docs(16-01): complete MergePermissions toggle and consolidated CSV export plan

- 16-01-SUMMARY.md created with all task outcomes and verification results
- STATE.md updated with decisions, session info, progress bar (98%)
- ROADMAP.md updated: phase 16 in-progress (1/2 summaries complete)
- REQUIREMENTS.md: RPT-03 marked complete

.planning/STATE.md

@@ -3,14 +3,14 @@ gsd_state_version: 1.0
 milestone: v2.3
 milestone_name: Tenant Management & Report Enhancements
 status: planning
-stopped_at: Completed 15-02-PLAN.md
-last_updated: "2026-04-09T09:49:21.960Z"
+stopped_at: Completed 16-01-PLAN.md
+last_updated: "2026-04-09T10:34:56.209Z"
 last_activity: 2026-04-09 — Roadmap created for v2.3 (phases 15-19)
 progress:
   total_phases: 5
   completed_phases: 1
-  total_plans: 2
-  completed_plans: 2
+  total_plans: 4
+  completed_plans: 3
 ---
 
 # Project State
@@ -64,6 +64,8 @@ Decisions are logged in PROJECT.md Key Decisions table.
 - [Phase 15]: MakeKey declared internal for test access via InternalsVisibleTo without exposing as public API
 - [Phase 15]: LINQ GroupBy+Select for consolidation merge instead of mutable dictionary — consistent with functional codebase style
 - [Phase 15-consolidation-data-model]: RPT-04-g test data uses 11 rows (not 10) to produce 7 consolidated rows — plan description had a counting error; 4 unique rows + 3 merged groups = 7
+- [Phase 16-01]: Consolidated branch uses early-return pattern inside WriteSingleFileAsync to leave existing code path untouched
+- [Phase 16-01]: PermissionsViewModel gets MergePermissions as no-op placeholder reserved for future use
 
 ### Pending Todos
 
@@ -75,7 +77,7 @@ None.
 
 ## Session Continuity
 
-Last session: 2026-04-09T09:46:35.243Z
-Stopped at: Completed 15-02-PLAN.md
+Last session: 2026-04-09T10:34:56.207Z
+Stopped at: Completed 16-01-PLAN.md
 Resume file: None
 Next step: `/gsd:plan-phase 15`