diff --git a/tests/AVEVA.Historian.Client.Tests/HandshakeReuseSpikeTests.cs b/tests/AVEVA.Historian.Client.Tests/HandshakeReuseSpikeTests.cs
new file mode 100644
index 0000000..0aba687
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+++ b/tests/AVEVA.Historian.Client.Tests/HandshakeReuseSpikeTests.cs
@@ -0,0 +1,168 @@
+using System.Diagnostics;
+using AVEVA.Historian.Client.Grpc;
+using AVEVA.Historian.Client.Models;
+using Xunit.Abstractions;
+
+namespace AVEVA.Historian.Client.Tests;
+
+/// <summary>
+/// SPIKE (pending.md A1): does the 2023 R2 historian honor REUSING one authenticated session across
+/// many operations — the precondition for handshake amortization? Env-gated exactly like
+/// <see cref="HistorianGrpcIntegrationTests"/> (silent skip without HISTORIAN_GRPC_HOST +
+/// HISTORIAN_TEST_TAG + HISTORIAN_USER). READ-ONLY — no writes, safe against live data. Reuse
+/// validity is ASSERTED; latency numbers are LOGGED only (no flaky perf gates).
+/// </summary>
+public sealed class HandshakeReuseSpikeTests
+{
+    private const int ReuseOps = 5;
+    private readonly ITestOutputHelper _output;
+
+    public HandshakeReuseSpikeTests(ITestOutputHelper output) => _output = output;
+
+    // (1) REUSE VALIDITY: one session, N reads on the same clientHandle. If the server rejects handle
+    // reuse, read #2+ throws -> RED finding. All succeed -> GREEN finding.
+    [Fact]
+    public void ReusedSession_RunsManyReads_AllSucceed()
+    {
+        if (!TryGetEnv(out string host, out string tag)) return;
+        HistorianClientOptions options = BuildOptions(host);
+        (DateTime startUtc, DateTime endUtc) = LastSevenDays();
+
+        using HistorianGrpcConnection connection = HistorianGrpcChannelFactory.Create(options);
+
+        var swHandshake = Stopwatch.StartNew();
+        HistorianGrpcHandshake.Session session = HistorianGrpcHandshake.OpenSession(connection, options, CancellationToken.None);
+        swHandshake.Stop();
+        _output.WriteLine($"open-session (handshake) = {swHandshake.ElapsedMilliseconds} ms");
+
+        var orchestrator = new HistorianGrpcReadOrchestrator(options);
+        for (int i = 0; i < ReuseOps; i++)
+        {
+            var sw = Stopwatch.StartNew();
+            List<HistorianSample> rows = orchestrator.RunRawQueryOnSession(
+                connection, session.ClientHandle, tag, startUtc, endUtc, maxValues: 8, CancellationToken.None);
+            sw.Stop();
+            _output.WriteLine($"reused-read[{i}] = {sw.ElapsedMilliseconds} ms, rows={rows.Count}");
+            Assert.NotEmpty(rows);
+            Assert.All(rows, r => Assert.Equal(tag, r.TagName));
+        }
+    }
+
+    // (2) WIN MAGNITUDE: full per-call path (fresh Create+handshake+query) vs amortized (one handshake,
+    // N reused reads). Logged only — quantifies whether amortization is worth the refactor.
+    [Fact]
+    public async Task ReusedSession_VsPerCallPath_LogsLatencyDelta()
+    {
+        if (!TryGetEnv(out string host, out string tag)) return;
+        HistorianClientOptions options = BuildOptions(host);
+        (DateTime startUtc, DateTime endUtc) = LastSevenDays();
+
+        HistorianClient client = new(options);
+        var swPerCall = Stopwatch.StartNew();
+        for (int i = 0; i < ReuseOps; i++)
+        {
+            await foreach (HistorianSample _ in client.ReadRawAsync(tag, startUtc, endUtc, 8, CancellationToken.None)) { }
+        }
+        swPerCall.Stop();
+
+        using HistorianGrpcConnection connection = HistorianGrpcChannelFactory.Create(options);
+        HistorianGrpcHandshake.Session session = HistorianGrpcHandshake.OpenSession(connection, options, CancellationToken.None);
+        var orchestrator = new HistorianGrpcReadOrchestrator(options);
+        var swAmortized = Stopwatch.StartNew();
+        for (int i = 0; i < ReuseOps; i++)
+        {
+            orchestrator.RunRawQueryOnSession(connection, session.ClientHandle, tag, startUtc, endUtc, 8, CancellationToken.None);
+        }
+        swAmortized.Stop();
+
+        _output.WriteLine($"per-call  ({ReuseOps} ops) = {swPerCall.ElapsedMilliseconds} ms");
+        _output.WriteLine($"amortized ({ReuseOps} ops) = {swAmortized.ElapsedMilliseconds} ms");
+        _output.WriteLine($"saving over {ReuseOps} ops = {swPerCall.ElapsedMilliseconds - swAmortized.ElapsedMilliseconds} ms");
+    }
+
+    // (3) EXPIRY SWEEP: reuse after idle gaps. Default bounded [0s, 30s]; longer tiers opt-in via
+    // HISTORIAN_REUSE_IDLE_SECONDS="0,30,120,600". Rethrows at the tier where reuse first breaks.
+    [Fact]
+    public void ReusedSession_IdleSweep_SurfacesExpiryTier()
+    {
+        if (!TryGetEnv(out string host, out string tag)) return;
+        HistorianClientOptions options = BuildOptions(host);
+        (DateTime startUtc, DateTime endUtc) = LastSevenDays();
+
+        using HistorianGrpcConnection connection = HistorianGrpcChannelFactory.Create(options);
+        HistorianGrpcHandshake.Session session = HistorianGrpcHandshake.OpenSession(connection, options, CancellationToken.None);
+        var orchestrator = new HistorianGrpcReadOrchestrator(options);
+
+        foreach (int delaySec in ParseIdleSweep())
+        {
+            if (delaySec > 0) Thread.Sleep(TimeSpan.FromSeconds(delaySec));
+            try
+            {
+                List<HistorianSample> rows = orchestrator.RunRawQueryOnSession(
+                    connection, session.ClientHandle, tag, startUtc, endUtc, 8, CancellationToken.None);
+                _output.WriteLine($"idle {delaySec,4}s -> OK (rows={rows.Count})");
+            }
+            catch (Exception ex)
+            {
+                _output.WriteLine($"idle {delaySec,4}s -> BROKE ({ex.GetType().Name})");
+                throw;
+            }
+        }
+    }
+
+    // --- helpers ---
+
+    private static bool TryGetEnv(out string host, out string tag)
+    {
+        host = Environment.GetEnvironmentVariable("HISTORIAN_GRPC_HOST") ?? "";
+        tag = Environment.GetEnvironmentVariable("HISTORIAN_TEST_TAG") ?? "";
+        return !string.IsNullOrWhiteSpace(host)
+            && !string.IsNullOrWhiteSpace(tag)
+            && !string.IsNullOrEmpty(Environment.GetEnvironmentVariable("HISTORIAN_USER"));
+    }
+
+    private static (DateTime StartUtc, DateTime EndUtc) LastSevenDays()
+    {
+        DateTime end = DateTime.UtcNow;
+        return (end - TimeSpan.FromDays(7), end);
+    }
+
+    private static int[] ParseIdleSweep()
+    {
+        string? raw = Environment.GetEnvironmentVariable("HISTORIAN_REUSE_IDLE_SECONDS");
+        if (string.IsNullOrWhiteSpace(raw)) return [0, 30];
+        return raw.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
+                  .Select(s => int.Parse(s, System.Globalization.CultureInfo.InvariantCulture)).ToArray();
+    }
+
+    private static HistorianClientOptions BuildOptions(string host)
+    {
+        string? user = Environment.GetEnvironmentVariable("HISTORIAN_USER");
+        string? password = Environment.GetEnvironmentVariable("HISTORIAN_PASSWORD");
+        bool explicitCreds = !string.IsNullOrEmpty(user);
+        int port = int.TryParse(Environment.GetEnvironmentVariable("HISTORIAN_GRPC_PORT"), out int parsed)
+            ? parsed
+            : HistorianClientOptions.DefaultGrpcPort;
+        bool tls = string.Equals(Environment.GetEnvironmentVariable("HISTORIAN_GRPC_TLS"), "true", StringComparison.OrdinalIgnoreCase);
+        // Optional per-call deadline override (seconds) for slow/remote boxes — heavier aggregate
+        // modes over a tunnelled link can exceed the 30s default. Falls back to the SDK default.
+        TimeSpan timeout = int.TryParse(Environment.GetEnvironmentVariable("HISTORIAN_GRPC_TIMEOUT"), out int secs) && secs > 0
+            ? TimeSpan.FromSeconds(secs)
+            : new HistorianClientOptions { Host = host }.RequestTimeout;
+
+        return new HistorianClientOptions
+        {
+            Host = host,
+            Port = port,
+            Transport = HistorianTransport.RemoteGrpc,
+            GrpcUseTls = tls,
+            AllowUntrustedServerCertificate = tls,
+            ServerDnsIdentity = Environment.GetEnvironmentVariable("HISTORIAN_GRPC_DNSID"),
+            IntegratedSecurity = !explicitCreds,
+            UserName = user ?? string.Empty,
+            Password = password ?? string.Empty,
+            RequestTimeout = timeout,
+            Compression = true // the stock client always advertises grpc gzip request encoding
+        };
+    }
+}