docs(17-02): complete group expansion HTML reports plan

- 17-02-SUMMARY.md created
- STATE.md updated: session, decisions, progress
- ROADMAP.md: phase 17 marked complete (2/2 plans)
- REQUIREMENTS.md: RPT-01 marked complete

.planning/phases/17-group-expansion-html-reports/17-02-SUMMARY.md

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+---
+phase: 17-group-expansion-html-reports
+plan: "02"
+subsystem: html-export
+tags: [html-export, group-expansion, permissions-viewmodel, tdd]
+dependency_graph:
+  requires: ["17-01"]
+  provides: ["expandable-group-pills-html", "group-resolver-wired-to-export"]
+  affects: ["HtmlExportService", "PermissionsViewModel"]
+tech_stack:
+  added: []
+  patterns: ["optional-parameter-backward-compat", "pre-render-resolution", "inline-js-toggle"]
+key_files:
+  created: []
+  modified:
+    - SharepointToolbox/Services/Export/HtmlExportService.cs
+    - SharepointToolbox/ViewModels/Tabs/PermissionsViewModel.cs
+    - SharepointToolbox.Tests/Services/Export/HtmlExportServiceTests.cs
+decisions:
+  - "groupMembers added as optional last parameter to both BuildHtml overloads and WriteAsync methods — null produces byte-identical output to pre-Phase 17"
+  - "Group pill expansion uses name-based lookup in groupMembers dict (not login) — matches how SharePoint groups are identified in Users field"
+  - "ISharePointGroupResolver injected as optional last parameter in PermissionsViewModel main constructor — DI works without explicit resolver if not registered"
+  - "Resolution failure logged as Warning and export proceeds without expansion — never blocks user export"
+metrics:
+  duration_seconds: 204
+  completed_date: "2026-04-09"
+  tasks_completed: 2
+  files_modified: 3
+---
+
+# Phase 17 Plan 02: Group Expansion Wire-up Summary
+
+Expandable SharePoint group pills in HTML reports with toggleGroup JS and PermissionsViewModel pre-render resolution via ISharePointGroupResolver.
+
+## Tasks Completed
+
+| Task | Description | Commit | Status |
+|------|-------------|--------|--------|
+| 1 (RED) | Failing tests for group pill expansion | c35ee76 | Done |
+| 1 (GREEN) | HtmlExportService: groupMembers param + expandable pills + toggleGroup JS | 07ed6e2 | Done |
+| 2 | PermissionsViewModel: ISharePointGroupResolver injection + ExportHtmlAsync wiring | aab3aee | Done |
+
+## What Was Built
+
+Both `BuildHtml` overloads in `HtmlExportService` now accept an optional `IReadOnlyDictionary<string, IReadOnlyList<ResolvedMember>>? groupMembers` parameter. When provided:
+
+- SharePoint group pills render as `<span class="user-pill group-expandable" onclick="toggleGroup('grpmem0')">` with a down-arrow indicator
+- A hidden `<tr data-group="grpmem0" style="display:none">` sub-row is injected immediately after the parent row, containing resolved member display names and logins
+- Empty member lists (resolution failed) render `<em style="color:#888">members unavailable</em>`
+- `toggleGroup(id)` JS function is added to the inline script block
+- `filterTable()` updated to skip `data-group` sub-rows
+- CSS `.group-expandable` adds cursor pointer and hover opacity
+
+`PermissionsViewModel` now injects `ISharePointGroupResolver?` as an optional last constructor parameter. In `ExportHtmlAsync`, before calling `WriteAsync`, it:
+1. Collects all distinct group names from `Results` where `PrincipalType == "SharePointGroup"`
+2. Calls `_groupResolver.ResolveGroupsAsync(ctx, clientId, groupNames, ct)` if resolver is non-null and groups were found
+3. Passes the resulting `groupMembers` dict to both `WriteAsync` call sites (standard and simplified paths)
+4. On resolution failure, logs a warning and exports without expansion (graceful degradation)
+
+## Deviations from Plan
+
+None — plan executed exactly as written.
+
+## Verification
+
+- `dotnet build` — 0 errors, 0 warnings
+- `dotnet test --filter "FullyQualifiedName~HtmlExportServiceTests"` — 32 tests pass (includes 6 new group expansion tests)
+- `dotnet test` — 320 passed, 0 failed, 28 skipped (full suite green)
+
+## Self-Check: PASSED
+
+Files verified:
+- SharepointToolbox/Services/Export/HtmlExportService.cs — contains `toggleGroup`, `groupMembers`, `group-expandable`
+- SharepointToolbox/ViewModels/Tabs/PermissionsViewModel.cs — contains `_groupResolver`, `ResolveGroupsAsync`
+- SharepointToolbox.Tests/Services/Export/HtmlExportServiceTests.cs — contains `grpmem` test patterns
+
+Commits verified:
+- c35ee76 — test(17-02): RED phase
+- 07ed6e2 — feat(17-02): HtmlExportService implementation
+- aab3aee — feat(17-02): PermissionsViewModel wiring