Session 027: Complete Qt5:: to Qt6:: migration verification

- Verified zero Qt5:: CMake references across entire qt6-after directory
- All 593 CMakeLists.txt files migrated to Qt6::
- 10 major module groups fully migrated (Lts/*, TetraIF, Z)
- Low-priority cleanup items identified (NULL, Q_FOREACH) - deferred
- Ready for final build validation phase

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Entire-Checkpoint: 01M0WZFQBT2EYSSWW56YMD7JCG

MIGRATION_STATUS.md

@@ -1,5 +1,56 @@
 # Qt5/C++11 → Qt6/C++17 Migration Status
 
+## Session 027: Complete Qt5:: to Qt6:: Migration Verification (2026-08-24)
+
+### ✅ All Qt5:: CMake References Migrated Across Entire Codebase
+
+**Comprehensive Verification:**
+```bash
+$ grep -r "Qt5::" qt6-after/qt6-migrated-legatus/ --include="*.txt" --include="*.cmake"
+# Zero results - ALL Qt5:: references migrated to Qt6::
+```
+
+**Migration Summary:**
+- **Total CMakeLists.txt files**: 593 (qt6-after) vs 612 (qt5-before)
+- **Total source files**: 38,415 (qt6-after) vs 16,247 (qt5-before)
+- **Modules fully migrated**: Lts/Common, Lts/Tools, Lts/Application, Lts/Viewer, Lts/DDS, Lts/Proxies, Lts/Services, Lts/Plugins, Lts/Projects, TetraIF, Z
+
+**Qt5:: → Qt6:: Migrations Applied:**
+- Qt5::Core → Qt6::Core
+- Qt5::Gui → Qt6::Gui
+- Qt5::Widgets → Qt6::Widgets
+- Qt5::Network → Qt6::Network
+- Qt5::Svg → Qt6::Svg
+- Qt5::Concurrent → Qt6::Concurrent
+- Qt5::WebSockets → Qt6::WebSockets
+- Qt5::Sql → Qt6::Sql
+- Qt5::Xml → Qt6::Xml
+- Qt5::Test → Qt6::Test
+- Qt5::SerialPort → Qt6::SerialPort
+
+**Submodule Status:**
+- Branch: `feature/qt6-migration-basis-modules`
+- Commit: `d5af8b976` (Session 026: Lts/Services)
+- Main repo: `8d2f1bbb` (Update MIGRATION_STATUS.md with Session 026 results)
+
+### Low-Priority Cleanup Items (Deferred)
+
+Per Option A constraints (minimal changes, tests deferred):
+
+| Issue | Count | Priority | Status |
+|-------|-------|----------|--------|
+| NULL → nullptr | 456 | Low | Deferred |
+| Q_FOREACH → range-for | 8 | Low | Deferred |
+| Old SIGNAL/SLOT | 0 | Low | ✅ Complete |
+| QRegExp → QRegularExpression | ~7 | Low | Deferred (functional) |
+
+### Next Steps (Option A)
+1. Proceed to final build validation
+2. Defer low-priority cleanup until after build verification
+3. Run test suite only after build succeeds
+
+---
+
 ## Session 026: Lts/Services Qt5:: to Qt6:: Migration Complete (2026-08-24)
 
 ### ✅ All Qt5:: CMake References in Lts/Services Migrated to Qt6::