docs(15-01): complete consolidation data model plan

- Add 15-01-SUMMARY.md with task commits, decisions, and next phase readiness
- Update STATE.md with decisions and session position
- Update ROADMAP.md phase 15 progress (1/2 plans complete)
- Mark requirement RPT-04 complete in REQUIREMENTS.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.planning/phases/15-consolidation-data-model/15-01-SUMMARY.md

@@ -0,0 +1,103 @@
+---
+phase: 15-consolidation-data-model
+plan: "01"
+subsystem: api
+tags: [csharp, records, linq, permission-consolidation]
+
+requires: []
+provides:
+  - LocationInfo record with five location fields (SiteUrl, SiteTitle, ObjectTitle, ObjectUrl, ObjectType)
+  - ConsolidatedPermissionEntry record grouping key fields with IReadOnlyList<LocationInfo> Locations
+  - PermissionConsolidator.Consolidate — pure static method merging UserAccessEntry list by composite key
+  - PermissionConsolidator.MakeKey — pipe-delimited case-insensitive key from UserLogin+PermissionLevel+AccessType+GrantedThrough
+affects: [16-report-consolidation-toggle]
+
+tech-stack:
+  added: []
+  patterns:
+    - "Positional C# records for immutable data shapes"
+    - "LINQ GroupBy+Select for pure-function merge without mutable state"
+    - "Internal MakeKey for composite key generation (pipe-delimited, ToLowerInvariant)"
+    - "Array.Empty<T>() short-circuit on empty input"
+
+key-files:
+  created:
+    - SharepointToolbox/Core/Models/LocationInfo.cs
+    - SharepointToolbox/Core/Models/ConsolidatedPermissionEntry.cs
+    - SharepointToolbox/Core/Helpers/PermissionConsolidator.cs
+  modified: []
+
+key-decisions:
+  - "MakeKey is internal (not private) to allow test access via InternalsVisibleTo without exposing as public API"
+  - "LINQ GroupBy+Select chosen over mutable Dictionary to match existing codebase functional style"
+  - "OrderBy UserLogin then PermissionLevel ensures deterministic output order for consistent exports"
+
+patterns-established:
+  - "Consolidation key: pipe-delimited lowercase composite of UserLogin|PermissionLevel|AccessType|GrantedThrough"
+  - "LocationInfo is the extraction unit — one per original UserAccessEntry row in a consolidated group"
+
+requirements-completed: [RPT-04]
+
+duration: 1min
+completed: "2026-04-09"
+---
+
+# Phase 15 Plan 01: Consolidation Data Model Summary
+
+**LocationInfo + ConsolidatedPermissionEntry records and PermissionConsolidator.Consolidate pure-function merge service using LINQ GroupBy over pipe-delimited composite key**
+
+## Performance
+
+- **Duration:** ~1 min
+- **Started:** 2026-04-09T09:40:40Z
+- **Completed:** 2026-04-09T09:41:37Z
+- **Tasks:** 2
+- **Files modified:** 3
+
+## Accomplishments
+
+- LocationInfo positional record extracts five location fields from UserAccessEntry during consolidation
+- ConsolidatedPermissionEntry record holds key fields plus computed LocationCount convenience property
+- PermissionConsolidator.Consolidate groups a flat UserAccessEntry list by (UserLogin, PermissionLevel, AccessType, GrantedThrough) composite key, returning deterministically ordered consolidated rows
+- Empty input short-circuits cleanly to Array.Empty without allocating
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Create LocationInfo and ConsolidatedPermissionEntry model records** - `270329b` (feat)
+2. **Task 2: Create PermissionConsolidator static helper** - `440b247` (feat)
+
+## Files Created/Modified
+
+- `SharepointToolbox/Core/Models/LocationInfo.cs` - Lightweight record holding five location fields extracted from UserAccessEntry when rows are merged
+- `SharepointToolbox/Core/Models/ConsolidatedPermissionEntry.cs` - Consolidated permission record with key fields, Locations list, and computed LocationCount property
+- `SharepointToolbox/Core/Helpers/PermissionConsolidator.cs` - Static helper with MakeKey (internal) and Consolidate (public) for pure-function merge logic
+
+## Decisions Made
+
+- `MakeKey` declared `internal` (not `private`) so test projects can access it via `[InternalsVisibleTo]` without exposing as public API surface
+- LINQ GroupBy+Select pattern used instead of mutable dictionary — consistent with functional style seen elsewhere in the codebase
+- Output ordered by UserLogin then PermissionLevel for deterministic, predictable export row ordering
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+
+None.
+
+## User Setup Required
+
+None - no external service configuration required.
+
+## Next Phase Readiness
+
+- Phase 16 (Report Consolidation Toggle) can now wire PermissionConsolidator.Consolidate into the export pipeline
+- All three files exist, compile without errors, and no existing files were modified
+- MakeKey is accessible to Phase 16 test projects via InternalsVisibleTo if needed
+
+---
+*Phase: 15-consolidation-data-model*
+*Completed: 2026-04-09*