diagnostics print the exact resolved final-install destination.
- Developer packaging uses an uncommented canonical outer carrier; the checkpoint comment appears only in the ZIP filename.

Validation
- validate_final_install_handoff.py proves ../../PHLEGM resolves to the sibling live install, verifies bootstrap -> Compiler UI -> matrix child path handoff, models the staged non-destructive merge, and checks the post-copy SHA-256 contract.
- validate_installer_layout.py rejects the former independently re-based clone path and validates the exact-path handoff contract.
- All 25 PHLEGM Python validators pass in the packaging environment.
- The shared Compiler-UI.ps1 and bootstrap Install-and-Compile.ps1 remain byte-for-byte identical to the Mindrealm counterparts in the parity workspace.
- Native Windows build/runtime execution is not available in this container.
