feat(management): parquet audit export and audit archive list/verify (ScadaBridge#42)

GET /api/audit/export?format=parquet returned 501. It now streams the same 24
columns as csv/jsonl (AuditExportRow, CsvHeader order) as one Parquet file,
one 10,000-row row group at a time. Each row group is encoded into a small
non-seekable staging buffer and copied to the response asynchronously, because
Kestrel rejects the synchronous writes the Parquet writer issues.

New management commands, with CLI parity:
- ListAuditArchives -> `audit archive list` (AuditArchiveListResult: enabled
  flag + every manifest).
- VerifyAuditArchive(Name) -> `audit archive verify --name` (files, chain,
  purge anchor); exit 0 verified, 3 not verified, 1 error, 2 unauthorized.
Both carry verify-chain's gate: OperationalAudit roles (Administrator, Viewer),
site-scoped non-Administrator refused because an archive spans every site.
VerifyAuditArchive uses the long-running Ask timeout. Error codes
ARCHIVE_NOT_CONFIGURED, INVALID_ARGUMENT, NOT_FOUND.

RequiredRoleMatrixTests freezes both gates; ManagementSurfaceParityTests now
probes `audit archive list|verify` alongside `audit verify-chain`.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

src/ZB.MOM.WW.ScadaBridge.CLI/Commands/AuditArchiveHelpers.cs

@@ -0,0 +1,117 @@
+using System.Globalization;
+using System.Text.Json;
+
+namespace ZB.MOM.WW.ScadaBridge.CLI.Commands;
+
+/// <summary>
+/// Helpers for the <c>audit archive list</c> / <c>audit archive verify</c> subcommands
+/// (AuditLog Parquet cold archive, ScadaBridge#42). Both send a management command
+/// (<c>ListAuditArchives</c>, <c>VerifyAuditArchive</c>); the archives live on the central
+/// nodes' archive directory, not on the operator's machine.
+/// </summary>
+/// <remarks>
+/// <c>verify</c> exit codes: <c>0</c> verified, <see cref="NotVerifiedExitCode"/> when the
+/// files, the chain or the purge anchor disagree, <c>1</c> on a request error, <c>2</c> on an
+/// authorization failure.
+/// </remarks>
+public static class AuditArchiveHelpers
+{
+    /// <summary>Process exit code when an archive failed verification (tamper evidence).</summary>
+    public const int NotVerifiedExitCode = 3;
+
+    /// <summary>
+    /// Client deadline for <c>verify</c>: the server hashes and re-chains a whole month under
+    /// the long-running management Ask (5 min); the client waits a little longer.
+    /// </summary>
+    public static readonly TimeSpan VerifyRequestTimeout = TimeSpan.FromMinutes(6);
+
+    /// <summary>Renders a <c>ListAuditArchives</c> result.</summary>
+    /// <param name="json">The success body (an <c>AuditArchiveListResult</c>, camelCase).</param>
+    /// <param name="format">Resolved output format.</param>
+    /// <param name="output">Writer for the report.</param>
+    /// <returns>Always <c>0</c>.</returns>
+    public static int RenderList(string json, string format, TextWriter output)
+    {
+        if (!string.Equals(format, "table", StringComparison.OrdinalIgnoreCase))
+        {
+            output.WriteLine(json);
+            output.Flush();
+            return 0;
+        }
+
+        using var doc = JsonDocument.Parse(json);
+        var root = doc.RootElement;
+        var enabled = root.TryGetProperty("enabled", out var e) && e.ValueKind == JsonValueKind.True;
+        output.WriteLine($"Archiving: {(enabled ? "enabled" : "disabled")}");
+        if (!root.TryGetProperty("archives", out var archives) || archives.GetArrayLength() == 0)
+        {
+            output.WriteLine("No archives.");
+            output.Flush();
+            return 0;
+        }
+
+        output.WriteLine($"{"NAME",-42} {"PARTITION",-9} {"STATUS",-8} {"ROWS",12} {"CHAINED",12} {"BYTES",14}");
+        foreach (var a in archives.EnumerateArray())
+        {
+            output.WriteLine(string.Create(CultureInfo.InvariantCulture,
+                $"{Str(a, "name"),-42} {Str(a, "partition"),-9} {Str(a, "status"),-8} {Num(a, "rowCount"),12} {Num(a, "chainedRowCount"),12} {Num(a, "dataBytes"),14}"));
+        }
+
+        output.Flush();
+        return 0;
+    }
+
+    /// <summary>Renders a <c>VerifyAuditArchive</c> result and maps it to the exit code.</summary>
+    /// <param name="json">The success body (an <c>AuditArchiveVerificationResult</c>, camelCase).</param>
+    /// <param name="format">Resolved output format.</param>
+    /// <param name="output">Writer for the report.</param>
+    /// <returns><c>0</c> when verified, <see cref="NotVerifiedExitCode"/> otherwise.</returns>
+    public static int RenderVerify(string json, string format, TextWriter output)
+    {
+        using var doc = JsonDocument.Parse(json);
+        var root = doc.RootElement;
+        var verified = root.TryGetProperty("verified", out var v) && v.ValueKind == JsonValueKind.True;
+
+        if (!string.Equals(format, "table", StringComparison.OrdinalIgnoreCase))
+        {
+            output.WriteLine(json);
+            output.Flush();
+            return verified ? 0 : NotVerifiedExitCode;
+        }
+
+        output.WriteLine($"Archive     : {Str(root, "name")}");
+        output.WriteLine($"Partition   : {Str(root, "partition")}");
+        output.WriteLine($"Manifest    : {Str(root, "manifestStatus")}");
+        output.WriteLine($"Verified    : {(verified ? "yes" : "NO")}");
+        output.WriteLine($"Files intact: {(root.TryGetProperty("filesIntact", out var f) && f.ValueKind == JsonValueKind.True ? "yes" : "NO")}");
+        if (Str(root, "fileProblem") is { Length: > 0 } problem)
+        {
+            output.WriteLine($"  problem   : {problem}");
+        }
+
+        output.WriteLine($"Rows read   : {Num(root, "rowsRead")}");
+        if (root.TryGetProperty("chains", out var chains) && chains.ValueKind == JsonValueKind.Array)
+        {
+            foreach (var c in chains.EnumerateArray())
+            {
+                var chain = c.GetProperty("chain");
+                output.WriteLine($"Chain {Str(chain, "partition")}: {Str(chain, "status")}, {Num(chain, "rowsVerified")} rows verified, "
+                    + $"{Num(chain, "tombstonesApplied")} tombstones, {Num(chain, "unchainedRows")} unchained; anchor {Str(c, "anchor")}");
+                output.WriteLine($"  {Str(c, "anchorDetail")}");
+                if (chain.TryGetProperty("firstBreak", out var brk) && brk.ValueKind == JsonValueKind.Object)
+                {
+                    output.WriteLine($"  first break: chainSeq {Num(brk, "chainSeq")}, eventId {Str(brk, "eventId", "-")}, {Str(brk, "kind")} — {Str(brk, "detail")}");
+                }
+            }
+        }
+
+        output.Flush();
+        return verified ? 0 : NotVerifiedExitCode;
+    }
+
+    private static string Str(JsonElement e, string name, string missing = "")
+        => e.TryGetProperty(name, out var v) && v.ValueKind == JsonValueKind.String ? v.GetString() ?? missing : missing;
+
+    private static string Num(JsonElement e, string name, string missing = "0")
+        => e.TryGetProperty(name, out var v) && v.ValueKind == JsonValueKind.Number ? v.GetInt64().ToString(CultureInfo.InvariantCulture) : missing;
+}

src/ZB.MOM.WW.ScadaBridge.CLI/Commands/AuditCommands.cs

@@ -9,7 +9,9 @@ namespace ZB.MOM.WW.ScadaBridge.CLI.Commands;
 /// the centralized append-only Audit Log via the REST endpoints
 /// (<c>GET /api/audit/query</c>, <c>GET /api/audit/export</c>,
 /// <c>GET /api/audit/tree</c>), plus <c>verify-chain</c>, which sends the
-/// <c>VerifyAuditChain</c> management command (hash-chain tamper evidence, ScadaBridge#41).
+/// <c>VerifyAuditChain</c> management command (hash-chain tamper evidence, ScadaBridge#41),
+/// and <c>archive list</c> / <c>archive verify</c>, which send <c>ListAuditArchives</c> /
+/// <c>VerifyAuditArchive</c> (Parquet cold archive, ScadaBridge#42).
 /// </summary>
 public static class AuditCommands
 {
@@ -31,6 +33,7 @@ public static class AuditCommands
         command.Add(BuildTree(urlOption, formatOption, usernameOption, passwordOption));
         command.Add(BuildVerifyChain(urlOption, formatOption, usernameOption, passwordOption));
         command.Add(BuildBackfillSourceNode(urlOption, formatOption, usernameOption, passwordOption));
+        command.Add(BuildArchive(urlOption, formatOption, usernameOption, passwordOption));
 
         return command;
     }
@@ -316,6 +319,49 @@ public static class AuditCommands
         return cmd;
     }
 
+    /// <summary>
+    /// Builds the <c>audit archive</c> group (ScadaBridge#42): <c>list</c> and <c>verify</c>
+    /// over the AuditLog Parquet cold archives on the central archive directory.
+    /// </summary>
+    private static Command BuildArchive(Option<string> urlOption, Option<string> formatOption, Option<string> usernameOption, Option<string> passwordOption)
+    {
+        var group = new Command("archive") { Description = "List and verify the AuditLog Parquet cold archives" };
+
+        var list = new Command("list") { Description = "List the AuditLog Parquet archives written by the retention purge" };
+        list.SetAction(async (ParseResult result) =>
+        {
+            var format = AuditCommandHelpers.ResolveFormat(result, formatOption);
+            return await CommandHelpers.ExecuteCommandAsync(
+                result, urlOption, formatOption, usernameOption, passwordOption,
+                new ListAuditArchivesCommand(),
+                onSuccess: json => AuditArchiveHelpers.RenderList(json, format, Console.Out));
+        });
+        group.Add(list);
+
+        var nameOption = new Option<string>("--name")
+        {
+            Description = "Archive name, as 'audit archive list' prints it (auditlog-YYYY-MM-yyyyMMddTHHmmssfffZ)",
+            Required = true,
+        };
+        var verify = new Command("verify")
+        {
+            Description = "Verify an archive's files, its hash chain and its purge anchor; exit 3 if it does not verify",
+        };
+        verify.Add(nameOption);
+        verify.SetAction(async (ParseResult result) =>
+        {
+            var format = AuditCommandHelpers.ResolveFormat(result, formatOption);
+            return await CommandHelpers.ExecuteCommandAsync(
+                result, urlOption, formatOption, usernameOption, passwordOption,
+                new VerifyAuditArchiveCommand(result.GetValue(nameOption)!),
+                timeout: AuditArchiveHelpers.VerifyRequestTimeout,
+                onSuccess: json => AuditArchiveHelpers.RenderVerify(json, format, Console.Out));
+        });
+        group.Add(verify);
+
+        return group;
+    }
+
     /// <summary>
     /// Builds the <c>audit backfill-source-node</c> sub-command.
     /// Sets <c>SourceNode</c> on historical pre-feature rows whose <c>SourceNode IS NULL</c>

src/ZB.MOM.WW.ScadaBridge.CLI/Commands/AuditExportHelpers.cs

@@ -134,8 +134,8 @@ public static class AuditExportHelpers
     /// Executes the export: GETs <c>/api/audit/export</c> and copies the response body
     /// stream directly to <see cref="AuditExportArgs.Output"/>. The body is never fully
     /// buffered — the copy streams in fixed-size chunks via <see cref="Stream.ReadAsync(Memory{byte}, CancellationToken)"/>.
-    /// A <c>501 Not Implemented</c> (parquet not yet supported server-side) prints the
+    /// A <c>501 Not Implemented</c> (a central older than ScadaBridge#42 does not serve
-    /// server message and returns a non-zero exit code.
+    /// <c>format=parquet</c>) prints the server message and returns a non-zero exit code.
     /// </summary>
     /// <param name="client">The management HTTP client for API communication.</param>
     /// <param name="args">The export arguments containing filters and output file path.</param>

src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/AuditLogCommands.cs

@@ -31,3 +31,19 @@ public record AuditLogQueryResult(IReadOnlyList<AuditLogEntry> Entries, int Tota
 /// </summary>
 /// <param name="Month">The month to verify, <c>YYYY-MM</c>.</param>
 public record VerifyAuditChainCommand(string Month);
+
+/// <summary>
+/// Lists the AuditLog Parquet cold archives under the configured archive directory (audit
+/// roadmap T2, ScadaBridge#42). Read-only; OperationalAudit roles, refused for a site-scoped
+/// caller because an archive holds every site's rows.
+/// </summary>
+public record ListAuditArchivesCommand;
+
+/// <summary>
+/// Verifies one AuditLog Parquet archive (ScadaBridge#42): file integrity against its
+/// manifest, the hash chain recomputed over the archived rows, and the chain end against the
+/// checkpoint anchor the partition purge left. Read-only; same gate as
+/// <see cref="ListAuditArchivesCommand"/>.
+/// </summary>
+/// <param name="Name">The archive name, as <c>audit archive list</c> reports it.</param>
+public record VerifyAuditArchiveCommand(string Name);

src/ZB.MOM.WW.ScadaBridge.ManagementService/AuditEndpoints.cs

@@ -22,8 +22,8 @@ namespace ZB.MOM.WW.ScadaBridge.ManagementService;
 /// <list type="bullet">
 ///   <item><c>GET /api/audit/query</c> — keyset-paged JSON page, gated on the
 ///   <see cref="AuthorizationPolicies.OperationalAudit"/> permission.</item>
-///   <item><c>GET /api/audit/export</c> — streamed bulk export (csv / jsonl;
+///   <item><c>GET /api/audit/export</c> — streamed bulk export (csv / jsonl /
-///   parquet returns HTTP 501), gated on the
+///   parquet), gated on the
 ///   <see cref="AuthorizationPolicies.AuditExport"/> permission.</item>
 ///   <item><c>GET /api/audit/tree</c> — execution-chain tree rooted at the
 ///   topmost ancestor of a given <c>executionId</c>, returned as a JSON array
@@ -47,11 +47,8 @@ namespace ZB.MOM.WW.ScadaBridge.ManagementService;
 /// </para>
 ///
 /// <para>
-/// <b>Parquet.</b> No Parquet library is referenced by the solution and
+/// <b>Parquet.</b> <c>format=parquet</c> (ScadaBridge#42) streams the same 24 columns as
-/// <c>Component-AuditLog.md</c> explicitly defers Parquet archival to v1.x, so
+/// csv / jsonl as one Parquet file (<see cref="AuditExportParquet"/>), a row group at a time.
-/// <c>format=parquet</c> returns <c>501 Not Implemented</c> with a guidance
-/// message rather than a half-built binary stream. csv + jsonl are fully
-/// implemented.
 /// </para>
 /// </summary>
 public static class AuditEndpoints
@@ -65,6 +62,9 @@ public static class AuditEndpoints
     /// <summary>Repository round-trip size used while streaming an export.</summary>
     public const int ExportPageSize = 1000;
 
+    /// <summary>Content type of a <c>format=parquet</c> export (ScadaBridge#42).</summary>
+    public const string ParquetContentType = "application/vnd.apache.parquet";
+
     /// <summary>
     /// Serializer for individual <see cref="AuditEvent"/> rows (query results +
     /// jsonl export lines). Drops null columns so a sparse audit row stays
@@ -185,10 +185,10 @@ public static class AuditEndpoints
     // ─────────────────────────────────────────────────────────────────────
 
     /// <summary>
-    /// Handles <c>GET /api/audit/export</c>: authenticates, checks the AuditExport permission, and streams the matching rows as CSV or JSONL.
+    /// Handles <c>GET /api/audit/export</c>: authenticates, checks the AuditExport permission, and streams the matching rows as CSV, JSONL or Parquet.
     /// </summary>
     /// <param name="context">The HTTP context for the current request.</param>
-    /// <returns>A task that resolves to the HTTP result (streaming CSV/JSONL, 400, 401, 403, or 501).</returns>
+    /// <returns>A task that resolves to the HTTP result (streaming CSV/JSONL/Parquet, 400, 401, or 403).</returns>
     internal static async Task<IResult> HandleExport(HttpContext context)
     {
         var auth = await AuthenticateAsync(context);
@@ -208,17 +208,7 @@ public static class AuditEndpoints
             format = "csv";
         }
 
-        if (format == "parquet")
+        if (format != "csv" && format != "jsonl" && format != "parquet")
-        {
-            // Deferred to v1.x (Component-AuditLog.md §"Deferred"): no Parquet
-            // library is in the solution. Return a 501 with actionable guidance
-            // rather than a partial binary stream.
-            return Results.Json(
-                new { error = "Parquet export deferred to v1.x; use csv or jsonl.", code = "NOT_IMPLEMENTED" },
-                statusCode: 501);
-        }
-
-        if (format != "csv" && format != "jsonl")
         {
             return Results.Json(
                 new { error = $"Unsupported export format '{format}'. Use csv, jsonl, or parquet.", code = "BAD_REQUEST" },
@@ -243,8 +233,12 @@ public static class AuditEndpoints
         filter = restricted;
         var repo = context.RequestServices.GetRequiredService<IAuditLogRepository>();
 
-        var contentType = format == "csv" ? "text/csv; charset=utf-8" : "application/x-ndjson";
+        var (contentType, extension) = format switch
-        var extension = format == "csv" ? "csv" : "jsonl";
+        {
+            "csv" => ("text/csv; charset=utf-8", "csv"),
+            "parquet" => (ParquetContentType, "parquet"),
+            _ => ("application/x-ndjson", "jsonl"),
+        };
         var fileName = $"audit-log-{DateTime.UtcNow:yyyyMMdd-HHmmss}.{extension}";
 
         context.Response.ContentType = contentType;
@@ -256,6 +250,12 @@ public static class AuditEndpoints
         {
             await StreamCsvAsync(repo, filter, context.Response.Body, context.RequestAborted);
         }
+        else if (format == "parquet")
+        {
+            // ScadaBridge#42: same 24 columns as csv/jsonl, one row group per 10k rows.
+            await AuditExportParquet.WriteAsync(
+                ExportRowPagesAsync(repo, filter, context.RequestAborted), context.Response.Body, context.RequestAborted);
+        }
         else
         {
             await StreamJsonlAsync(repo, filter, context.Response.Body, context.RequestAborted);
@@ -494,6 +494,18 @@ public static class AuditEndpoints
         }
     }
 
+    /// <summary>Projects <see cref="PageAsync"/> pages onto the flat export row shape.</summary>
+    private static async IAsyncEnumerable<IReadOnlyList<AuditExportRow>> ExportRowPagesAsync(
+        IAuditLogRepository repo,
+        AuditLogQueryFilter filter,
+        [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken ct)
+    {
+        await foreach (var page in PageAsync(repo, filter, ct))
+        {
+            yield return page.Select(AuditExportRow.From).ToList();
+        }
+    }
+
     /// <summary>
     /// Lazily yields full repository pages, advancing the keyset cursor until a
     /// short page signals the end. Shared by the csv + jsonl streamers.

src/ZB.MOM.WW.ScadaBridge.ManagementService/AuditExportParquet.cs

@@ -0,0 +1,219 @@
+using Parquet;
+using Parquet.Schema;
+
+namespace ZB.MOM.WW.ScadaBridge.ManagementService;
+
+/// <summary>
+/// <c>GET /api/audit/export?format=parquet</c> (ScadaBridge#42): the same 24 columns as the
+/// csv / jsonl export (<see cref="AuditExportRow"/>, in <see cref="AuditEndpoints.CsvHeader"/>
+/// order) as one Parquet file, one row group per <see cref="RowGroupRows"/> rows.
+/// </summary>
+/// <remarks>
+/// <para>
+/// Types: ids are <c>D</c>-format strings, timestamps are UTC Parquet timestamps
+/// (microseconds), enums are their names, <c>HttpStatus</c>/<c>DurationMs</c> are int32,
+/// <c>PayloadTruncated</c> is boolean, everything else is a UTF-8 string.
+/// </para>
+/// <para>
+/// <b>Streaming.</b> Kestrel forbids synchronous writes to the response body and the Parquet
+/// writer issues some, so each row group is encoded into a small in-memory buffer and then
+/// copied to the response asynchronously. Memory is bounded by one row group, and the client
+/// starts receiving bytes after the first one. A Parquet file's footer is written last, so a
+/// response cut off mid-stream is not a readable file — the CLI treats it as a failed export.
+/// </para>
+/// <para>
+/// This is the ad-hoc export. The retention archive (alog.md §15.2) is a different layout
+/// that carries the hash-chain columns; see <c>AuditArchiveParquet</c>.
+/// </para>
+/// </remarks>
+public static class AuditExportParquet
+{
+    /// <summary>Rows per Parquet row group.</summary>
+    public const int RowGroupRows = 10_000;
+
+    private static readonly DataField<string> EventId = new(nameof(AuditExportRow.EventId), false);
+    private static readonly DateTimeDataField OccurredAtUtc = Timestamp(nameof(AuditExportRow.OccurredAtUtc), false);
+    private static readonly DateTimeDataField IngestedAtUtc = Timestamp(nameof(AuditExportRow.IngestedAtUtc), true);
+    private static readonly DataField<string> Channel = new(nameof(AuditExportRow.Channel), false);
+    private static readonly DataField<string> Kind = new(nameof(AuditExportRow.Kind), false);
+    private static readonly DataField<string> CorrelationId = Text(nameof(AuditExportRow.CorrelationId));
+    private static readonly DataField<string> ExecutionId = Text(nameof(AuditExportRow.ExecutionId));
+    private static readonly DataField<string> ParentExecutionId = Text(nameof(AuditExportRow.ParentExecutionId));
+    private static readonly DataField<string> SourceSiteId = Text(nameof(AuditExportRow.SourceSiteId));
+    private static readonly DataField<string> SourceNode = Text(nameof(AuditExportRow.SourceNode));
+    private static readonly DataField<string> SourceInstanceId = Text(nameof(AuditExportRow.SourceInstanceId));
+    private static readonly DataField<string> SourceScript = Text(nameof(AuditExportRow.SourceScript));
+    private static readonly DataField<string> Actor = Text(nameof(AuditExportRow.Actor));
+    private static readonly DataField<string> Target = Text(nameof(AuditExportRow.Target));
+    private static readonly DataField<string> Status = new(nameof(AuditExportRow.Status), false);
+    private static readonly DataField<int> HttpStatus = new(nameof(AuditExportRow.HttpStatus), true);
+    private static readonly DataField<int> DurationMs = new(nameof(AuditExportRow.DurationMs), true);
+    private static readonly DataField<string> ErrorMessage = Text(nameof(AuditExportRow.ErrorMessage));
+    private static readonly DataField<string> ErrorDetail = Text(nameof(AuditExportRow.ErrorDetail));
+    private static readonly DataField<string> RequestSummary = Text(nameof(AuditExportRow.RequestSummary));
+    private static readonly DataField<string> ResponseSummary = Text(nameof(AuditExportRow.ResponseSummary));
+    private static readonly DataField<bool> PayloadTruncated = new(nameof(AuditExportRow.PayloadTruncated), false);
+    private static readonly DataField<string> Extra = Text(nameof(AuditExportRow.Extra));
+    private static readonly DataField<string> ForwardState = Text(nameof(AuditExportRow.ForwardState));
+
+    /// <summary>The export schema; column names and order equal <see cref="AuditEndpoints.CsvHeader"/>.</summary>
+    public static ParquetSchema Schema { get; } = new(
+        EventId, OccurredAtUtc, IngestedAtUtc, Channel, Kind, CorrelationId, ExecutionId, ParentExecutionId,
+        SourceSiteId, SourceNode, SourceInstanceId, SourceScript, Actor, Target, Status, HttpStatus, DurationMs,
+        ErrorMessage, ErrorDetail, RequestSummary, ResponseSummary, PayloadTruncated, Extra, ForwardState);
+
+    /// <summary>Writes every row of <paramref name="pages"/> to <paramref name="output"/> as one Parquet file.</summary>
+    /// <param name="pages">Export rows, page by page.</param>
+    /// <param name="output">The destination (e.g. the HTTP response body); written asynchronously only.</param>
+    /// <param name="ct">Cancellation token.</param>
+    /// <returns>The number of rows written.</returns>
+    public static async Task<long> WriteAsync(
+        IAsyncEnumerable<IReadOnlyList<AuditExportRow>> pages, Stream output, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(pages);
+        ArgumentNullException.ThrowIfNull(output);
+
+        // Non-seekable on purpose: the writer then tracks file offsets itself, so emptying the
+        // buffer after each drain cannot corrupt the column-chunk offsets in the footer.
+        var staging = new StagingStream();
+        long total = 0;
+        var buffer = new List<AuditExportRow>(RowGroupRows);
+        await using (var writer = await ParquetWriter.CreateAsync(Schema, staging, cancellationToken: ct).ConfigureAwait(false))
+        {
+            await foreach (var page in pages.WithCancellation(ct).ConfigureAwait(false))
+            {
+                foreach (var row in page)
+                {
+                    buffer.Add(row);
+                    if (buffer.Count == RowGroupRows)
+                    {
+                        total += await WriteGroupAsync(writer, buffer, ct).ConfigureAwait(false);
+                        await DrainAsync(staging, output, ct).ConfigureAwait(false);
+                    }
+                }
+            }
+
+            total += await WriteGroupAsync(writer, buffer, ct).ConfigureAwait(false);
+        }
+
+        // The footer is written when the writer is disposed.
+        await DrainAsync(staging, output, ct).ConfigureAwait(false);
+        return total;
+    }
+
+    private static async Task<int> WriteGroupAsync(ParquetWriter writer, List<AuditExportRow> rows, CancellationToken ct)
+    {
+        if (rows.Count == 0)
+        {
+            return 0;
+        }
+
+        using (var group = writer.CreateRowGroup())
+        {
+            await group.WriteAsync(EventId, Map(rows, r => r.EventId.ToString("D"))).ConfigureAwait(false);
+            await group.WriteAsync<DateTime>(OccurredAtUtc, rows.Select(r => DateTime.SpecifyKind(r.OccurredAtUtc, DateTimeKind.Utc)).ToArray(), cancellationToken: ct).ConfigureAwait(false);
+            await group.WriteAsync<DateTime>(IngestedAtUtc, rows.Select(r => r.IngestedAtUtc is { } i ? DateTime.SpecifyKind(i, DateTimeKind.Utc) : (DateTime?)null).ToArray(), cancellationToken: ct).ConfigureAwait(false);
+            await group.WriteAsync(Channel, Map(rows, r => r.Channel.ToString())).ConfigureAwait(false);
+            await group.WriteAsync(Kind, Map(rows, r => r.Kind.ToString())).ConfigureAwait(false);
+            await group.WriteAsync(CorrelationId, Map(rows, r => r.CorrelationId?.ToString("D"))!).ConfigureAwait(false);
+            await group.WriteAsync(ExecutionId, Map(rows, r => r.ExecutionId?.ToString("D"))!).ConfigureAwait(false);
+            await group.WriteAsync(ParentExecutionId, Map(rows, r => r.ParentExecutionId?.ToString("D"))!).ConfigureAwait(false);
+            await group.WriteAsync(SourceSiteId, Map(rows, r => r.SourceSiteId)!).ConfigureAwait(false);
+            await group.WriteAsync(SourceNode, Map(rows, r => r.SourceNode)!).ConfigureAwait(false);
+            await group.WriteAsync(SourceInstanceId, Map(rows, r => r.SourceInstanceId)!).ConfigureAwait(false);
+            await group.WriteAsync(SourceScript, Map(rows, r => r.SourceScript)!).ConfigureAwait(false);
+            await group.WriteAsync(Actor, Map(rows, r => r.Actor)!).ConfigureAwait(false);
+            await group.WriteAsync(Target, Map(rows, r => r.Target)!).ConfigureAwait(false);
+            await group.WriteAsync(Status, Map(rows, r => r.Status.ToString())).ConfigureAwait(false);
+            await group.WriteAsync<int>(HttpStatus, rows.Select(r => r.HttpStatus).ToArray(), cancellationToken: ct).ConfigureAwait(false);
+            await group.WriteAsync<int>(DurationMs, rows.Select(r => r.DurationMs).ToArray(), cancellationToken: ct).ConfigureAwait(false);
+            await group.WriteAsync(ErrorMessage, Map(rows, r => r.ErrorMessage)!).ConfigureAwait(false);
+            await group.WriteAsync(ErrorDetail, Map(rows, r => r.ErrorDetail)!).ConfigureAwait(false);
+            await group.WriteAsync(RequestSummary, Map(rows, r => r.RequestSummary)!).ConfigureAwait(false);
+            await group.WriteAsync(ResponseSummary, Map(rows, r => r.ResponseSummary)!).ConfigureAwait(false);
+            await group.WriteAsync<bool>(PayloadTruncated, rows.Select(r => r.PayloadTruncated).ToArray(), cancellationToken: ct).ConfigureAwait(false);
+            await group.WriteAsync(Extra, Map(rows, r => r.Extra)!).ConfigureAwait(false);
+            await group.WriteAsync(ForwardState, Map(rows, r => r.ForwardState?.ToString())!).ConfigureAwait(false);
+        }
+
+        var count = rows.Count;
+        rows.Clear();
+        return count;
+    }
+
+    private static async Task DrainAsync(StagingStream staging, Stream output, CancellationToken ct)
+    {
+        var pending = staging.Pending;
+        if (pending.Length == 0)
+        {
+            return;
+        }
+
+        await output.WriteAsync(pending, ct).ConfigureAwait(false);
+        await output.FlushAsync(ct).ConfigureAwait(false);
+        staging.Clear();
+    }
+
+    private static string?[] Map(List<AuditExportRow> rows, Func<AuditExportRow, string?> select)
+        => rows.Select(select).ToArray();
+
+    private static DataField<string> Text(string name) => new(name, true);
+
+    private static DateTimeDataField Timestamp(string name, bool nullable)
+        => new(name, DateTimeFormat.Timestamp, isAdjustedToUTC: true, unit: DateTimeTimeUnit.Micros, isNullable: nullable);
+
+    /// <summary>
+    /// Forward-only, non-seekable buffer the Parquet writer writes into (synchronously or
+    /// not); <see cref="DrainAsync"/> moves its bytes to the real output asynchronously.
+    /// </summary>
+    private sealed class StagingStream : Stream
+    {
+        private readonly MemoryStream _buffer = new();
+
+        public ReadOnlyMemory<byte> Pending => _buffer.GetBuffer().AsMemory(0, (int)_buffer.Length);
+
+        public override bool CanRead => false;
+
+        public override bool CanSeek => false;
+
+        public override bool CanWrite => true;
+
+        public override long Length => throw new NotSupportedException();
+
+        public override long Position
+        {
+            get => throw new NotSupportedException();
+            set => throw new NotSupportedException();
+        }
+
+        public void Clear() => _buffer.SetLength(0);
+
+        public override void Write(byte[] buffer, int offset, int count) => _buffer.Write(buffer, offset, count);
+
+        public override void Write(ReadOnlySpan<byte> buffer) => _buffer.Write(buffer);
+
+        public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default)
+        {
+            _buffer.Write(buffer.Span);
+            return ValueTask.CompletedTask;
+        }
+
+        public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        {
+            _buffer.Write(buffer, offset, count);
+            return Task.CompletedTask;
+        }
+
+        public override void Flush()
+        {
+        }
+
+        public override Task FlushAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+        public override int Read(byte[] buffer, int offset, int count) => throw new NotSupportedException();
+
+        public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
+
+        public override void SetLength(long value) => throw new NotSupportedException();
+    }
+}

src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs

@@ -393,6 +393,11 @@ public class ManagementActor : ReceiveActor
         // spans every site.
         VerifyAuditChainCommand => OperationalAuditReaders,
 
+        // AuditLog Parquet archives (ScadaBridge#42): audit reads with verify-chain's gate —
+        // OperationalAudit roles, site-scoped callers refused in the handler.
+        ListAuditArchivesCommand => OperationalAuditReaders,
+        VerifyAuditArchiveCommand => OperationalAuditReaders,
+
         // Read-only queries -- any authenticated user
         _ => null
     };
@@ -564,6 +569,8 @@ public class ManagementActor : ReceiveActor
             // Audit Log
             QueryAuditLogCommand cmd => await HandleQueryAuditLog(sp, cmd),
             VerifyAuditChainCommand cmd => await HandleVerifyAuditChain(sp, cmd, user),
+            ListAuditArchivesCommand => await HandleListAuditArchives(sp, user),
+            VerifyAuditArchiveCommand cmd => await HandleVerifyAuditArchive(sp, cmd, user),
 
             // Health
             GetHealthSummaryCommand => HandleGetHealthSummary(sp),
@@ -3256,6 +3263,59 @@ public class ManagementActor : ReceiveActor
         }
     }
 
+    /// <summary>
+    /// Lists the AuditLog Parquet archives (ScadaBridge#42). Refused for a site-scoped,
+    /// non-Administrator caller: an archive holds every site's rows.
+    /// </summary>
+    private static async Task<object?> HandleListAuditArchives(IServiceProvider sp, AuthenticatedUser user)
+    {
+        var archive = RequireAuditArchive(sp, user);
+        return new AuditArchiveListResult(archive.IsEnabled, await archive.ListAsync());
+    }
+
+    /// <summary>
+    /// Verifies one AuditLog Parquet archive (ScadaBridge#42): files against the manifest,
+    /// the chain recomputed from the archived rows, the chain end against the purge anchor.
+    /// </summary>
+    private static async Task<object?> HandleVerifyAuditArchive(
+        IServiceProvider sp, VerifyAuditArchiveCommand cmd, AuthenticatedUser user)
+    {
+        var archive = RequireAuditArchive(sp, user);
+        try
+        {
+            return await archive.VerifyAsync(cmd.Name);
+        }
+        catch (ArgumentException ex)
+        {
+            throw new ManagementCommandException(ex.Message, "INVALID_ARGUMENT");
+        }
+        catch (FileNotFoundException ex)
+        {
+            throw new ManagementCommandException(ex.Message, "NOT_FOUND");
+        }
+    }
+
+    private static IAuditLogArchive RequireAuditArchive(IServiceProvider sp, AuthenticatedUser user)
+    {
+        if (user.PermittedSiteIds.Length > 0
+            && !user.Roles.Contains(Roles.Administrator, StringComparer.OrdinalIgnoreCase))
+        {
+            throw new SiteScopeViolationException(
+                "Access denied: AuditLog archives hold every site's rows; they need an "
+                + "OperationalAudit role that is not scoped to specific sites.");
+        }
+
+        var archive = sp.GetService<IAuditLogArchive>();
+        if (archive is null || !archive.IsConfigured)
+        {
+            throw new ManagementCommandException(
+                "No AuditLog archive directory is configured on this central node (AuditLog:Archive:Directory).",
+                "ARCHIVE_NOT_CONFIGURED");
+        }
+
+        return archive;
+    }
+
     // ========================================================================
     // Health handlers
     // ========================================================================

src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementEndpoints.cs

@@ -63,6 +63,9 @@ public static class ManagementEndpoints
         // AuditLog hash-chain verification (ScadaBridge#41) recomputes one hash per row of
         // a whole month — millions of rows on a busy central.
         typeof(VerifyAuditChainCommand),
+        // AuditLog archive verification (ScadaBridge#42) hashes and re-chains a whole month's
+        // Parquet archive.
+        typeof(VerifyAuditArchiveCommand),
     ];
 
     /// <summary>

src/ZB.MOM.WW.ScadaBridge.ManagementService/ZB.MOM.WW.ScadaBridge.ManagementService.csproj

@@ -12,6 +12,7 @@
     <InternalsVisibleTo Include="ZB.MOM.WW.ScadaBridge.ManagementService.Tests" />
   </ItemGroup>
   <ItemGroup>
+    <PackageReference Include="Parquet.Net" />
     <PackageReference Include="Akka" />
     <PackageReference Include="Akka.Cluster.Tools" />
     <PackageReference Include="ZB.MOM.WW.Configuration" />

tests/ZB.MOM.WW.ScadaBridge.CLI.Tests/CommandTreeTests.cs

@@ -69,7 +69,7 @@ public class CommandTreeTests
         Assert.Contains("bundle", groupNames);
     }
 
-    /// <summary>Verifies that the audit command group exposes the query, export and verify-chain subcommands.</summary>
+    /// <summary>Verifies that the audit command group exposes the query, export, verify-chain and archive subcommands.</summary>
     [Fact]
     public void AuditCommandGroup_HasQueryExportAndVerifyChain()
     {
@@ -80,6 +80,7 @@ public class CommandTreeTests
         Assert.Contains("query", subNames);
         Assert.Contains("export", subNames);
         Assert.Contains("verify-chain", subNames);
+        Assert.Contains("archive", subNames);
     }
 
     /// <summary>Verifies that the bundle command group exposes the export, preview and import subcommands.</summary>

tests/ZB.MOM.WW.ScadaBridge.CLI.Tests/Commands/AuditArchiveCommandTests.cs

@@ -0,0 +1,136 @@
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+using System.Text.Json;
+using ZB.MOM.WW.ScadaBridge.CLI.Commands;
+
+namespace ZB.MOM.WW.ScadaBridge.CLI.Tests.Commands;
+
+/// <summary>
+/// Tests for <c>scadabridge audit archive list</c> / <c>verify</c> (ScadaBridge#42): each
+/// sends its management command (<c>ListAuditArchives</c>, <c>VerifyAuditArchive</c>), and
+/// <c>verify</c> maps the verdict onto the exit code (0 verified, 3 not verified).
+/// </summary>
+[Collection("Console")]
+public class AuditArchiveCommandTests
+{
+    private const string Name = "auditlog-2025-10-20261109T120000123Z";
+
+    private const string ListBody =
+        "{\"enabled\":true,\"archives\":[{\"name\":\"" + Name + "\",\"partition\":\"2025-10\",\"status\":\"Purged\"," +
+        "\"rowCount\":11,\"chainedRowCount\":10,\"dataBytes\":4096}]}";
+
+    private const string VerifiedBody =
+        "{\"name\":\"" + Name + "\",\"partition\":\"2025-10\",\"manifestStatus\":\"Purged\",\"verified\":true,\"filesIntact\":true," +
+        "\"rowsRead\":11,\"chains\":[{\"chain\":{\"partition\":\"2025-10\",\"status\":\"Intact\",\"rowsVerified\":10," +
+        "\"tombstonesApplied\":2,\"unchainedRows\":1},\"anchor\":\"Matches\",\"anchorDetail\":\"ends at the anchor\"}]}";
+
+    private const string MismatchBody =
+        "{\"name\":\"" + Name + "\",\"partition\":\"2025-10\",\"manifestStatus\":\"Purged\",\"verified\":false,\"filesIntact\":true," +
+        "\"rowsRead\":11,\"chains\":[{\"chain\":{\"partition\":\"2025-10\",\"status\":\"Intact\",\"rowsVerified\":10," +
+        "\"tombstonesApplied\":0,\"unchainedRows\":0},\"anchor\":\"Mismatch\",\"anchorDetail\":\"hash differs\"}]}";
+
+    /// <summary>The audit group carries the archive group with list + verify.</summary>
+    [Fact]
+    public void AuditGroup_HasArchiveListAndVerify()
+    {
+        var root = AuditCommandTestHarness.BuildRoot();
+        var archive = root.Subcommands.Single(c => c.Name == "audit").Subcommands.Single(c => c.Name == "archive");
+        Assert.Equal(["list", "verify"], archive.Subcommands.Select(c => c.Name).Order());
+    }
+
+    /// <summary><c>list</c> sends ListAuditArchives and prints the archives.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
+    [Fact]
+    public async Task List_SendsListAuditArchives_AndPrintsTheArchives()
+    {
+        var (exit, output, request) = await RunAsync(ListBody, "audit", "archive", "list", "--format", "table");
+
+        Assert.Equal(0, exit);
+        Assert.Contains(Name, output);
+        Assert.Contains("Archiving: enabled", output);
+        using var payload = JsonDocument.Parse(request);
+        Assert.Equal("ListAuditArchives", payload.RootElement.GetProperty("command").GetString());
+    }
+
+    /// <summary><c>verify</c> sends VerifyAuditArchive with the name and maps the verdict to the exit code.</summary>
+    /// <param name="body">The verification result the fake endpoint serves.</param>
+    /// <param name="format">Output format.</param>
+    /// <param name="expectedExit">Expected exit code.</param>
+    /// <param name="expectedText">Text the report must contain.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
+    [Theory]
+    [InlineData(VerifiedBody, "table", 0, "anchor Matches")]
+    [InlineData(VerifiedBody, "json", 0, "\"verified\":true")]
+    [InlineData(MismatchBody, "table", 3, "Verified    : NO")]
+    [InlineData(MismatchBody, "json", 3, "\"anchor\":\"Mismatch\"")]
+    public async Task Verify_SendsVerifyAuditArchive_AndMapsVerdictToExitCode(
+        string body, string format, int expectedExit, string expectedText)
+    {
+        var (exit, output, request) = await RunAsync(body, "audit", "archive", "verify", "--name", Name, "--format", format);
+
+        Assert.Equal(expectedExit, exit);
+        Assert.Contains(expectedText, output);
+        using var payload = JsonDocument.Parse(request);
+        Assert.Equal("VerifyAuditArchive", payload.RootElement.GetProperty("command").GetString());
+        var name = payload.RootElement.GetProperty("payload").EnumerateObject()
+            .First(p => string.Equals(p.Name, "name", StringComparison.OrdinalIgnoreCase)).Value.GetString();
+        Assert.Equal(Name, name);
+    }
+
+    /// <summary><c>verify</c> without <c>--name</c> is a usage error.</summary>
+    [Fact]
+    public void Verify_MissingName_ProducesRequiredFlagError()
+    {
+        var root = AuditCommandTestHarness.BuildRoot();
+        var (exit, _, err) = AuditCommandTestHarness.Invoke(root, "audit", "archive", "verify");
+
+        Assert.NotEqual(0, exit);
+        Assert.Contains("--name", err);
+    }
+
+    private static async Task<(int Exit, string Output, string Request)> RunAsync(string body, params string[] args)
+    {
+        var listener = new TcpListener(IPAddress.Loopback, 0);
+        listener.Start();
+        try
+        {
+            var port = ((IPEndPoint)listener.LocalEndpoint).Port;
+            string? requestBody = null;
+            var server = Task.Run(async () =>
+            {
+                using var client = await listener.AcceptTcpClientAsync();
+                await using var stream = client.GetStream();
+                using var reader = new StreamReader(stream, Encoding.UTF8, leaveOpen: true);
+                var length = 0;
+                while (await reader.ReadLineAsync() is { Length: > 0 } line)
+                    if (line.StartsWith("Content-Length:", StringComparison.OrdinalIgnoreCase))
+                        length = int.Parse(line[15..].Trim());
+                var buffer = new char[length];
+                var read = 0;
+                while (read < length)
+                {
+                    var count = await reader.ReadAsync(buffer.AsMemory(read));
+                    if (count == 0) throw new EndOfStreamException();
+                    read += count;
+                }
+                requestBody = new string(buffer);
+                var bytes = Encoding.UTF8.GetBytes(body);
+                var headers = Encoding.ASCII.GetBytes(
+                    $"HTTP/1.1 200 OK\r\nContent-Type: application/json\r\nContent-Length: {bytes.Length}\r\nConnection: close\r\n\r\n");
+                await stream.WriteAsync(headers);
+                await stream.WriteAsync(bytes);
+            });
+
+            var root = AuditCommandTestHarness.BuildRoot();
+            var (exit, output, _) = AuditCommandTestHarness.Invoke(
+                root, [.. args, "--url", $"http://127.0.0.1:{port}", "--username", "u", "--password", "p"]);
+            await server.WaitAsync(TimeSpan.FromSeconds(5));
+            return (exit, output, requestBody!);
+        }
+        finally
+        {
+            listener.Stop();
+        }
+    }
+}

tests/ZB.MOM.WW.ScadaBridge.CLI.Tests/Commands/AuditCommandsScaffoldTests.cs

@@ -27,14 +27,14 @@ public class AuditCommandsScaffoldTests
         Assert.False(string.IsNullOrWhiteSpace(audit.Description));
     }
 
-    /// <summary>Verifies that the audit group exposes the query, export, tree, verify-chain and backfill-source-node subcommands.</summary>
+    /// <summary>Verifies that the audit group exposes the query, export, tree, verify-chain, backfill-source-node and archive subcommands.</summary>
     [Fact]
-    public void Audit_HasFiveSubcommands_QueryExportTreeVerifyChainBackfillSourceNode()
+    public void Audit_HasSixSubcommands_QueryExportTreeVerifyChainBackfillSourceNodeArchive()
     {
         var audit = BuildAudit();
         var names = audit.Subcommands.Select(c => c.Name).OrderBy(n => n).ToArray();
         Assert.Equal(
-            new[] { "backfill-source-node", "export", "query", "tree", "verify-chain" },
+            new[] { "archive", "backfill-source-node", "export", "query", "tree", "verify-chain" },
             names);
     }
 
@@ -62,8 +62,11 @@ public class AuditCommandsScaffoldTests
     [Fact]
     public void Audit_EveryLeafCommand_HasAnAction()
     {
+        // `archive` is a group (list / verify, ScadaBridge#42): check its leaves, not it.
         var audit = BuildAudit();
-        Assert.All(audit.Subcommands, sub =>
+        var leaves = audit.Subcommands.SelectMany(c => c.Subcommands.Count == 0 ? [c] : c.Subcommands).ToList();
+        Assert.Equal(7, leaves.Count);
+        Assert.All(leaves, sub =>
             Assert.True(sub.Action != null, $"Leaf command '{sub.Name}' has no action."));
     }
 }

tests/ZB.MOM.WW.ScadaBridge.CLI.Tests/ManagementSurfaceParityTests.cs

@@ -44,6 +44,9 @@ public class ManagementSurfaceParityTests
         Assert.Contains("ListSharedScripts", sent.Keys);
     }
 
+    private static readonly HashSet<string> AuditManagementLeaves =
+        ["audit verify-chain", "audit archive list", "audit archive verify"];
+
     private static async Task<ConcurrentDictionary<string, string>> ProbeProductionTree(string? omitGroup = null)
     {
         var root = CliApplication.BuildRoot();
@@ -93,9 +96,10 @@ public class ManagementSurfaceParityTests
             foreach (var (leaf, path) in Leaves(root, []))
             {
                 // Separate REST and persistent SignalR surfaces, not management contracts.
-                // `audit verify-chain` is the one audit leaf that IS a management contract
+                // `audit verify-chain` (VerifyAuditChain, ScadaBridge#41) and `audit archive
-                // (VerifyAuditChain, ScadaBridge#41), so it stays in the probe.
+                // list|verify` (ListAuditArchives / VerifyAuditArchive, ScadaBridge#42) are the
-                if (path.Length == 0 || (path[0] == "audit" && string.Join(' ', path) != "audit verify-chain")
+                // audit leaves that ARE management contracts, so they stay in the probe.
+                if (path.Length == 0 || (path[0] == "audit" && !AuditManagementLeaves.Contains(string.Join(' ', path)))
                     || path[0] == omitGroup
                     || string.Join(' ', path) == "debug stream") continue;
                 currentPath = string.Join(' ', path);

tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/AuditArchiveCommandTests.cs

@@ -0,0 +1,147 @@
+using System.Text.Json;
+using Akka.Actor;
+using Akka.TestKit.Xunit2;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using NSubstitute;
+using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
+using ZB.MOM.WW.ScadaBridge.Commons.Messages.Management;
+using ZB.MOM.WW.ScadaBridge.Commons.Types.Audit;
+
+namespace ZB.MOM.WW.ScadaBridge.ManagementService.Tests;
+
+/// <summary>
+/// The <c>ListAuditArchives</c> / <c>VerifyAuditArchive</c> management commands
+/// (ScadaBridge#42): role gate, site-scope refusal, an unconfigured archive directory, bad
+/// names, and the results reaching the wire with enums as names.
+/// </summary>
+public class AuditArchiveCommandTests : TestKit
+{
+    private const string Name = "auditlog-2025-10-20261109T120000123Z";
+
+    private readonly IAuditLogArchive _archive = Substitute.For<IAuditLogArchive>();
+
+    /// <summary>Configures the archive substitute as a configured, enabled archive.</summary>
+    public AuditArchiveCommandTests()
+    {
+        _archive.IsConfigured.Returns(true);
+        _archive.IsEnabled.Returns(true);
+    }
+
+    private IActorRef CreateActor(bool registerArchive = true)
+    {
+        var services = new ServiceCollection().AddTestConfigurationTransaction();
+        if (registerArchive)
+        {
+            services.AddScoped(_ => _archive);
+        }
+
+        return Sys.ActorOf(Props.Create(() => new ManagementActor(
+            services.BuildServiceProvider(), NullLogger<ManagementActor>.Instance)));
+    }
+
+    private static ManagementEnvelope Envelope(object command, string[] sites, params string[] roles) =>
+        new(new AuthenticatedUser("u", "U", roles, sites), command, Guid.NewGuid().ToString("N"));
+
+    private static AuditArchiveManifest Manifest() => new(
+        1, Name, new DateTime(2025, 10, 1, 0, 0, 0, DateTimeKind.Utc), "2025-10",
+        new DateTime(2026, 11, 9, 12, 0, 0, DateTimeKind.Utc), AuditArchiveStatus.Purged,
+        new DateTime(2026, 11, 9, 12, 0, 1, DateTimeKind.Utc), 10, 9, 1, null, null,
+        Name + ".parquet", "ab", 1234, Name + ".tombstones.parquet", "cd", 0,
+        [new AuditArchiveChainState("2025-10", 9, new string('0', 64), null, null, 0)]);
+
+    /// <summary>A Viewer lists the archives; status renders as a name.</summary>
+    [Fact]
+    public void Viewer_ListsArchives()
+    {
+        _archive.ListAsync(Arg.Any<CancellationToken>()).Returns([Manifest()]);
+
+        CreateActor().Tell(Envelope(new ListAuditArchivesCommand(), [], "Viewer"));
+
+        var response = ExpectMsg<ManagementSuccess>(TimeSpan.FromSeconds(5));
+        using var json = JsonDocument.Parse(response.JsonData);
+        Assert.True(json.RootElement.GetProperty("enabled").GetBoolean());
+        var archive = json.RootElement.GetProperty("archives")[0];
+        Assert.Equal(Name, archive.GetProperty("name").GetString());
+        Assert.Equal("Purged", archive.GetProperty("status").GetString());
+    }
+
+    /// <summary>Verification results reach the wire with the anchor and chain status as names.</summary>
+    [Fact]
+    public void Viewer_GetsVerificationResult()
+    {
+        var chain = new AuditChainVerificationResult("2025-10", AuditChainStatus.Intact, 9, 0, null, 9, 1, null);
+        _archive.VerifyAsync(Name, Arg.Any<CancellationToken>()).Returns(new AuditArchiveVerificationResult(
+            Name, "2025-10", AuditArchiveStatus.Purged, true, true, null, 10,
+            [new AuditArchiveChainVerification(chain, AuditArchiveAnchorStatus.Matches, "ends at the anchor")]));
+
+        CreateActor().Tell(Envelope(new VerifyAuditArchiveCommand(Name), [], "Viewer"));
+
+        var response = ExpectMsg<ManagementSuccess>(TimeSpan.FromSeconds(5));
+        using var json = JsonDocument.Parse(response.JsonData);
+        Assert.True(json.RootElement.GetProperty("verified").GetBoolean());
+        var c = json.RootElement.GetProperty("chains")[0];
+        Assert.Equal("Matches", c.GetProperty("anchor").GetString());
+        Assert.Equal("Intact", c.GetProperty("chain").GetProperty("status").GetString());
+    }
+
+    /// <summary>Designer/Deployer without an OperationalAudit role are refused both commands.</summary>
+    [Fact]
+    public void NonAuditRole_IsUnauthorized()
+    {
+        var actor = CreateActor();
+        actor.Tell(Envelope(new ListAuditArchivesCommand(), [], "Designer", "Deployer"));
+        ExpectMsg<ManagementUnauthorized>(TimeSpan.FromSeconds(5));
+        actor.Tell(Envelope(new VerifyAuditArchiveCommand(Name), [], "Designer", "Deployer"));
+        ExpectMsg<ManagementUnauthorized>(TimeSpan.FromSeconds(5));
+        _archive.DidNotReceiveWithAnyArgs().ListAsync(default);
+        _archive.DidNotReceiveWithAnyArgs().VerifyAsync(default!, default);
+    }
+
+    /// <summary>A site-scoped Viewer is refused: an archive holds every site's rows.</summary>
+    [Fact]
+    public void SiteScopedViewer_IsRefused()
+    {
+        CreateActor().Tell(Envelope(new VerifyAuditArchiveCommand(Name), ["3"], "Viewer"));
+
+        var response = ExpectMsg<ManagementUnauthorized>(TimeSpan.FromSeconds(5));
+        Assert.Contains("every site", response.Message);
+        _archive.DidNotReceiveWithAnyArgs().VerifyAsync(default!, default);
+    }
+
+    /// <summary>No archive directory configured is an explicit error code, not an empty list.</summary>
+    [Fact]
+    public void UnconfiguredArchive_IsArchiveNotConfigured()
+    {
+        _archive.IsConfigured.Returns(false);
+
+        CreateActor().Tell(Envelope(new ListAuditArchivesCommand(), [], "Administrator"));
+
+        var response = ExpectMsg<ManagementError>(TimeSpan.FromSeconds(5));
+        Assert.Equal("ARCHIVE_NOT_CONFIGURED", response.ErrorCode);
+    }
+
+    /// <summary>A malformed name is INVALID_ARGUMENT; an unknown one is NOT_FOUND.</summary>
+    [Fact]
+    public void BadNames_MapToCallerErrors()
+    {
+        _archive.VerifyAsync("../etc", Arg.Any<CancellationToken>())
+            .Returns<Task<AuditArchiveVerificationResult>>(_ => throw new ArgumentException("not an archive name"));
+        _archive.VerifyAsync(Name, Arg.Any<CancellationToken>())
+            .Returns<Task<AuditArchiveVerificationResult>>(_ => throw new FileNotFoundException("no archive"));
+
+        var actor = CreateActor();
+        actor.Tell(Envelope(new VerifyAuditArchiveCommand("../etc"), [], "Administrator"));
+        Assert.Equal("INVALID_ARGUMENT", ExpectMsg<ManagementError>(TimeSpan.FromSeconds(5)).ErrorCode);
+        actor.Tell(Envelope(new VerifyAuditArchiveCommand(Name), [], "Administrator"));
+        Assert.Equal("NOT_FOUND", ExpectMsg<ManagementError>(TimeSpan.FromSeconds(5)).ErrorCode);
+    }
+
+    /// <summary>Archive verification runs under the long-running Ask timeout.</summary>
+    [Fact]
+    public void VerifyAuditArchive_UsesLongRunningAskTimeout()
+    {
+        Assert.Equal(TimeSpan.FromMinutes(5),
+            ManagementEndpoints.ResolveAskTimeout(new ManagementServiceOptions(), typeof(VerifyAuditArchiveCommand)));
+    }
+}

tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/AuditEndpointsTests.cs

@@ -506,21 +506,43 @@ public class AuditEndpointsTests
         Assert.Equal(propertyNames, AuditEndpoints.CsvHeader.Split(','));
     }
 
-    /// <summary>Verifies that a Parquet export returns 501.</summary>
+    /// <summary>
+    /// <c>format=parquet</c> (ScadaBridge#42; it used to be a 501) streams one readable Parquet
+    /// file whose columns are the csv/jsonl export's columns, in order, holding every row.
+    /// </summary>
     /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
-    public async Task Export_Parquet_Returns501()
+    public async Task Export_Parquet_StreamsReadableParquet_WithTheCsvColumns()
     {
-        // Parquet archival is deferred to v1.x (Component-AuditLog.md) — no
+        var (client, _, host) = await BuildHostAsync(
-        // library is referenced, so the endpoint returns 501 with guidance.
+            roles: new[] { "Administrator" },
-        var (client, _, host) = await BuildHostAsync(roles: new[] { "Administrator" });
+            queryPages: new[]
+            {
+                (IReadOnlyList<AuditEvent>)new[]
+                {
+                    SampleEvent(Guid.Parse("cccccccc-0000-0000-0000-000000000001")),
+                    SampleEvent(Guid.Parse("cccccccc-0000-0000-0000-000000000002")),
+                },
+                (IReadOnlyList<AuditEvent>)Array.Empty<AuditEvent>(),
+            });
         using (host)
         {
-            var response = await client.SendAsync(Get("/api/audit/export?format=parquet"));
+            var response = await client.SendAsync(Get("/api/audit/export?format=Parquet"));
 
-            Assert.Equal(HttpStatusCode.NotImplemented, response.StatusCode);
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
-            var body = await response.Content.ReadAsStringAsync();
+            Assert.Equal(AuditEndpoints.ParquetContentType, response.Content.Headers.ContentType!.MediaType);
-            Assert.Contains("Parquet export deferred to v1.x", body);
+            Assert.Contains(".parquet", response.Content.Headers.ContentDisposition?.ToString()
+                ?? response.Headers.GetValues("Content-Disposition").FirstOrDefault()
+                ?? response.Content.Headers.GetValues("Content-Disposition").First());
+
+            var bytes = await response.Content.ReadAsByteArrayAsync();
+            await using var reader = await Parquet.ParquetReader.CreateAsync(new MemoryStream(bytes));
+            Assert.Equal(AuditEndpoints.CsvHeader.Split(','), reader.Schema.GetDataFields().Select(f => f.Name));
+            using var group = reader.OpenRowGroupReader(0);
+            Assert.Equal(2, group.RowCount);
+            var ids = new string?[2];
+            await group.ReadAsync(reader.Schema.GetDataFields()[0], ids!);
+            Assert.Equal(new[] { "cccccccc-0000-0000-0000-000000000001", "cccccccc-0000-0000-0000-000000000002" }, ids);
         }
     }
 

tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/AuditExportParquetTests.cs

@@ -0,0 +1,150 @@
+using Parquet;
+using ZB.MOM.WW.ScadaBridge.Commons.Types.Audit;
+using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
+
+namespace ZB.MOM.WW.ScadaBridge.ManagementService.Tests;
+
+/// <summary>
+/// <see cref="AuditExportParquet"/> (ScadaBridge#42): the Parquet export round-trips every
+/// one of the 24 export columns, splits into row groups, and never writes synchronously to
+/// the output (Kestrel rejects synchronous response writes).
+/// </summary>
+public class AuditExportParquetTests
+{
+    /// <summary>Rows written and read back are equal, column for column, across row groups.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
+    [Fact]
+    public async Task RoundTrip_EveryColumn_AcrossRowGroups()
+    {
+        var rows = Enumerable.Range(0, AuditExportParquet.RowGroupRows + 7).Select(Row).ToList();
+        var output = new AsyncOnlyStream();
+
+        var written = await AuditExportParquet.WriteAsync(Pages(rows, 1000), output);
+
+        Assert.Equal(rows.Count, written);
+        await using var reader = await ParquetReader.CreateAsync(new MemoryStream(output.ToArray()));
+        Assert.Equal(2, reader.RowGroupCount);
+        var back = new List<AuditExportRow>();
+        var fields = reader.Schema.GetDataFields();
+        for (var g = 0; g < reader.RowGroupCount; g++)
+        {
+            using var group = reader.OpenRowGroupReader(g);
+            var n = (int)group.RowCount;
+            async Task<string?[]> S(int i) { var a = new string?[n]; await group.ReadAsync(fields[i], a!); return a; }
+            async Task<T?[]> V<T>(int i) where T : struct { var a = new T?[n]; await group.ReadAsync<T>(fields[i], a); return a; }
+            var id = await S(0); var occurred = await V<DateTime>(1); var ingested = await V<DateTime>(2);
+            var channel = await S(3); var kind = await S(4); var corr = await S(5); var exec = await S(6); var parent = await S(7);
+            var site = await S(8); var node = await S(9); var inst = await S(10); var script = await S(11); var actor = await S(12);
+            var target = await S(13); var status = await S(14); var http = await V<int>(15); var dur = await V<int>(16);
+            var errMsg = await S(17); var errDetail = await S(18); var req = await S(19); var resp = await S(20);
+            var trunc = await V<bool>(21); var extra = await S(22); var fwd = await S(23);
+            for (var i = 0; i < n; i++)
+            {
+                back.Add(new AuditExportRow
+                {
+                    EventId = Guid.Parse(id[i]!),
+                    OccurredAtUtc = occurred[i]!.Value,
+                    IngestedAtUtc = ingested[i],
+                    Channel = Enum.Parse<AuditChannel>(channel[i]!),
+                    Kind = Enum.Parse<AuditKind>(kind[i]!),
+                    CorrelationId = corr[i] is { } c ? Guid.Parse(c) : null,
+                    ExecutionId = exec[i] is { } e ? Guid.Parse(e) : null,
+                    ParentExecutionId = parent[i] is { } p ? Guid.Parse(p) : null,
+                    SourceSiteId = site[i],
+                    SourceNode = node[i],
+                    SourceInstanceId = inst[i],
+                    SourceScript = script[i],
+                    Actor = actor[i],
+                    Target = target[i],
+                    Status = Enum.Parse<AuditStatus>(status[i]!),
+                    HttpStatus = http[i],
+                    DurationMs = dur[i],
+                    ErrorMessage = errMsg[i],
+                    ErrorDetail = errDetail[i],
+                    RequestSummary = req[i],
+                    ResponseSummary = resp[i],
+                    PayloadTruncated = trunc[i]!.Value,
+                    Extra = extra[i],
+                    ForwardState = fwd[i] is { } f ? Enum.Parse<AuditForwardState>(f) : null,
+                });
+            }
+        }
+
+        Assert.Equal(rows, back);
+    }
+
+    /// <summary>An export with no rows is still a valid (empty) Parquet file.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
+    [Fact]
+    public async Task NoRows_IsAValidEmptyFile()
+    {
+        var output = new AsyncOnlyStream();
+        Assert.Equal(0, await AuditExportParquet.WriteAsync(Pages([], 10), output));
+        await using var reader = await ParquetReader.CreateAsync(new MemoryStream(output.ToArray()));
+        Assert.Equal(0, reader.RowGroupCount);
+        Assert.Equal(24, reader.Schema.GetDataFields().Length);
+    }
+
+    private static AuditExportRow Row(int i) => new()
+    {
+        EventId = Guid.NewGuid(),
+        // Microsecond precision: the export timestamp column is TIMESTAMP(MICROS).
+        OccurredAtUtc = new DateTime(2026, 5, 20, 12, 0, 0, DateTimeKind.Utc).AddTicks(i * 10L),
+        IngestedAtUtc = i % 3 == 0 ? null : new DateTime(2026, 5, 20, 12, 0, 1, DateTimeKind.Utc),
+        Channel = (AuditChannel)(i % Enum.GetValues<AuditChannel>().Length),
+        Kind = AuditKind.ApiCall,
+        CorrelationId = i % 2 == 0 ? Guid.NewGuid() : null,
+        ExecutionId = Guid.NewGuid(),
+        ParentExecutionId = i % 5 == 0 ? Guid.NewGuid() : null,
+        SourceSiteId = i % 4 == 0 ? null : "plant-a",
+        SourceNode = "node-a",
+        SourceInstanceId = "Plant1.Boiler",
+        SourceScript = i % 2 == 0 ? "OnTick" : null,
+        Actor = i % 7 == 0 ? string.Empty : "api-key-1",
+        Target = "erp",
+        Status = AuditStatus.Delivered,
+        HttpStatus = i % 2 == 0 ? 200 : null,
+        DurationMs = i,
+        ErrorMessage = i % 9 == 0 ? "boom, \"quoted\"\nline" : null,
+        ErrorDetail = null,
+        RequestSummary = "{\"ü\":\"日本\"}",
+        ResponseSummary = null,
+        PayloadTruncated = i % 2 == 1,
+        Extra = null,
+        ForwardState = i % 11 == 0 ? AuditForwardState.Forwarded : null,
+    };
+
+    private static async IAsyncEnumerable<IReadOnlyList<AuditExportRow>> Pages(List<AuditExportRow> rows, int size)
+    {
+        for (var i = 0; i < rows.Count; i += size)
+        {
+            await Task.Yield();
+            yield return rows.Skip(i).Take(size).ToList();
+        }
+    }
+
+    /// <summary>A response-body stand-in that fails any synchronous write, like Kestrel.</summary>
+    private sealed class AsyncOnlyStream : Stream
+    {
+        private readonly MemoryStream _inner = new();
+
+        public byte[] ToArray() => _inner.ToArray();
+
+        public override bool CanRead => false;
+        public override bool CanSeek => false;
+        public override bool CanWrite => true;
+        public override long Length => throw new NotSupportedException();
+        public override long Position { get => throw new NotSupportedException(); set => throw new NotSupportedException(); }
+        public override void Flush() => throw new InvalidOperationException("Synchronous operations are disallowed.");
+        public override Task FlushAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+        public override int Read(byte[] buffer, int offset, int count) => throw new NotSupportedException();
+        public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
+        public override void SetLength(long value) => throw new NotSupportedException();
+        public override void Write(byte[] buffer, int offset, int count) => throw new InvalidOperationException("Synchronous operations are disallowed.");
+        public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default)
+        {
+            _inner.Write(buffer.Span);
+            return ValueTask.CompletedTask;
+        }
+    }
+}

tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/RequiredRoleMatrixTests.cs

@@ -171,6 +171,9 @@ public class RequiredRoleMatrixTests
         // AuditLog hash-chain verification (ScadaBridge#41) carries audit query's
         // OperationalAudit permission (alog.md §15.1); written out by hand to keep the freeze.
         ["VerifyAuditChain"] = [Roles.Administrator, Roles.Viewer],
+        // AuditLog Parquet archives (ScadaBridge#42): same audit-read gate as verify-chain.
+        ["ListAuditArchives"] = [Roles.Administrator, Roles.Viewer],
+        ["VerifyAuditArchive"] = [Roles.Administrator, Roles.Viewer],
 
         // ---- Two-person secured write ----------------------------------------------
         ["SubmitSecuredWrite"] = [Roles.Operator],