Initial commit

Services/Export/BrandingHtmlHelper.cs

@@ -0,0 +1,37 @@
+using System.Text;
+using SharepointToolbox.Web.Core.Models;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Generates the branding header HTML fragment for HTML reports.
+/// Called by each HTML export service between &lt;body&gt; and &lt;h1&gt;.
+/// Returns empty string when no logos are configured (no broken images).
+/// </summary>
+internal static class BrandingHtmlHelper
+{
+    public static string BuildBrandingHeader(ReportBranding? branding)
+    {
+        if (branding is null) return string.Empty;
+
+        var msp = branding.MspLogo;
+        var client = branding.ClientLogo;
+
+        if (msp is null && client is null) return string.Empty;
+
+        var sb = new StringBuilder();
+        sb.AppendLine("<div style=\"display:flex;gap:16px;align-items:center;padding:12px 24px 0;\">");
+
+        if (msp is not null)
+            sb.AppendLine($"  <img src=\"data:{msp.MimeType};base64,{msp.Base64}\" alt=\"\" style=\"max-height:60px;max-width:200px;object-fit:contain;\">");
+
+        if (msp is not null && client is not null)
+            sb.AppendLine("  <div style=\"flex:1\"></div>");
+
+        if (client is not null)
+            sb.AppendLine($"  <img src=\"data:{client.MimeType};base64,{client.Base64}\" alt=\"\" style=\"max-height:60px;max-width:200px;object-fit:contain;\">");
+
+        sb.AppendLine("</div>");
+        return sb.ToString();
+    }
+}

Services/Export/BulkResultCsvExportService.cs

@@ -0,0 +1,61 @@
+using System.Globalization;
+using System.IO;
+using System.Text;
+using CsvHelper;
+using CsvHelper.Configuration;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports the failed subset of a <see cref="BulkOperationSummary{T}"/> run
+/// to CSV. CsvHelper is used so the <typeparamref name="T"/> payload's
+/// properties become columns automatically, plus one error-message and one
+/// timestamp column appended at the end.
+/// </summary>
+public class BulkResultCsvExportService
+{
+    private static readonly CsvConfiguration CsvConfig = new(CultureInfo.InvariantCulture)
+    {
+        // Prevent CSV formula injection: prefix =, +, -, @, tab, CR with single quote
+        InjectionOptions = InjectionOptions.Escape,
+    };
+
+    /// <summary>
+    /// Builds a CSV containing only items whose <see cref="BulkItemResult{T}.IsSuccess"/>
+    /// is <c>false</c>. Columns: every public property of <typeparamref name="T"/>
+    /// followed by Error and Timestamp (ISO-8601).
+    /// </summary>
+    public string BuildFailedItemsCsv<T>(IReadOnlyList<BulkItemResult<T>> failedItems)
+    {
+        var TL = TranslationSource.Instance;
+        using var writer = new StringWriter();
+        using var csv = new CsvWriter(writer, CsvConfig);
+
+        csv.WriteHeader<T>();
+        csv.WriteField(TL["report.col.error"]);
+        csv.WriteField(TL["report.col.timestamp"]);
+        csv.NextRecord();
+
+        foreach (var item in failedItems.Where(r => !r.IsSuccess))
+        {
+            csv.WriteRecord(item.Item);
+            csv.WriteField(item.ErrorMessage);
+            csv.WriteField(item.Timestamp.ToString("o"));
+            csv.NextRecord();
+        }
+
+        return writer.ToString();
+    }
+
+    /// <summary>Writes the failed-items CSV to <paramref name="filePath"/> with UTF-8 BOM.</summary>
+    public async Task WriteFailedItemsCsvAsync<T>(
+        IReadOnlyList<BulkItemResult<T>> failedItems,
+        string filePath,
+        CancellationToken ct)
+    {
+        var content = BuildFailedItemsCsv(failedItems);
+        await ExportFileWriter.WriteCsvAsync(filePath, content, ct);
+    }
+}

Services/Export/CsvExportService.cs

@@ -0,0 +1,180 @@
+using System.IO;
+using System.Text;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports permission entries to CSV format.
+/// Ports PowerShell Merge-PermissionRows + Export-Csv functionality.
+/// </summary>
+public class CsvExportService
+{
+    private static string BuildHeader()
+    {
+        var T = TranslationSource.Instance;
+        return $"\"{T["report.col.object"]}\",\"{T["report.col.title"]}\",\"{T["report.col.url"]}\",\"HasUniquePermissions\",\"Users\",\"UserLogins\",\"Type\",\"Permissions\",\"GrantedThrough\",\"TargetLabel\",\"TargetUrl\",\"SharingLinkType\"";
+    }
+
+    /// <summary>
+    /// Builds a CSV string from the supplied permission entries.
+    /// Merges rows with identical (Users, PermissionLevels, GrantedThrough) by pipe-joining URLs and Titles.
+    /// </summary>
+    public string BuildCsv(IReadOnlyList<PermissionEntry> entries)
+    {
+        var sb = new StringBuilder();
+        sb.AppendLine(BuildHeader());
+
+        // Merge: group by (Users, PermissionLevels, GrantedThrough) — port of PS Merge-PermissionRows
+        var merged = entries
+            .GroupBy(e => (e.Users, e.PermissionLevels, e.GrantedThrough))
+            .Select(g => new
+            {
+                ObjectType    = g.First().ObjectType,
+                Title         = string.Join(" | ", g.Select(e => e.Title).Distinct()),
+                Url           = string.Join(" | ", g.Select(e => e.Url).Distinct()),
+                HasUnique     = g.First().HasUniquePermissions,
+                Users         = g.Key.Users,
+                UserLogins    = g.First().UserLogins,
+                PrincipalType = g.First().PrincipalType,
+                Permissions   = g.Key.PermissionLevels,
+                GrantedThrough = g.Key.GrantedThrough,
+                TargetLabel   = g.First().TargetLabel ?? string.Empty,
+                TargetUrl     = g.First().TargetUrl ?? string.Empty,
+                SharingLinkType = g.First().SharingLinkType ?? string.Empty
+            });
+
+        foreach (var row in merged)
+            sb.AppendLine(string.Join(",", new[]
+            {
+                Csv(row.ObjectType), Csv(row.Title), Csv(row.Url),
+                Csv(row.HasUnique.ToString()), Csv(row.Users), Csv(row.UserLogins),
+                Csv(row.PrincipalType), Csv(row.Permissions), Csv(row.GrantedThrough),
+                Csv(row.TargetLabel), Csv(row.TargetUrl), Csv(row.SharingLinkType)
+            }));
+
+        return sb.ToString();
+    }
+
+    /// <summary>
+    /// Writes the CSV to the specified file path using UTF-8 with BOM (for Excel compatibility).
+    /// </summary>
+    public async Task WriteAsync(IReadOnlyList<PermissionEntry> entries, string filePath, CancellationToken ct)
+    {
+        var csv = BuildCsv(entries);
+        await ExportFileWriter.WriteCsvAsync(filePath, csv, ct);
+    }
+
+    /// <summary>
+    /// Header for simplified CSV export — includes "SimplifiedLabels" and "RiskLevel" columns.
+    /// </summary>
+    private static string BuildSimplifiedHeader()
+    {
+        var T = TranslationSource.Instance;
+        return $"\"{T["report.col.object"]}\",\"{T["report.col.title"]}\",\"{T["report.col.url"]}\",\"HasUniquePermissions\",\"Users\",\"UserLogins\",\"Type\",\"Permissions\",\"SimplifiedLabels\",\"RiskLevel\",\"GrantedThrough\",\"TargetLabel\",\"TargetUrl\",\"SharingLinkType\"";
+    }
+
+    /// <summary>
+    /// Builds a CSV string from simplified permission entries.
+    /// Includes SimplifiedLabels and RiskLevel columns after raw Permissions.
+    /// Uses the same merge logic as the standard BuildCsv.
+    /// </summary>
+    public string BuildCsv(IReadOnlyList<SimplifiedPermissionEntry> entries)
+    {
+        var sb = new StringBuilder();
+        sb.AppendLine(BuildSimplifiedHeader());
+
+        var merged = entries
+            .GroupBy(e => (e.Users, e.PermissionLevels, e.GrantedThrough))
+            .Select(g => new
+            {
+                ObjectType     = g.First().ObjectType,
+                Title          = string.Join(" | ", g.Select(e => e.Title).Distinct()),
+                Url            = string.Join(" | ", g.Select(e => e.Url).Distinct()),
+                HasUnique      = g.First().HasUniquePermissions,
+                Users          = g.Key.Users,
+                UserLogins     = g.First().UserLogins,
+                PrincipalType  = g.First().PrincipalType,
+                Permissions    = g.Key.PermissionLevels,
+                SimplifiedLabels = g.First().SimplifiedLabels,
+                RiskLevel      = g.First().RiskLevel.ToString(),
+                GrantedThrough = g.Key.GrantedThrough,
+                TargetLabel    = g.First().TargetLabel ?? string.Empty,
+                TargetUrl      = g.First().TargetUrl ?? string.Empty,
+                SharingLinkType = g.First().SharingLinkType ?? string.Empty
+            });
+
+        foreach (var row in merged)
+            sb.AppendLine(string.Join(",", new[]
+            {
+                Csv(row.ObjectType), Csv(row.Title), Csv(row.Url),
+                Csv(row.HasUnique.ToString()), Csv(row.Users), Csv(row.UserLogins),
+                Csv(row.PrincipalType), Csv(row.Permissions), Csv(row.SimplifiedLabels),
+                Csv(row.RiskLevel), Csv(row.GrantedThrough),
+                Csv(row.TargetLabel), Csv(row.TargetUrl), Csv(row.SharingLinkType)
+            }));
+
+        return sb.ToString();
+    }
+
+    /// <summary>
+    /// Writes simplified CSV to the specified file path.
+    /// </summary>
+    public async Task WriteAsync(IReadOnlyList<SimplifiedPermissionEntry> entries, string filePath, CancellationToken ct)
+    {
+        var csv = BuildCsv(entries);
+        await ExportFileWriter.WriteCsvAsync(filePath, csv, ct);
+    }
+
+    /// <summary>
+    /// Writes permission entries with optional per-site partitioning.
+    /// Single → writes one file at <paramref name="basePath"/>.
+    /// BySite → one file per site-collection URL, suffixed on the base path.
+    /// </summary>
+    public Task WriteAsync(
+        IReadOnlyList<PermissionEntry> entries,
+        string basePath,
+        ReportSplitMode splitMode,
+        CancellationToken ct)
+        => ReportSplitHelper.WritePartitionedAsync(
+            entries, basePath, splitMode,
+            PartitionBySite,
+            (part, path, c) => WriteAsync(part, path, c),
+            ct);
+
+    /// <summary>Simplified-entry split variant.</summary>
+    public Task WriteAsync(
+        IReadOnlyList<SimplifiedPermissionEntry> entries,
+        string basePath,
+        ReportSplitMode splitMode,
+        CancellationToken ct)
+        => ReportSplitHelper.WritePartitionedAsync(
+            entries, basePath, splitMode,
+            PartitionBySite,
+            (part, path, c) => WriteAsync(part, path, c),
+            ct);
+
+    internal static IEnumerable<(string Label, IReadOnlyList<PermissionEntry> Partition)> PartitionBySite(
+        IReadOnlyList<PermissionEntry> entries)
+    {
+        return entries
+            .GroupBy(e => ReportSplitHelper.DeriveSiteCollectionUrl(e.Url), StringComparer.OrdinalIgnoreCase)
+            .Select(g => (
+                Label: ReportSplitHelper.DeriveSiteLabel(g.Key),
+                Partition: (IReadOnlyList<PermissionEntry>)g.ToList()));
+    }
+
+    internal static IEnumerable<(string Label, IReadOnlyList<SimplifiedPermissionEntry> Partition)> PartitionBySite(
+        IReadOnlyList<SimplifiedPermissionEntry> entries)
+    {
+        return entries
+            .GroupBy(e => ReportSplitHelper.DeriveSiteCollectionUrl(e.Url), StringComparer.OrdinalIgnoreCase)
+            .Select(g => (
+                Label: ReportSplitHelper.DeriveSiteLabel(g.Key),
+                Partition: (IReadOnlyList<SimplifiedPermissionEntry>)g.ToList()));
+    }
+
+    /// <summary>RFC 4180 CSV field escaping with formula-injection guard.</summary>
+    private static string Csv(string value) => CsvSanitizer.Escape(value);
+}

Services/Export/CsvSanitizer.cs

@@ -0,0 +1,47 @@
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// CSV field sanitization. Adds RFC 4180 quoting plus formula-injection
+/// protection: Excel and other spreadsheet apps treat cells starting with
+/// '=', '+', '-', '@', tab, or CR as formulas. Prefixing with a single
+/// quote neutralizes the formula while remaining readable.
+/// </summary>
+internal static class CsvSanitizer
+{
+    /// <summary>
+    /// Escapes a value for inclusion in a CSV row. Always wraps in double
+    /// quotes. Doubles internal quotes per RFC 4180. Prepends an apostrophe
+    /// when the value begins with a character a spreadsheet would evaluate.
+    /// </summary>
+    public static string Escape(string? value)
+    {
+        if (string.IsNullOrEmpty(value)) return "\"\"";
+        var safe = NeutralizeFormulaPrefix(value).Replace("\"", "\"\"");
+        return $"\"{safe}\"";
+    }
+
+    /// <summary>
+    /// Minimal quoting variant: only wraps in quotes when the value contains
+    /// a delimiter, quote, or newline. Still guards against formula injection.
+    /// </summary>
+    public static string EscapeMinimal(string? value)
+    {
+        if (string.IsNullOrEmpty(value)) return string.Empty;
+        var safe = NeutralizeFormulaPrefix(value);
+        if (safe.Contains(',') || safe.Contains('"') || safe.Contains('\n') || safe.Contains('\r'))
+            return $"\"{safe.Replace("\"", "\"\"")}\"";
+        return safe;
+    }
+
+    private static string NeutralizeFormulaPrefix(string value)
+    {
+        if (value.Length == 0) return value;
+        char first = value[0];
+        if (first == '=' || first == '+' || first == '-' || first == '@'
+            || first == '\t' || first == '\r')
+        {
+            return "'" + value;
+        }
+        return value;
+    }
+}

Services/Export/DuplicatesCsvExportService.cs

@@ -0,0 +1,112 @@
+using System.IO;
+using System.Text;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports DuplicateGroup list to CSV. Each duplicate item becomes one row;
+/// the Group column ties copies together and a Copies column gives the group size.
+/// Header row is built at write-time so culture switches are honoured.
+/// </summary>
+public class DuplicatesCsvExportService
+{
+    /// <summary>Writes the CSV to <paramref name="filePath"/> with UTF-8 BOM (Excel-compatible).</summary>
+    public async Task WriteAsync(
+        IReadOnlyList<DuplicateGroup> groups,
+        string filePath,
+        CancellationToken ct)
+    {
+        var csv = BuildCsv(groups);
+        await ExportFileWriter.WriteCsvAsync(filePath, csv, ct);
+    }
+
+    /// <summary>
+    /// Writes one or more CSVs depending on <paramref name="splitMode"/>.
+    /// Single → <paramref name="basePath"/> as-is. BySite → one file per site,
+    /// filenames derived from <paramref name="basePath"/> with a site suffix.
+    /// </summary>
+    public Task WriteAsync(
+        IReadOnlyList<DuplicateGroup> groups,
+        string basePath,
+        ReportSplitMode splitMode,
+        CancellationToken ct)
+        => ReportSplitHelper.WritePartitionedAsync(
+            groups, basePath, splitMode,
+            PartitionBySite,
+            (part, path, c) => WriteAsync(part, path, c),
+            ct);
+
+    internal static IEnumerable<(string Label, IReadOnlyList<DuplicateGroup> Partition)> PartitionBySite(
+        IReadOnlyList<DuplicateGroup> groups)
+    {
+        return groups
+            .GroupBy(g =>
+            {
+                var first = g.Items.FirstOrDefault();
+                return (Url: first?.SiteUrl ?? string.Empty, Title: first?.SiteTitle ?? string.Empty);
+            })
+            .Select(g => (
+                Label: ReportSplitHelper.DeriveSiteLabel(g.Key.Url, g.Key.Title),
+                Partition: (IReadOnlyList<DuplicateGroup>)g.ToList()));
+    }
+
+    /// <summary>
+    /// Builds the CSV payload. Emits a header summary (group count, generated
+    /// timestamp), then one row per duplicate item with its group index and
+    /// group size. CSV fields are escaped via <see cref="CsvSanitizer.Escape"/>.
+    /// </summary>
+    public string BuildCsv(IReadOnlyList<DuplicateGroup> groups)
+    {
+        var T = TranslationSource.Instance;
+        var sb = new StringBuilder();
+
+        // Summary
+        sb.AppendLine($"\"{T["report.title.duplicates_short"]}\"");
+        sb.AppendLine($"\"{T["report.text.duplicate_groups_found"]}\",\"{groups.Count}\"");
+        sb.AppendLine($"\"{T["report.text.generated"]}\",\"{DateTime.Now:yyyy-MM-dd HH:mm:ss}\"");
+        sb.AppendLine();
+
+        // Header
+        sb.AppendLine(string.Join(",", new[]
+        {
+            Csv(T["report.col.number"]),
+            Csv(T["report.col.group"]),
+            Csv(T["report.text.copies"]),
+            Csv(T["report.col.site"]),
+            Csv(T["report.col.name"]),
+            Csv(T["report.col.library"]),
+            Csv(T["report.col.path"]),
+            Csv(T["report.col.size_bytes"]),
+            Csv(T["report.col.created"]),
+            Csv(T["report.col.modified"]),
+        }));
+
+        foreach (var g in groups)
+        {
+            int i = 0;
+            foreach (var item in g.Items)
+            {
+                i++;
+                sb.AppendLine(string.Join(",", new[]
+                {
+                    Csv(i.ToString()),
+                    Csv(g.Name),
+                    Csv(g.Items.Count.ToString()),
+                    Csv(item.SiteTitle),
+                    Csv(item.Name),
+                    Csv(item.Library),
+                    Csv(item.Path),
+                    Csv(item.SizeBytes?.ToString() ?? string.Empty),
+                    Csv(item.Created?.ToString("yyyy-MM-dd") ?? string.Empty),
+                    Csv(item.Modified?.ToString("yyyy-MM-dd") ?? string.Empty),
+                }));
+            }
+        }
+
+        return sb.ToString();
+    }
+
+    private static string Csv(string value) => CsvSanitizer.Escape(value);
+}

Services/Export/DuplicatesHtmlExportService.cs

@@ -0,0 +1,187 @@
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+using System.Text;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports DuplicateGroup list to a self-contained HTML with collapsible group cards.
+/// Port of PS Export-DuplicatesToHTML (PS lines 2235-2406).
+/// Each group gets a card showing item count badge and a table of paths.
+/// </summary>
+public class DuplicatesHtmlExportService
+{
+    /// <summary>
+    /// Builds a self-contained HTML string rendering one collapsible card per
+    /// <see cref="DuplicateGroup"/>. The document ships with inline CSS and a
+    /// tiny JS toggle so no external assets are needed.
+    /// </summary>
+    public string BuildHtml(IReadOnlyList<DuplicateGroup> groups, ReportBranding? branding = null)
+    {
+        var T = TranslationSource.Instance;
+        var sb = new StringBuilder();
+
+        sb.AppendLine("<!DOCTYPE html>");
+        sb.AppendLine("<html lang=\"en\">");
+        sb.AppendLine("<head>");
+        sb.AppendLine("<meta charset=\"UTF-8\">");
+        sb.AppendLine("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">");
+        sb.AppendLine($"<title>{T["report.title.duplicates"]}</title>");
+        sb.AppendLine("""
+            <style>
+              body { font-family: 'Segoe UI', Arial, sans-serif; font-size: 13px; margin: 20px; background: #f5f5f5; }
+              h1 { color: #0078d4; }
+              .summary { margin-bottom: 16px; font-size: 12px; color: #444; }
+              .group-card { background: #fff; border: 1px solid #ddd; border-radius: 6px;
+                            margin-bottom: 12px; box-shadow: 0 1px 3px rgba(0,0,0,.1); overflow: hidden; }
+              .group-header { background: #0078d4; color: #fff; padding: 8px 14px;
+                              display: flex; align-items: center; justify-content: space-between;
+                              cursor: pointer; user-select: none; }
+              .group-header:hover { background: #106ebe; }
+              .group-name { font-weight: 600; font-size: 14px; }
+              .badge { display: inline-block; padding: 2px 8px; border-radius: 10px;
+                       font-size: 11px; font-weight: 700; }
+              .badge-dup  { background: #e53935; color: #fff; }
+              .group-body { padding: 0; }
+              table { width: 100%; border-collapse: collapse; }
+              th { background: #f0f7ff; color: #333; padding: 6px 12px; text-align: left;
+                   font-weight: 600; border-bottom: 1px solid #ddd; font-size: 12px; }
+              td { padding: 5px 12px; border-bottom: 1px solid #eee; font-size: 12px; word-break: break-all; }
+              tr:last-child td { border-bottom: none; }
+              .collapsed { display: none; }
+              .generated { font-size: 11px; color: #888; margin-top: 16px; }
+            </style>
+            <script>
+              function toggleGroup(id) {
+                var body = document.getElementById('gb-' + id);
+                if (body) body.classList.toggle('collapsed');
+              }
+            </script>
+            </head>
+            <body>
+            """);
+        sb.Append(BrandingHtmlHelper.BuildBrandingHeader(branding));
+        sb.AppendLine($"<h1>{T["report.title.duplicates_short"]}</h1>");
+
+        sb.AppendLine($"<p class=\"summary\">{groups.Count:N0} {T["report.text.duplicate_groups_found"]}</p>");
+
+        for (int i = 0; i < groups.Count; i++)
+        {
+            var g = groups[i];
+            int count = g.Items.Count;
+            string badgeClass = "badge-dup";
+
+            sb.AppendLine($"""
+                <div class="group-card">
+                  <div class="group-header" onclick="toggleGroup({i})">
+                    <span class="group-name">{H(g.Name)}</span>
+                    <span class="badge {badgeClass}">{count} {T["report.text.copies"]}</span>
+                  </div>
+                  <div class="group-body" id="gb-{i}">
+                    <table>
+                      <thead>
+                        <tr>
+                          <th>{T["report.col.number"]}</th>
+                          <th>{T["report.col.name"]}</th>
+                          <th>{T["report.col.library"]}</th>
+                          <th>{T["report.col.path"]}</th>
+                          <th>{T["report.col.size"]}</th>
+                          <th>{T["report.col.created"]}</th>
+                          <th>{T["report.col.modified"]}</th>
+                        </tr>
+                      </thead>
+                      <tbody>
+                """);
+
+            for (int j = 0; j < g.Items.Count; j++)
+            {
+                var item = g.Items[j];
+                string size     = item.SizeBytes.HasValue ? FormatSize(item.SizeBytes.Value) : string.Empty;
+                string created  = item.Created.HasValue  ? item.Created.Value.ToString("yyyy-MM-dd")  : string.Empty;
+                string modified = item.Modified.HasValue ? item.Modified.Value.ToString("yyyy-MM-dd") : string.Empty;
+
+                sb.AppendLine($"""
+                          <tr>
+                            <td>{j + 1}</td>
+                            <td>{H(item.Name)}</td>
+                            <td>{H(item.Library)}</td>
+                            <td><a href="{H(item.Path)}" target="_blank">{H(item.Path)}</a></td>
+                            <td>{size}</td>
+                            <td>{created}</td>
+                            <td>{modified}</td>
+                          </tr>
+                    """);
+            }
+
+            sb.AppendLine("""
+                      </tbody>
+                    </table>
+                  </div>
+                </div>
+                """);
+        }
+
+        sb.AppendLine($"<p class=\"generated\">{T["report.text.generated_colon"]} {DateTime.Now:yyyy-MM-dd HH:mm}</p>");
+        sb.AppendLine("</body></html>");
+
+        return sb.ToString();
+    }
+
+    /// <summary>Writes the HTML report to the specified file path using UTF-8.</summary>
+    public async Task WriteAsync(IReadOnlyList<DuplicateGroup> groups, string filePath, CancellationToken ct, ReportBranding? branding = null)
+    {
+        var html = BuildHtml(groups, branding);
+        await System.IO.File.WriteAllTextAsync(filePath, html, Encoding.UTF8, ct);
+    }
+
+    /// <summary>
+    /// Writes one or more HTML reports depending on <paramref name="splitMode"/> and
+    /// <paramref name="layout"/>. Single → one file. BySite + SeparateFiles → one
+    /// file per site. BySite + SingleTabbed → one file with per-site iframe tabs.
+    /// </summary>
+    public async Task WriteAsync(
+        IReadOnlyList<DuplicateGroup> groups,
+        string basePath,
+        ReportSplitMode splitMode,
+        HtmlSplitLayout layout,
+        CancellationToken ct,
+        ReportBranding? branding = null)
+    {
+        if (splitMode != ReportSplitMode.BySite)
+        {
+            await WriteAsync(groups, basePath, ct, branding);
+            return;
+        }
+
+        var partitions = DuplicatesCsvExportService.PartitionBySite(groups).ToList();
+
+        if (layout == HtmlSplitLayout.SingleTabbed)
+        {
+            var parts = partitions
+                .Select(p => (p.Label, Html: BuildHtml(p.Partition, branding)))
+                .ToList();
+            var T = TranslationSource.Instance;
+            var tabbed = ReportSplitHelper.BuildTabbedHtml(parts, T["report.title.duplicates_short"]);
+            await System.IO.File.WriteAllTextAsync(basePath, tabbed, Encoding.UTF8, ct);
+            return;
+        }
+
+        foreach (var partition in partitions)
+        {
+            ct.ThrowIfCancellationRequested();
+            var path = ReportSplitHelper.BuildPartitionPath(basePath, partition.Label);
+            await WriteAsync(partition.Partition, path, ct, branding);
+        }
+    }
+
+    private static string H(string value) =>
+        System.Net.WebUtility.HtmlEncode(value ?? string.Empty);
+
+    private static string FormatSize(long bytes)
+    {
+        if (bytes >= 1_073_741_824L) return $"{bytes / 1_073_741_824.0:F2} GB";
+        if (bytes >= 1_048_576L)     return $"{bytes / 1_048_576.0:F2} MB";
+        if (bytes >= 1024L)          return $"{bytes / 1024.0:F2} KB";
+        return $"{bytes} B";
+    }
+}

Services/Export/ExportFileWriter.cs

@@ -0,0 +1,64 @@
+using System.IO;
+using System.Text;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Central file-write plumbing for export services so every CSV and HTML
+/// artefact gets a consistent encoding: CSV files are written with a UTF-8
+/// BOM (required for Excel to detect the encoding when opening a
+/// double-clicked .csv), HTML files are written without a BOM (some browsers
+/// and iframe <c>srcdoc</c> paths render the BOM as a visible character).
+/// Export services should call these helpers rather than constructing
+/// <see cref="UTF8Encoding"/> inline.
+/// </summary>
+internal static class ExportFileWriter
+{
+    private static readonly UTF8Encoding Utf8WithBom = new(encoderShouldEmitUTF8Identifier: true);
+    private static readonly UTF8Encoding Utf8NoBom   = new(encoderShouldEmitUTF8Identifier: false);
+
+    /// <summary>Writes <paramref name="csv"/> to <paramref name="filePath"/> as UTF-8 with BOM.</summary>
+    public static Task WriteCsvAsync(string filePath, string csv, CancellationToken ct)
+        => File.WriteAllTextAsync(filePath, csv, Utf8WithBom, ct);
+
+    /// <summary>Writes <paramref name="html"/> to <paramref name="filePath"/> as UTF-8 without BOM.</summary>
+    public static Task WriteHtmlAsync(string filePath, string html, CancellationToken ct)
+        => File.WriteAllTextAsync(filePath, html, Utf8NoBom, ct);
+
+    /// <summary>
+    /// Streams a <see cref="StringBuilder"/> directly to disk as UTF-8 with
+    /// BOM, chunk by chunk. Avoids the full-document <c>ToString()</c> copy
+    /// and the separate UTF-8 byte buffer that <see cref="File.WriteAllTextAsync(string, string, Encoding, CancellationToken)"/>
+    /// would otherwise allocate — meaningful for large CSV exports.
+    /// </summary>
+    public static Task WriteCsvChunksAsync(string filePath, StringBuilder builder, CancellationToken ct)
+        => WriteChunksAsync(filePath, builder, Utf8WithBom, ct);
+
+    /// <summary>
+    /// Streams a <see cref="StringBuilder"/> directly to disk as UTF-8 without
+    /// BOM. Same rationale as <see cref="WriteCsvChunksAsync"/> — for large
+    /// HTML reports it halves peak memory by skipping the intermediate string.
+    /// </summary>
+    public static Task WriteHtmlChunksAsync(string filePath, StringBuilder builder, CancellationToken ct)
+        => WriteChunksAsync(filePath, builder, Utf8NoBom, ct);
+
+    private static async Task WriteChunksAsync(string filePath, StringBuilder builder, Encoding encoding, CancellationToken ct)
+    {
+        // FileOptions.Asynchronous lets StreamWriter use true async I/O.
+        await using var fs = new FileStream(
+            filePath,
+            FileMode.Create,
+            FileAccess.Write,
+            FileShare.None,
+            bufferSize: 64 * 1024,
+            options: FileOptions.Asynchronous | FileOptions.SequentialScan);
+        await using var sw = new StreamWriter(fs, encoding, bufferSize: 64 * 1024);
+
+        foreach (var chunk in builder.GetChunks())
+        {
+            ct.ThrowIfCancellationRequested();
+            await sw.WriteAsync(chunk, ct);
+        }
+        await sw.FlushAsync(ct);
+    }
+}

Services/Export/HtmlExportService.cs

@@ -0,0 +1,314 @@
+using System.IO;
+using System.Text;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+using static SharepointToolbox.Web.Services.Export.PermissionHtmlFragments;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports permission entries to a self-contained interactive HTML report.
+/// Ports PowerShell <c>Export-PermissionsToHTML</c> functionality.
+/// No external CSS/JS dependencies — everything is inline so the file can be
+/// emailed or served from any static host. The standard and simplified
+/// variants share their document shell, stats cards, CSS, pill rendering, and
+/// inline script via <see cref="PermissionHtmlFragments"/>; this class only
+/// owns the table column sets and the simplified risk summary.
+/// </summary>
+public class HtmlExportService
+{
+    /// <summary>
+    /// Builds a self-contained HTML string from the supplied permission
+    /// entries. Standard report: columns are Object / Title / URL / Unique /
+    /// Users / Permission / Granted Through. When
+    /// <paramref name="groupMembers"/> is provided, SharePoint group pills
+    /// become expandable rows listing resolved members.
+    /// </summary>
+    public string BuildHtml(
+        IReadOnlyList<PermissionEntry> entries,
+        ReportBranding? branding = null,
+        IReadOnlyDictionary<string, IReadOnlyList<ResolvedMember>>? groupMembers = null,
+        bool hideSystemGroupRaw = false)
+    {
+        var T = TranslationSource.Instance;
+        var (totalEntries, uniquePermSets, distinctUsers) = ComputeStats(
+            entries.Count,
+            entries.Select(e => e.PermissionLevels),
+            entries.SelectMany(e => e.UserLogins.Split(';', StringSplitOptions.RemoveEmptyEntries)));
+
+        var sb = new StringBuilder();
+        AppendHead(sb, T["report.title.permissions"], includeRiskCss: false);
+        sb.AppendLine("<body>");
+        sb.Append(BrandingHtmlHelper.BuildBrandingHeader(branding));
+        sb.AppendLine($"<h1>{T["report.title.permissions"]}</h1>");
+        AppendStatsCards(sb, totalEntries, uniquePermSets, distinctUsers);
+        AppendFilterInput(sb);
+        AppendTableOpen(sb);
+        sb.AppendLine("<thead><tr>");
+        sb.AppendLine($"  <th>{T["report.col.object"]}</th><th>{T["report.col.title"]}</th><th>{T["report.col.url"]}</th><th>{T["report.badge.unique"]}</th><th>{T["report.col.users_groups"]}</th><th>{T["report.col.permission_level"]}</th><th>{T["report.col.granted_through"]}</th>");
+        sb.AppendLine("</tr></thead>");
+        sb.AppendLine("<tbody>");
+
+        int grpMemIdx = 0;
+        foreach (var entry in entries)
+        {
+            var typeCss   = ObjectTypeCss(entry.ObjectType);
+            var uniqueCss = entry.HasUniquePermissions ? "badge unique" : "badge inherited";
+            var uniqueLbl = entry.HasUniquePermissions ? T["report.badge.unique"] : T["report.badge.inherited"];
+
+            var (pills, subRows) = BuildUserPillsCell(
+                entry.UserLogins, entry.Users, entry.PrincipalType, groupMembers,
+                colSpan: 7, grpMemIdx: ref grpMemIdx,
+                targetLabel: entry.TargetLabel, sharingLinkType: entry.SharingLinkType,
+                hideSystemGroupRaw: hideSystemGroupRaw);
+
+            sb.AppendLine("<tr>");
+            sb.AppendLine($"  <td><span class=\"{typeCss}\">{HtmlEncode(entry.ObjectType)}</span></td>");
+            sb.AppendLine($"  <td>{HtmlEncode(entry.Title)}</td>");
+            sb.AppendLine($"  <td><a href=\"{HtmlEncode(entry.Url)}\" target=\"_blank\">{T["report.text.link"]}</a></td>");
+            sb.AppendLine($"  <td><span class=\"{uniqueCss}\">{uniqueLbl}</span></td>");
+            sb.AppendLine($"  <td>{pills}</td>");
+            sb.AppendLine($"  <td>{HtmlEncode(entry.PermissionLevels)}</td>");
+            sb.AppendLine($"  <td>{BuildGrantedThroughCell(entry.GrantedThrough, entry.TargetUrl, entry.TargetLabel, entry.SharingLinkType, hideSystemGroupRaw)}</td>");
+            sb.AppendLine("</tr>");
+            if (subRows.Length > 0) sb.Append(subRows);
+        }
+
+        AppendTableClose(sb);
+        AppendInlineJs(sb);
+        sb.AppendLine("</body>");
+        sb.AppendLine("</html>");
+        return sb.ToString();
+    }
+
+    /// <summary>
+    /// Builds a self-contained HTML string from simplified permission entries.
+    /// Adds a risk-level summary card strip plus two columns (Simplified,
+    /// Risk) relative to <see cref="BuildHtml(IReadOnlyList{PermissionEntry}, ReportBranding?, IReadOnlyDictionary{string, IReadOnlyList{ResolvedMember}}?)"/>.
+    /// Color-coded risk badges use <see cref="RiskLevelColors(RiskLevel)"/>.
+    /// </summary>
+    public string BuildHtml(
+        IReadOnlyList<SimplifiedPermissionEntry> entries,
+        ReportBranding? branding = null,
+        IReadOnlyDictionary<string, IReadOnlyList<ResolvedMember>>? groupMembers = null,
+        bool hideSystemGroupRaw = false)
+    {
+        var T = TranslationSource.Instance;
+        var summaries = PermissionSummaryBuilder.Build(entries);
+        var (totalEntries, uniquePermSets, distinctUsers) = ComputeStats(
+            entries.Count,
+            entries.Select(e => e.PermissionLevels),
+            entries.SelectMany(e => e.UserLogins.Split(';', StringSplitOptions.RemoveEmptyEntries)));
+
+        var sb = new StringBuilder();
+        AppendHead(sb, T["report.title.permissions_simplified"], includeRiskCss: true);
+        sb.AppendLine("<body>");
+        sb.Append(BrandingHtmlHelper.BuildBrandingHeader(branding));
+        sb.AppendLine($"<h1>{T["report.title.permissions_simplified"]}</h1>");
+        AppendStatsCards(sb, totalEntries, uniquePermSets, distinctUsers);
+
+        sb.AppendLine("<div class=\"risk-cards\">");
+        foreach (var s in summaries)
+        {
+            var (bg, text, border) = RiskLevelColors(s.RiskLevel);
+            sb.AppendLine($"  <div class=\"risk-card\" style=\"background:{bg};color:{text};border-color:{border}\">");
+            sb.AppendLine($"    <div class=\"count\">{s.Count}</div>");
+            sb.AppendLine($"    <div class=\"rlabel\">{HtmlEncode(s.Label)}</div>");
+            sb.AppendLine($"    <div class=\"users\">{s.DistinctUsers} {T["report.text.users_parens"]}</div>");
+            sb.AppendLine("  </div>");
+        }
+        sb.AppendLine("</div>");
+
+        AppendFilterInput(sb);
+        AppendTableOpen(sb);
+        sb.AppendLine("<thead><tr>");
+        sb.AppendLine($"  <th>{T["report.col.users_groups"]}</th><th>{T["report.col.permission_level"]}</th><th>{T["report.col.simplified"]}</th><th>{T["report.col.risk"]}</th><th>{T["report.col.granted_through"]}</th>");
+        sb.AppendLine("</tr></thead>");
+        sb.AppendLine("<tbody>");
+
+        int grpMemIdx = 0;
+        int sectionIdx = 0;
+        var groups = entries.GroupBy(e => (e.ObjectType, e.Title, e.Url)).ToList();
+        foreach (var group in groups)
+        {
+            var sectionId = $"sec{sectionIdx++}";
+            var first     = group.First();
+            var typeCss   = ObjectTypeCss(group.Key.ObjectType);
+            var uniqueCss = first.HasUniquePermissions ? "badge unique" : "badge inherited";
+            var uniqueLbl = first.HasUniquePermissions ? T["report.badge.unique"] : T["report.badge.inherited"];
+            var count     = group.Count();
+
+            sb.AppendLine($"<tr class=\"section-header collapsed\" data-section=\"{sectionId}\">");
+            sb.AppendLine($"  <td colspan=\"5\"><span class=\"chevron\">&#9660;</span><span class=\"{typeCss}\">{HtmlEncode(group.Key.ObjectType)}</span> <strong>{HtmlEncode(group.Key.Title)}</strong> <a href=\"{HtmlEncode(group.Key.Url)}\" target=\"_blank\">&#8599;</a> <span class=\"{uniqueCss}\">{uniqueLbl}</span><span class=\"entry-badge\">{count} {T["report.text.entries_unit"]}</span></td>");
+            sb.AppendLine("</tr>");
+
+            foreach (var entry in group)
+            {
+                var (riskBg, riskText, riskBorder) = RiskLevelColors(entry.RiskLevel);
+
+                var (pills, subRows) = BuildUserPillsCell(
+                    entry.UserLogins, entry.Inner.Users, entry.Inner.PrincipalType, groupMembers,
+                    colSpan: 5, grpMemIdx: ref grpMemIdx,
+                    targetLabel: entry.TargetLabel, sharingLinkType: entry.SharingLinkType,
+                    hideSystemGroupRaw: hideSystemGroupRaw,
+                    sectionId: sectionId);
+
+                sb.AppendLine($"<tr data-section-member=\"{sectionId}\" style=\"display:none\">");
+                sb.AppendLine($"  <td>{pills}</td>");
+                sb.AppendLine($"  <td>{HtmlEncode(entry.PermissionLevels)}</td>");
+                sb.AppendLine($"  <td>{HtmlEncode(entry.SimplifiedLabels)}</td>");
+                sb.AppendLine($"  <td><span class=\"risk-badge\" style=\"background:{riskBg};color:{riskText};border-color:{riskBorder}\">{HtmlEncode(entry.RiskLevel.ToString())}</span></td>");
+                sb.AppendLine($"  <td>{BuildGrantedThroughCell(entry.GrantedThrough, entry.TargetUrl, entry.TargetLabel, entry.SharingLinkType, hideSystemGroupRaw)}</td>");
+                sb.AppendLine("</tr>");
+                if (subRows.Length > 0) sb.Append(subRows);
+            }
+        }
+
+        AppendTableClose(sb);
+        AppendInlineJs(sb);
+        sb.AppendLine("</body>");
+        sb.AppendLine("</html>");
+        return sb.ToString();
+    }
+
+    /// <summary>Writes the HTML report to the specified file path using UTF-8 without BOM.</summary>
+    public async Task WriteAsync(
+        IReadOnlyList<PermissionEntry> entries,
+        string filePath,
+        CancellationToken ct,
+        ReportBranding? branding = null,
+        IReadOnlyDictionary<string, IReadOnlyList<ResolvedMember>>? groupMembers = null,
+        bool hideSystemGroupRaw = false)
+    {
+        var html = BuildHtml(entries, branding, groupMembers, hideSystemGroupRaw);
+        await ExportFileWriter.WriteHtmlAsync(filePath, html, ct);
+    }
+
+    /// <summary>Writes the simplified HTML report to the specified file path using UTF-8 without BOM.</summary>
+    public async Task WriteAsync(
+        IReadOnlyList<SimplifiedPermissionEntry> entries,
+        string filePath,
+        CancellationToken ct,
+        ReportBranding? branding = null,
+        IReadOnlyDictionary<string, IReadOnlyList<ResolvedMember>>? groupMembers = null,
+        bool hideSystemGroupRaw = false)
+    {
+        var html = BuildHtml(entries, branding, groupMembers, hideSystemGroupRaw);
+        await ExportFileWriter.WriteHtmlAsync(filePath, html, ct);
+    }
+
+    /// <summary>
+    /// Split-aware write for permission entries.
+    /// Single → one file. BySite + SeparateFiles → one file per site.
+    /// BySite + SingleTabbed → one file with per-site iframe tabs.
+    /// </summary>
+    public async Task WriteAsync(
+        IReadOnlyList<PermissionEntry> entries,
+        string basePath,
+        ReportSplitMode splitMode,
+        HtmlSplitLayout layout,
+        CancellationToken ct,
+        ReportBranding? branding = null,
+        IReadOnlyDictionary<string, IReadOnlyList<ResolvedMember>>? groupMembers = null,
+        bool hideSystemGroupRaw = false)
+    {
+        if (splitMode != ReportSplitMode.BySite)
+        {
+            await WriteAsync(entries, basePath, ct, branding, groupMembers, hideSystemGroupRaw);
+            return;
+        }
+
+        var partitions = CsvExportService.PartitionBySite(entries).ToList();
+        if (layout == HtmlSplitLayout.SingleTabbed)
+        {
+            var parts = partitions
+                .Select(p => (p.Label, Html: BuildHtml(p.Partition, branding, groupMembers, hideSystemGroupRaw)))
+                .ToList();
+            var title = TranslationSource.Instance["report.title.permissions"];
+            var tabbed = ReportSplitHelper.BuildTabbedHtml(parts, title);
+            await ExportFileWriter.WriteHtmlAsync(basePath, tabbed, ct);
+            return;
+        }
+
+        foreach (var (label, partEntries) in partitions)
+        {
+            ct.ThrowIfCancellationRequested();
+            var path = ReportSplitHelper.BuildPartitionPath(basePath, label);
+            await WriteAsync(partEntries, path, ct, branding, groupMembers, hideSystemGroupRaw);
+        }
+    }
+
+    /// <summary>Simplified-entry split variant.</summary>
+    public async Task WriteAsync(
+        IReadOnlyList<SimplifiedPermissionEntry> entries,
+        string basePath,
+        ReportSplitMode splitMode,
+        HtmlSplitLayout layout,
+        CancellationToken ct,
+        ReportBranding? branding = null,
+        IReadOnlyDictionary<string, IReadOnlyList<ResolvedMember>>? groupMembers = null,
+        bool hideSystemGroupRaw = false)
+    {
+        if (splitMode != ReportSplitMode.BySite)
+        {
+            await WriteAsync(entries, basePath, ct, branding, groupMembers, hideSystemGroupRaw);
+            return;
+        }
+
+        var partitions = CsvExportService.PartitionBySite(entries).ToList();
+        if (layout == HtmlSplitLayout.SingleTabbed)
+        {
+            var parts = partitions
+                .Select(p => (p.Label, Html: BuildHtml(p.Partition, branding, groupMembers, hideSystemGroupRaw)))
+                .ToList();
+            var title = TranslationSource.Instance["report.title.permissions_simplified"];
+            var tabbed = ReportSplitHelper.BuildTabbedHtml(parts, title);
+            await ExportFileWriter.WriteHtmlAsync(basePath, tabbed, ct);
+            return;
+        }
+
+        foreach (var (label, partEntries) in partitions)
+        {
+            ct.ThrowIfCancellationRequested();
+            var path = ReportSplitHelper.BuildPartitionPath(basePath, label);
+            await WriteAsync(partEntries, path, ct, branding, groupMembers, hideSystemGroupRaw);
+        }
+    }
+
+    private static (int total, int uniquePerms, int distinctUsers) ComputeStats(
+        int totalEntries,
+        IEnumerable<string> permissionLevels,
+        IEnumerable<string> userLogins)
+    {
+        var uniquePermSets = permissionLevels.Distinct().Count();
+        var distinctUsers = userLogins
+            .Select(u => u.Trim())
+            .Where(u => u.Length > 0)
+            .Distinct()
+            .Count();
+        return (totalEntries, uniquePermSets, distinctUsers);
+    }
+
+    private static void AppendTableOpen(StringBuilder sb)
+    {
+        sb.AppendLine("<div class=\"table-wrap\">");
+        sb.AppendLine("<table id=\"permTable\">");
+    }
+
+    private static void AppendTableClose(StringBuilder sb)
+    {
+        sb.AppendLine("</tbody>");
+        sb.AppendLine("</table>");
+        sb.AppendLine("</div>");
+    }
+
+    /// <summary>Returns inline CSS background, text, and border colors for a risk level.</summary>
+    private static (string bg, string text, string border) RiskLevelColors(RiskLevel level) => level switch
+    {
+        RiskLevel.High     => ("#FEE2E2", "#991B1B", "#FECACA"),
+        RiskLevel.Medium   => ("#FEF3C7", "#92400E", "#FDE68A"),
+        RiskLevel.Low      => ("#D1FAE5", "#065F46", "#A7F3D0"),
+        RiskLevel.ReadOnly => ("#DBEAFE", "#1E40AF", "#BFDBFE"),
+        _                  => ("#F3F4F6", "#374151", "#E5E7EB")
+    };
+}

Services/Export/PermissionHtmlFragments.cs

@@ -0,0 +1,378 @@
+using System.Text;
+using SharepointToolbox.Web.Core.Helpers;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Shared HTML-rendering fragments for the permission exports (standard and
+/// simplified). Extracted so the two <see cref="HtmlExportService"/> variants
+/// share the document shell, stats cards, filter input, user-pill logic, and
+/// inline script — leaving each caller only its own table headers and row
+/// cells to render.
+/// </summary>
+internal static class PermissionHtmlFragments
+{
+    internal const string BaseCss = @"
+* { box-sizing: border-box; margin: 0; padding: 0; }
+body { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; background: #f5f5f5; color: #333; }
+h1 { padding: 20px 24px 10px; font-size: 1.5rem; color: #1a1a2e; }
+.stats { display: flex; gap: 16px; padding: 0 24px 16px; flex-wrap: wrap; }
+.stat-card { background: #fff; border-radius: 8px; padding: 14px 20px; min-width: 160px; box-shadow: 0 1px 4px rgba(0,0,0,.1); }
+.stat-card .value { font-size: 2rem; font-weight: 700; color: #1a1a2e; }
+.stat-card .label { font-size: .8rem; color: #666; margin-top: 2px; }
+.filter-wrap { padding: 0 24px 12px; }
+#filter { width: 320px; padding: 8px 12px; border: 1px solid #ccc; border-radius: 6px; font-size: .95rem; }
+.table-wrap { overflow-x: auto; padding: 0 24px 32px; }
+table { width: 100%; border-collapse: collapse; background: #fff; border-radius: 8px; overflow: hidden; box-shadow: 0 1px 4px rgba(0,0,0,.1); }
+th { background: #1a1a2e; color: #fff; padding: 10px 14px; text-align: left; font-size: .85rem; white-space: nowrap; }
+td { padding: 9px 14px; border-bottom: 1px solid #eee; vertical-align: top; font-size: .875rem; }
+tr:last-child td { border-bottom: none; }
+tr:hover td { background: #fafafa; }
+.badge { display: inline-block; padding: 2px 8px; border-radius: 4px; font-size: .75rem; font-weight: 600; white-space: nowrap; }
+.badge.site-coll { background: #dbeafe; color: #1e40af; }
+.badge.site      { background: #dcfce7; color: #166534; }
+.badge.list      { background: #fef9c3; color: #854d0e; }
+.badge.folder    { background: #f3f4f6; color: #374151; }
+.badge.unique    { background: #dcfce7; color: #166534; }
+.badge.inherited { background: #f3f4f6; color: #374151; }
+.user-pill { display: inline-block; background: #e0e7ff; color: #3730a3; border-radius: 12px; padding: 2px 10px; font-size: .75rem; margin: 2px 3px 2px 0; white-space: nowrap; }
+.user-pill.external-user { background: #fff7ed; color: #9a3412; border: 1px solid #fed7aa; }
+.group-expandable { cursor: pointer; }
+.group-expandable:hover { opacity: 0.8; }
+a { color: #2563eb; text-decoration: none; }
+a:hover { text-decoration: underline; }
+";
+
+    internal const string RiskCardsCss = @"
+.risk-cards { display: flex; gap: 12px; padding: 0 24px 16px; flex-wrap: wrap; }
+.risk-card { border-radius: 8px; padding: 12px 18px; min-width: 140px; border: 1px solid; }
+.risk-card .count { font-size: 1.5rem; font-weight: 700; }
+.risk-card .rlabel { font-size: .8rem; margin-top: 2px; }
+.risk-card .users { font-size: .7rem; margin-top: 2px; opacity: 0.8; }
+.risk-badge { display: inline-block; padding: 2px 8px; border-radius: 4px; font-size: .75rem; font-weight: 600; border: 1px solid; }
+.section-header td { background: #edf2f7; font-weight: 600; cursor: pointer; padding: 8px 14px; border-bottom: 2px solid #cbd5e0; user-select: none; }
+.section-header:hover td { background: #e2e8f0; }
+.section-header .chevron { margin-right: 8px; display: inline-block; transition: transform 0.15s; }
+.section-header.collapsed .chevron { transform: rotate(-90deg); }
+.entry-badge { display: inline-block; background: #e2e8f0; color: #4a5568; border-radius: 10px; padding: 1px 8px; font-size: .75rem; font-weight: 600; margin-left: 8px; }
+";
+
+    internal const string InlineJs = @"function filterTable() {
+  var input = document.getElementById('filter').value.toLowerCase();
+  var sections = document.querySelectorAll('#permTable tbody tr.section-header');
+  if (sections.length === 0) {
+    document.querySelectorAll('#permTable tbody tr').forEach(function(row) {
+      if (row.hasAttribute('data-group')) return;
+      row.style.display = row.textContent.toLowerCase().indexOf(input) > -1 ? '' : 'none';
+    });
+    return;
+  }
+  if (!input) {
+    sections.forEach(function(hdr) {
+      hdr.style.display = '';
+      var sid = hdr.getAttribute('data-section');
+      var collapsed = hdr.classList.contains('collapsed');
+      document.querySelectorAll('[data-section-member=' + sid + ']:not([data-group])').forEach(function(r) {
+        r.style.display = collapsed ? 'none' : '';
+      });
+    });
+    return;
+  }
+  sections.forEach(function(hdr) {
+    var sid = hdr.getAttribute('data-section');
+    var members = document.querySelectorAll('[data-section-member=' + sid + ']:not([data-group])');
+    var anyMatch = false;
+    members.forEach(function(r) {
+      var match = r.textContent.toLowerCase().indexOf(input) > -1;
+      r.style.display = match ? '' : 'none';
+      if (match) anyMatch = true;
+    });
+    if (!anyMatch && hdr.textContent.toLowerCase().indexOf(input) > -1) {
+      anyMatch = true;
+      members.forEach(function(r) { r.style.display = ''; });
+    }
+    hdr.style.display = anyMatch ? '' : 'none';
+  });
+}
+document.addEventListener('click', function(ev) {
+  var hdr = ev.target.closest('.section-header');
+  if (hdr) {
+    var sid = hdr.getAttribute('data-section');
+    hdr.classList.toggle('collapsed');
+    var collapsed = hdr.classList.contains('collapsed');
+    document.querySelectorAll('[data-section-member=' + sid + ']').forEach(function(r) {
+      if (r.hasAttribute('data-group')) { r.style.display = 'none'; return; }
+      r.style.display = collapsed ? 'none' : '';
+    });
+    return;
+  }
+  var trigger = ev.target.closest('.group-expandable');
+  if (!trigger) return;
+  var id = trigger.getAttribute('data-group-target');
+  if (!id) return;
+  document.querySelectorAll('#permTable tbody tr').forEach(function(r) {
+    if (r.getAttribute('data-group') === id) {
+      r.style.display = r.style.display === 'none' ? '' : 'none';
+    }
+  });
+});";
+
+    /// <summary>
+    /// Appends the shared HTML head (doctype, meta, inline CSS, title) to
+    /// <paramref name="sb"/>. Pass <paramref name="includeRiskCss"/> when the
+    /// caller renders risk cards/badges (simplified report only).
+    /// </summary>
+    internal static void AppendHead(StringBuilder sb, string title, bool includeRiskCss)
+    {
+        sb.AppendLine("<!DOCTYPE html>");
+        sb.AppendLine("<html lang=\"en\">");
+        sb.AppendLine("<head>");
+        sb.AppendLine("<meta charset=\"UTF-8\">");
+        sb.AppendLine("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">");
+        sb.AppendLine($"<title>{title}</title>");
+        sb.AppendLine("<style>");
+        sb.AppendLine(BaseCss);
+        if (includeRiskCss)
+            sb.AppendLine(RiskCardsCss);
+        sb.AppendLine("</style>");
+        sb.AppendLine("</head>");
+    }
+
+    /// <summary>
+    /// Appends the three stat cards (total entries, unique permission sets,
+    /// distinct users/groups) inside a single <c>.stats</c> row.
+    /// </summary>
+    internal static void AppendStatsCards(StringBuilder sb, int totalEntries, int uniquePermSets, int distinctUsers)
+    {
+        var T = TranslationSource.Instance;
+        sb.AppendLine("<div class=\"stats\">");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{totalEntries}</div><div class=\"label\">{T["report.stat.total_entries"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{uniquePermSets}</div><div class=\"label\">{T["report.stat.unique_permission_sets"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{distinctUsers}</div><div class=\"label\">{T["report.stat.distinct_users_groups"]}</div></div>");
+        sb.AppendLine("</div>");
+    }
+
+    /// <summary>Appends the live-filter input bound to <c>#permTable</c>.</summary>
+    internal static void AppendFilterInput(StringBuilder sb)
+    {
+        var T = TranslationSource.Instance;
+        sb.AppendLine("<div class=\"filter-wrap\">");
+        sb.AppendLine($"  <input type=\"text\" id=\"filter\" placeholder=\"{T["report.filter.placeholder_permissions"]}\" onkeyup=\"filterTable()\" />");
+        sb.AppendLine("</div>");
+    }
+
+    /// <summary>Appends the inline &lt;script&gt; that powers filter and group toggle.</summary>
+    internal static void AppendInlineJs(StringBuilder sb)
+    {
+        sb.AppendLine("<script>");
+        sb.AppendLine(InlineJs);
+        sb.AppendLine("</script>");
+    }
+
+    /// <summary>
+    /// Renders the user-pill cell content plus any group-member sub-rows for a
+    /// single permission entry. Callers pass their row colspan so sub-rows
+    /// span the full table; <paramref name="grpMemIdx"/> must be mutated
+    /// across rows so sub-row IDs stay unique.
+    /// </summary>
+    internal static (string Pills, string MemberSubRows) BuildUserPillsCell(
+        string userLogins,
+        string userNames,
+        string? principalType,
+        IReadOnlyDictionary<string, IReadOnlyList<ResolvedMember>>? groupMembers,
+        int colSpan,
+        ref int grpMemIdx,
+        string? targetLabel = null,
+        string? sharingLinkType = null,
+        bool hideSystemGroupRaw = false,
+        string? sectionId = null)
+    {
+        var T = TranslationSource.Instance;
+        var logins = userLogins.Split(';', StringSplitOptions.RemoveEmptyEntries);
+        var names  = userNames.Split(';', StringSplitOptions.RemoveEmptyEntries);
+        var pills = new StringBuilder();
+        var subRows = new StringBuilder();
+
+        for (int i = 0; i < logins.Length; i++)
+        {
+            var login = logins[i].Trim();
+            var name  = i < names.Length ? names[i].Trim() : login;
+            var isExt = login.Contains("#EXT#", StringComparison.OrdinalIgnoreCase);
+
+            // When the principal is a resolved system group and the user wants the raw
+            // name hidden, replace the pill's visible text with the link-type badge
+            // (sharing links) and/or the target label. Falls back to the raw name when
+            // resolution failed (no targetLabel).
+            var classification = principalType == "SharePointGroup"
+                ? PermissionEntryHelper.Classify(name)
+                : new SystemGroupClassification(SystemGroupKind.None, null, null, null, null, null);
+            bool isResolvedSystemGroup = hideSystemGroupRaw
+                && classification.Kind != SystemGroupKind.None
+                && classification.Kind != SystemGroupKind.LimitedAccessBare
+                && !string.IsNullOrEmpty(targetLabel);
+
+            bool hasResolvedMembers = principalType == "SharePointGroup"
+                && groupMembers != null
+                && groupMembers.TryGetValue(name, out _);
+
+            if (hasResolvedMembers && groupMembers!.TryGetValue(name, out var resolved))
+            {
+                if (resolved.Count == 0)
+                {
+                    // Members unavailable — render plain pill, skip expandable sub-row.
+                    var cls2 = isResolvedSystemGroup ? "user-pill\" data-system-group=\"1" : "user-pill";
+                    pills.Append($"<span class=\"{cls2}\" title=\"{HtmlEncode(T["report.text.empty_group"])}\" data-email=\"{HtmlEncode(login)}\">");
+                    if (isResolvedSystemGroup)
+                    {
+                        if (!string.IsNullOrEmpty(sharingLinkType))
+                            pills.Append(BuildSharingLinkBadge(sharingLinkType!));
+                        pills.Append(HtmlEncode(targetLabel!));
+                    }
+                    else
+                    {
+                        pills.Append(HtmlEncode(name));
+                    }
+                    pills.Append("</span>");
+                }
+                else
+                {
+                    var grpId = $"grpmem{grpMemIdx}";
+                    pills.Append("<span class=\"user-pill group-expandable\"");
+                    if (isResolvedSystemGroup)
+                        pills.Append(" data-system-group=\"1\"");
+                    pills.Append($" data-group-target=\"{HtmlEncode(grpId)}\" data-email=\"{HtmlEncode(login)}\">");
+                    if (isResolvedSystemGroup)
+                    {
+                        if (!string.IsNullOrEmpty(sharingLinkType))
+                            pills.Append(BuildSharingLinkBadge(sharingLinkType!));
+                        pills.Append(HtmlEncode(targetLabel!));
+                    }
+                    else
+                    {
+                        pills.Append(HtmlEncode(name));
+                    }
+                    pills.Append(" &#9660;</span>");
+
+                    var parts = resolved.Select(m => $"{HtmlEncode(m.DisplayName)} &lt;{HtmlEncode(m.Login)}&gt;");
+                    var memberContent = string.Join(" &bull; ", parts);
+                    var sectionAttr = sectionId != null ? $" data-section-member=\"{HtmlEncode(sectionId)}\"" : "";
+                    subRows.AppendLine($"<tr data-group=\"{HtmlEncode(grpId)}\"{sectionAttr} style=\"display:none\"><td colspan=\"{colSpan}\" style=\"padding-left:2em;font-size:.8rem;color:#555\">{memberContent}</td></tr>");
+                    grpMemIdx++;
+                }
+            }
+            else if (isResolvedSystemGroup)
+            {
+                pills.Append("<span class=\"user-pill\" data-system-group=\"1\">");
+                if (!string.IsNullOrEmpty(sharingLinkType))
+                    pills.Append(BuildSharingLinkBadge(sharingLinkType!));
+                pills.Append(HtmlEncode(targetLabel!));
+                pills.Append("</span>");
+            }
+            else
+            {
+                var cls = isExt ? "user-pill external-user" : "user-pill";
+                pills.Append($"<span class=\"{cls}\" data-email=\"{HtmlEncode(login)}\">{HtmlEncode(name)}</span>");
+            }
+        }
+
+        return (pills.ToString(), subRows.ToString());
+    }
+
+    /// <summary>
+    /// Renders the Granted Through cell. When the entry carries a resolved system-group
+    /// target (Limited Access For Web/List or SharingLinks), a clickable link to the
+    /// targeted resource is appended on a second line. For sharing links the link type
+    /// (OrganizationEdit / AnonymousView / …) is surfaced alongside the target.
+    ///
+    /// When <paramref name="hideSystemGroupRaw"/> is true and a target was resolved, the
+    /// raw "SharePoint Group: SharingLinks.{guid}…" / "Limited Access System Group For
+    /// Web|List {guid}" prefix is suppressed and only the link-type badge + clickable
+    /// target are shown — keeps the report readable without losing information.
+    /// </summary>
+    internal static string BuildGrantedThroughCell(
+        string grantedThrough,
+        string? targetUrl,
+        string? targetLabel,
+        string? sharingLinkType,
+        bool hideSystemGroupRaw = false)
+    {
+        var hasTarget = !string.IsNullOrEmpty(targetUrl) && !string.IsNullOrEmpty(targetLabel);
+        var hasLinkType = !string.IsNullOrEmpty(sharingLinkType);
+        var suppressRaw = hideSystemGroupRaw && hasTarget;
+
+        var sb = new StringBuilder();
+        if (!suppressRaw)
+            sb.Append(HtmlEncode(grantedThrough));
+
+        if (!hasTarget && !hasLinkType)
+            return sb.ToString();
+
+        if (suppressRaw)
+        {
+            // Inline layout — no leading raw text to wrap under.
+            if (hasLinkType)
+                sb.Append(BuildSharingLinkBadge(sharingLinkType!));
+            if (hasTarget)
+            {
+                sb.Append("<a href=\"");
+                sb.Append(HtmlEncode(targetUrl!));
+                sb.Append("\" target=\"_blank\">");
+                sb.Append(HtmlEncode(targetLabel!));
+                sb.Append("</a>");
+            }
+            return sb.ToString();
+        }
+
+        sb.Append("<div style=\"margin-top:4px;font-size:.75rem;color:#555\">");
+        if (hasLinkType)
+            sb.Append(BuildSharingLinkBadge(sharingLinkType!));
+        if (hasTarget)
+        {
+            sb.Append("&rarr; <a href=\"");
+            sb.Append(HtmlEncode(targetUrl!));
+            sb.Append("\" target=\"_blank\">");
+            sb.Append(HtmlEncode(targetLabel!));
+            sb.Append("</a>");
+        }
+        sb.Append("</div>");
+        return sb.ToString();
+    }
+
+    /// <summary>
+    /// Builds the colored badge for a SharePoint sharing-link type. Translates the
+    /// raw <c>linkType</c> code (e.g. <c>OrganizationEdit</c>) into a human label
+    /// (e.g. <c>Org link · Edit</c>) and tints by risk tier; raw code surfaces as a
+    /// <c>title</c> tooltip so operators can still trace it back to the source.
+    /// </summary>
+    internal static string BuildSharingLinkBadge(string rawLinkType)
+    {
+        var (label, risk) = SharingLinkLabels.Describe(rawLinkType);
+        var (bg, fg) = SharingLinkLabels.Colors(risk);
+        return $"<span class=\"badge\" style=\"background:{bg};color:{fg};margin-right:6px\" " +
+               $"title=\"{HtmlEncode(rawLinkType)}\">{HtmlEncode(label)}</span>";
+    }
+
+    /// <summary>Returns the CSS class for the object-type badge.</summary>
+    internal static string ObjectTypeCss(string t) => t switch
+    {
+        "Site Collection" => "badge site-coll",
+        "Site"            => "badge site",
+        "List"            => "badge list",
+        "Folder"          => "badge folder",
+        _                 => "badge"
+    };
+
+    /// <summary>Minimal HTML encoding for text content and attribute values.</summary>
+    internal static string HtmlEncode(string value)
+    {
+        if (string.IsNullOrEmpty(value)) return string.Empty;
+        return value
+            .Replace("&",  "&amp;")
+            .Replace("<",  "&lt;")
+            .Replace(">",  "&gt;")
+            .Replace("\"", "&quot;")
+            .Replace("'",  "&#39;");
+    }
+}

Services/Export/ReportSplitHelper.cs

@@ -0,0 +1,199 @@
+using System.Diagnostics;
+using System.IO;
+using System.Net;
+using System.Text;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Shared helpers for split report exports: filename partitioning, site label
+/// derivation, and bundling per-partition HTML into a single tabbed document.
+/// </summary>
+public static class ReportSplitHelper
+{
+    /// <summary>
+    /// Returns a file-safe variant of <paramref name="name"/>. Invalid filename
+    /// characters are replaced with underscores; whitespace runs are collapsed.
+    /// </summary>
+    public static string SanitizeFileName(string name)
+    {
+        if (string.IsNullOrWhiteSpace(name)) return "part";
+        var invalid = Path.GetInvalidFileNameChars();
+        var sb = new StringBuilder(name.Length);
+        foreach (var c in name)
+            sb.Append(invalid.Contains(c) || c == ' ' ? '_' : c);
+        var trimmed = sb.ToString().Trim('_');
+        if (trimmed.Length > 80) trimmed = trimmed.Substring(0, 80);
+        return trimmed.Length == 0 ? "part" : trimmed;
+    }
+
+    /// <summary>
+    /// Given a user-selected <paramref name="basePath"/> (e.g. "C:\reports\duplicates.csv"),
+    /// returns a partitioned path like "C:\reports\duplicates_{label}.csv".
+    /// </summary>
+    public static string BuildPartitionPath(string basePath, string partitionLabel)
+    {
+        var dir = Path.GetDirectoryName(basePath);
+        var stem = Path.GetFileNameWithoutExtension(basePath);
+        var ext = Path.GetExtension(basePath);
+        var safe = SanitizeFileName(partitionLabel);
+        var file = $"{stem}_{safe}{ext}";
+        return string.IsNullOrEmpty(dir) ? file : Path.Combine(dir, file);
+    }
+
+    /// <summary>
+    /// Extracts the site-collection root URL from an arbitrary SharePoint object URL.
+    /// e.g. https://t.sharepoint.com/sites/hr/Shared%20Documents/foo.docx →
+    ///      https://t.sharepoint.com/sites/hr
+    /// Falls back to scheme+host for root site collections.
+    /// </summary>
+    public static string DeriveSiteCollectionUrl(string objectUrl)
+    {
+        if (string.IsNullOrWhiteSpace(objectUrl)) return string.Empty;
+        if (!Uri.TryCreate(objectUrl, UriKind.Absolute, out var uri))
+            return objectUrl.TrimEnd('/');
+
+        var baseUrl = $"{uri.Scheme}://{uri.Host}";
+        var segments = uri.AbsolutePath.Trim('/').Split('/', StringSplitOptions.RemoveEmptyEntries);
+
+        if (segments.Length >= 2 &&
+            (segments[0].Equals("sites", StringComparison.OrdinalIgnoreCase) ||
+             segments[0].Equals("teams", StringComparison.OrdinalIgnoreCase)))
+        {
+            return $"{baseUrl}/{segments[0]}/{segments[1]}";
+        }
+        return baseUrl;
+    }
+
+    /// <summary>
+    /// Derives a short, human-friendly site label from a SharePoint site URL.
+    /// Falls back to the raw URL (sanitized) when parsing fails.
+    /// </summary>
+    public static string DeriveSiteLabel(string siteUrl, string? siteTitle = null)
+    {
+        if (!string.IsNullOrWhiteSpace(siteTitle)) return siteTitle!;
+        if (string.IsNullOrWhiteSpace(siteUrl)) return "site";
+        try
+        {
+            var uri = new Uri(siteUrl);
+            var segments = uri.AbsolutePath.Trim('/').Split('/', StringSplitOptions.RemoveEmptyEntries);
+            if (segments.Length >= 2 &&
+                (segments[0].Equals("sites", StringComparison.OrdinalIgnoreCase) ||
+                 segments[0].Equals("teams", StringComparison.OrdinalIgnoreCase)))
+            {
+                return segments[1];
+            }
+            return uri.Host;
+        }
+        catch (Exception ex) when (ex is UriFormatException or ArgumentException)
+        {
+            Debug.WriteLine($"[ReportSplitHelper] DeriveSiteLabel: malformed URL '{siteUrl}' ({ex.GetType().Name}: {ex.Message}) — falling back to raw value.");
+            return siteUrl;
+        }
+    }
+
+    /// <summary>
+    /// Generic dispatcher for split-aware export: if
+    /// <paramref name="splitMode"/> is not BySite, writes a single file via
+    /// <paramref name="writer"/>; otherwise partitions via
+    /// <paramref name="partitioner"/> and writes one file per partition,
+    /// each at a filename derived from <paramref name="basePath"/> plus the
+    /// partition label.
+    /// </summary>
+    public static async Task WritePartitionedAsync<T>(
+        IReadOnlyList<T> items,
+        string basePath,
+        ReportSplitMode splitMode,
+        Func<IReadOnlyList<T>, IEnumerable<(string Label, IReadOnlyList<T> Partition)>> partitioner,
+        Func<IReadOnlyList<T>, string, CancellationToken, Task> writer,
+        CancellationToken ct)
+    {
+        if (splitMode != ReportSplitMode.BySite)
+        {
+            await writer(items, basePath, ct);
+            return;
+        }
+
+        foreach (var (label, partition) in partitioner(items))
+        {
+            ct.ThrowIfCancellationRequested();
+            var path = BuildPartitionPath(basePath, label);
+            await writer(partition, path, ct);
+        }
+    }
+
+    /// <summary>
+    /// Bundles per-partition HTML documents into one self-contained tabbed
+    /// HTML. Each partition HTML is embedded in an &lt;iframe srcdoc&gt; so
+    /// their inline styles and scripts remain isolated.
+    /// </summary>
+    public static string BuildTabbedHtml(
+        IReadOnlyList<(string Label, string Html)> parts,
+        string title)
+    {
+        var sb = new StringBuilder();
+        sb.AppendLine("<!DOCTYPE html>");
+        sb.AppendLine("<html lang=\"en\">");
+        sb.AppendLine("<head>");
+        sb.AppendLine("<meta charset=\"UTF-8\">");
+        sb.AppendLine("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">");
+        sb.AppendLine($"<title>{WebUtility.HtmlEncode(title)}</title>");
+        sb.AppendLine("""
+            <style>
+              html, body { margin: 0; padding: 0; height: 100%; font-family: 'Segoe UI', Arial, sans-serif; background: #1a1a2e; }
+              .tabbar { display: flex; flex-wrap: wrap; gap: 4px; background: #1a1a2e; padding: 8px; position: sticky; top: 0; z-index: 10; }
+              .tab { padding: 6px 12px; background: #2d2d4e; color: #fff; cursor: pointer; border-radius: 4px;
+                     font-size: 13px; user-select: none; white-space: nowrap; }
+              .tab:hover { background: #3d3d6e; }
+              .tab.active { background: #0078d4; }
+              .frame-host { background: #f5f5f5; }
+              iframe { width: 100%; height: calc(100vh - 52px); border: 0; display: none; background: #f5f5f5; }
+              iframe.active { display: block; }
+            </style>
+            </head>
+            <body>
+            """);
+        sb.Append("<div class=\"tabbar\">");
+        for (int i = 0; i < parts.Count; i++)
+        {
+            var cls = i == 0 ? "tab active" : "tab";
+            sb.Append($"<div class=\"{cls}\" onclick=\"showTab({i})\">{WebUtility.HtmlEncode(parts[i].Label)}</div>");
+        }
+        sb.AppendLine("</div>");
+
+        for (int i = 0; i < parts.Count; i++)
+        {
+            var cls = i == 0 ? "active" : string.Empty;
+            var escaped = EscapeForSrcdoc(parts[i].Html);
+            sb.AppendLine($"<iframe class=\"{cls}\" srcdoc=\"{escaped}\"></iframe>");
+        }
+        sb.AppendLine("""
+            <script>
+              function showTab(i) {
+                var frames = document.querySelectorAll('iframe');
+                var tabs = document.querySelectorAll('.tab');
+                for (var j = 0; j < frames.length; j++) {
+                  frames[j].classList.toggle('active', i === j);
+                  tabs[j].classList.toggle('active', i === j);
+                }
+              }
+            </script>
+            </body></html>
+            """);
+        return sb.ToString();
+    }
+
+    /// <summary>
+    /// Escapes an HTML document so it can safely appear inside an
+    /// &lt;iframe srcdoc="..."&gt; attribute. Only ampersands and double
+    /// quotes must be encoded; angle brackets are kept literal because the
+    /// parser treats srcdoc as CDATA-like content.
+    /// </summary>
+    private static string EscapeForSrcdoc(string html)
+    {
+        if (string.IsNullOrEmpty(html)) return string.Empty;
+        return html
+            .Replace("&", "&amp;")
+            .Replace("\"", "&quot;");
+    }
+}

Services/Export/ReportSplitMode.cs

@@ -0,0 +1,16 @@
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>How a report export is partitioned.</summary>
+public enum ReportSplitMode
+{
+    Single,
+    BySite,
+    ByUser
+}
+
+/// <summary>When a report is split, how HTML output is laid out.</summary>
+public enum HtmlSplitLayout
+{
+    SeparateFiles,
+    SingleTabbed
+}

Services/Export/SearchCsvExportService.cs

@@ -0,0 +1,53 @@
+using System.IO;
+using System.Text;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports SearchResult list to a UTF-8 BOM CSV file.
+/// Header matches the column order in SearchHtmlExportService for consistency.
+/// </summary>
+public class SearchCsvExportService
+{
+    /// <summary>
+    /// Builds the CSV payload. Column order mirrors
+    /// <see cref="SearchHtmlExportService.BuildHtml(IReadOnlyList{SearchResult}, ReportBranding?)"/>.
+    /// </summary>
+    public string BuildCsv(IReadOnlyList<SearchResult> results)
+    {
+        var T = TranslationSource.Instance;
+        var sb = new StringBuilder();
+
+        // Header
+        sb.AppendLine($"{T["report.col.file_name"]},{T["report.col.extension"]},{T["report.col.path"]},{T["report.col.created"]},{T["report.col.created_by"]},{T["report.col.modified"]},{T["report.col.modified_by"]},{T["report.col.size_bytes"]}");
+
+        foreach (var r in results)
+        {
+            sb.AppendLine(string.Join(",",
+                Csv(IfEmpty(System.IO.Path.GetFileName(r.Path), r.Title)),
+                Csv(r.FileExtension),
+                Csv(r.Path),
+                r.Created.HasValue      ? Csv(r.Created.Value.ToString("yyyy-MM-dd"))      : string.Empty,
+                Csv(r.Author),
+                r.LastModified.HasValue ? Csv(r.LastModified.Value.ToString("yyyy-MM-dd")) : string.Empty,
+                Csv(r.ModifiedBy),
+                r.SizeBytes.ToString()));
+        }
+
+        return sb.ToString();
+    }
+
+    /// <summary>Writes the CSV to <paramref name="filePath"/> with UTF-8 BOM.</summary>
+    public async Task WriteAsync(IReadOnlyList<SearchResult> results, string filePath, CancellationToken ct)
+    {
+        var csv = BuildCsv(results);
+        await ExportFileWriter.WriteCsvAsync(filePath, csv, ct);
+    }
+
+    private static string Csv(string value) => CsvSanitizer.EscapeMinimal(value);
+
+    private static string IfEmpty(string? value, string fallback = "")
+        => string.IsNullOrEmpty(value) ? fallback : value!;
+}

Services/Export/SearchHtmlExportService.cs

@@ -0,0 +1,165 @@
+using System.IO;
+using System.Text;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports SearchResult list to a self-contained sortable/filterable HTML report.
+/// Port of PS Export-SearchToHTML (PS lines 2112-2233).
+/// Columns are sortable by clicking the header. A filter input narrows rows by text match.
+/// </summary>
+public class SearchHtmlExportService
+{
+    /// <summary>
+    /// Builds a self-contained HTML table with inline sort/filter scripts.
+    /// Each <see cref="SearchResult"/> becomes one row; the document has no
+    /// external dependencies.
+    /// </summary>
+    public string BuildHtml(IReadOnlyList<SearchResult> results, ReportBranding? branding = null)
+    {
+        var T = TranslationSource.Instance;
+        var sb = new StringBuilder();
+
+        sb.AppendLine("<!DOCTYPE html>");
+        sb.AppendLine("<html lang=\"en\">");
+        sb.AppendLine("<head>");
+        sb.AppendLine("<meta charset=\"UTF-8\">");
+        sb.AppendLine("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">");
+        sb.AppendLine($"<title>{T["report.title.search"]}</title>");
+        sb.AppendLine("""
+            <style>
+              body { font-family: 'Segoe UI', Arial, sans-serif; font-size: 13px; margin: 20px; background: #f5f5f5; }
+              h1 { color: #0078d4; }
+              .toolbar { margin-bottom: 10px; display: flex; gap: 12px; align-items: center; }
+              .toolbar label { font-weight: 600; }
+              #filterInput { padding: 6px 10px; border: 1px solid #ccc; border-radius: 4px; width: 280px; font-size: 13px; }
+              #resultCount { font-size: 12px; color: #666; }
+              table { border-collapse: collapse; width: 100%; background: #fff; box-shadow: 0 1px 3px rgba(0,0,0,.15); }
+              th { background: #0078d4; color: #fff; padding: 8px 12px; text-align: left; cursor: pointer;
+                   font-weight: 600; user-select: none; white-space: nowrap; }
+              th:hover { background: #106ebe; }
+              th.sorted-asc::after  { content: ' ▲'; font-size: 10px; }
+              th.sorted-desc::after { content: ' ▼'; font-size: 10px; }
+              td { padding: 6px 12px; border-bottom: 1px solid #e0e0e0; word-break: break-all; }
+              tr:hover td { background: #f0f7ff; }
+              tr.hidden { display: none; }
+              .num { text-align: right; font-variant-numeric: tabular-nums; white-space: nowrap; }
+              .generated { font-size: 11px; color: #888; margin-top: 12px; }
+            </style>
+            </head>
+            <body>
+            """);
+        sb.Append(BrandingHtmlHelper.BuildBrandingHeader(branding));
+        sb.AppendLine($"""
+            <h1>{T["report.title.search_short"]}</h1>
+            <div class="toolbar">
+              <label for="filterInput">{T["report.filter.label"]}</label>
+              <input id="filterInput" type="text" placeholder="{T["report.filter.placeholder_rows"]}" oninput="filterTable()" />
+              <span id="resultCount"></span>
+            </div>
+            """);
+
+        sb.AppendLine($"""
+            <table id="resultsTable">
+              <thead>
+                <tr>
+                  <th onclick="sortTable(0)">{T["report.col.file_name"]}</th>
+                  <th onclick="sortTable(1)">{T["report.col.extension"]}</th>
+                  <th onclick="sortTable(2)">{T["report.col.path"]}</th>
+                  <th onclick="sortTable(3)">{T["report.col.created"]}</th>
+                  <th onclick="sortTable(4)">{T["report.col.created_by"]}</th>
+                  <th onclick="sortTable(5)">{T["report.col.modified"]}</th>
+                  <th onclick="sortTable(6)">{T["report.col.modified_by"]}</th>
+                  <th class="num" onclick="sortTable(7)">{T["report.col.size"]}</th>
+                </tr>
+              </thead>
+              <tbody>
+            """);
+
+        foreach (var r in results)
+        {
+            string fileName = System.IO.Path.GetFileName(r.Path);
+            if (string.IsNullOrEmpty(fileName)) fileName = r.Title;
+
+            sb.AppendLine($"""
+                  <tr>
+                    <td>{H(fileName)}</td>
+                    <td>{H(r.FileExtension)}</td>
+                    <td><a href="{H(r.Path)}" target="_blank">{H(r.Path)}</a></td>
+                    <td>{(r.Created.HasValue ? r.Created.Value.ToString("yyyy-MM-dd") : string.Empty)}</td>
+                    <td>{H(r.Author)}</td>
+                    <td>{(r.LastModified.HasValue ? r.LastModified.Value.ToString("yyyy-MM-dd") : string.Empty)}</td>
+                    <td>{H(r.ModifiedBy)}</td>
+                    <td class="num" data-sort="{r.SizeBytes}">{FormatSize(r.SizeBytes)}</td>
+                  </tr>
+                """);
+        }
+
+        sb.AppendLine("  </tbody>\n</table>");
+
+        int count = results.Count;
+        sb.AppendLine($"<p class=\"generated\">{T["report.text.generated_colon"]} {DateTime.Now:yyyy-MM-dd HH:mm} — {count:N0} {T["report.text.results_parens"]}</p>");
+
+        sb.AppendLine($$"""
+            <script>
+            var sortDir = {};
+            function sortTable(col) {
+              var tbl = document.getElementById('resultsTable');
+              var tbody = tbl.tBodies[0];
+              var rows = Array.from(tbody.rows);
+              var asc = sortDir[col] !== 'asc';
+              sortDir[col] = asc ? 'asc' : 'desc';
+              rows.sort(function(a, b) {
+                var av = a.cells[col].dataset.sort || a.cells[col].innerText;
+                var bv = b.cells[col].dataset.sort || b.cells[col].innerText;
+                var an = parseFloat(av), bn = parseFloat(bv);
+                if (!isNaN(an) && !isNaN(bn)) return asc ? an - bn : bn - an;
+                return asc ? av.localeCompare(bv) : bv.localeCompare(av);
+              });
+              rows.forEach(function(r) { tbody.appendChild(r); });
+              var ths = tbl.tHead.rows[0].cells;
+              for (var i = 0; i < ths.length; i++) {
+                ths[i].className = (i === col) ? (asc ? 'sorted-asc' : 'sorted-desc') : '';
+              }
+            }
+            function filterTable() {
+              var q = document.getElementById('filterInput').value.toLowerCase();
+              var rows = document.getElementById('resultsTable').tBodies[0].rows;
+              var visible = 0;
+              for (var i = 0; i < rows.length; i++) {
+                var match = rows[i].innerText.toLowerCase().indexOf(q) >= 0;
+                rows[i].className = match ? '' : 'hidden';
+                if (match) visible++;
+              }
+              document.getElementById('resultCount').innerText = q ? (visible + ' {{T["report.text.of"]}} {{count:N0}} {{T["report.text.shown"]}}') : '';
+            }
+            window.onload = function() {
+              document.getElementById('resultCount').innerText = '{{count:N0}} {{T["report.text.results_parens"]}}';
+            };
+            </script>
+            </body></html>
+            """);
+
+        return sb.ToString();
+    }
+
+    /// <summary>Writes the HTML report to <paramref name="filePath"/>.</summary>
+    public async Task WriteAsync(IReadOnlyList<SearchResult> results, string filePath, CancellationToken ct, ReportBranding? branding = null)
+    {
+        var html = BuildHtml(results, branding);
+        await System.IO.File.WriteAllTextAsync(filePath, html, Encoding.UTF8, ct);
+    }
+
+    private static string H(string value) =>
+        System.Net.WebUtility.HtmlEncode(value ?? string.Empty);
+
+    private static string FormatSize(long bytes)
+    {
+        if (bytes >= 1_073_741_824L) return $"{bytes / 1_073_741_824.0:F2} GB";
+        if (bytes >= 1_048_576L)     return $"{bytes / 1_048_576.0:F2} MB";
+        if (bytes >= 1024L)          return $"{bytes / 1024.0:F2} KB";
+        return $"{bytes} B";
+    }
+}

Services/Export/StorageCsvExportService.cs

@@ -0,0 +1,227 @@
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+using System.Globalization;
+using System.IO;
+using System.Text;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports a flat list of StorageNode objects to a UTF-8 BOM CSV.
+/// Compatible with Microsoft Excel (BOM signals UTF-8 encoding).
+/// </summary>
+public class StorageCsvExportService
+{
+    /// <summary>
+    /// Builds a single-section CSV: header row plus one row per
+    /// <see cref="StorageNode"/> with library, site, file count, total size
+    /// (MB), version size (MB), and last-modified date.
+    /// </summary>
+    public string BuildCsv(IReadOnlyList<StorageNode> nodes)
+    {
+        // Pre-size: ~110 chars/row + header avoids most StringBuilder growth.
+        var sb = new StringBuilder(128 + nodes.Count * 110);
+        WriteCsv(sb, nodes);
+        return sb.ToString();
+    }
+
+    private static void WriteCsv(StringBuilder sb, IReadOnlyList<StorageNode> nodes)
+    {
+        var T = TranslationSource.Instance;
+        // Hoist resource lookups out of the row loop: ResourceManager.GetString
+        // is a culture-aware dictionary probe — caching once per export saves
+        // O(rows × columns) lookups on large tenants.
+        string colLibrary  = T["report.col.library"];
+        string colKind     = T["stor.col.kind"];
+        string colSite     = T["report.col.site"];
+        string colFiles    = T["report.stat.files"];
+        string colTotalMb  = T["report.col.total_size_mb"];
+        string colVerMb    = T["report.col.version_size_mb"];
+        string colLastMod  = T["report.col.last_modified"];
+
+        sb.Append(colLibrary).Append(',')
+          .Append(colKind).Append(',')
+          .Append(colSite).Append(',')
+          .Append(colFiles).Append(',')
+          .Append(colTotalMb).Append(',')
+          .Append(colVerMb).Append(',')
+          .AppendLine(colLastMod);
+
+        var kindLabels = BuildKindLabelCache();
+
+        foreach (var node in nodes)
+        {
+            AppendCsvField(sb, node.Name).Append(',');
+            AppendCsvField(sb, kindLabels[(int)node.Kind]).Append(',');
+            AppendCsvField(sb, node.SiteTitle).Append(',');
+            sb.Append(node.TotalFileCount).Append(',');
+            AppendMb(sb, node.TotalSizeBytes).Append(',');
+            AppendMb(sb, node.VersionSizeBytes).Append(',');
+            if (node.LastModified.HasValue)
+                AppendCsvField(sb, node.LastModified.Value.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture));
+            sb.AppendLine();
+        }
+    }
+
+    /// <summary>Writes the library-level CSV to <paramref name="filePath"/> with UTF-8 BOM.</summary>
+    public async Task WriteAsync(IReadOnlyList<StorageNode> nodes, string filePath, CancellationToken ct)
+    {
+        // Stream straight to disk: skip the StringBuilder→string copy and the
+        // separate UTF-8 buffer that File.WriteAllTextAsync materializes.
+        var sb = new StringBuilder(128 + nodes.Count * 110);
+        WriteCsv(sb, nodes);
+        await ExportFileWriter.WriteCsvChunksAsync(filePath, sb, ct);
+    }
+
+    /// <summary>
+    /// Builds a CSV with library details followed by a file-type breakdown section.
+    /// </summary>
+    public string BuildCsv(IReadOnlyList<StorageNode> nodes, IReadOnlyList<FileTypeMetric> fileTypeMetrics)
+    {
+        var sb = new StringBuilder(192 + nodes.Count * 100 + fileTypeMetrics.Count * 40);
+        WriteCsv(sb, nodes, fileTypeMetrics);
+        return sb.ToString();
+    }
+
+    private static void WriteCsv(StringBuilder sb, IReadOnlyList<StorageNode> nodes, IReadOnlyList<FileTypeMetric> fileTypeMetrics)
+    {
+        var T = TranslationSource.Instance;
+        string colLibrary  = T["report.col.library"];
+        string colSite     = T["report.col.site"];
+        string colFiles    = T["report.stat.files"];
+        string colTotalMb  = T["report.col.total_size_mb"];
+        string colVerMb    = T["report.col.version_size_mb"];
+        string colLastMod  = T["report.col.last_modified"];
+
+        sb.Append(colLibrary).Append(',')
+          .Append(colSite).Append(',')
+          .Append(colFiles).Append(',')
+          .Append(colTotalMb).Append(',')
+          .Append(colVerMb).Append(',')
+          .AppendLine(colLastMod);
+
+        foreach (var node in nodes)
+        {
+            AppendCsvField(sb, node.Name).Append(',');
+            AppendCsvField(sb, node.SiteTitle).Append(',');
+            sb.Append(node.TotalFileCount).Append(',');
+            AppendMb(sb, node.TotalSizeBytes).Append(',');
+            AppendMb(sb, node.VersionSizeBytes).Append(',');
+            if (node.LastModified.HasValue)
+                AppendCsvField(sb, node.LastModified.Value.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture));
+            sb.AppendLine();
+        }
+
+        if (fileTypeMetrics.Count > 0)
+        {
+            string colFileType = T["report.col.file_type"];
+            string colSizeMb   = T["report.col.size_mb"];
+            string colFileCnt  = T["report.col.file_count"];
+            string noExtLabel  = T["report.text.no_extension"];
+
+            sb.AppendLine();
+            sb.Append(colFileType).Append(',')
+              .Append(colSizeMb).Append(',')
+              .AppendLine(colFileCnt);
+
+            foreach (var m in fileTypeMetrics)
+            {
+                string label = string.IsNullOrEmpty(m.Extension) ? noExtLabel : m.Extension;
+                AppendCsvField(sb, label).Append(',');
+                AppendMb(sb, m.TotalSizeBytes).Append(',');
+                sb.Append(m.FileCount).AppendLine();
+            }
+        }
+    }
+
+    /// <summary>Writes the two-section CSV (libraries + file-type breakdown) with UTF-8 BOM.</summary>
+    public async Task WriteAsync(IReadOnlyList<StorageNode> nodes, IReadOnlyList<FileTypeMetric> fileTypeMetrics, string filePath, CancellationToken ct)
+    {
+        var sb = new StringBuilder(192 + nodes.Count * 100 + fileTypeMetrics.Count * 40);
+        WriteCsv(sb, nodes, fileTypeMetrics);
+        await ExportFileWriter.WriteCsvChunksAsync(filePath, sb, ct);
+    }
+
+    /// <summary>
+    /// Writes storage metrics with optional per-site partitioning.
+    /// Single → one file. BySite → one file per SiteTitle. File-type metrics
+    /// are replicated across all partitions because the tenant-level scan
+    /// does not retain per-site breakdowns.
+    /// </summary>
+    public Task WriteAsync(
+        IReadOnlyList<StorageNode> nodes,
+        IReadOnlyList<FileTypeMetric> fileTypeMetrics,
+        string basePath,
+        ReportSplitMode splitMode,
+        CancellationToken ct)
+        => ReportSplitHelper.WritePartitionedAsync(
+            nodes, basePath, splitMode,
+            PartitionBySite,
+            (part, path, c) => WriteAsync(part, fileTypeMetrics, path, c),
+            ct);
+
+    /// <summary>
+    /// Splits the flat StorageNode list into per-site slices while preserving
+    /// the DFS hierarchy (each root library followed by its indented descendants).
+    /// Siblings sharing a SiteTitle roll up into the same partition.
+    /// </summary>
+    internal static IEnumerable<(string Label, IReadOnlyList<StorageNode> Partition)> PartitionBySite(
+        IReadOnlyList<StorageNode> nodes)
+    {
+        var buckets = new Dictionary<string, List<StorageNode>>(StringComparer.OrdinalIgnoreCase);
+        string currentSite = string.Empty;
+        foreach (var node in nodes)
+        {
+            if (node.IndentLevel == 0)
+                currentSite = string.IsNullOrWhiteSpace(node.SiteTitle)
+                    ? ReportSplitHelper.DeriveSiteLabel(node.Url)
+                    : node.SiteTitle;
+            if (!buckets.TryGetValue(currentSite, out var list))
+            {
+                list = new List<StorageNode>();
+                buckets[currentSite] = list;
+            }
+            list.Add(node);
+        }
+        return buckets.Select(kv => (kv.Key, (IReadOnlyList<StorageNode>)kv.Value));
+    }
+
+    // ── Helpers ───────────────────────────────────────────────────────────────
+
+    private static StringBuilder AppendMb(StringBuilder sb, long bytes)
+        => sb.Append((bytes / (1024.0 * 1024.0)).ToString("F2", CultureInfo.InvariantCulture));
+
+    private static StringBuilder AppendCsvField(StringBuilder sb, string value)
+        => sb.Append(CsvSanitizer.EscapeMinimal(value));
+
+    /// <summary>
+    /// Pre-resolves localized labels for every <see cref="StorageNodeKind"/>
+    /// once per export, indexed by the enum's int value. Avoids a
+    /// <c>ResourceManager.GetString</c> call per row in hot CSV loops.
+    /// </summary>
+    private static string[] BuildKindLabelCache()
+    {
+        var values = (StorageNodeKind[])Enum.GetValues(typeof(StorageNodeKind));
+        int max = 0;
+        foreach (var v in values) { int i = (int)v; if (i > max) max = i; }
+        var cache = new string[max + 1];
+        for (int i = 0; i < cache.Length; i++) cache[i] = ((StorageNodeKind)i).ToString();
+        foreach (var v in values) cache[(int)v] = KindLabel(v);
+        return cache;
+    }
+
+    private static string KindLabel(StorageNodeKind kind)
+    {
+        var T = TranslationSource.Instance;
+        return kind switch
+        {
+            StorageNodeKind.Library          => T["stor.kind.library"],
+            StorageNodeKind.HiddenLibrary    => T["stor.kind.hidden"],
+            StorageNodeKind.PreservationHold => T["stor.kind.preservation"],
+            StorageNodeKind.ListAttachments  => T["stor.kind.attachments"],
+            StorageNodeKind.RecycleBin       => T["stor.kind.recyclebin"],
+            StorageNodeKind.Subsite          => T["stor.kind.subsite"],
+            _ => kind.ToString()
+        };
+    }
+}

Services/Export/StorageHtmlExportService.cs

@@ -0,0 +1,465 @@
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+using System.IO;
+using System.Text;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports StorageNode tree to a self-contained HTML file with collapsible subfolder rows.
+/// Port of PS Export-StorageToHTML (PS lines 1621-1780).
+/// Uses a toggle(i) JS pattern where each collapsible row has id="sf-{i}".
+/// </summary>
+public class StorageHtmlExportService
+{
+    private int _togIdx;
+    private string[] _kindLabels = Array.Empty<string>();
+    private string[] _kindLabelsHtml = Array.Empty<string>();
+
+    /// <summary>
+    /// Builds a self-contained HTML report with one collapsible row per
+    /// library and indented child folders. Library-only variant — use the
+    /// overload that accepts <see cref="FileTypeMetric"/>s when a file-type
+    /// breakdown section is desired.
+    /// </summary>
+    public string BuildHtml(IReadOnlyList<StorageNode> nodes, ReportBranding? branding = null)
+    {
+        var sb = new StringBuilder(3072 + nodes.Count * 340);
+        BuildHtmlCore(sb, nodes, branding);
+        return sb.ToString();
+    }
+
+    private void BuildHtmlCore(StringBuilder sb, IReadOnlyList<StorageNode> nodes, ReportBranding? branding)
+    {
+        var T = TranslationSource.Instance;
+        _togIdx = 0;
+        _kindLabels = BuildKindLabelCache();
+        _kindLabelsHtml = BuildHtmlEncodedCache(_kindLabels);
+
+        sb.AppendLine("<!DOCTYPE html>");
+        sb.AppendLine("<html lang=\"en\">");
+        sb.AppendLine("<head>");
+        sb.AppendLine("<meta charset=\"UTF-8\">");
+        sb.AppendLine("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">");
+        sb.AppendLine($"<title>{T["report.title.storage"]}</title>");
+        sb.AppendLine("""
+            <style>
+              body { font-family: 'Segoe UI', Arial, sans-serif; font-size: 13px; margin: 20px; background: #f5f5f5; }
+              h1 { color: #0078d4; }
+              table { border-collapse: collapse; width: 100%; background: #fff; box-shadow: 0 1px 3px rgba(0,0,0,.15); }
+              th { background: #0078d4; color: #fff; padding: 8px 12px; text-align: left; font-weight: 600; }
+              td { padding: 6px 12px; border-bottom: 1px solid #e0e0e0; vertical-align: top; }
+              tr:hover { background: #f0f7ff; }
+              .toggle-btn { background: none; border: 1px solid #0078d4; color: #0078d4; border-radius: 3px;
+                            cursor: pointer; font-size: 11px; padding: 1px 6px; margin-right: 6px; }
+              .toggle-btn:hover { background: #e5f1fb; }
+              .sf-tbl { width: 100%; border: none; box-shadow: none; margin: 0; }
+              .sf-tbl td { background: #fafcff; font-size: 12px; }
+              .num { text-align: right; font-variant-numeric: tabular-nums; }
+              .generated { font-size: 11px; color: #888; margin-top: 12px; }
+            </style>
+            <script>
+              function toggle(i) {
+                var row = document.getElementById('sf-' + i);
+                if (row) row.style.display = (row.style.display === 'none' || row.style.display === '') ? 'table-row' : 'none';
+              }
+            </script>
+            </head>
+            <body>
+            """);
+        sb.Append(BrandingHtmlHelper.BuildBrandingHeader(branding));
+        sb.AppendLine($"<h1>{T["report.title.storage"]}</h1>");
+
+        // Single-pass root aggregation: replaces 4 separate enumerations
+        // (.Where().ToList() + 3× .Sum() + a final .Where() during render).
+        var rootNodes0 = new List<StorageNode>(Math.Min(nodes.Count, 64));
+        long siteTotal0 = 0, versionTotal0 = 0, fileTotal0 = 0;
+        foreach (var n in nodes)
+        {
+            if (n.IndentLevel != 0) continue;
+            rootNodes0.Add(n);
+            siteTotal0    += n.TotalSizeBytes;
+            versionTotal0 += n.VersionSizeBytes;
+            fileTotal0    += n.TotalFileCount;
+        }
+
+        sb.AppendLine($"""
+            <div style="display:flex;gap:16px;margin:16px 0;flex-wrap:wrap">
+              <div style="background:#fff;border-radius:8px;padding:14px 20px;min-width:160px;box-shadow:0 1px 4px rgba(0,0,0,.1)"><div style="font-size:1.8rem;font-weight:700;color:#0078d4">{FormatSize(siteTotal0)}</div><div style="font-size:.8rem;color:#666">{T["report.stat.total_size"]}</div></div>
+              <div style="background:#fff;border-radius:8px;padding:14px 20px;min-width:160px;box-shadow:0 1px 4px rgba(0,0,0,.1)"><div style="font-size:1.8rem;font-weight:700;color:#0078d4">{FormatSize(versionTotal0)}</div><div style="font-size:.8rem;color:#666">{T["report.stat.version_size"]}</div></div>
+              <div style="background:#fff;border-radius:8px;padding:14px 20px;min-width:160px;box-shadow:0 1px 4px rgba(0,0,0,.1)"><div style="font-size:1.8rem;font-weight:700;color:#0078d4">{fileTotal0:N0}</div><div style="font-size:.8rem;color:#666">{T["report.stat.files"]}</div></div>
+            </div>
+            """);
+
+        sb.AppendLine($"""
+            <table>
+              <thead>
+                <tr>
+                  <th>{T["report.col.library_folder"]}</th>
+                  <th>{T["stor.col.kind"]}</th>
+                  <th>{T["report.col.site"]}</th>
+                  <th class="num">{T["report.stat.files"]}</th>
+                  <th class="num">{T["report.stat.total_size"]}</th>
+                  <th class="num">{T["report.stat.version_size"]}</th>
+                  <th>{T["report.col.last_modified"]}</th>
+                </tr>
+              </thead>
+              <tbody>
+            """);
+
+        // Render only the pre-materialized root list — recursing into
+        // Children handles descendants. Iterating the flat list would render
+        // every descendant a second time as a top-level row.
+        foreach (var node in rootNodes0)
+        {
+            RenderNode(sb, node);
+        }
+
+        sb.AppendLine("""
+              </tbody>
+            </table>
+            """);
+
+        sb.AppendLine($"<p class=\"generated\">{T["report.text.generated_colon"]} {DateTime.Now:yyyy-MM-dd HH:mm}</p>");
+        sb.AppendLine("</body></html>");
+    }
+
+    /// <summary>
+    /// Builds an HTML report including a file-type breakdown chart section.
+    /// </summary>
+    public string BuildHtml(IReadOnlyList<StorageNode> nodes, IReadOnlyList<FileTypeMetric> fileTypeMetrics, ReportBranding? branding = null)
+    {
+        var sb = new StringBuilder(4096 + nodes.Count * 340 + fileTypeMetrics.Count * 220);
+        BuildHtmlCore(sb, nodes, fileTypeMetrics, branding);
+        return sb.ToString();
+    }
+
+    private void BuildHtmlCore(StringBuilder sb, IReadOnlyList<StorageNode> nodes, IReadOnlyList<FileTypeMetric> fileTypeMetrics, ReportBranding? branding)
+    {
+        var T = TranslationSource.Instance;
+        _togIdx = 0;
+        _kindLabels = BuildKindLabelCache();
+        _kindLabelsHtml = BuildHtmlEncodedCache(_kindLabels);
+
+        sb.AppendLine("<!DOCTYPE html>");
+        sb.AppendLine("<html lang=\"en\">");
+        sb.AppendLine("<head>");
+        sb.AppendLine("<meta charset=\"UTF-8\">");
+        sb.AppendLine("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">");
+        sb.AppendLine($"<title>{T["report.title.storage"]}</title>");
+        sb.AppendLine("""
+            <style>
+              body { font-family: 'Segoe UI', Arial, sans-serif; font-size: 13px; margin: 20px; background: #f5f5f5; }
+              h1 { color: #0078d4; }
+              h2 { color: #333; margin-top: 24px; }
+              table { border-collapse: collapse; width: 100%; background: #fff; box-shadow: 0 1px 3px rgba(0,0,0,.15); }
+              th { background: #0078d4; color: #fff; padding: 8px 12px; text-align: left; font-weight: 600; }
+              td { padding: 6px 12px; border-bottom: 1px solid #e0e0e0; vertical-align: top; }
+              tr:hover { background: #f0f7ff; }
+              .toggle-btn { background: none; border: 1px solid #0078d4; color: #0078d4; border-radius: 3px;
+                            cursor: pointer; font-size: 11px; padding: 1px 6px; margin-right: 6px; }
+              .toggle-btn:hover { background: #e5f1fb; }
+              .sf-tbl { width: 100%; border: none; box-shadow: none; margin: 0; }
+              .sf-tbl td { background: #fafcff; font-size: 12px; }
+              .num { text-align: right; font-variant-numeric: tabular-nums; }
+              .generated { font-size: 11px; color: #888; margin-top: 12px; }
+              .chart-section { margin: 20px 0; padding: 16px; background: #fff; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,.15); }
+              .bar-row { display: flex; align-items: center; margin: 4px 0; }
+              .bar-label { width: 80px; font-size: 12px; font-weight: 600; text-align: right; padding-right: 10px; }
+              .bar-track { flex: 1; background: #eee; border-radius: 4px; height: 22px; position: relative; }
+              .bar-fill { height: 100%; border-radius: 4px; background: #0078d4; min-width: 2px; }
+              .bar-value { font-size: 11px; color: #555; padding-left: 8px; white-space: nowrap; min-width: 140px; }
+              .stats { display: flex; gap: 16px; margin: 16px 0; flex-wrap: wrap; }
+              .stat-card { background: #fff; border-radius: 8px; padding: 14px 20px; min-width: 160px; box-shadow: 0 1px 4px rgba(0,0,0,.1); }
+              .stat-card .value { font-size: 1.8rem; font-weight: 700; color: #0078d4; }
+              .stat-card .label { font-size: .8rem; color: #666; margin-top: 2px; }
+            </style>
+            <script>
+              function toggle(i) {
+                var row = document.getElementById('sf-' + i);
+                if (row) row.style.display = (row.style.display === 'none' || row.style.display === '') ? 'table-row' : 'none';
+              }
+            </script>
+            </head>
+            <body>
+            """);
+        sb.Append(BrandingHtmlHelper.BuildBrandingHeader(branding));
+        sb.AppendLine($"<h1>{T["report.title.storage"]}</h1>");
+
+        // ── Summary cards (single-pass aggregation) ──
+        var rootNodes = new List<StorageNode>(Math.Min(nodes.Count, 64));
+        long siteTotal = 0, versionTotal = 0, fileTotal = 0;
+        foreach (var n in nodes)
+        {
+            if (n.IndentLevel != 0) continue;
+            rootNodes.Add(n);
+            siteTotal    += n.TotalSizeBytes;
+            versionTotal += n.VersionSizeBytes;
+            fileTotal    += n.TotalFileCount;
+        }
+
+        sb.AppendLine("<div class=\"stats\">");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{FormatSize(siteTotal)}</div><div class=\"label\">{T["report.stat.total_size"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{FormatSize(versionTotal)}</div><div class=\"label\">{T["report.stat.version_size"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{fileTotal:N0}</div><div class=\"label\">{T["report.stat.files"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{rootNodes.Count}</div><div class=\"label\">{T["report.stat.libraries"]}</div></div>");
+        sb.AppendLine("</div>");
+
+        // ── File type chart section ──
+        if (fileTypeMetrics.Count > 0)
+        {
+            var maxSize = fileTypeMetrics.Max(m => m.TotalSizeBytes);
+            var totalSize = fileTypeMetrics.Sum(m => m.TotalSizeBytes);
+            var totalFiles = fileTypeMetrics.Sum(m => m.FileCount);
+
+            sb.AppendLine("<div class=\"chart-section\">");
+            sb.AppendLine($"<h2>{T["report.section.storage_by_file_type"]} ({totalFiles:N0} {T["report.text.files_unit"]}, {FormatSize(totalSize)})</h2>");
+
+            var colors = new[] { "#0078d4", "#2b88d8", "#106ebe", "#005a9e", "#004578",
+                                 "#00bcf2", "#009e49", "#8cbd18", "#ffb900", "#d83b01" };
+
+            int idx = 0;
+            foreach (var m in fileTypeMetrics.Take(15))
+            {
+                double pct = maxSize > 0 ? m.TotalSizeBytes * 100.0 / maxSize : 0;
+                string color = colors[idx % colors.Length];
+                string label = string.IsNullOrEmpty(m.Extension) ? T["report.text.no_ext"] : m.Extension;
+
+                sb.AppendLine($"""
+                    <div class="bar-row">
+                      <span class="bar-label">{HtmlEncode(label)}</span>
+                      <div class="bar-track"><div class="bar-fill" style="width:{pct:F1}%;background:{color}"></div></div>
+                      <span class="bar-value">{FormatSize(m.TotalSizeBytes)} &middot; {m.FileCount:N0} {T["report.text.files_unit"]}</span>
+                    </div>
+                    """);
+                idx++;
+            }
+
+            sb.AppendLine("</div>");
+        }
+
+        // ── Storage table ──
+        sb.AppendLine($"<h2>{T["report.section.library_details"]}</h2>");
+        sb.AppendLine($"""
+            <table>
+              <thead>
+                <tr>
+                  <th>{T["report.col.library_folder"]}</th>
+                  <th>{T["stor.col.kind"]}</th>
+                  <th>{T["report.col.site"]}</th>
+                  <th class="num">{T["report.stat.files"]}</th>
+                  <th class="num">{T["report.stat.total_size"]}</th>
+                  <th class="num">{T["report.stat.version_size"]}</th>
+                  <th>{T["report.col.last_modified"]}</th>
+                </tr>
+              </thead>
+              <tbody>
+            """);
+
+        // Render only the pre-materialized root list — recursing into
+        // Children handles descendants. Iterating the flat list would render
+        // every descendant a second time as a top-level row.
+        foreach (var node in rootNodes)
+        {
+            RenderNode(sb, node);
+        }
+
+        sb.AppendLine("""
+              </tbody>
+            </table>
+            """);
+
+        sb.AppendLine($"<p class=\"generated\">{T["report.text.generated_colon"]} {DateTime.Now:yyyy-MM-dd HH:mm}</p>");
+        sb.AppendLine("</body></html>");
+    }
+
+    /// <summary>Writes the library-only HTML report to <paramref name="filePath"/>.</summary>
+    public async Task WriteAsync(IReadOnlyList<StorageNode> nodes, string filePath, CancellationToken ct, ReportBranding? branding = null)
+    {
+        // Build into StringBuilder, stream chunks straight to disk —
+        // skips a full-document char-array copy from sb.ToString().
+        var sb = new StringBuilder(3072 + nodes.Count * 340);
+        BuildHtmlCore(sb, nodes, branding);
+        await ExportFileWriter.WriteHtmlChunksAsync(filePath, sb, ct);
+    }
+
+    /// <summary>Writes the HTML report including the file-type breakdown chart.</summary>
+    public async Task WriteAsync(IReadOnlyList<StorageNode> nodes, IReadOnlyList<FileTypeMetric> fileTypeMetrics, string filePath, CancellationToken ct, ReportBranding? branding = null)
+    {
+        var sb = new StringBuilder(4096 + nodes.Count * 340 + fileTypeMetrics.Count * 220);
+        BuildHtmlCore(sb, nodes, fileTypeMetrics, branding);
+        await ExportFileWriter.WriteHtmlChunksAsync(filePath, sb, ct);
+    }
+
+    /// <summary>
+    /// Split-aware HTML export for storage metrics.
+    /// Single → one file. BySite + SeparateFiles → one file per site.
+    /// BySite + SingleTabbed → one HTML with per-site iframe tabs. File-type
+    /// metrics are replicated across partitions because they are not
+    /// attributed per-site by the scanner.
+    /// </summary>
+    public async Task WriteAsync(
+        IReadOnlyList<StorageNode> nodes,
+        IReadOnlyList<FileTypeMetric> fileTypeMetrics,
+        string basePath,
+        ReportSplitMode splitMode,
+        HtmlSplitLayout layout,
+        CancellationToken ct,
+        ReportBranding? branding = null)
+    {
+        if (splitMode != ReportSplitMode.BySite)
+        {
+            await WriteAsync(nodes, fileTypeMetrics, basePath, ct, branding);
+            return;
+        }
+
+        var partitions = StorageCsvExportService.PartitionBySite(nodes).ToList();
+        if (layout == HtmlSplitLayout.SingleTabbed)
+        {
+            var parts = partitions
+                .Select(p => (p.Label, Html: BuildHtml(p.Partition, fileTypeMetrics, branding)))
+                .ToList();
+            var title = TranslationSource.Instance["report.title.storage"];
+            var tabbed = ReportSplitHelper.BuildTabbedHtml(parts, title);
+            await File.WriteAllTextAsync(basePath, tabbed, Encoding.UTF8, ct);
+            return;
+        }
+
+        foreach (var (label, partNodes) in partitions)
+        {
+            ct.ThrowIfCancellationRequested();
+            var path = ReportSplitHelper.BuildPartitionPath(basePath, label);
+            await WriteAsync(partNodes, fileTypeMetrics, path, ct, branding);
+        }
+    }
+
+    // ── Private rendering ────────────────────────────────────────────────────
+
+    private void RenderNode(StringBuilder sb, StorageNode node)
+    {
+        bool hasChildren = node.Children.Count > 0;
+        int myIdx = hasChildren ? ++_togIdx : 0;
+
+        string nameCell = hasChildren
+            ? $"<button class=\"toggle-btn\" onclick=\"toggle({myIdx})\">&#9654;</button>{HtmlEncode(node.Name)}"
+            : $"<span style=\"margin-left:{node.IndentLevel * 16}px\">{HtmlEncode(node.Name)}</span>";
+
+        AppendRow(sb, node, nameCell);
+
+        if (hasChildren)
+        {
+            sb.AppendLine($"<tr id=\"sf-{myIdx}\" style=\"display:none\"><td colspan=\"7\" style=\"padding:0\">");
+            sb.AppendLine("<table class=\"sf-tbl\"><tbody>");
+            foreach (var child in node.Children)
+            {
+                RenderChildNode(sb, child);
+            }
+            sb.AppendLine("</tbody></table>");
+            sb.AppendLine("</td></tr>");
+        }
+    }
+
+    private void RenderChildNode(StringBuilder sb, StorageNode node)
+    {
+        bool hasChildren = node.Children.Count > 0;
+        int myIdx = hasChildren ? ++_togIdx : 0;
+
+        string indent = $"margin-left:{(node.IndentLevel + 1) * 16}px";
+        string nameCell = hasChildren
+            ? $"<span style=\"{indent}\"><button class=\"toggle-btn\" onclick=\"toggle({myIdx})\">&#9654;</button>{HtmlEncode(node.Name)}</span>"
+            : $"<span style=\"{indent}\">{HtmlEncode(node.Name)}</span>";
+
+        AppendRow(sb, node, nameCell);
+
+        if (hasChildren)
+        {
+            sb.AppendLine($"<tr id=\"sf-{myIdx}\" style=\"display:none\"><td colspan=\"7\" style=\"padding:0\">");
+            sb.AppendLine("<table class=\"sf-tbl\"><tbody>");
+            foreach (var child in node.Children)
+            {
+                RenderChildNode(sb, child);
+            }
+            sb.AppendLine("</tbody></table>");
+            sb.AppendLine("</td></tr>");
+        }
+    }
+
+    /// <summary>
+    /// Appends one data row given the pre-rendered name cell. Hot path:
+    /// pulls localized kind labels from <see cref="_kindLabelsHtml"/> instead
+    /// of going through <c>ResourceManager.GetString</c> + <c>HtmlEncode</c>
+    /// per row.
+    /// </summary>
+    private void AppendRow(StringBuilder sb, StorageNode node, string nameCell)
+    {
+        int kindIdx = (int)node.Kind;
+        string kindLabel = (uint)kindIdx < (uint)_kindLabelsHtml.Length
+            ? _kindLabelsHtml[kindIdx]
+            : HtmlEncode(node.Kind.ToString());
+        string lastMod = node.LastModified.HasValue
+            ? node.LastModified.Value.ToString("yyyy-MM-dd")
+            : string.Empty;
+
+        sb.AppendLine($"""
+              <tr>
+                <td>{nameCell}</td>
+                <td>{kindLabel}</td>
+                <td>{HtmlEncode(node.SiteTitle)}</td>
+                <td class="num">{node.TotalFileCount:N0}</td>
+                <td class="num">{FormatSize(node.TotalSizeBytes)}</td>
+                <td class="num">{FormatSize(node.VersionSizeBytes)}</td>
+                <td>{lastMod}</td>
+              </tr>
+            """);
+    }
+
+    private static string FormatSize(long bytes)
+    {
+        if (bytes >= 1_073_741_824L) return $"{bytes / 1_073_741_824.0:F2} GB";
+        if (bytes >= 1_048_576L)     return $"{bytes / 1_048_576.0:F2} MB";
+        if (bytes >= 1024L)          return $"{bytes / 1024.0:F2} KB";
+        return $"{bytes} B";
+    }
+
+    private static string HtmlEncode(string value)
+        => System.Net.WebUtility.HtmlEncode(value ?? string.Empty);
+
+    private static string KindLabel(StorageNodeKind kind)
+    {
+        var T = TranslationSource.Instance;
+        return kind switch
+        {
+            StorageNodeKind.Library          => T["stor.kind.library"],
+            StorageNodeKind.HiddenLibrary    => T["stor.kind.hidden"],
+            StorageNodeKind.PreservationHold => T["stor.kind.preservation"],
+            StorageNodeKind.ListAttachments  => T["stor.kind.attachments"],
+            StorageNodeKind.RecycleBin       => T["stor.kind.recyclebin"],
+            StorageNodeKind.Subsite          => T["stor.kind.subsite"],
+            _ => kind.ToString()
+        };
+    }
+
+    /// <summary>
+    /// Pre-resolves localized labels for every <see cref="StorageNodeKind"/>
+    /// once per export. Cached array index lookup avoids
+    /// <c>ResourceManager.GetString</c> per row in hot rendering loops.
+    /// </summary>
+    private static string[] BuildKindLabelCache()
+    {
+        var values = (StorageNodeKind[])Enum.GetValues(typeof(StorageNodeKind));
+        int max = 0;
+        foreach (var v in values) { int i = (int)v; if (i > max) max = i; }
+        var cache = new string[max + 1];
+        for (int i = 0; i < cache.Length; i++) cache[i] = ((StorageNodeKind)i).ToString();
+        foreach (var v in values) cache[(int)v] = KindLabel(v);
+        return cache;
+    }
+
+    /// <summary>HTML-encodes each entry of <paramref name="raw"/> once.</summary>
+    private static string[] BuildHtmlEncodedCache(string[] raw)
+    {
+        var encoded = new string[raw.Length];
+        for (int i = 0; i < raw.Length; i++) encoded[i] = HtmlEncode(raw[i]);
+        return encoded;
+    }
+}

Services/Export/UserAccessCsvExportService.cs

@@ -0,0 +1,257 @@
+using System.IO;
+using System.Text;
+using SharepointToolbox.Web.Core.Helpers;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports user access audit results to CSV format.
+/// Produces one CSV file per audited user with a summary section at the top.
+/// </summary>
+public class UserAccessCsvExportService
+{
+    private static string BuildDataHeader()
+    {
+        var T = TranslationSource.Instance;
+        return $"\"{T["report.col.site"]}\",\"{T["report.col.object_type"]}\",\"{T["report.col.object"]}\",\"{T["report.col.url"]}\",\"{T["report.col.permission_level"]}\",\"{T["report.col.access_type"]}\",\"{T["report.col.granted_through"]}\",\"TargetLabel\",\"TargetUrl\",\"SharingLinkType\"";
+    }
+
+    /// <summary>
+    /// Builds a CSV string for a single user's access entries.
+    /// Includes a summary section at the top followed by data rows.
+    /// </summary>
+    public string BuildCsv(string userDisplayName, string userLogin, IReadOnlyList<UserAccessEntry> entries)
+    {
+        var T = TranslationSource.Instance;
+        var sb = new StringBuilder();
+
+        // Summary section
+        var sitesCount = entries.Select(e => e.SiteUrl).Distinct().Count();
+        var highPrivCount = entries.Count(e => e.IsHighPrivilege);
+
+        sb.AppendLine($"\"{T["report.title.user_access"]}\"");
+        sb.AppendLine($"\"{T["report.col.user"]}\",\"{Csv(userDisplayName)} ({Csv(userLogin)})\"");
+        sb.AppendLine($"\"{T["report.stat.total_accesses"]}\",\"{entries.Count}\"");
+        sb.AppendLine($"\"{T["report.col.sites"]}\",\"{sitesCount}\"");
+        sb.AppendLine($"\"{T["report.stat.high_privilege"]}\",\"{highPrivCount}\"");
+        sb.AppendLine($"\"{T["report.text.generated"]}\",\"{DateTime.Now:yyyy-MM-dd HH:mm:ss}\"");
+        sb.AppendLine(); // Blank line separating summary from data
+
+        // Data rows
+        sb.AppendLine(BuildDataHeader());
+        foreach (var entry in entries)
+        {
+            sb.AppendLine(string.Join(",", new[]
+            {
+                Csv(entry.SiteTitle),
+                Csv(entry.ObjectType),
+                Csv(entry.ObjectTitle),
+                Csv(entry.ObjectUrl),
+                Csv(entry.PermissionLevel),
+                Csv(entry.AccessType.ToString()),
+                Csv(entry.GrantedThrough),
+                Csv(entry.TargetLabel ?? string.Empty),
+                Csv(entry.TargetUrl ?? string.Empty),
+                Csv(entry.SharingLinkType ?? string.Empty)
+            }));
+        }
+
+        return sb.ToString();
+    }
+
+    /// <summary>
+    /// Writes one CSV file per user to the specified directory.
+    /// File names: audit_{email}_{date}.csv
+    /// </summary>
+    public async Task WriteAsync(
+        IReadOnlyList<UserAccessEntry> allEntries,
+        string directoryPath,
+        CancellationToken ct)
+    {
+        Directory.CreateDirectory(directoryPath);
+        var dateStr = DateTime.Now.ToString("yyyy-MM-dd");
+
+        // Group by user
+        var byUser = allEntries.GroupBy(e => e.UserLogin);
+
+        foreach (var group in byUser)
+        {
+            ct.ThrowIfCancellationRequested();
+
+            var userLogin = group.Key;
+            var displayName = group.First().UserDisplayName;
+            var entries = group.ToList();
+
+            // Sanitize email for filename (replace @ and other invalid chars)
+            var safeLogin = SanitizeFileName(userLogin);
+            var fileName = $"audit_{safeLogin}_{dateStr}.csv";
+            var filePath = Path.Combine(directoryPath, fileName);
+
+            var csv = BuildCsv(displayName, userLogin, entries);
+            await ExportFileWriter.WriteCsvAsync(filePath, csv, ct);
+        }
+    }
+
+    /// <summary>
+    /// Writes all entries split per site. File naming: "{base}_{siteLabel}.csv".
+    /// </summary>
+    public async Task WriteBySiteAsync(
+        IReadOnlyList<UserAccessEntry> allEntries,
+        string basePath,
+        CancellationToken ct,
+        bool mergePermissions = false)
+    {
+        foreach (var group in allEntries.GroupBy(e => (e.SiteUrl, e.SiteTitle)))
+        {
+            ct.ThrowIfCancellationRequested();
+            var label = ReportSplitHelper.DeriveSiteLabel(group.Key.SiteUrl, group.Key.SiteTitle);
+            var path = ReportSplitHelper.BuildPartitionPath(basePath, label);
+            await WriteSingleFileAsync(group.ToList(), path, ct, mergePermissions);
+        }
+    }
+
+    /// <summary>
+    /// Split-aware export dispatcher.
+    /// Single → one file at <paramref name="basePath"/>.
+    /// BySite → one file per site. ByUser → one file per user.
+    /// </summary>
+    public async Task WriteAsync(
+        IReadOnlyList<UserAccessEntry> allEntries,
+        string basePath,
+        ReportSplitMode splitMode,
+        CancellationToken ct,
+        bool mergePermissions = false)
+    {
+        switch (splitMode)
+        {
+            case ReportSplitMode.Single:
+                await WriteSingleFileAsync(allEntries, basePath, ct, mergePermissions);
+                break;
+            case ReportSplitMode.BySite:
+                await WriteBySiteAsync(allEntries, basePath, ct, mergePermissions);
+                break;
+            case ReportSplitMode.ByUser:
+                await WriteByUserAsync(allEntries, basePath, ct, mergePermissions);
+                break;
+        }
+    }
+
+    /// <summary>
+    /// Writes one CSV per user using <paramref name="basePath"/> as a filename template.
+    /// </summary>
+    public async Task WriteByUserAsync(
+        IReadOnlyList<UserAccessEntry> allEntries,
+        string basePath,
+        CancellationToken ct,
+        bool mergePermissions = false)
+    {
+        foreach (var group in allEntries.GroupBy(e => e.UserLogin))
+        {
+            ct.ThrowIfCancellationRequested();
+            var label = ReportSplitHelper.SanitizeFileName(group.Key);
+            var path = ReportSplitHelper.BuildPartitionPath(basePath, label);
+            await WriteSingleFileAsync(group.ToList(), path, ct, mergePermissions);
+        }
+    }
+
+    /// <summary>
+    /// Writes all entries to a single CSV file (alternative for single-file export).
+    /// Used when the ViewModel export command picks a single file path.
+    /// When <paramref name="mergePermissions"/> is true, entries are consolidated using
+    /// <see cref="PermissionConsolidator"/> and written in a compact multi-location format.
+    /// </summary>
+    public async Task WriteSingleFileAsync(
+        IReadOnlyList<UserAccessEntry> entries,
+        string filePath,
+        CancellationToken ct,
+        bool mergePermissions = false)
+    {
+        var T = TranslationSource.Instance;
+        if (mergePermissions)
+        {
+            var consolidated = PermissionConsolidator.Consolidate(entries);
+            var sb = new StringBuilder();
+
+            // Summary section
+            sb.AppendLine($"\"{T["report.title.user_access_consolidated"]}\"");
+            sb.AppendLine($"\"{T["report.stat.users_audited"]}\",\"{consolidated.Select(e => e.UserLogin).Distinct().Count()}\"");
+            sb.AppendLine($"\"{T["report.stat.total_entries"]}\",\"{consolidated.Count}\"");
+            sb.AppendLine($"\"{T["report.text.generated"]}\",\"{DateTime.Now:yyyy-MM-dd HH:mm:ss}\"");
+            sb.AppendLine();
+
+            // Header
+            sb.AppendLine($"\"{T["report.col.user"]}\",\"User Login\",\"{T["report.col.permission_level"]}\",\"{T["report.col.access_type"]}\",\"{T["report.col.granted_through"]}\",\"TargetLabel\",\"TargetUrl\",\"SharingLinkType\",\"Locations\",\"Location Count\"");
+
+            // Data rows
+            foreach (var entry in consolidated)
+            {
+                var locations = string.Join("; ", entry.Locations.Select(l => l.SiteTitle));
+                sb.AppendLine(string.Join(",", new[]
+                {
+                    Csv(entry.UserDisplayName),
+                    Csv(entry.UserLogin),
+                    Csv(entry.PermissionLevel),
+                    Csv(entry.AccessType.ToString()),
+                    Csv(entry.GrantedThrough),
+                    Csv(entry.TargetLabel ?? string.Empty),
+                    Csv(entry.TargetUrl ?? string.Empty),
+                    Csv(entry.SharingLinkType ?? string.Empty),
+                    Csv(locations),
+                    Csv(entry.LocationCount.ToString())
+                }));
+            }
+
+            await File.WriteAllTextAsync(filePath, sb.ToString(), new UTF8Encoding(false), ct);
+            return;
+        }
+
+        {
+        var sb = new StringBuilder();
+        var fullHeader = $"\"{T["report.col.user"]}\",\"User Login\"," + BuildDataHeader();
+
+        // Summary
+        var users = entries.Select(e => e.UserLogin).Distinct().ToList();
+        sb.AppendLine($"\"{T["report.title.user_access"]}\"");
+        sb.AppendLine($"\"{T["report.stat.users_audited"]}\",\"{users.Count}\"");
+        sb.AppendLine($"\"{T["report.stat.total_accesses"]}\",\"{entries.Count}\"");
+        sb.AppendLine($"\"{T["report.text.generated"]}\",\"{DateTime.Now:yyyy-MM-dd HH:mm:ss}\"");
+        sb.AppendLine();
+
+        sb.AppendLine(fullHeader);
+        foreach (var entry in entries)
+        {
+            sb.AppendLine(string.Join(",", new[]
+            {
+                Csv(entry.UserDisplayName),
+                Csv(entry.UserLogin),
+                Csv(entry.SiteTitle),
+                Csv(entry.ObjectType),
+                Csv(entry.ObjectTitle),
+                Csv(entry.ObjectUrl),
+                Csv(entry.PermissionLevel),
+                Csv(entry.AccessType.ToString()),
+                Csv(entry.GrantedThrough),
+                Csv(entry.TargetLabel ?? string.Empty),
+                Csv(entry.TargetUrl ?? string.Empty),
+                Csv(entry.SharingLinkType ?? string.Empty)
+            }));
+        }
+
+        await ExportFileWriter.WriteCsvAsync(filePath, sb.ToString(), ct);
+        }
+    }
+
+    /// <summary>RFC 4180 CSV field escaping with formula-injection guard.</summary>
+    private static string Csv(string value) => CsvSanitizer.Escape(value);
+
+    private static string SanitizeFileName(string name)
+    {
+        var invalid = Path.GetInvalidFileNameChars();
+        var sb = new StringBuilder(name.Length);
+        foreach (var c in name)
+            sb.Append(invalid.Contains(c) ? '_' : c);
+        return sb.ToString();
+    }
+}

Services/Export/UserAccessHtmlExportService.cs

@@ -0,0 +1,708 @@
+using System.IO;
+using System.Text;
+using SharepointToolbox.Web.Core.Helpers;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports user access audit results to a self-contained interactive HTML report.
+/// Produces a single HTML file with dual-view toggle (by-user / by-site),
+/// collapsible groups, sortable columns, filter input, and risk highlighting.
+/// No external CSS/JS dependencies — everything is inline.
+/// </summary>
+public class UserAccessHtmlExportService
+{
+    /// <summary>
+    /// Builds a self-contained HTML string from the supplied user access entries.
+    /// When <paramref name="mergePermissions"/> is true, renders a consolidated by-user
+    /// report with an expandable Sites column instead of the dual by-user/by-site view.
+    /// </summary>
+    /// <summary>
+    /// Split-aware HTML export. Single → one file.
+    /// BySite/ByUser + SeparateFiles → one file per site/user.
+    /// BySite/ByUser + SingleTabbed → one file with per-partition iframe tabs.
+    /// </summary>
+    public async Task WriteAsync(
+        IReadOnlyList<UserAccessEntry> entries,
+        string basePath,
+        ReportSplitMode splitMode,
+        HtmlSplitLayout layout,
+        CancellationToken ct,
+        bool mergePermissions = false,
+        ReportBranding? branding = null)
+    {
+        if (splitMode == ReportSplitMode.Single)
+        {
+            await WriteAsync(entries, basePath, ct, mergePermissions, branding);
+            return;
+        }
+
+        IEnumerable<(string Label, IReadOnlyList<UserAccessEntry> Entries)> partitions;
+        if (splitMode == ReportSplitMode.BySite)
+        {
+            partitions = entries
+                .GroupBy(e => (e.SiteUrl, e.SiteTitle))
+                .Select(g => (
+                    Label: ReportSplitHelper.DeriveSiteLabel(g.Key.SiteUrl, g.Key.SiteTitle),
+                    Entries: (IReadOnlyList<UserAccessEntry>)g.ToList()));
+        }
+        else // ByUser
+        {
+            partitions = entries
+                .GroupBy(e => e.UserLogin)
+                .Select(g => (
+                    Label: ReportSplitHelper.SanitizeFileName(g.Key),
+                    Entries: (IReadOnlyList<UserAccessEntry>)g.ToList()));
+        }
+
+        var partList = partitions.ToList();
+        if (layout == HtmlSplitLayout.SingleTabbed)
+        {
+            var parts = partList
+                .Select(p => (p.Label, Html: BuildHtml(p.Entries, mergePermissions, branding)))
+                .ToList();
+            var title = TranslationSource.Instance["report.title.user_access"];
+            var tabbed = ReportSplitHelper.BuildTabbedHtml(parts, title);
+            await ExportFileWriter.WriteHtmlAsync(basePath, tabbed, ct);
+            return;
+        }
+
+        foreach (var (label, partEntries) in partList)
+        {
+            ct.ThrowIfCancellationRequested();
+            var path = ReportSplitHelper.BuildPartitionPath(basePath, label);
+            await WriteAsync(partEntries, path, ct, mergePermissions, branding);
+        }
+    }
+
+    /// <summary>
+    /// Builds the user-access HTML report. Default layout is a per-entry
+    /// grouped-by-user table; when <paramref name="mergePermissions"/> is true
+    /// entries are consolidated via <see cref="PermissionConsolidator"/> into
+    /// a single-row-per-user format with a Locations column.
+    /// </summary>
+    public string BuildHtml(IReadOnlyList<UserAccessEntry> entries, bool mergePermissions = false, ReportBranding? branding = null)
+    {
+        if (mergePermissions)
+        {
+            var consolidated = PermissionConsolidator.Consolidate(entries);
+            return BuildConsolidatedHtml(consolidated, entries, branding);
+        }
+
+        var T = TranslationSource.Instance;
+
+        // Compute stats
+        var totalAccesses    = entries.Count;
+        var usersAudited     = entries.Select(e => e.UserLogin).Distinct().Count();
+        var sitesScanned     = entries.Select(e => e.SiteUrl).Distinct().Count();
+        var highPrivCount    = entries.Count(e => e.IsHighPrivilege);
+        var externalCount    = entries.Count(e => e.IsExternalUser);
+
+        var sb = new StringBuilder();
+
+        // ── HTML HEAD ──────────────────────────────────────────────────────────
+        sb.AppendLine("<!DOCTYPE html>");
+        sb.AppendLine("<html lang=\"en\">");
+        sb.AppendLine("<head>");
+        sb.AppendLine("<meta charset=\"UTF-8\">");
+        sb.AppendLine("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">");
+        sb.AppendLine($"<title>{T["report.title.user_access"]}</title>");
+        sb.AppendLine("<style>");
+        sb.AppendLine(@"
+* { box-sizing: border-box; margin: 0; padding: 0; }
+body { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; background: #f5f5f5; color: #333; }
+h1 { padding: 20px 24px 10px; font-size: 1.5rem; color: #1a1a2e; }
+.stats { display: flex; gap: 16px; padding: 0 24px 16px; flex-wrap: wrap; }
+.stat-card { background: #fff; border-radius: 8px; padding: 14px 20px; min-width: 160px; box-shadow: 0 1px 4px rgba(0,0,0,.1); }
+.stat-card .value { font-size: 2rem; font-weight: 700; color: #1a1a2e; }
+.stat-card .label { font-size: .8rem; color: #666; margin-top: 2px; }
+/* View toggle */
+.view-toggle { display: flex; gap: 8px; padding: 0 24px 12px; }
+.view-toggle button { padding: 7px 18px; border: 1px solid #ccc; border-radius: 6px; background: #fff; cursor: pointer; font-size: .9rem; }
+.view-toggle button.active { background: #1a1a2e; color: #fff; border-color: #1a1a2e; }
+/* Filter */
+.filter-wrap { padding: 0 24px 12px; }
+#filter { width: 320px; padding: 8px 12px; border: 1px solid #ccc; border-radius: 6px; font-size: .95rem; }
+/* Per-user summary cards */
+.user-summary { padding: 0 24px 16px; display: flex; gap: 12px; flex-wrap: wrap; }
+.user-card { background: #fff; border-radius: 8px; padding: 12px 16px; min-width: 200px; box-shadow: 0 1px 4px rgba(0,0,0,.1); }
+.user-card .user-name { font-weight: 600; font-size: .95rem; color: #1a1a2e; margin-bottom: 4px; }
+.user-card .user-stats { font-size: .8rem; color: #555; }
+.user-card.has-high-priv { border-left: 4px solid #dc2626; }
+/* Table wrap */
+.table-wrap { overflow-x: auto; padding: 0 24px 32px; }
+table { width: 100%; border-collapse: collapse; background: #fff; border-radius: 8px; overflow: hidden; box-shadow: 0 1px 4px rgba(0,0,0,.1); }
+th { background: #1a1a2e; color: #fff; padding: 10px 14px; text-align: left; font-size: .85rem; white-space: nowrap; cursor: pointer; user-select: none; }
+th:hover { background: #2d2d4e; }
+td { padding: 9px 14px; border-bottom: 1px solid #eee; vertical-align: top; font-size: .875rem; }
+tr:last-child td { border-bottom: none; }
+tr:hover td { background: #fafafa; }
+/* Group headers */
+.group-header { cursor: pointer; background: #f0f0f0; padding: 10px 14px; font-weight: 600; font-size: .875rem; }
+.group-header:hover { background: #e8e8e8; }
+.group-header td { background: inherit !important; font-weight: 600; }
+/* Badges */
+.badge { display: inline-block; padding: 2px 8px; border-radius: 4px; font-size: .75rem; font-weight: 600; white-space: nowrap; }
+/* Access type badges */
+.access-direct    { background: #dbeafe; color: #1e40af; }
+.access-group     { background: #dcfce7; color: #166534; }
+.access-inherited { background: #f3f4f6; color: #374151; }
+/* High privilege */
+.high-priv { font-weight: 700; }
+/* Guest badge */
+.guest-badge { display: inline-block; padding: 2px 8px; border-radius: 12px; font-size: .75rem; font-weight: 600; background: #fff7ed; color: #9a3412; border: 1px solid #fed7aa; margin-left: 4px; }
+/* User pills */
+.user-pill { display: inline-block; background: #e0e7ff; color: #3730a3; border-radius: 12px; padding: 2px 10px; font-size: .75rem; margin: 2px 3px 2px 0; white-space: nowrap; }
+a { color: #2563eb; text-decoration: none; }
+a:hover { text-decoration: underline; }
+.hidden { display: none; }
+");
+        sb.AppendLine("</style>");
+        sb.AppendLine("</head>");
+
+        // ── BODY ───────────────────────────────────────────────────────────────
+        sb.AppendLine("<body>");
+        sb.Append(BrandingHtmlHelper.BuildBrandingHeader(branding));
+        sb.AppendLine($"<h1>{T["report.title.user_access"]}</h1>");
+
+        // Stats cards
+        sb.AppendLine("<div class=\"stats\">");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{totalAccesses}</div><div class=\"label\">{T["report.stat.total_accesses"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{usersAudited}</div><div class=\"label\">{T["report.stat.users_audited"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{sitesScanned}</div><div class=\"label\">{T["report.stat.sites_scanned"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{highPrivCount}</div><div class=\"label\">{T["report.stat.high_privilege"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{externalCount}</div><div class=\"label\">{T["report.stat.external_users"]}</div></div>");
+        sb.AppendLine("</div>");
+
+        // Per-user summary cards
+        sb.AppendLine("<div class=\"user-summary\">");
+        var userGroups = entries.GroupBy(e => e.UserLogin).OrderBy(g => g.Key).ToList();
+        foreach (var ug in userGroups)
+        {
+            var uName     = HtmlEncode(ug.First().UserDisplayName);
+            var uLogin    = HtmlEncode(ug.Key);
+            var uTotal    = ug.Count();
+            var uSites    = ug.Select(e => e.SiteUrl).Distinct().Count();
+            var uHighPriv = ug.Count(e => e.IsHighPrivilege);
+            var uIsExt    = ug.First().IsExternalUser;
+            var cardClass = uHighPriv > 0 ? "user-card has-high-priv" : "user-card";
+
+            sb.AppendLine($"  <div class=\"{cardClass}\">");
+            sb.AppendLine($"    <div class=\"user-name\">{uName}{(uIsExt ? $" <span class=\"guest-badge\">{T["report.badge.guest"]}</span>" : "")}</div>");
+            sb.AppendLine($"    <div class=\"user-stats\">{uLogin}</div>");
+            sb.AppendLine($"    <div class=\"user-stats\">{uTotal} {T["report.text.accesses"]} &bull; {uSites} {T["report.text.sites_parens"]}{(uHighPriv > 0 ? $" &bull; <span style=\"color:#dc2626\">{uHighPriv} {T["report.text.high_priv"]}</span>" : "")}</div>");
+            sb.AppendLine("  </div>");
+        }
+        sb.AppendLine("</div>");
+
+        // View toggle buttons
+        sb.AppendLine("<div class=\"view-toggle\">");
+        sb.AppendLine($"  <button id=\"btn-user\" class=\"active\" onclick=\"toggleView('user')\">{T["report.view.by_user"]}</button>");
+        sb.AppendLine($"  <button id=\"btn-site\" onclick=\"toggleView('site')\">{T["report.view.by_site"]}</button>");
+        sb.AppendLine("</div>");
+
+        // Filter input
+        sb.AppendLine("<div class=\"filter-wrap\">");
+        sb.AppendLine($"  <input type=\"text\" id=\"filter\" placeholder=\"{T["report.filter.placeholder_results"]}\" oninput=\"filterTable()\" />");
+        sb.AppendLine("</div>");
+
+        // ── BY-USER VIEW ───────────────────────────────────────────────────────
+        sb.AppendLine("<div id=\"view-user\" class=\"table-wrap\">");
+        sb.AppendLine("<table id=\"tbl-user\">");
+        sb.AppendLine("<thead><tr>");
+        sb.AppendLine($"  <th onclick=\"sortTable('user',0)\">{T["report.col.site"]}</th>");
+        sb.AppendLine($"  <th onclick=\"sortTable('user',1)\">{T["report.col.object_type"]}</th>");
+        sb.AppendLine($"  <th onclick=\"sortTable('user',2)\">{T["report.col.object"]}</th>");
+        sb.AppendLine($"  <th onclick=\"sortTable('user',3)\">{T["report.col.permission_level"]}</th>");
+        sb.AppendLine($"  <th onclick=\"sortTable('user',4)\">{T["report.col.access_type"]}</th>");
+        sb.AppendLine($"  <th onclick=\"sortTable('user',5)\">{T["report.col.granted_through"]}</th>");
+        sb.AppendLine("</tr></thead>");
+        sb.AppendLine("<tbody id=\"tbody-user\">");
+
+        int userGroupIdx = 0;
+        foreach (var ug in userGroups)
+        {
+            var groupId  = $"ugrp{userGroupIdx++}";
+            var uName    = HtmlEncode(ug.First().UserDisplayName);
+            var uIsExt   = ug.First().IsExternalUser;
+            var uCount   = ug.Count();
+            var guestBadge = uIsExt ? $" <span class=\"guest-badge\">{T["report.badge.guest"]}</span>" : "";
+
+            sb.AppendLine($"<tr class=\"group-header\" onclick=\"toggleGroup('{groupId}')\">");
+            sb.AppendLine($"  <td colspan=\"6\">{uName}{guestBadge} &mdash; {uCount} {T["report.text.access_es"]}</td>");
+            sb.AppendLine("</tr>");
+
+            foreach (var entry in ug)
+            {
+                var rowClass   = entry.IsHighPrivilege ? " class=\"high-priv\"" : "";
+                var accessBadge = AccessTypeBadge(entry.AccessType);
+                var highIcon   = entry.IsHighPrivilege ? " &#9888;" : "";
+
+                var objectCell = IsRedundantObjectTitle(entry.SiteTitle, entry.ObjectTitle)
+                    ? "&mdash;"
+                    : HtmlEncode(entry.ObjectTitle);
+
+                sb.AppendLine($"<tr data-group=\"{groupId}\">");
+                sb.AppendLine($"  <td{rowClass}>{HtmlEncode(entry.SiteTitle)}</td>");
+                sb.AppendLine($"  <td>{HtmlEncode(entry.ObjectType)}</td>");
+                sb.AppendLine($"  <td>{objectCell}</td>");
+                sb.AppendLine($"  <td{rowClass}>{HtmlEncode(entry.PermissionLevel)}{highIcon}</td>");
+                sb.AppendLine($"  <td>{accessBadge}</td>");
+                sb.AppendLine($"  <td>{PermissionHtmlFragments.BuildGrantedThroughCell(entry.GrantedThrough, entry.TargetUrl, entry.TargetLabel, entry.SharingLinkType)}</td>");
+                sb.AppendLine("</tr>");
+            }
+        }
+
+        sb.AppendLine("</tbody>");
+        sb.AppendLine("</table>");
+        sb.AppendLine("</div>");
+
+        // ── BY-SITE VIEW ───────────────────────────────────────────────────────
+        sb.AppendLine("<div id=\"view-site\" class=\"table-wrap hidden\">");
+        sb.AppendLine("<table id=\"tbl-site\">");
+        sb.AppendLine("<thead><tr>");
+        sb.AppendLine($"  <th onclick=\"sortTable('site',0)\">{T["report.col.user"]}</th>");
+        sb.AppendLine($"  <th onclick=\"sortTable('site',1)\">{T["report.col.object_type"]}</th>");
+        sb.AppendLine($"  <th onclick=\"sortTable('site',2)\">{T["report.col.object"]}</th>");
+        sb.AppendLine($"  <th onclick=\"sortTable('site',3)\">{T["report.col.permission_level"]}</th>");
+        sb.AppendLine($"  <th onclick=\"sortTable('site',4)\">{T["report.col.access_type"]}</th>");
+        sb.AppendLine($"  <th onclick=\"sortTable('site',5)\">{T["report.col.granted_through"]}</th>");
+        sb.AppendLine("</tr></thead>");
+        sb.AppendLine("<tbody id=\"tbody-site\">");
+
+        var siteGroups = entries.GroupBy(e => e.SiteUrl).OrderBy(g => g.Key).ToList();
+        int siteGroupIdx = 0;
+        foreach (var sg in siteGroups)
+        {
+            var groupId   = $"sgrp{siteGroupIdx++}";
+            var siteTitle = HtmlEncode(sg.First().SiteTitle);
+            var sCount    = sg.Count();
+
+            sb.AppendLine($"<tr class=\"group-header\" onclick=\"toggleGroup('{groupId}')\">");
+            sb.AppendLine($"  <td colspan=\"6\">{siteTitle} &mdash; {sCount} {T["report.text.access_es"]}</td>");
+            sb.AppendLine("</tr>");
+
+            foreach (var entry in sg)
+            {
+                var rowClass   = entry.IsHighPrivilege ? " class=\"high-priv\"" : "";
+                var accessBadge = AccessTypeBadge(entry.AccessType);
+                var highIcon   = entry.IsHighPrivilege ? " &#9888;" : "";
+                var guestBadge = entry.IsExternalUser ? $" <span class=\"guest-badge\">{T["report.badge.guest"]}</span>" : "";
+
+                var objectCell = IsRedundantObjectTitle(entry.SiteTitle, entry.ObjectTitle)
+                    ? "&mdash;"
+                    : HtmlEncode(entry.ObjectTitle);
+
+                sb.AppendLine($"<tr data-group=\"{groupId}\">");
+                sb.AppendLine($"  <td>{HtmlEncode(entry.UserDisplayName)}{guestBadge}</td>");
+                sb.AppendLine($"  <td>{HtmlEncode(entry.ObjectType)}</td>");
+                sb.AppendLine($"  <td>{objectCell}</td>");
+                sb.AppendLine($"  <td{rowClass}>{HtmlEncode(entry.PermissionLevel)}{highIcon}</td>");
+                sb.AppendLine($"  <td>{accessBadge}</td>");
+                sb.AppendLine($"  <td>{PermissionHtmlFragments.BuildGrantedThroughCell(entry.GrantedThrough, entry.TargetUrl, entry.TargetLabel, entry.SharingLinkType)}</td>");
+                sb.AppendLine("</tr>");
+            }
+        }
+
+        sb.AppendLine("</tbody>");
+        sb.AppendLine("</table>");
+        sb.AppendLine("</div>");
+
+        // ── INLINE JS ─────────────────────────────────────────────────────────
+        sb.AppendLine("<script>");
+        sb.AppendLine(@"
+var _currentView = 'user';
+var _sortState = {};
+
+function toggleView(view) {
+  _currentView = view;
+  document.getElementById('view-user').classList.toggle('hidden', view !== 'user');
+  document.getElementById('view-site').classList.toggle('hidden', view !== 'site');
+  document.getElementById('btn-user').classList.toggle('active', view === 'user');
+  document.getElementById('btn-site').classList.toggle('active', view === 'site');
+  // Re-apply filter to new view
+  filterTable();
+}
+
+function filterTable() {
+  var input = document.getElementById('filter').value.toLowerCase();
+  var tbodyId = _currentView === 'user' ? 'tbody-user' : 'tbody-site';
+  var tbody = document.getElementById(tbodyId);
+  var rows = tbody.querySelectorAll('tr[data-group]');
+  var groupsWithVisible = {};
+
+  rows.forEach(function(row) {
+    var matches = row.textContent.toLowerCase().indexOf(input) > -1;
+    row.style.display = matches ? '' : 'none';
+    if (matches) {
+      groupsWithVisible[row.getAttribute('data-group')] = true;
+    }
+  });
+
+  // Show/hide group headers based on whether they have visible children
+  var headers = tbody.querySelectorAll('tr.group-header');
+  headers.forEach(function(hdr) {
+    // find next sibling rows until next header
+    var next = hdr.nextElementSibling;
+    var groupId = null;
+    while (next && next.getAttribute('data-group')) {
+      groupId = next.getAttribute('data-group');
+      break;
+    }
+    if (groupId) {
+      hdr.style.display = groupsWithVisible[groupId] ? '' : 'none';
+    }
+  });
+}
+
+function toggleGroup(id) {
+  var rows = document.querySelectorAll('tr[data-group=""' + id + '""]');
+  var isHidden = rows.length > 0 && rows[0].style.display === 'none';
+  rows.forEach(function(r) { r.style.display = isHidden ? '' : 'none'; });
+}
+
+function sortTable(view, col) {
+  var tbodyId = view === 'user' ? 'tbody-user' : 'tbody-site';
+  var tbody = document.getElementById(tbodyId);
+  var key = view + '_' + col;
+  var asc = _sortState[key] !== true;
+  _sortState[key] = asc;
+
+  // Sort within each group separately
+  var groupHeaders = Array.from(tbody.querySelectorAll('tr.group-header'));
+  groupHeaders.forEach(function(hdr) {
+    var groupId = null;
+    var next = hdr.nextElementSibling;
+    while (next && next.getAttribute('data-group')) {
+      groupId = next.getAttribute('data-group');
+      break;
+    }
+    if (!groupId) return;
+    var groupRows = Array.from(tbody.querySelectorAll('tr[data-group=""' + groupId + '""]'));
+    groupRows.sort(function(a, b) {
+      var aText = (a.cells[col] ? a.cells[col].textContent : '').trim().toLowerCase();
+      var bText = (b.cells[col] ? b.cells[col].textContent : '').trim().toLowerCase();
+      return asc ? aText.localeCompare(bText) : bText.localeCompare(aText);
+    });
+    // Re-insert sorted rows after the group header
+    var insertAfter = hdr;
+    groupRows.forEach(function(row) {
+      tbody.insertBefore(row, insertAfter.nextSibling);
+      insertAfter = row;
+    });
+  });
+}
+");
+        sb.AppendLine("</script>");
+        sb.AppendLine("</body>");
+        sb.AppendLine("</html>");
+
+        return sb.ToString();
+    }
+
+    /// <summary>
+    /// Writes the HTML report to the specified file path using UTF-8 without BOM.
+    /// </summary>
+    public async Task WriteAsync(IReadOnlyList<UserAccessEntry> entries, string filePath, CancellationToken ct, bool mergePermissions = false, ReportBranding? branding = null)
+    {
+        var html = BuildHtml(entries, mergePermissions, branding);
+        await ExportFileWriter.WriteHtmlAsync(filePath, html, ct);
+    }
+
+    /// <summary>
+    /// Builds the consolidated HTML report: single by-user table with a Sites column.
+    /// By-site view and view-toggle are omitted. Uses the same CSS shell as BuildHtml.
+    /// </summary>
+    private string BuildConsolidatedHtml(
+        IReadOnlyList<ConsolidatedPermissionEntry> consolidated,
+        IReadOnlyList<UserAccessEntry> entries,
+        ReportBranding? branding)
+    {
+        var T = TranslationSource.Instance;
+
+        // Stats computed from the original flat list for accurate counts
+        var totalAccesses = entries.Count;
+        var usersAudited  = entries.Select(e => e.UserLogin).Distinct().Count();
+        var sitesScanned  = entries.Select(e => e.SiteUrl).Distinct().Count();
+        var highPrivCount = entries.Count(e => e.IsHighPrivilege);
+        var externalCount = entries.Count(e => e.IsExternalUser);
+
+        var sb = new StringBuilder();
+
+        // ── HTML HEAD (same as BuildHtml) ──────────────────────────────────────
+        sb.AppendLine("<!DOCTYPE html>");
+        sb.AppendLine("<html lang=\"en\">");
+        sb.AppendLine("<head>");
+        sb.AppendLine("<meta charset=\"UTF-8\">");
+        sb.AppendLine("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">");
+        sb.AppendLine($"<title>{T["report.title.user_access_consolidated"]}</title>");
+        sb.AppendLine("<style>");
+        sb.AppendLine(@"
+* { box-sizing: border-box; margin: 0; padding: 0; }
+body { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; background: #f5f5f5; color: #333; }
+h1 { padding: 20px 24px 10px; font-size: 1.5rem; color: #1a1a2e; }
+.stats { display: flex; gap: 16px; padding: 0 24px 16px; flex-wrap: wrap; }
+.stat-card { background: #fff; border-radius: 8px; padding: 14px 20px; min-width: 160px; box-shadow: 0 1px 4px rgba(0,0,0,.1); }
+.stat-card .value { font-size: 2rem; font-weight: 700; color: #1a1a2e; }
+.stat-card .label { font-size: .8rem; color: #666; margin-top: 2px; }
+/* View toggle */
+.view-toggle { display: flex; gap: 8px; padding: 0 24px 12px; }
+.view-toggle button { padding: 7px 18px; border: 1px solid #ccc; border-radius: 6px; background: #fff; cursor: pointer; font-size: .9rem; }
+.view-toggle button.active { background: #1a1a2e; color: #fff; border-color: #1a1a2e; }
+/* Filter */
+.filter-wrap { padding: 0 24px 12px; }
+#filter { width: 320px; padding: 8px 12px; border: 1px solid #ccc; border-radius: 6px; font-size: .95rem; }
+/* Per-user summary cards */
+.user-summary { padding: 0 24px 16px; display: flex; gap: 12px; flex-wrap: wrap; }
+.user-card { background: #fff; border-radius: 8px; padding: 12px 16px; min-width: 200px; box-shadow: 0 1px 4px rgba(0,0,0,.1); }
+.user-card .user-name { font-weight: 600; font-size: .95rem; color: #1a1a2e; margin-bottom: 4px; }
+.user-card .user-stats { font-size: .8rem; color: #555; }
+.user-card.has-high-priv { border-left: 4px solid #dc2626; }
+/* Table wrap */
+.table-wrap { overflow-x: auto; padding: 0 24px 32px; }
+table { width: 100%; border-collapse: collapse; background: #fff; border-radius: 8px; overflow: hidden; box-shadow: 0 1px 4px rgba(0,0,0,.1); }
+th { background: #1a1a2e; color: #fff; padding: 10px 14px; text-align: left; font-size: .85rem; white-space: nowrap; cursor: pointer; user-select: none; }
+th:hover { background: #2d2d4e; }
+td { padding: 9px 14px; border-bottom: 1px solid #eee; vertical-align: top; font-size: .875rem; }
+tr:last-child td { border-bottom: none; }
+tr:hover td { background: #fafafa; }
+/* Group headers */
+.group-header { cursor: pointer; background: #f0f0f0; padding: 10px 14px; font-weight: 600; font-size: .875rem; }
+.group-header:hover { background: #e8e8e8; }
+.group-header td { background: inherit !important; font-weight: 600; }
+/* Badges */
+.badge { display: inline-block; padding: 2px 8px; border-radius: 4px; font-size: .75rem; font-weight: 600; white-space: nowrap; }
+/* Access type badges */
+.access-direct    { background: #dbeafe; color: #1e40af; }
+.access-group     { background: #dcfce7; color: #166534; }
+.access-inherited { background: #f3f4f6; color: #374151; }
+/* High privilege */
+.high-priv { font-weight: 700; }
+/* Guest badge */
+.guest-badge { display: inline-block; padding: 2px 8px; border-radius: 12px; font-size: .75rem; font-weight: 600; background: #fff7ed; color: #9a3412; border: 1px solid #fed7aa; margin-left: 4px; }
+/* User pills */
+.user-pill { display: inline-block; background: #e0e7ff; color: #3730a3; border-radius: 12px; padding: 2px 10px; font-size: .75rem; margin: 2px 3px 2px 0; white-space: nowrap; }
+a { color: #2563eb; text-decoration: none; }
+a:hover { text-decoration: underline; }
+.hidden { display: none; }
+");
+        sb.AppendLine("</style>");
+        sb.AppendLine("</head>");
+
+        // ── BODY ───────────────────────────────────────────────────────────────
+        sb.AppendLine("<body>");
+        sb.Append(BrandingHtmlHelper.BuildBrandingHeader(branding));
+        sb.AppendLine($"<h1>{T["report.title.user_access_consolidated"]}</h1>");
+
+        // Stats cards
+        sb.AppendLine("<div class=\"stats\">");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{totalAccesses}</div><div class=\"label\">{T["report.stat.total_accesses"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{usersAudited}</div><div class=\"label\">{T["report.stat.users_audited"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{sitesScanned}</div><div class=\"label\">{T["report.stat.sites_scanned"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{highPrivCount}</div><div class=\"label\">{T["report.stat.high_privilege"]}</div></div>");
+        sb.AppendLine($"  <div class=\"stat-card\"><div class=\"value\">{externalCount}</div><div class=\"label\">{T["report.stat.external_users"]}</div></div>");
+        sb.AppendLine("</div>");
+
+        // Per-user summary cards (from original flat entries)
+        sb.AppendLine("<div class=\"user-summary\">");
+        var userGroups = entries.GroupBy(e => e.UserLogin).OrderBy(g => g.Key).ToList();
+        foreach (var ug in userGroups)
+        {
+            var uName     = HtmlEncode(ug.First().UserDisplayName);
+            var uLogin    = HtmlEncode(ug.Key);
+            var uTotal    = ug.Count();
+            var uSites    = ug.Select(e => e.SiteUrl).Distinct().Count();
+            var uHighPriv = ug.Count(e => e.IsHighPrivilege);
+            var uIsExt    = ug.First().IsExternalUser;
+            var cardClass = uHighPriv > 0 ? "user-card has-high-priv" : "user-card";
+
+            sb.AppendLine($"  <div class=\"{cardClass}\">");
+            sb.AppendLine($"    <div class=\"user-name\">{uName}{(uIsExt ? $" <span class=\"guest-badge\">{T["report.badge.guest"]}</span>" : "")}</div>");
+            sb.AppendLine($"    <div class=\"user-stats\">{uLogin}</div>");
+            sb.AppendLine($"    <div class=\"user-stats\">{uTotal} {T["report.text.accesses"]} &bull; {uSites} {T["report.text.sites_parens"]}{(uHighPriv > 0 ? $" &bull; <span style=\"color:#dc2626\">{uHighPriv} {T["report.text.high_priv"]}</span>" : "")}</div>");
+            sb.AppendLine("  </div>");
+        }
+        sb.AppendLine("</div>");
+
+        // View toggle — only By User (By Site is suppressed for consolidated view)
+        sb.AppendLine("<div class=\"view-toggle\">");
+        sb.AppendLine($"  <button id=\"btn-user\" class=\"active\">{T["report.view.by_user"]}</button>");
+        sb.AppendLine("</div>");
+
+        // Filter input
+        sb.AppendLine("<div class=\"filter-wrap\">");
+        sb.AppendLine($"  <input type=\"text\" id=\"filter\" placeholder=\"{T["report.filter.placeholder_results"]}\" oninput=\"filterTable()\" />");
+        sb.AppendLine("</div>");
+
+        // ── CONSOLIDATED BY-USER TABLE ────────────────────────────────────────
+        sb.AppendLine("<div id=\"view-user\" class=\"table-wrap\">");
+        sb.AppendLine("<table id=\"tbl-user\">");
+        sb.AppendLine("<thead><tr>");
+        sb.AppendLine($"  <th>{T["report.col.user"]}</th>");
+        sb.AppendLine($"  <th>{T["report.col.permission_level"]}</th>");
+        sb.AppendLine($"  <th>{T["report.col.access_type"]}</th>");
+        sb.AppendLine($"  <th>{T["report.col.granted_through"]}</th>");
+        sb.AppendLine($"  <th>{T["report.col.sites"]}</th>");
+        sb.AppendLine("</tr></thead>");
+        sb.AppendLine("<tbody id=\"tbody-user\">");
+
+        // Group consolidated entries by UserLogin for group headers
+        var consolidatedByUser = consolidated
+            .GroupBy(c => c.UserLogin)
+            .OrderBy(g => g.Key)
+            .ToList();
+
+        int grpIdx = 0;
+        int locIdx = 0;  // SEPARATE counter for location group IDs — Pitfall 2
+
+        foreach (var cug in consolidatedByUser)
+        {
+            var groupId    = $"ugrp{grpIdx++}";
+            var cuName     = HtmlEncode(cug.First().UserDisplayName);
+            var cuIsExt    = cug.First().IsExternalUser;
+            var cuCount    = cug.Count();
+            var guestBadge = cuIsExt ? $" <span class=\"guest-badge\">{T["report.badge.guest"]}</span>" : "";
+
+            sb.AppendLine($"<tr class=\"group-header\" onclick=\"toggleGroup('{groupId}')\">");
+            sb.AppendLine($"  <td colspan=\"5\">{cuName}{guestBadge} &mdash; {cuCount} {T["report.text.permissions_parens"]}</td>");
+            sb.AppendLine("</tr>");
+
+            foreach (var entry in cug)
+            {
+                var rowClass    = entry.IsHighPrivilege ? " class=\"high-priv\"" : "";
+                var accessBadge = AccessTypeBadge(entry.AccessType);
+                var highIcon    = entry.IsHighPrivilege ? " &#9888;" : "";
+
+                sb.AppendLine($"<tr data-group=\"{groupId}\">");
+                sb.AppendLine($"  <td{rowClass}>{HtmlEncode(entry.UserDisplayName)}{guestBadge}</td>");
+                sb.AppendLine($"  <td{rowClass}>{HtmlEncode(entry.PermissionLevel)}{highIcon}</td>");
+                sb.AppendLine($"  <td>{accessBadge}</td>");
+                sb.AppendLine($"  <td>{PermissionHtmlFragments.BuildGrantedThroughCell(entry.GrantedThrough, entry.TargetUrl, entry.TargetLabel, entry.SharingLinkType)}</td>");
+
+                if (entry.LocationCount == 1)
+                {
+                    // Single location — inline site title + object title
+                    var loc0 = entry.Locations[0];
+                    var locLabel = IsRedundantObjectTitle(loc0.SiteTitle, loc0.ObjectTitle)
+                        ? HtmlEncode(loc0.SiteTitle)
+                        : $"{HtmlEncode(loc0.SiteTitle)} &rsaquo; {HtmlEncode(loc0.ObjectTitle)}";
+                    sb.AppendLine($"  <td>{locLabel}</td>");
+                    sb.AppendLine("</tr>");
+                }
+                else
+                {
+                    // Multiple locations — expandable badge
+                    var currentLocId = $"loc{locIdx++}";
+                    sb.AppendLine($"  <td><span class=\"badge\" onclick=\"toggleGroup('{currentLocId}')\" style=\"cursor:pointer\">{entry.LocationCount} {TranslationSource.Instance["report.text.sites_unit"]}</span></td>");
+                    sb.AppendLine("</tr>");
+
+                    // Hidden sub-rows — one per location
+                    foreach (var loc in entry.Locations)
+                    {
+                        var subLabel = IsRedundantObjectTitle(loc.SiteTitle, loc.ObjectTitle)
+                            ? $"<a href=\"{HtmlEncode(loc.SiteUrl)}\">{HtmlEncode(loc.SiteTitle)}</a>"
+                            : $"<a href=\"{HtmlEncode(loc.SiteUrl)}\">{HtmlEncode(loc.SiteTitle)}</a> &rsaquo; {HtmlEncode(loc.ObjectTitle)}";
+                        sb.AppendLine($"<tr data-group=\"{currentLocId}\" style=\"display:none\">");
+                        sb.AppendLine($"  <td colspan=\"5\" style=\"padding-left:2em\">");
+                        sb.AppendLine($"    {subLabel}");
+                        sb.AppendLine("  </td>");
+                        sb.AppendLine("</tr>");
+                    }
+                }
+            }
+        }
+
+        sb.AppendLine("</tbody>");
+        sb.AppendLine("</table>");
+        sb.AppendLine("</div>");
+
+        // ── INLINE JS ─────────────────────────────────────────────────────────
+        sb.AppendLine("<script>");
+        sb.AppendLine(@"
+var _sortState = {};
+
+function filterTable() {
+  var input = document.getElementById('filter').value.toLowerCase();
+  var tbody = document.getElementById('tbody-user');
+  var rows = tbody.querySelectorAll('tr[data-group]');
+  var groupsWithVisible = {};
+
+  rows.forEach(function(row) {
+    // Skip hidden sub-rows that belong to location groups (loc...)
+    if (row.getAttribute('data-group').indexOf('loc') === 0) return;
+    var matches = row.textContent.toLowerCase().indexOf(input) > -1;
+    row.style.display = matches ? '' : 'none';
+    if (matches) {
+      groupsWithVisible[row.getAttribute('data-group')] = true;
+    }
+  });
+
+  // Show/hide group headers based on whether they have visible children
+  var headers = tbody.querySelectorAll('tr.group-header');
+  headers.forEach(function(hdr) {
+    var next = hdr.nextElementSibling;
+    var groupId = null;
+    while (next && next.getAttribute('data-group')) {
+      groupId = next.getAttribute('data-group');
+      break;
+    }
+    if (groupId) {
+      hdr.style.display = groupsWithVisible[groupId] ? '' : 'none';
+    }
+  });
+}
+
+function toggleGroup(id) {
+  var rows = document.querySelectorAll('tr[data-group=""' + id + '""]');
+  var isHidden = rows.length > 0 && rows[0].style.display === 'none';
+  rows.forEach(function(r) { r.style.display = isHidden ? '' : 'none'; });
+}
+");
+        sb.AppendLine("</script>");
+        sb.AppendLine("</body>");
+        sb.AppendLine("</html>");
+
+        return sb.ToString();
+    }
+
+    /// <summary>Returns a colored badge span for the given access type.</summary>
+    private static string AccessTypeBadge(AccessType accessType)
+    {
+        var T = TranslationSource.Instance;
+        return accessType switch
+        {
+            AccessType.Direct    => $"<span class=\"badge access-direct\">{T["report.badge.direct"]}</span>",
+            AccessType.Group     => $"<span class=\"badge access-group\">{T["report.badge.group"]}</span>",
+            AccessType.Inherited => $"<span class=\"badge access-inherited\">{T["report.badge.inherited"]}</span>",
+            _                    => $"<span class=\"badge\">{HtmlEncode(accessType.ToString())}</span>"
+        };
+    }
+
+    /// <summary>
+    /// Returns true when the ObjectTitle adds no information beyond the SiteTitle:
+    /// empty, identical (case-insensitive), or one is a whitespace-trimmed duplicate
+    /// of the other. Used to collapse "All Company &rsaquo; All Company" to "All Company".
+    /// </summary>
+    private static bool IsRedundantObjectTitle(string siteTitle, string objectTitle)
+    {
+        if (string.IsNullOrWhiteSpace(objectTitle)) return true;
+        return string.Equals(
+            (siteTitle ?? string.Empty).Trim(),
+            objectTitle.Trim(),
+            StringComparison.OrdinalIgnoreCase);
+    }
+
+    /// <summary>Minimal HTML encoding for text content and attribute values.</summary>
+    private static string HtmlEncode(string value)
+    {
+        if (string.IsNullOrEmpty(value)) return string.Empty;
+        return value
+            .Replace("&",  "&amp;")
+            .Replace("<",  "&lt;")
+            .Replace(">",  "&gt;")
+            .Replace("\"", "&quot;")
+            .Replace("'",  "&#39;");
+    }
+}

Services/Export/VersionCleanupHtmlExportService.cs

@@ -0,0 +1,180 @@
+using System.Text;
+using SharepointToolbox.Web.Core.Models;
+using SharepointToolbox.Web.Localization;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Exports VersionCleanupResult list to a self-contained sortable/filterable HTML report.
+/// Summary header shows totals (files trimmed, versions deleted, bytes freed); a single
+/// table lists every processed file with sort/filter controls. No external assets.
+/// </summary>
+public class VersionCleanupHtmlExportService
+{
+    public string BuildHtml(IReadOnlyList<VersionCleanupResult> results, ReportBranding? branding = null)
+    {
+        var T = TranslationSource.Instance;
+        var sb = new StringBuilder();
+
+        long totalBytes = results.Sum(r => r.BytesFreed);
+        int totalDeleted = results.Sum(r => r.VersionsDeleted);
+        int totalFiles = results.Count(r => r.VersionsDeleted > 0);
+
+        sb.AppendLine("<!DOCTYPE html>");
+        sb.AppendLine("<html lang=\"en\">");
+        sb.AppendLine("<head>");
+        sb.AppendLine("<meta charset=\"UTF-8\">");
+        sb.AppendLine("<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">");
+        sb.AppendLine($"<title>{T["report.title.versions"]}</title>");
+        sb.AppendLine("""
+            <style>
+              body { font-family: 'Segoe UI', Arial, sans-serif; font-size: 13px; margin: 20px; background: #f5f5f5; }
+              h1 { color: #0078d4; }
+              .summary { display: flex; gap: 24px; margin: 12px 0 16px 0; padding: 12px 16px;
+                         background: #e8f1fb; border-radius: 6px; }
+              .summary .item { display: flex; flex-direction: column; }
+              .summary .label { font-size: 11px; color: #555; text-transform: uppercase; letter-spacing: .5px; }
+              .summary .value { font-size: 18px; font-weight: 600; color: #0078d4; }
+              .toolbar { margin-bottom: 10px; display: flex; gap: 12px; align-items: center; }
+              .toolbar label { font-weight: 600; }
+              #filterInput { padding: 6px 10px; border: 1px solid #ccc; border-radius: 4px; width: 280px; font-size: 13px; }
+              #resultCount { font-size: 12px; color: #666; }
+              table { border-collapse: collapse; width: 100%; background: #fff; box-shadow: 0 1px 3px rgba(0,0,0,.15); }
+              th { background: #0078d4; color: #fff; padding: 8px 12px; text-align: left; cursor: pointer;
+                   font-weight: 600; user-select: none; white-space: nowrap; }
+              th:hover { background: #106ebe; }
+              th.sorted-asc::after  { content: ' ▲'; font-size: 10px; }
+              th.sorted-desc::after { content: ' ▼'; font-size: 10px; }
+              td { padding: 6px 12px; border-bottom: 1px solid #e0e0e0; word-break: break-all; }
+              tr:hover td { background: #f0f7ff; }
+              tr.hidden { display: none; }
+              tr.err td { background: #fff4f4; }
+              .num { text-align: right; font-variant-numeric: tabular-nums; white-space: nowrap; }
+              .err-cell { color: #b00020; }
+              .generated { font-size: 11px; color: #888; margin-top: 12px; }
+            </style>
+            </head>
+            <body>
+            """);
+        sb.Append(BrandingHtmlHelper.BuildBrandingHeader(branding));
+        sb.AppendLine($"<h1>{T["report.title.versions_short"]}</h1>");
+
+        sb.AppendLine($"""
+            <div class="summary">
+              <div class="item"><span class="label">{T["versions.summary.files"]}</span><span class="value">{totalFiles:N0}</span></div>
+              <div class="item"><span class="label">{T["versions.summary.deleted"]}</span><span class="value">{totalDeleted:N0}</span></div>
+              <div class="item"><span class="label">{T["versions.summary.freed"]}</span><span class="value">{FormatSize(totalBytes)}</span></div>
+            </div>
+            <div class="toolbar">
+              <label for="filterInput">{T["report.filter.label"]}</label>
+              <input id="filterInput" type="text" placeholder="{T["report.filter.placeholder_rows"]}" oninput="filterTable()" />
+              <span id="resultCount"></span>
+            </div>
+            """);
+
+        sb.AppendLine($"""
+            <table id="resultsTable">
+              <thead>
+                <tr>
+                  <th onclick="sortTable(0)">{T["report.col.site"]}</th>
+                  <th onclick="sortTable(1)">{T["versions.col.library"]}</th>
+                  <th onclick="sortTable(2)">{T["versions.col.file"]}</th>
+                  <th onclick="sortTable(3)">{T["versions.col.path"]}</th>
+                  <th class="num" onclick="sortTable(4)">{T["versions.col.before"]}</th>
+                  <th class="num" onclick="sortTable(5)">{T["versions.col.deleted"]}</th>
+                  <th class="num" onclick="sortTable(6)">{T["versions.col.remaining"]}</th>
+                  <th class="num" onclick="sortTable(7)">{T["versions.col.freed"]}</th>
+                  <th onclick="sortTable(8)">{T["versions.col.error"]}</th>
+                </tr>
+              </thead>
+              <tbody>
+            """);
+
+        foreach (var r in results)
+        {
+            string rowClass = string.IsNullOrEmpty(r.Error) ? string.Empty : " class=\"err\"";
+            string errCell = string.IsNullOrEmpty(r.Error)
+                ? string.Empty
+                : $"<span class=\"err-cell\">{H(r.Error)}</span>";
+
+            sb.AppendLine($"""
+                  <tr{rowClass}>
+                    <td>{H(r.SiteUrl)}</td>
+                    <td>{H(r.Library)}</td>
+                    <td>{H(r.FileName)}</td>
+                    <td>{H(r.FileServerRelativeUrl)}</td>
+                    <td class="num" data-sort="{r.VersionsBefore}">{r.VersionsBefore:N0}</td>
+                    <td class="num" data-sort="{r.VersionsDeleted}">{r.VersionsDeleted:N0}</td>
+                    <td class="num" data-sort="{r.VersionsRemaining}">{r.VersionsRemaining:N0}</td>
+                    <td class="num" data-sort="{r.BytesFreed}">{FormatSize(r.BytesFreed)}</td>
+                    <td>{errCell}</td>
+                  </tr>
+                """);
+        }
+
+        sb.AppendLine("  </tbody>\n</table>");
+
+        int count = results.Count;
+        sb.AppendLine($"<p class=\"generated\">{T["report.text.generated_colon"]} {DateTime.Now:yyyy-MM-dd HH:mm} — {count:N0} {T["report.text.results_parens"]}</p>");
+
+        sb.AppendLine($$"""
+            <script>
+            var sortDir = {};
+            function sortTable(col) {
+              var tbl = document.getElementById('resultsTable');
+              var tbody = tbl.tBodies[0];
+              var rows = Array.from(tbody.rows);
+              var asc = sortDir[col] !== 'asc';
+              sortDir[col] = asc ? 'asc' : 'desc';
+              rows.sort(function(a, b) {
+                var av = a.cells[col].dataset.sort || a.cells[col].innerText;
+                var bv = b.cells[col].dataset.sort || b.cells[col].innerText;
+                var an = parseFloat(av), bn = parseFloat(bv);
+                if (!isNaN(an) && !isNaN(bn)) return asc ? an - bn : bn - an;
+                return asc ? av.localeCompare(bv) : bv.localeCompare(av);
+              });
+              rows.forEach(function(r) { tbody.appendChild(r); });
+              var ths = tbl.tHead.rows[0].cells;
+              for (var i = 0; i < ths.length; i++) {
+                ths[i].className = (i === col) ? (asc ? 'sorted-asc' : 'sorted-desc') : '';
+              }
+            }
+            function filterTable() {
+              var q = document.getElementById('filterInput').value.toLowerCase();
+              var rows = document.getElementById('resultsTable').tBodies[0].rows;
+              var visible = 0;
+              for (var i = 0; i < rows.length; i++) {
+                var match = rows[i].innerText.toLowerCase().indexOf(q) >= 0;
+                rows[i].className = (rows[i].className.indexOf('err') >= 0 ? 'err ' : '') + (match ? '' : 'hidden');
+                if (match) visible++;
+              }
+              document.getElementById('resultCount').innerText = q ? (visible + ' {{T["report.text.of"]}} {{count:N0}} {{T["report.text.shown"]}}') : '';
+            }
+            window.onload = function() {
+              document.getElementById('resultCount').innerText = '{{count:N0}} {{T["report.text.results_parens"]}}';
+            };
+            </script>
+            </body></html>
+            """);
+
+        return sb.ToString();
+    }
+
+    /// <summary>Writes the HTML report to <paramref name="filePath"/> as UTF-8.</summary>
+    public async Task WriteAsync(IReadOnlyList<VersionCleanupResult> results, string filePath, CancellationToken ct, ReportBranding? branding = null)
+    {
+        var html = BuildHtml(results, branding);
+        await System.IO.File.WriteAllTextAsync(filePath, html, Encoding.UTF8, ct);
+    }
+
+    private static string H(string value) =>
+        System.Net.WebUtility.HtmlEncode(value ?? string.Empty);
+
+    private static string FormatSize(long bytes)
+    {
+        if (bytes >= 1_073_741_824L) return $"{bytes / 1_073_741_824.0:F2} GB";
+        if (bytes >= 1_048_576L)     return $"{bytes / 1_048_576.0:F2} MB";
+        if (bytes >= 1024L)          return $"{bytes / 1024.0:F2} KB";
+        return $"{bytes} B";
+    }
+}

Services/Export/WebExportService.cs

@@ -0,0 +1,28 @@
+using System.Text;
+using Microsoft.AspNetCore.Components;
+using Microsoft.JSInterop;
+
+namespace SharepointToolbox.Web.Services.Export;
+
+/// <summary>
+/// Triggers browser file downloads from Blazor Server components.
+/// Converts string export outputs to bytes and invokes JS download.
+/// </summary>
+public class WebExportService
+{
+    private readonly IJSRuntime _js;
+
+    public WebExportService(IJSRuntime js) { _js = js; }
+
+    public async Task DownloadCsvAsync(string content, string fileName)
+    {
+        var bytes = new UTF8Encoding(encoderShouldEmitUTF8Identifier: true).GetBytes(content);
+        await _js.InvokeVoidAsync("sptb.downloadFile", fileName, "text/csv;charset=utf-8", Convert.ToBase64String(bytes));
+    }
+
+    public async Task DownloadHtmlAsync(string content, string fileName)
+    {
+        var bytes = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false).GetBytes(content);
+        await _js.InvokeVoidAsync("sptb.downloadFile", fileName, "text/html;charset=utf-8", Convert.ToBase64String(bytes));
+    }
+}