diff --git a/src/ScadaLink.Transport/Import/BundleSessionStore.cs b/src/ScadaLink.Transport/Import/BundleSessionStore.cs
new file mode 100644
index 0000000..a647623
--- /dev/null
+++ b/src/ScadaLink.Transport/Import/BundleSessionStore.cs
@@ -0,0 +1,74 @@
+using System.Collections.Concurrent;
+using Microsoft.Extensions.Options;
+using ScadaLink.Commons.Interfaces.Transport;
+using ScadaLink.Commons.Types.Transport;
+
+namespace ScadaLink.Transport.Import;
+
+/// <summary>
+/// In-memory implementation of <see cref="IBundleSessionStore"/> backed by a
+/// <see cref="ConcurrentDictionary{TKey,TValue}"/>. Sessions are evicted lazily
+/// at read time (<see cref="Get"/>) and on-demand via <see cref="EvictExpired"/>;
+/// there is no background timer.
+/// <para>
+/// TTL is supplied by the importer via <see cref="BundleSession.ExpiresAt"/>;
+/// this store does not impose its own. The injected <see cref="TimeProvider"/>
+/// is used purely to determine <c>now</c> when checking <c>ExpiresAt</c>, which
+/// keeps unit tests deterministic.
+/// </para>
+/// <para>
+/// The 3-strike unlock lockout is owned by <see cref="BundleSession"/>
+/// (<c>FailedUnlockAttempts</c> / <c>Locked</c>); the store just hands out the
+/// shared session reference so the importer can mutate the counter in place.
+/// </para>
+/// </summary>
+public sealed class BundleSessionStore : IBundleSessionStore
+{
+    private readonly ConcurrentDictionary<Guid, BundleSession> _sessions = new();
+    private readonly TimeProvider _timeProvider;
+
+    // Options are accepted to honor the documented constructor contract and to
+    // be ready for future per-store knobs (e.g. max in-flight sessions). The
+    // current store does not read any field — TTL is on the session itself.
+    public BundleSessionStore(IOptions<TransportOptions> options, TimeProvider timeProvider)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        _ = options.Value;
+        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
+    }
+
+    public BundleSession Open(BundleSession session)
+    {
+        ArgumentNullException.ThrowIfNull(session);
+        // Overwrite on collision is defensive: GUIDs are random so practical
+        // collisions don't happen, but if a caller reuses an id we always
+        // honor the latest Open call.
+        _sessions[session.SessionId] = session;
+        return session;
+    }
+
+    public BundleSession? Get(Guid sessionId)
+    {
+        if (!_sessions.TryGetValue(sessionId, out var session)) return null;
+        if (session.ExpiresAt > _timeProvider.GetUtcNow()) return session;
+        _sessions.TryRemove(sessionId, out _);
+        return null;
+    }
+
+    public void Remove(Guid sessionId)
+    {
+        _sessions.TryRemove(sessionId, out _);
+    }
+
+    public void EvictExpired()
+    {
+        var now = _timeProvider.GetUtcNow();
+        foreach (var kv in _sessions)
+        {
+            if (kv.Value.ExpiresAt <= now)
+            {
+                _sessions.TryRemove(kv.Key, out _);
+            }
+        }
+    }
+}
diff --git a/src/ScadaLink.Transport/ServiceCollectionExtensions.cs b/src/ScadaLink.Transport/ServiceCollectionExtensions.cs
index 99700aa..bf0f7be 100644
--- a/src/ScadaLink.Transport/ServiceCollectionExtensions.cs
+++ b/src/ScadaLink.Transport/ServiceCollectionExtensions.cs
@@ -1,6 +1,9 @@
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Options;
+using ScadaLink.Commons.Interfaces.Transport;
 using ScadaLink.Transport.Export;
+using ScadaLink.Transport.Import;
 
 namespace ScadaLink.Transport;
 
@@ -12,7 +15,9 @@ public static class ServiceCollectionExtensions
     {
         ArgumentNullException.ThrowIfNull(services);
         services.AddOptions<TransportOptions>().BindConfiguration(OptionsSection);
+        services.TryAddSingleton(TimeProvider.System);
         services.AddScoped<DependencyResolver>();
+        services.AddSingleton<IBundleSessionStore, BundleSessionStore>();
         // Remaining concrete services added in later tasks.
         return services;
     }
diff --git a/tests/ScadaLink.Transport.Tests/Import/BundleSessionStoreTests.cs b/tests/ScadaLink.Transport.Tests/Import/BundleSessionStoreTests.cs
new file mode 100644
index 0000000..271de05
--- /dev/null
+++ b/tests/ScadaLink.Transport.Tests/Import/BundleSessionStoreTests.cs
@@ -0,0 +1,136 @@
+using Microsoft.Extensions.Options;
+using ScadaLink.Commons.Types.Transport;
+using ScadaLink.Transport;
+using ScadaLink.Transport.Import;
+
+namespace ScadaLink.Transport.Tests.Import;
+
+public sealed class BundleSessionStoreTests
+{
+    private static IOptions<TransportOptions> Options() => Microsoft.Extensions.Options.Options.Create(new TransportOptions());
+
+    private static BundleSession SessionExpiringAt(DateTimeOffset expiresAt) => new()
+    {
+        SessionId = Guid.NewGuid(),
+        Manifest = StubManifest(),
+        DecryptedContent = Array.Empty<byte>(),
+        ExpiresAt = expiresAt,
+    };
+
+    private static BundleManifest StubManifest() => new(
+        BundleFormatVersion: 1,
+        SchemaVersion: "1.0",
+        CreatedAtUtc: DateTimeOffset.UnixEpoch,
+        SourceEnvironment: "test",
+        ExportedBy: "t",
+        ScadaLinkVersion: "1",
+        ContentHash: "0",
+        Encryption: null,
+        Summary: new BundleSummary(0, 0, 0, 0, 0, 0, 0, 0, 0),
+        Contents: Array.Empty<ManifestContentEntry>());
+
+    [Fact]
+    public void Open_then_Get_returns_session()
+    {
+        var clock = new TestTimeProvider(DateTimeOffset.UtcNow);
+        var sut = new BundleSessionStore(Options(), clock);
+        var session = SessionExpiringAt(clock.GetUtcNow().AddMinutes(30));
+
+        sut.Open(session);
+
+        var fetched = sut.Get(session.SessionId);
+        Assert.NotNull(fetched);
+        Assert.Same(session, fetched);
+    }
+
+    [Fact]
+    public void Get_after_TTL_returns_null_and_evicts()
+    {
+        var start = DateTimeOffset.UtcNow;
+        var clock = new TestTimeProvider(start);
+        var sut = new BundleSessionStore(Options(), clock);
+        var session = SessionExpiringAt(start.AddMinutes(1));
+        sut.Open(session);
+
+        clock.Advance(TimeSpan.FromMinutes(2));
+
+        Assert.Null(sut.Get(session.SessionId));
+        // Lookup with no time advancement now returns null again — proves the
+        // entry was evicted, not merely filtered.
+        Assert.Null(sut.Get(session.SessionId));
+    }
+
+    [Fact]
+    public void Remove_evicts_session()
+    {
+        var clock = new TestTimeProvider(DateTimeOffset.UtcNow);
+        var sut = new BundleSessionStore(Options(), clock);
+        var session = SessionExpiringAt(clock.GetUtcNow().AddHours(1));
+        sut.Open(session);
+
+        sut.Remove(session.SessionId);
+
+        Assert.Null(sut.Get(session.SessionId));
+    }
+
+    [Fact]
+    public void EvictExpired_removes_all_past_ttl()
+    {
+        var start = DateTimeOffset.UtcNow;
+        var clock = new TestTimeProvider(start);
+        var sut = new BundleSessionStore(Options(), clock);
+
+        var keep = SessionExpiringAt(start.AddMinutes(30));
+        var dropA = SessionExpiringAt(start.AddSeconds(10));
+        var dropB = SessionExpiringAt(start.AddMinutes(1));
+        sut.Open(keep);
+        sut.Open(dropA);
+        sut.Open(dropB);
+
+        clock.Advance(TimeSpan.FromMinutes(2));
+        sut.EvictExpired();
+
+        Assert.NotNull(sut.Get(keep.SessionId));
+        Assert.Null(sut.Get(dropA.SessionId));
+        Assert.Null(sut.Get(dropB.SessionId));
+    }
+
+    [Fact]
+    public void Three_failed_unlock_attempts_locks_session()
+    {
+        var clock = new TestTimeProvider(DateTimeOffset.UtcNow);
+        var sut = new BundleSessionStore(Options(), clock);
+        var session = SessionExpiringAt(clock.GetUtcNow().AddMinutes(30));
+        sut.Open(session);
+
+        var live = sut.Get(session.SessionId);
+        Assert.NotNull(live);
+
+        live!.FailedUnlockAttempts++;
+        Assert.False(live.Locked);
+        live.FailedUnlockAttempts++;
+        Assert.False(live.Locked);
+        live.FailedUnlockAttempts++;
+        Assert.True(live.Locked);
+
+        // Mutations are observable via re-fetch — confirms the store hands out
+        // the shared reference (not a snapshot).
+        var refetch = sut.Get(session.SessionId);
+        Assert.NotNull(refetch);
+        Assert.True(refetch!.Locked);
+    }
+
+    /// <summary>
+    /// Minimal in-test <see cref="TimeProvider"/> with a mutable clock. Used in
+    /// place of <c>Microsoft.Extensions.TimeProvider.Testing</c> (not in the
+    /// central package list). Only <see cref="GetUtcNow"/> is overridden; the
+    /// store does not use timers, so the base implementations suffice elsewhere.
+    /// </summary>
+    private sealed class TestTimeProvider : TimeProvider
+    {
+        private DateTimeOffset _now;
+        public TestTimeProvider(DateTimeOffset start) { _now = start; }
+        public override DateTimeOffset GetUtcNow() => _now;
+        public void Advance(TimeSpan by) => _now = _now.Add(by);
+    }
+}