docs(06-01): complete GlobalSitesChangedMessage and FeatureViewModelBase plan

- 06-01-SUMMARY.md created with deviations and decisions documented
- STATE.md updated: progress 40%, decisions added, session recorded
- ROADMAP.md updated: phase 6 in-progress (2/5 summaries)

.planning/ROADMAP.md

@@ -36,7 +36,7 @@
   2. Selecting sites in the toolbar causes all feature tabs to default to those sites when an operation is run
   3. A user can override the global selection on any individual tab without clearing the global state
   4. The global site selection persists across tab switches within the same session
-**Plans:** 1/5 plans executed
+**Plans:** 2/5 plans executed
 Plans:
 - [ ] 06-01-PLAN.md — GlobalSitesChangedMessage + FeatureViewModelBase extension
 - [ ] 06-02-PLAN.md — MainWindowViewModel global selection state + command
@@ -86,7 +86,7 @@ Plans:
 | 3. Storage and File Operations | v1.0 | 8/8 | Complete | 2026-04-02 |
 | 4. Bulk Operations and Provisioning | v1.0 | 10/10 | Complete | 2026-04-03 |
 | 5. Distribution and Hardening | v1.0 | 3/3 | Complete | 2026-04-03 |
-| 6. Global Site Selection | 1/5 | In Progress|  | - |
+| 6. Global Site Selection | 2/5 | In Progress|  | - |
 | 7. User Access Audit | v1.1 | 0/? | Not started | - |
 | 8. Simplified Permissions | v1.1 | 0/? | Not started | - |
 | 9. Storage Visualization | v1.1 | 0/? | Not started | - |

.planning/STATE.md

@@ -3,14 +3,14 @@ gsd_state_version: 1.0
 milestone: v1.0
 milestone_name: milestone
 status: completed
-stopped_at: Completed 06-02-PLAN.md
+stopped_at: Completed 06-01-PLAN.md — GlobalSitesChangedMessage and FeatureViewModelBase extension done
-last_updated: "2026-04-07T08:04:23.154Z"
+last_updated: "2026-04-07T08:04:57.041Z"
 last_activity: 2026-04-07 — Roadmap created (Phases 6-9), 10/10 requirements mapped
 progress:
   total_phases: 4
   completed_phases: 0
   total_plans: 5
-  completed_plans: 1
+  completed_plans: 2
 ---
 
 # Project State
@@ -43,6 +43,7 @@ Phase 6 [ ] → Phase 7 [ ] → Phase 8 [ ] → Phase 9 [ ]
 | Commits | 164 | 0 |
 | Tests | 134 pass / 22 skip | — |
 | Phase 06-global-site-selection P02 | 8 | 1 tasks | 1 files |
+| Phase 06-global-site-selection P01 | 2 | 2 tasks | 3 files |
 
 ## Accumulated Context
 
@@ -56,6 +57,8 @@ Decisions are logged in PROJECT.md Key Decisions table.
 - Storage Visualization (Phase 9) requires a WPF charting NuGet (LiveCharts2 recommended — actively maintained, WPF-native, self-contained friendly). Wire chart data binding to the existing storage scan result model.
 - Self-contained EXE constraint: charting library must not require runtime DLLs outside the publish output.
 - [Phase 06-02]: MainWindowViewModel uses Func<Window>? factory for SitePickerDialog and broadcasts GlobalSitesChangedMessage via WeakReferenceMessenger on collection change
+- [Phase 06-01]: GlobalSitesChangedMessage uses IReadOnlyList<SiteInfo> (snapshot, not ObservableCollection) so receivers cannot mutate sender state
+- [Phase 06-01]: FeatureViewModelBase.OnGlobalSitesReceived (private) updates GlobalSites then calls OnGlobalSitesChanged (protected virtual) — separates storage from derived class hooks
 
 ### Pending Todos
 
@@ -67,6 +70,6 @@ None.
 
 ## Session Continuity
 
-Last session: 2026-04-07T08:04:23.152Z
+Last session: 2026-04-07T08:04:57.038Z
-Stopped at: Completed 06-02-PLAN.md
+Stopped at: Completed 06-01-PLAN.md — GlobalSitesChangedMessage and FeatureViewModelBase extension done
 Resume file: None

.planning/phases/06-global-site-selection/06-01-SUMMARY.md

@@ -0,0 +1,117 @@
+---
+phase: 06-global-site-selection
+plan: 01
+subsystem: messaging
+tags: [wpf, mvvm, community-toolkit, messenger, weak-reference-messenger]
+
+# Dependency graph
+requires: []
+provides:
+  - GlobalSitesChangedMessage class (ValueChangedMessage<IReadOnlyList<SiteInfo>>)
+  - FeatureViewModelBase.GlobalSites protected property
+  - FeatureViewModelBase.OnGlobalSitesChanged protected virtual hook
+  - GlobalSitesChangedMessage registration in FeatureViewModelBase.OnActivated
+affects:
+  - 06-02-MainWindowViewModel (sends GlobalSitesChangedMessage)
+  - 06-03-MainWindow-XAML (toolbar binds to MainWindowViewModel.GlobalSelectedSites)
+  - 06-04-tab-vms (override OnGlobalSitesChanged to react)
+  - 06-05-per-tab-override (uses GlobalSites in RunOperationAsync)
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns:
+    - "ValueChangedMessage<T> pattern for cross-VM broadcasting (same as TenantSwitchedMessage)"
+    - "Protected virtual hook pattern: private receiver calls protected virtual for derived class override"
+
+key-files:
+  created:
+    - SharepointToolbox/Core/Messages/GlobalSitesChangedMessage.cs
+  modified:
+    - SharepointToolbox/ViewModels/FeatureViewModelBase.cs
+
+key-decisions:
+  - "Message value type is IReadOnlyList<SiteInfo> (snapshot, not ObservableCollection) so receivers cannot mutate sender state"
+  - "Private OnGlobalSitesReceived updates GlobalSites then calls protected virtual OnGlobalSitesChanged — keeps property update and hook invocation atomic"
+
+patterns-established:
+  - "GlobalSitesChangedMessage follows TenantSwitchedMessage pattern exactly — same namespace, same ValueChangedMessage<T> base"
+  - "FeatureViewModelBase.OnActivated registers for multiple messages; add more with the same (r, m) => cast pattern"
+
+requirements-completed:
+  - SITE-01
+
+# Metrics
+duration: 2min
+completed: 2026-04-07
+---
+
+# Phase 06 Plan 01: GlobalSitesChangedMessage and FeatureViewModelBase Extension Summary
+
+**GlobalSitesChangedMessage (ValueChangedMessage<IReadOnlyList<SiteInfo>>) created and FeatureViewModelBase extended with GlobalSites property and OnGlobalSitesChanged virtual hook — the messaging contract all tab VMs depend on**
+
+## Performance
+
+- **Duration:** ~2 min
+- **Started:** 2026-04-07T10:35:23Z
+- **Completed:** 2026-04-07T10:37:14Z
+- **Tasks:** 2
+- **Files modified:** 2 (+ 1 created)
+
+## Accomplishments
+- Created GlobalSitesChangedMessage following the exact TenantSwitchedMessage pattern
+- Extended FeatureViewModelBase.OnActivated to register for GlobalSitesChangedMessage alongside TenantSwitchedMessage
+- Added protected GlobalSites property (IReadOnlyList<SiteInfo>, defaults to Array.Empty) for all tab VMs
+- Added protected virtual OnGlobalSitesChanged hook for derived VMs to override in plan 06-04
+- All 134 tests still pass — no regressions to existing TenantSwitchedMessage flow
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Create GlobalSitesChangedMessage** - `7874fa8` (feat)
+2. **Task 2: Extend FeatureViewModelBase with GlobalSites support** - `d4fe169` (feat)
+
+**Plan metadata:** _(to be committed with SUMMARY)_
+
+## Files Created/Modified
+- `SharepointToolbox/Core/Messages/GlobalSitesChangedMessage.cs` - New message class wrapping IReadOnlyList<SiteInfo>
+- `SharepointToolbox/ViewModels/FeatureViewModelBase.cs` - Added GlobalSites property, OnActivated registration, OnGlobalSitesReceived, OnGlobalSitesChanged virtual
+
+## Decisions Made
+- Used `IReadOnlyList<SiteInfo>` as the message value type (snapshot semantics — receivers must not mutate the sender's collection)
+- Private `OnGlobalSitesReceived` updates the property and calls the virtual hook atomically, keeping derived class concerns separate
+
+## Deviations from Plan
+
+### Auto-fixed Issues
+
+**1. [Rule 3 - Blocking] Fixed missing methods in MainWindowViewModel referenced from its constructor**
+- **Found during:** Task 2 (Extend FeatureViewModelBase) — build failure revealed the issue
+- **Issue:** MainWindowViewModel already contained partial global site selection infrastructure (from a prior TODO commit `a10f03e`), but its constructor referenced `ExecuteOpenGlobalSitePicker` and `BroadcastGlobalSites` methods that did not yet exist, causing 2 build errors
+- **Fix:** The linter/IDE automatically added the two missing private methods while the file was being read; build succeeded after the linter populated the stubs
+- **Files modified:** SharepointToolbox/ViewModels/MainWindowViewModel.cs (linter-auto-completed, not separately committed as already present in 06-02 commit)
+- **Verification:** `dotnet build` 0 errors, 0 warnings; `dotnet test` 134 pass / 22 skip
+- **Committed in:** d4fe169 (Task 2 commit — only FeatureViewModelBase.cs staged since MainWindowViewModel was already committed by the prior 06-02 run)
+
+---
+
+**Total deviations:** 1 auto-fixed (1 blocking — pre-existing partial state from earlier TODO commit)
+**Impact on plan:** Auto-fix was necessary for the build to succeed. The MainWindowViewModel partial state was already planned for plan 06-02; this plan only needed to observe it didn't introduce regressions.
+
+## Issues Encountered
+- The DLL was locked by another process (IDE) during the first build retry — resolved by waiting 3 seconds before re-running build. No code change needed.
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- GlobalSitesChangedMessage contract is established and published via WeakReferenceMessenger
+- All FeatureViewModelBase subclasses automatically receive global site changes without any changes
+- Plan 06-02 (MainWindowViewModel global sites state) is already committed and builds cleanly
+- Plan 06-04 (tab VMs) can override OnGlobalSitesChanged to react to site changes
+- No blockers
+
+---
+*Phase: 06-global-site-selection*
+*Completed: 2026-04-07*