diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Office/OfficeInstallDetectorTests.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Office/OfficeInstallDetectorTests.cs
index b9aba67a..6193c5db 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Office/OfficeInstallDetectorTests.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Office/OfficeInstallDetectorTests.cs
@@ -31,16 +31,20 @@ namespace AutopilotMonitor.Agent.V2.Core.Tests.Monitoring.Office
             public VirtualClock Clock { get; }
             public OfficeInstallDetector Sut { get; }
             public OfficeC2RSnapshot Current { get; set; }
+            public OfficeInstallStatePersistence? Persistence { get; }
             private readonly TempDirectory _tmp;
 
-            public Rig(OfficeC2RSnapshot initial)
+            public Rig(OfficeC2RSnapshot initial, bool withPersistence = false)
             {
                 _tmp = new TempDirectory();
                 Sink = new FakeSignalIngressSink();
                 Clock = new VirtualClock(At);
                 Current = initial;
+                var logger = NewLogger(_tmp.Path);
+                Persistence = withPersistence ? new OfficeInstallStatePersistence(_tmp.Path, logger) : null;
                 var post = new InformationalEventPost(Sink, Clock);
-                Sut = new OfficeInstallDetector("S1", "T1", post, NewLogger(_tmp.Path), Clock)
+                Sut = new OfficeInstallDetector("S1", "T1", post, logger, Clock,
+                    statePersistence: Persistence)
                 {
                     SnapshotProvider = () => Current,
                 };
@@ -420,6 +424,182 @@ namespace AutopilotMonitor.Agent.V2.Core.Tests.Monitoring.Office
             Assert.False(OfficeInstallDetector.CoreBinariesPresentOnDisk(System.IO.Path.Combine(tmp.Path, "does-not-exist"), logger));
         }
 
+        // ---------------------------------------------------------------- persistence across restarts
+
+        [Fact]
+        public void Started_persists_active_state_with_trigger_and_start_time()
+        {
+            using var rig = new Rig(ActiveStreaming(), withPersistence: true);
+
+            rig.Sut.OnOfficeDoSample(new OfficeDoSample { JobCount = 2, FileSize = 1000, TotalBytesDownloaded = 100 });
+
+            var state = rig.Persistence!.Load();
+            Assert.NotNull(state);
+            Assert.Equal(OfficeInstallStateData.StateActive, state!.State);
+            Assert.Equal(At, state.StartedAtUtc);
+            Assert.Equal("do", state.StartedTrigger);
+            Assert.Equal(100, state.PeakDo!.TotalBytesDownloaded);
+        }
+
+        [Fact]
+        public void Completed_persists_terminal_state()
+        {
+            using var rig = new Rig(ActiveStreaming(), withPersistence: true);
+            rig.Sut.OnWorkerStarted();
+
+            rig.Current = CompletedIdle();
+            rig.Sut.CoreBinariesProbe = _ => true;
+            Assert.Equal(OfficeInstallDetector.CompletionOutcome.Completed, rig.Sut.TryFinalizeCompletion());
+
+            var state = rig.Persistence!.Load();
+            Assert.Equal(OfficeInstallStateData.StateCompleted, state!.State);
+            Assert.True(state.IsTerminal);
+        }
+
+        [Fact]
+        public void Failed_persists_terminal_state()
+        {
+            using var rig = new Rig(ActiveStreaming(), withPersistence: true);
+            rig.Sut.OnWorkerStarted();
+
+            var withError = ActiveStreaming();
+            withError.ErrorCode = "0x80070005";
+            rig.Current = withError;
+            rig.Sut.OnRegistryChanged();
+
+            var state = rig.Persistence!.Load();
+            Assert.Equal(OfficeInstallStateData.StateFailed, state!.State);
+            Assert.True(state.IsTerminal);
+        }
+
+        [Fact]
+        public void AbandonSilently_does_not_persist_a_terminal_state()
+        {
+            // AbandonSilently fires on every host dispose/shutdown. Persisting it as terminal would
+            // block the next agent run from resuming the open lifecycle — and the resume is exactly
+            // what delivers a completion missed across a mid-install reboot.
+            using var rig = new Rig(ActiveStreaming(), withPersistence: true);
+            rig.Sut.OnWorkerStarted();
+
+            rig.Sut.AbandonSilently();
+
+            var state = rig.Persistence!.Load();
+            Assert.Equal(OfficeInstallStateData.StateActive, state!.State);
+            Assert.False(state.IsTerminal);
+        }
+
+        [Fact]
+        public void Active_peak_growth_is_persisted_with_throttle()
+        {
+            using var rig = new Rig(ActiveStreaming(), withPersistence: true);
+            rig.Sut.OnOfficeDoSample(new OfficeDoSample { JobCount = 2, FileSize = 1000, TotalBytesDownloaded = 100 }); // started + persisted
+
+            // Within the 30s throttle window: peak grows in memory but the file is not rewritten.
+            rig.Sut.OnOfficeDoSample(new OfficeDoSample { JobCount = 2, FileSize = 1000, TotalBytesDownloaded = 300 });
+            Assert.Equal(100, rig.Persistence!.Load()!.PeakDo!.TotalBytesDownloaded);
+
+            // After the throttle window the next grown peak is persisted.
+            rig.Clock.Advance(TimeSpan.FromSeconds(31));
+            rig.Sut.OnOfficeDoSample(new OfficeDoSample { JobCount = 2, FileSize = 1000, TotalBytesDownloaded = 600 });
+            Assert.Equal(600, rig.Persistence.Load()!.PeakDo!.TotalBytesDownloaded);
+        }
+
+        [Fact]
+        public void ResumeActive_completes_without_second_started_using_original_start_time_and_peak()
+        {
+            // Agent restart after a mid-install reboot: started went out in the previous run. The
+            // resumed lifecycle must not emit a second started, and the completion proven in this
+            // run reports the true total duration + the persisted DO summary.
+            using var rig = new Rig(CompletedIdle(), withPersistence: true);
+
+            rig.Sut.ResumeActive(new OfficeInstallStateData
+            {
+                State = OfficeInstallStateData.StateActive,
+                StartedAtUtc = At.AddMinutes(-10),
+                StartedTrigger = "do",
+                PeakDo = new OfficeDoPeakData
+                {
+                    JobCount = 3,
+                    FileSize = 1200,
+                    TotalBytesDownloaded = 1000,
+                    BytesFromHttp = 1000,
+                    BytesFromCacheServer = 800,
+                    DownloadMode = 1,
+                },
+            });
+            Assert.Empty(rig.OfficeEvents()); // no second started
+
+            // New start triggers must not re-open a window either — the lifecycle is already open.
+            rig.Sut.OnWorkerStarted();
+            Assert.Empty(rig.OfficeEvents());
+
+            rig.Sut.CoreBinariesProbe = _ => true;
+            Assert.Equal(OfficeInstallDetector.CompletionOutcome.Completed, rig.Sut.TryFinalizeCompletion());
+
+            var completed = Assert.Single(rig.OfficeEvents());
+            Assert.Equal(Constants.EventTypes.OfficeInstallCompleted, EventType(completed));
+            Assert.Equal(600, Data(completed)["durationSeconds"]); // 10 min across the restart
+            Assert.Equal("do", Data(completed)["startedTrigger"]);
+            var summary = Assert.IsType<Dictionary<string, object>>(Data(completed)["doSummary"]);
+            Assert.Equal(1000L, summary["totalBytesDownloaded"]);
+            Assert.Equal(800L, summary["bytesFromCacheServer"]);
+            Assert.Equal(200L, summary["bytesFromCdn"]);
+            Assert.Equal(OfficeInstallStateData.StateCompleted, rig.Persistence!.Load()!.State);
+        }
+
+        [Fact]
+        public void ResumeActive_surfaces_installation_path_for_synchronous_completion()
+        {
+            // Office finished installing while the agent was down: the resume reads a fresh snapshot
+            // and surfaces the InstallationPath; the host's binary watcher (wired here via the
+            // callback) finds the binaries immediately and completes the lifecycle synchronously —
+            // the previously missed completed is delivered, with no started this run.
+            using var tmp = new TempDirectory();
+            var sink = new FakeSignalIngressSink();
+            var clock = new VirtualClock(At);
+            var post = new InformationalEventPost(sink, clock);
+
+            OfficeInstallDetector sut = null!;
+            sut = new OfficeInstallDetector("S1", "T1", post, NewLogger(tmp.Path), clock,
+                onInstallationPathObserved: _ =>
+                {
+                    sut.CoreBinariesProbe = __ => true;
+                    sut.TryFinalizeCompletion();
+                });
+            var snap = CompletedIdle();
+            snap.InstallationPath = @"C:\Program Files\Microsoft Office";
+            sut.SnapshotProvider = () => snap;
+
+            sut.ResumeActive(new OfficeInstallStateData
+            {
+                State = OfficeInstallStateData.StateActive,
+                StartedAtUtc = At.AddMinutes(-5),
+                StartedTrigger = "registry",
+            });
+
+            var office = sink.Posted
+                .Where(p => p.Payload != null
+                    && p.Payload.TryGetValue(SignalPayloadKeys.EventType, out var et)
+                    && et != null && et.StartsWith("office_install_", StringComparison.Ordinal))
+                .ToList();
+            var completed = Assert.Single(office);
+            Assert.Equal(Constants.EventTypes.OfficeInstallCompleted, completed.Payload![SignalPayloadKeys.EventType]);
+        }
+
+        [Fact]
+        public void ResumeActive_ignores_terminal_or_invalid_state()
+        {
+            using var rig = new Rig(ActiveStreaming(), withPersistence: true);
+
+            rig.Sut.ResumeActive(new OfficeInstallStateData { State = OfficeInstallStateData.StateCompleted });
+            rig.Sut.ResumeActive(new OfficeInstallStateData { State = null });
+
+            // Still Idle — a real start trigger opens a fresh lifecycle normally.
+            rig.Sut.OnWorkerStarted();
+            var started = Assert.Single(rig.OfficeEvents());
+            Assert.Equal(Constants.EventTypes.OfficeInstallStarted, EventType(started));
+        }
+
         // ---------------------------------------------------------------- ctor
 
         [Fact]
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Office/OfficeInstallStatePersistenceTests.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Office/OfficeInstallStatePersistenceTests.cs
new file mode 100644
index 00000000..05270f44
--- /dev/null
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Office/OfficeInstallStatePersistenceTests.cs
@@ -0,0 +1,130 @@
+#nullable enable
+using System;
+using System.IO;
+using AutopilotMonitor.Agent.V2.Core.Logging;
+using AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office;
+using AutopilotMonitor.Agent.V2.Core.Tests.Harness;
+using Xunit;
+
+namespace AutopilotMonitor.Agent.V2.Core.Tests.Monitoring.Office
+{
+    /// <summary>
+    /// OfficeInstallStatePersistence — the office-install-state.json file that carries the
+    /// detector lifecycle across agent restarts/reboots. Fail-soft: missing/corrupt files load
+    /// as null (fresh start), saves never throw.
+    /// </summary>
+    public sealed class OfficeInstallStatePersistenceTests
+    {
+        private static AgentLogger NewLogger(string dir) => new AgentLogger(dir, AgentLogLevel.Info);
+
+        [Fact]
+        public void Save_then_load_roundtrips_all_fields()
+        {
+            using var tmp = new TempDirectory();
+            var sut = new OfficeInstallStatePersistence(tmp.Path, NewLogger(tmp.Path));
+            var startedAt = new DateTime(2026, 6, 8, 12, 0, 0, DateTimeKind.Utc);
+
+            sut.Save(new OfficeInstallStateData
+            {
+                State = OfficeInstallStateData.StateActive,
+                StartedAtUtc = startedAt,
+                StartedTrigger = "do",
+                PeakDo = new OfficeDoPeakData
+                {
+                    JobCount = 3,
+                    FileSize = 1200,
+                    TotalBytesDownloaded = 1000,
+                    BytesFromPeers = 0,
+                    BytesFromHttp = 1000,
+                    BytesFromCacheServer = 800,
+                    DownloadMode = 1,
+                },
+            });
+
+            var loaded = sut.Load();
+            Assert.NotNull(loaded);
+            Assert.Equal(OfficeInstallStateData.StateActive, loaded!.State);
+            Assert.False(loaded.IsTerminal);
+            Assert.Equal(startedAt, loaded.StartedAtUtc);
+            Assert.Equal("do", loaded.StartedTrigger);
+            Assert.NotNull(loaded.PeakDo);
+            Assert.Equal(3, loaded.PeakDo!.JobCount);
+            Assert.Equal(1200, loaded.PeakDo.FileSize);
+            Assert.Equal(1000, loaded.PeakDo.TotalBytesDownloaded);
+            Assert.Equal(1000, loaded.PeakDo.BytesFromHttp);
+            Assert.Equal(800, loaded.PeakDo.BytesFromCacheServer);
+            Assert.Equal(1, loaded.PeakDo.DownloadMode);
+        }
+
+        [Fact]
+        public void Save_overwrites_a_previous_state()
+        {
+            using var tmp = new TempDirectory();
+            var sut = new OfficeInstallStatePersistence(tmp.Path, NewLogger(tmp.Path));
+
+            sut.Save(new OfficeInstallStateData { State = OfficeInstallStateData.StateActive });
+            sut.Save(new OfficeInstallStateData { State = OfficeInstallStateData.StateCompleted });
+
+            var loaded = sut.Load();
+            Assert.Equal(OfficeInstallStateData.StateCompleted, loaded!.State);
+            Assert.True(loaded.IsTerminal);
+        }
+
+        [Fact]
+        public void Load_returns_null_when_no_file_exists()
+        {
+            using var tmp = new TempDirectory();
+            var sut = new OfficeInstallStatePersistence(tmp.Path, NewLogger(tmp.Path));
+
+            Assert.Null(sut.Load());
+        }
+
+        [Theory]
+        [InlineData("not json at all {{{")]
+        [InlineData("null")]
+        [InlineData("{}")] // deserializes but State is empty → invalid
+        public void Load_returns_null_for_corrupt_or_empty_state(string content)
+        {
+            using var tmp = new TempDirectory();
+            var sut = new OfficeInstallStatePersistence(tmp.Path, NewLogger(tmp.Path));
+            File.WriteAllText(sut.StateFilePath, content);
+
+            Assert.Null(sut.Load());
+        }
+
+        [Theory]
+        [InlineData(OfficeInstallStateData.StateActive, false)]
+        [InlineData(OfficeInstallStateData.StateCompleted, true)]
+        [InlineData(OfficeInstallStateData.StateFailed, true)]
+        public void IsTerminal_only_for_completed_and_failed(string state, bool expected)
+        {
+            Assert.Equal(expected, new OfficeInstallStateData { State = state }.IsTerminal);
+        }
+
+        [Fact]
+        public void OfficeDoPeakData_maps_to_and_from_sample()
+        {
+            var sample = new OfficeDoSample
+            {
+                JobCount = 2,
+                FileSize = 500,
+                TotalBytesDownloaded = 400,
+                BytesFromPeers = 50,
+                BytesFromHttp = 350,
+                BytesFromCacheServer = 300,
+                DownloadMode = 3,
+            };
+
+            var roundtripped = OfficeDoPeakData.FromSample(sample)!.ToSample();
+
+            Assert.Equal(sample.JobCount, roundtripped.JobCount);
+            Assert.Equal(sample.FileSize, roundtripped.FileSize);
+            Assert.Equal(sample.TotalBytesDownloaded, roundtripped.TotalBytesDownloaded);
+            Assert.Equal(sample.BytesFromPeers, roundtripped.BytesFromPeers);
+            Assert.Equal(sample.BytesFromHttp, roundtripped.BytesFromHttp);
+            Assert.Equal(sample.BytesFromCacheServer, roundtripped.BytesFromCacheServer);
+            Assert.Equal(sample.DownloadMode, roundtripped.DownloadMode);
+            Assert.Null(OfficeDoPeakData.FromSample(null));
+        }
+    }
+}
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Telemetry/Office/OfficeInstallDetector.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Telemetry/Office/OfficeInstallDetector.cs
index 0f544cc1..f9147253 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Telemetry/Office/OfficeInstallDetector.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Telemetry/Office/OfficeInstallDetector.cs
@@ -64,14 +64,20 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office
         // exclude products (e.g. no Outlook), so requiring all would miss legitimate completions.
         internal static readonly string[] CoreBinaries = { "WINWORD.EXE", "EXCEL.EXE", "POWERPNT.EXE", "OUTLOOK.EXE" };
 
+        // While Active, a grown DO peak is re-persisted at most this often — keeps the doSummary
+        // data of a mid-install restart fresh without writing the state file on every 3s DO poll.
+        private const int PeakPersistThrottleSeconds = 30;
+
         private readonly string _sessionId;
         private readonly string _tenantId;
         private readonly InformationalEventPost _post;
         private readonly AgentLogger _logger;
         private readonly IClock _clock;
         private readonly Action<string?>? _onInstallationPathObserved;
+        private readonly OfficeInstallStatePersistence? _statePersistence;
         private readonly object _lock = new object();
         private bool _pathObservedRaised;
+        private DateTime? _lastStatePersistUtc;
 
         // Test seam: when set, used instead of reading the live registry/process state. Production
         // never assigns it. Surfaced to the test assembly via InternalsVisibleTo.
@@ -98,7 +104,8 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office
             InformationalEventPost post,
             AgentLogger logger,
             IClock clock,
-            Action<string?>? onInstallationPathObserved = null)
+            Action<string?>? onInstallationPathObserved = null,
+            OfficeInstallStatePersistence? statePersistence = null)
         {
             _sessionId = sessionId ?? throw new ArgumentNullException(nameof(sessionId));
             _tenantId = tenantId ?? throw new ArgumentNullException(nameof(tenantId));
@@ -106,6 +113,32 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office
             _logger = logger ?? throw new ArgumentNullException(nameof(logger));
             _clock = clock ?? throw new ArgumentNullException(nameof(clock));
             _onInstallationPathObserved = onInstallationPathObserved;
+            _statePersistence = statePersistence;
+        }
+
+        /// <summary>
+        /// Restores a persisted open lifecycle after an agent restart (an enrollment commonly spans
+        /// several reboots): started was already emitted in a previous run, so none is re-emitted
+        /// here. The original start time and DO peak are restored, so a completion proven in THIS
+        /// run reports the true total duration and doSummary. A fresh snapshot is read to surface
+        /// the InstallationPath, which lets the host arm the binary watcher — when Office finished
+        /// installing while the agent was down, that completes the lifecycle synchronously.
+        /// </summary>
+        internal void ResumeActive(OfficeInstallStateData state)
+        {
+            if (state == null || state.State != OfficeInstallStateData.StateActive) return;
+            lock (_lock)
+            {
+                if (_state != DetectorState.Idle) return;
+                _state = DetectorState.Active;
+                _startedAtUtc = state.StartedAtUtc ?? _clock.UtcNow;
+                _startedTrigger = state.StartedTrigger;
+                if (state.PeakDo != null) _peakDo = state.PeakDo.ToSample();
+                _logger.Info($"[{SourceName}] resumed open install lifecycle from persisted state (started {_startedAtUtc:O}, trigger={_startedTrigger ?? "?"})");
+
+                var snap = ReadSnapshotSafe();
+                if (snap != null) ObserveInstallationPath(snap);
+            }
         }
 
         /// <summary>
@@ -177,8 +210,8 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office
             lock (_lock)
             {
                 _lastDo = sample;
-                if (_peakDo == null || sample.TotalBytesDownloaded > _peakDo.TotalBytesDownloaded)
-                    _peakDo = sample;
+                var peakGrew = _peakDo == null || sample.TotalBytesDownloaded > _peakDo.TotalBytesDownloaded;
+                if (peakGrew) _peakDo = sample;
                 if (_state == DetectorState.Terminal) return;
 
                 if (_state == DetectorState.Idle)
@@ -187,8 +220,17 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office
                     var snapStart = ReadSnapshotSafe();
                     if (snapStart == null) return;
                     BeginIfIdle("do", snapStart);
+                    return;
+                }
+
+                // Active: no progress event — the sample only updates the DO summary data. A grown
+                // peak is re-persisted (throttled) so a mid-install agent restart keeps the doSummary.
+                if (peakGrew && _statePersistence != null
+                    && (!_lastStatePersistUtc.HasValue
+                        || (_clock.UtcNow - _lastStatePersistUtc.Value).TotalSeconds >= PeakPersistThrottleSeconds))
+                {
+                    PersistState(OfficeInstallStateData.StateActive);
                 }
-                // Active: no progress event — the sample only updates the DO summary data.
             }
         }
 
@@ -219,6 +261,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office
                 {
                     _state = DetectorState.Terminal;
                     EmitLifecycle(Constants.EventTypes.OfficeInstallCompleted, snap, EventSeverity.Info, "Completed", isTerminal: true, coreBinariesPresent: true);
+                    PersistState(OfficeInstallStateData.StateCompleted);
                     return CompletionOutcome.Completed;
                 }
 
@@ -260,6 +303,10 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office
             // Emitting started first guarantees the correct order (started → completed); otherwise a
             // pre-installed Office produced completed-before-started (field session a7525e97).
             EmitLifecycle(Constants.EventTypes.OfficeInstallStarted, snap, EventSeverity.Info, PhaseOf(snap), isTerminal: false);
+            // Persist Active BEFORE ObserveInstallationPath: when Office is already on disk the
+            // host's binary watcher completes the lifecycle synchronously from inside that callback
+            // (and persists Completed) — persisting Active afterwards would overwrite the terminal.
+            PersistState(OfficeInstallStateData.StateActive);
             ObserveInstallationPath(snap);
         }
 
@@ -280,6 +327,27 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office
             if (_state == DetectorState.Terminal) return;
             _state = DetectorState.Terminal;
             EmitLifecycle(Constants.EventTypes.OfficeInstallFailed, snap, EventSeverity.Error, "Failed", isTerminal: true);
+            PersistState(OfficeInstallStateData.StateFailed);
+        }
+
+        /// <summary>
+        /// Persists the lifecycle state (fail-soft). Active and the two terminals are persisted;
+        /// <see cref="AbandonSilently"/> deliberately is NOT — it fires on every dispose/shutdown
+        /// and persisting it as terminal would block the next run from resuming the open lifecycle
+        /// (the resume is what delivers a completion missed across a mid-install reboot).
+        /// Caller holds the lock.
+        /// </summary>
+        private void PersistState(string state)
+        {
+            if (_statePersistence == null) return;
+            _lastStatePersistUtc = _clock.UtcNow;
+            _statePersistence.Save(new OfficeInstallStateData
+            {
+                State = state,
+                StartedAtUtc = _startedAtUtc,
+                StartedTrigger = _startedTrigger,
+                PeakDo = OfficeDoPeakData.FromSample(_peakDo),
+            });
         }
 
         /// <summary>
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Telemetry/Office/OfficeInstallStatePersistence.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Telemetry/Office/OfficeInstallStatePersistence.cs
new file mode 100644
index 00000000..ea10391d
--- /dev/null
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Telemetry/Office/OfficeInstallStatePersistence.cs
@@ -0,0 +1,146 @@
+#nullable enable
+using System;
+using System.IO;
+using AutopilotMonitor.Agent.V2.Core.Logging;
+using Newtonsoft.Json;
+
+namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office
+{
+    /// <summary>
+    /// Persists the <see cref="OfficeInstallDetector"/> lifecycle state across agent restarts
+    /// (one enrollment commonly spans several reboots). Without it every restart re-armed the
+    /// detector from Idle and all three start triggers fire falsely on an already-installed
+    /// Office: the <c>Scenario\INSTALL</c> registry key persists post-install, OfficeC2RClient.exe
+    /// runs again for update checks, and Office updates stream from the same CDN — each restart
+    /// then emitted a duplicate started+completed pair (~0s duration).
+    /// <para>
+    /// Semantics: <c>Active</c> means "started was emitted, no terminal yet" — the next run resumes
+    /// the open lifecycle (no second started; a missed completion is delivered with the original
+    /// start time). <c>Completed</c>/<c>Failed</c> mean the terminal event went out — the next run
+    /// does not arm the detector at all. <see cref="OfficeInstallDetector.AbandonSilently"/> is
+    /// deliberately NOT persisted as terminal: it fires on every dispose/shutdown and would
+    /// otherwise block the resume that catches the completion after a mid-install reboot.
+    /// </para>
+    /// Fail-soft like <c>ImeTrackerStatePersistence</c>: I/O errors never throw; a missing or
+    /// corrupt file loads as null (fresh start — worst case is today's duplicate-pair behavior).
+    /// </summary>
+    public class OfficeInstallStatePersistence
+    {
+        private readonly string _stateDirectory;
+        private readonly string _stateFilePath;
+        private readonly AgentLogger _logger;
+
+        public OfficeInstallStatePersistence(string stateDirectory, AgentLogger logger)
+        {
+            _stateDirectory = Environment.ExpandEnvironmentVariables(stateDirectory);
+            _stateFilePath = Path.Combine(_stateDirectory, "office-install-state.json");
+            _logger = logger;
+        }
+
+        public string StateFilePath => _stateFilePath;
+
+        /// <summary>Loads the persisted lifecycle state, or null when absent/unreadable.</summary>
+        public OfficeInstallStateData? Load()
+        {
+            if (!File.Exists(_stateFilePath)) return null;
+            try
+            {
+                var json = File.ReadAllText(_stateFilePath);
+                var state = JsonConvert.DeserializeObject<OfficeInstallStateData>(json);
+                if (state == null || string.IsNullOrEmpty(state.State))
+                {
+                    _logger.Warning($"[{OfficeInstallDetector.SourceName}] persisted state file was empty or invalid — starting fresh");
+                    return null;
+                }
+                return state;
+            }
+            catch (Exception ex)
+            {
+                _logger.Warning($"[{OfficeInstallDetector.SourceName}] failed to load persisted state, starting fresh: {ex.Message}");
+                return null;
+            }
+        }
+
+        /// <summary>Persists the lifecycle state (atomic write via temp file). Never throws.</summary>
+        public void Save(OfficeInstallStateData state)
+        {
+            try
+            {
+                Directory.CreateDirectory(_stateDirectory);
+                var tempPath = _stateFilePath + ".tmp";
+                File.WriteAllText(tempPath, JsonConvert.SerializeObject(state));
+                if (File.Exists(_stateFilePath))
+                {
+                    File.Replace(tempPath, _stateFilePath, destinationBackupFileName: null, ignoreMetadataErrors: true);
+                }
+                else
+                {
+                    File.Move(tempPath, _stateFilePath);
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.Debug($"[{OfficeInstallDetector.SourceName}] failed to save state: {ex.Message}");
+            }
+        }
+    }
+
+    // ---- DTOs for state serialization ----
+
+    public class OfficeInstallStateData
+    {
+        public const string StateActive = "Active";
+        public const string StateCompleted = "Completed";
+        public const string StateFailed = "Failed";
+
+        /// <summary><see cref="StateActive"/>, <see cref="StateCompleted"/> or <see cref="StateFailed"/>.</summary>
+        public string? State { get; set; }
+
+        public DateTime? StartedAtUtc { get; set; }
+        public string? StartedTrigger { get; set; }
+
+        /// <summary>Highest-bytes DO sample seen — basis for the doSummary on a resumed completion.</summary>
+        public OfficeDoPeakData? PeakDo { get; set; }
+
+        [JsonIgnore]
+        public bool IsTerminal => State == StateCompleted || State == StateFailed;
+    }
+
+    /// <summary>Persisted mirror of the <see cref="OfficeDoSample"/> fields the completed doSummary needs.</summary>
+    public class OfficeDoPeakData
+    {
+        public int JobCount { get; set; }
+        public long FileSize { get; set; }
+        public long TotalBytesDownloaded { get; set; }
+        public long BytesFromPeers { get; set; }
+        public long BytesFromHttp { get; set; }
+        public long BytesFromCacheServer { get; set; }
+        public int DownloadMode { get; set; }
+
+        public static OfficeDoPeakData? FromSample(OfficeDoSample? sample)
+        {
+            if (sample == null) return null;
+            return new OfficeDoPeakData
+            {
+                JobCount = sample.JobCount,
+                FileSize = sample.FileSize,
+                TotalBytesDownloaded = sample.TotalBytesDownloaded,
+                BytesFromPeers = sample.BytesFromPeers,
+                BytesFromHttp = sample.BytesFromHttp,
+                BytesFromCacheServer = sample.BytesFromCacheServer,
+                DownloadMode = sample.DownloadMode,
+            };
+        }
+
+        public OfficeDoSample ToSample() => new OfficeDoSample
+        {
+            JobCount = JobCount,
+            FileSize = FileSize,
+            TotalBytesDownloaded = TotalBytesDownloaded,
+            BytesFromPeers = BytesFromPeers,
+            BytesFromHttp = BytesFromHttp,
+            BytesFromCacheServer = BytesFromCacheServer,
+            DownloadMode = DownloadMode,
+        };
+    }
+}
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core/Orchestration/DefaultComponentFactory.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core/Orchestration/DefaultComponentFactory.cs
index e68f49d2..08311535 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2.Core/Orchestration/DefaultComponentFactory.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core/Orchestration/DefaultComponentFactory.cs
@@ -8,6 +8,7 @@ using AutopilotMonitor.Agent.V2.Core.Logging;
 using AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime;
 using AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals;
 using AutopilotMonitor.Agent.V2.Core.Monitoring.Runtime;
+using AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Office;
 using AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Periodic;
 using AutopilotMonitor.Agent.V2.Core.Monitoring.Transport;
 using AutopilotMonitor.Agent.V2.Core.SignalAdapters;
@@ -275,13 +276,31 @@ namespace AutopilotMonitor.Agent.V2.Core.Orchestration
             OfficeInstallDetectorHost? officeHost = null;
             if (collectors.EnableOfficeInstallDetector)
             {
-                officeHost = new OfficeInstallDetectorHost(
-                    sessionId: sessionId,
-                    tenantId: tenantId,
-                    ingress: ingress,
-                    clock: clock,
-                    logger: logger,
-                    settleSeconds: collectors.OfficeInstallSettleSeconds);
+                // The lifecycle state is persisted across agent restarts (an enrollment spans
+                // several reboots, and Scenario\INSTALL persists post-install / OfficeC2RClient.exe
+                // runs again for update checks / Office updates stream from the same CDN — all three
+                // start triggers would falsely re-open the window and emit a duplicate
+                // started+completed pair every restart). A persisted terminal means the install was
+                // already reported → don't arm the detector at all this run; a persisted Active is
+                // resumed inside the host (no second started, missed completion delivered late).
+                var officeStatePersistence = new OfficeInstallStatePersistence(_stateDirectory, logger);
+                var officeState = officeStatePersistence.Load();
+                if (officeState != null && officeState.IsTerminal)
+                {
+                    logger.Info($"[{OfficeInstallDetector.SourceName}] persisted lifecycle is already terminal ({officeState.State}) — detector not armed this run");
+                }
+                else
+                {
+                    officeHost = new OfficeInstallDetectorHost(
+                        sessionId: sessionId,
+                        tenantId: tenantId,
+                        ingress: ingress,
+                        clock: clock,
+                        logger: logger,
+                        settleSeconds: collectors.OfficeInstallSettleSeconds,
+                        statePersistence: officeStatePersistence,
+                        resumeState: officeState);
+                }
             }
 
             // M4.6.γ — Delivery-Optimization telemetry. Dormant-by-default: polls only when the IME log
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core/Orchestration/Hosts/OfficeInstallDetectorHost.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core/Orchestration/Hosts/OfficeInstallDetectorHost.cs
index 29bf7333..ea9dcf4c 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2.Core/Orchestration/Hosts/OfficeInstallDetectorHost.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core/Orchestration/Hosts/OfficeInstallDetectorHost.cs
@@ -45,6 +45,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Orchestration
         private readonly AgentLogger _logger;
         private readonly object _lock = new object();
 
+        private readonly OfficeInstallStateData? _resumeState;
         private RegistryChangeWatcher? _registryWatcher;
         private OfficeBinaryWatcher? _binaryWatcher;
         private bool _pathObserved;       // InstallationPath known → stop poking the DO collector
@@ -64,15 +65,19 @@ namespace AutopilotMonitor.Agent.V2.Core.Orchestration
             ISignalIngressSink ingress,
             IClock clock,
             AgentLogger logger,
-            int settleSeconds)
+            int settleSeconds,
+            OfficeInstallStatePersistence? statePersistence = null,
+            OfficeInstallStateData? resumeState = null)
         {
             if (ingress == null) throw new ArgumentNullException(nameof(ingress));
             if (clock == null) throw new ArgumentNullException(nameof(clock));
             _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+            _resumeState = resumeState;
 
             var post = new InformationalEventPost(ingress, clock);
             _detector = new OfficeInstallDetector(sessionId, tenantId, post, logger, clock,
-                onInstallationPathObserved: OnInstallationPathObserved);
+                onInstallationPathObserved: OnInstallationPathObserved,
+                statePersistence: statePersistence);
             _processWatcher = new OfficeProcessWatcher(logger, settleSeconds);
             _processWatcher.Started += OnWorkerStarted;
         }
@@ -96,6 +101,12 @@ namespace AutopilotMonitor.Agent.V2.Core.Orchestration
                 _registryWatcher.Start();
             }
             _processWatcher.Start();
+
+            // Resume a lifecycle left open by a previous agent run (enrollments span reboots) AFTER
+            // the watchers are armed: the resume surfaces the InstallationPath, which arms the binary
+            // watcher — when Office finished installing while the agent was down, its initial scan
+            // completes the lifecycle synchronously and the teardown disposes the watchers again.
+            if (_resumeState != null) _detector.ResumeActive(_resumeState);
         }
 
         private void OnWorkerStarted(object? sender, EventArgs e) => _detector.OnWorkerStarted();