fix(agent): neutral aggregated 2800 observations; reboot claim gated on observed reboot

Rework after the first real enrollment (session b2e890c1) exposed three defects in a654c730: - Shell-Core "RebootCoalescing" match was a false positive by construction: the token appears in the ROUTINE SubcategoryProcessing_Started bootstrap marker ("Starting subcategory DeviceSetup.RebootCoalescing...") on EVERY enrollment. esp_reboot_coalescing removed entirely (branch, constant, catalog, tests). - 2800 reboot-required flags fire at every policy sync; only DeviceSetup-time flags cause the coalesced reboot. The session's flags fired during AccountSetup - no reboot - yet our Warning events claimed "device will restart". Raw event is now a neutral Info observation; the reboot CLAIM moved to ANALYZE-ESP-005 with a REQUIRED system_reboot_detected >= 1 condition (no observed reboot -> advisory silent). - One event per 2800 record was spam: records are now buffered and debounced (10 s) into ONE aggregated event per burst (rebootUris[]/uriCount/ firstRebootUri/recordCount/unparsedCount). Watermark is persisted at FLUSH, not claim - a pre-emit reboot kill loses nothing, the post-restart backfill re-emits the burst at its historical time. Verified 2800 description shape recorded in code, tests, and concept doc: "The following URI has triggered a reboot: (./Device/...)."; extraction covered by a real-text regression test. Lesson added to tasks/lessons.md (observation-level events vs outcome-gated claims; substring tokens appear in framework bookkeeping records). Tests: Agent.V2.Core 1867/1867, Functions 3099/3099, MCP 400 passed, solution build 0 errors. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
feat(agent): attribute mid-ESP coalesced reboots to MDM policy URIs (second sign-in detection)
2026-10-25 13:10:13 +00:00 · 2026-07-20 18:41:47 +02:00 · 2026-07-20 18:05:11 +02:00
15 changed files with 1380 additions and 1 deletions
@@ -7,5 +7,6 @@ How the on-device agent works:
 * [Logs, Persistence & Crash Recovery](logs-and-persistence.md) - every persisted file and why it exists; signal log vs spool; snapshot/journal; the replay-based recovery flow and quarantine.
 * [Hello Wizard Un-Skip](hello-wizard-unskip.md) - why a single "WHfB disabled" policy read never decides completion: the HelloWizardStarted signal (prevention + cure) and the HelloTracker confirmation second read.
 * [Autopilot ZTD Diagnostics](autopilot-ztd-diagnostics.md) - Windows' own diagnostic surfaces for the profile-download flow: ModernDeployment event IDs (807/815/164/...), the Diagnostics\Autopilot registry key, deployment-service endpoints, and the known-issue error-code map.
+* [MDM Reboot Coalescing](mdm-reboot-coalescing.md) - attributing the mid-ESP coalesced reboot ("second sign-in") to the device-assigned policy URIs that forced it: aggregated 2800 observations (neutral, flush-time watermark) + ANALYZE-ESP-005 gated on an actually-observed reboot.

 Reading order for newcomers: overview → decision engine → persistence.
@@ -0,0 +1,100 @@
+---
+type: Concept
+title: MDM Reboot Coalescing — attributing the mid-ESP reboot and second sign-in to policy URIs
+description: How the agent observes reboot-required MDM policy flags (DM-Enterprise EventID 2800, aggregated) and how ANALYZE-ESP-005 attributes an actually-observed enrollment reboot to them — including why the raw events stay neutral and why the Shell-Core RebootCoalescing match was removed.
+resource: /src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/SystemSignals
+tags:
+  - agent
+  - esp
+  - reboot
+  - policy-attribution
+  - second-sign-in
+timestamp: 2026-07-20T00:00:00+02:00
+---
+
+# MDM Reboot Coalescing
+
+Device-assigned MDM policies whose CSP URIs match the OS reboot-required catalog
+(`HKLM\SOFTWARE\Microsoft\Provisioning\SyncML\RebootRequiredURIs`) force a **coalesced
+reboot at the end of ESP DeviceSetup** — the user sees an unexpected restart and a
+**second sign-in screen** before AccountSetup. Invisible in the Intune console; most
+admins live with it, not knowing that reassigning the profiles to user groups removes the
+reboot entirely. Source research: Patch My PC,
+["Avoid the second sign-in screen after Autopilot"](https://patchmypc.com/blog/autopilot-unexpected-reboot-autopilot-second-login-screen/).
+
+The session already counts reboots (`system_reboot_detected` → `session.rebootCount`);
+this feature adds the **cause attribution**.
+
+# Verified signal facts (session b2e890c1, 2026-07-20)
+
+* **EventID 2800**, `Microsoft-Windows-DeviceManagement-Enterprise-Diagnostics-Provider/Admin`,
+  one record per URI, verified description shape:
+  `The following URI has triggered a reboot: (./Device/Vendor/MSFT/Policy/Config/ServiceControlManager/SvchostProcessMitigation).`
+  Records arrive in sub-second bursts during policy sync.
+* **Timing semantics (the critical nuance)**: 2800 fires at EVERY policy sync. Only URIs
+  applied **during ESP DeviceSetup** are coalesced into the forced mid-ESP restart. In the
+  verified session the flags fired during AccountSetup (after DeviceSetup completed) —
+  **no reboot occurred**, and `omadmRebootRequiredFlag` read `false`. A detector that
+  claims "reboot incoming" on every 2800 is therefore wrong.
+* **Shell-Core 62407 "RebootCoalescing" — REMOVED as a signal.** The token appears in the
+  ROUTINE bootstrap marker on every enrollment:
+  `Name: 'CommercialOOBE_BootstrapStatusCategory_SubcategoryProcessing_Started', Value: '{"message":"BootstrapStatus: Starting subcategory DeviceSetup.RebootCoalescing...","errorCode":0}'`
+  — the ESP merely *processes* the RebootCoalescing subcategory (which checks whether a
+  reboot is needed). A substring match on it is a false positive by construction. If a
+  real coalesced-reboot record is ever captured on the E2E VM, a precise pattern can be
+  added then.
+
+# Detector — `MdmRebootPolicyTracker` (`MdmRebootPolicyWatcherHost`)
+
+Live `EventLogWatcher` on the DM-Enterprise Admin channel (EventID 2800) + startup
+backfill (default 60 min lookback). Records are **buffered and debounced (10 s)**, then
+flushed as **ONE aggregated `mdm_policy_reboot_required` event** per burst:
+
+* `Severity=Info`, neutral message ("Windows flagged N MDM policy URIs as
+  reboot-required: … (+N more)") — the raw event never claims a reboot.
+* `Data`: `rebootUris` (distinct, sorted, capped 20), `uriCount` (uncapped distinct),
+  `firstRebootUri` (record-time order, drives rule interpolation), `recordCount`,
+  `unparsedCount`/`sampleDescription` (extraction diagnostics), `backfilled` (all-backfill),
+  fail-soft `omadmRebootRequiredFlag` probe of
+  `HKLM\SOFTWARE\Microsoft\Provisioning\OMADM\SyncML\RebootRequired` (null = unknown).
+* `Timestamp` = earliest record time (backfilled bursts land at their historical instant);
+  `ImmediateUpload=true` (one event per burst is cheap, and a DeviceSetup burst precedes a
+  reboot that kills the agent).
+* **Watermark is persisted at FLUSH, not at claim** (`mdm-reboot-watermark.json`): if the
+  coalesced reboot kills the process before the debounced emit, nothing is marked — the
+  post-restart backfill re-reads and emits the burst. A flushed burst is never repeated.
+
+URI extraction: EventData values starting with `./` preferred, permissive regex over the
+description as fallback (trailing punctuation trimmed — the verified text wraps the URI in
+parens and ends with a period). Unparsed records still count into the aggregate.
+
+Config (internal steering only, no admin UI — agent-native collector, NOT an
+`IAgentAnalyzer`): `Collectors.MdmRebootPolicyWatcherEnabled` (default true),
+`Collectors.MdmRebootPolicyBackfillLookbackMinutes` (default 60). ConfigVersion 35.
+
+# Advisory — ANALYZE-ESP-005
+
+The reboot **claim** lives here, and only here. Required conditions (BOTH):
+
+1. `mdm_policy_reboot_required.firstRebootUri` exists (→ `{{firstRebootUri}}` interpolation)
+2. `system_reboot_detected` count ≥ 1 — **an actually-observed reboot**
+
+Policy flags alone (e.g. AccountSetup user-policy sync) stay advisory-silent. Optional
+confidence: `uriCount ≥ 2` (+10), `omadmRebootRequiredFlag == true` (+15) on base 70 /
+threshold 70. Remediation: map URIs to Intune profiles, reassign device → user groups (or
+exclude the Autopilot device group), or accept + communicate the restart.
+
+# Non-goals / invariants
+
+* Event type **deliberately distinct from `system_reboot_detected`** — the backend
+  RebootCount matches that string exactly in two places
+  (`EventIngestProcessor.Classification` + terminal recount); attribution must never
+  inflate the reboot count.
+* No session-level field / SessionInfoCard change in this iteration (follow-up candidate).
+* The `RebootRequiredURIs` catalog itself is not read; only the 2800 events (which carry
+  the actually-triggered URIs) are consumed.
+
+# Citations
+
+* [Patch My PC — Avoid the second sign-in screen after Autopilot](https://patchmypc.com/blog/autopilot-unexpected-reboot-autopilot-second-login-screen/)
+* [Microsoft Learn — Enrollment Status Page tracking](https://learn.microsoft.com/en-us/autopilot/enrollment-status)
@@ -18,6 +18,7 @@ https://docs.autopilotmonitor.com (separate repository).
 * [V2 Agent](agent/index.md) - How the on-device agent works: [runtime overview](agent/overview.md), [decision engine](agent/decision-engine.md) (reducer, signals, completion arms), [logs & persistence](agent/logs-and-persistence.md) (signal log, snapshot, crash recovery), [Hello wizard un-skip](agent/hello-wizard-unskip.md) (why a single "WHfB disabled" read never decides completion), [Autopilot ZTD diagnostics](agent/autopilot-ztd-diagnostics.md) (event IDs, diagnostic registry, endpoints, error-code map).
 * [Build Counter Blob](agent/build-counter-blob.md) - How agent build numbers are minted: shared counter blob with ETag-CAS so local and CI builds never collide; CI additionally attests build provenance (Sigstore).
 * [Agent Endpoint Migration](agent/endpoint-migration.md) - How the backend re-homes agents to a new API base URL via the config channel (backend move or per-tenant region move): live-fetch-only, allowlist-validated on both sides, one hop, kill wins.
+* [MDM Reboot Coalescing](agent/mdm-reboot-coalescing.md) - Attributing the mid-ESP coalesced reboot ("second sign-in") to the device-assigned policy URIs that forced it: aggregated DM-Enterprise 2800 observations (neutral, flush-time watermark) + the ANALYZE-ESP-005 advisory gated on an actually-observed reboot.

 # Rules

@@ -2,6 +2,9 @@

 ## 2026-07-20

+* **Update**: Reworked `agent/mdm-reboot-coalescing.md` after the first real enrollment (session b2e890c1): 2800 records are now **aggregated per burst** into ONE neutral Info event (`rebootUris[]`/`uriCount`/`firstRebootUri`; watermark persisted at flush so a pre-emit reboot kill loses nothing); the raw event no longer claims a reboot — ANALYZE-ESP-005 is gated on an actually-observed `system_reboot_detected`. **Removed** the Shell-Core `esp_reboot_coalescing` event entirely: the "RebootCoalescing" token appears in the routine `SubcategoryProcessing_Started` bootstrap marker on every enrollment (false positive by construction). Verified 2800 description shape recorded.
+* **Creation**: Added `agent/mdm-reboot-coalescing.md` — the agent now attributes the "unexpected mid-ESP reboot + second sign-in" pattern (PMPC research) to the device-assigned policy URIs that forced it: new `MdmRebootPolicyTracker` (DM-Enterprise EventID 2800, per-URI `mdm_policy_reboot_required` events, cross-restart RecordId watermark), a `RebootCoalescing` branch in `ShellCoreTracker` (`esp_reboot_coalescing`, backfill-emitting by design), and the `ANALYZE-ESP-005` advisory (reassign device → user groups). ConfigVersion 35; event types deliberately distinct from `system_reboot_detected` so RebootCount stays uninflated.
+
 * **Creation**: Added `backend/business-timestamps.md` (new `backend/` section) — the 2026-07-18 migration reset every row's system Timestamp, exposing that AuditLogs/OpsEvents/Events had (unknowingly) displayed and filtered on it all along; documents the `OccurredUtc` column, the RowKey decoders and RowKey-range date/retention clauses in `BusinessTimestamp`, the GUID-guard trap, the audit/ops backfill endpoint, and the "system Timestamp is never authoritative" migration rule.
 * **Creation**: Added `rules/gather-rule-phase-scoping.md` (new `rules/` section) — gather rules gain `activePhases` (run only during listed phases), `activeFromPhase` (sticky latch from a phase onwards, never via Failed) and `emitMode: "on_change"` (canonical-hash result dedup with `suppressedPolls` observability), ConfigVersion 34. Includes the prerequisite backend fix: the custom-rule toggle PUT no longer wipes the stored rule definition (partial-merge in `GatherRuleService.UpdateRuleAsync`).

@@ -0,0 +1,85 @@
+{
+  "$schema": "../schema/analyze-rule.schema.json",
+  "ruleId": "ANALYZE-ESP-005",
+  "title": "MDM Policy Forced a Mid-ESP Reboot (Second Sign-In)",
+  "description": "Attributes an observed enrollment reboot to device-assigned MDM policies that Windows flagged as reboot-required. Fires ONLY when both facts are present in the session: at least one actually-observed reboot (system_reboot_detected) AND reboot-required policy flags (mdm_policy_reboot_required). Policy flags alone — e.g. from a user-policy sync during AccountSetup — force no reboot and stay advisory-silent.",
+  "severity": "warning",
+  "category": "esp",
+  "version": "1.1.0",
+  "author": "Autopilot Monitor",
+  "enabled": true,
+  "trigger": "single",
+  "baseConfidence": 70,
+  "conditions": [
+    {
+      "signal": "reboot_forcing_policy_uri",
+      "source": "event_data",
+      "eventType": "mdm_policy_reboot_required",
+      "dataField": "firstRebootUri",
+      "operator": "exists",
+      "required": true
+    },
+    {
+      "signal": "reboot_observed",
+      "source": "event_count",
+      "eventType": "system_reboot_detected",
+      "operator": "count_gte",
+      "value": "1",
+      "required": true
+    },
+    {
+      "signal": "multiple_reboot_uris",
+      "source": "event_data",
+      "eventType": "mdm_policy_reboot_required",
+      "dataField": "uriCount",
+      "operator": "gte",
+      "value": "2",
+      "required": false
+    },
+    {
+      "signal": "omadm_reboot_flag_set",
+      "source": "event_data",
+      "eventType": "mdm_policy_reboot_required",
+      "dataField": "omadmRebootRequiredFlag",
+      "operator": "equals",
+      "value": "true",
+      "required": false
+    }
+  ],
+  "confidenceFactors": [
+    { "signal": "multiple_reboot_uris", "condition": "exists", "weight": 10 },
+    { "signal": "omadm_reboot_flag_set", "condition": "exists", "weight": 15 }
+  ],
+  "confidenceThreshold": 70,
+  "explanation": "This session **rebooted during enrollment**, and Windows flagged one or more device-assigned MDM policies as **reboot-required** — the classic cause of the coalesced mid-ESP restart and the unexpected **second sign-in screen** before AccountSetup.\n\nFirst reboot-forcing policy URI: `{{firstRebootUri}}`\n\nThe complete URI list is in the `mdm_policy_reboot_required` timeline event (`rebootUris`). Policies applied DURING ESP DeviceSetup are coalesced into one forced restart at the end of DeviceSetup; the same flags raised later (e.g. user-policy sync in AccountSetup) have no immediate effect — this advisory only fires when a reboot was actually observed.\n\nThis is expected OS behavior, not a failure — but it degrades the enrollment experience, confuses users, and is invisible in the Intune console.",
+  "remediation": [
+    {
+      "title": "Reassign the reboot-forcing policies to user groups",
+      "steps": [
+        "Open the `mdm_policy_reboot_required` timeline event and note the CSP URIs in `rebootUris` (e.g. `./Device/Vendor/MSFT/...`)",
+        "Map each URI to its Intune profile (Settings Catalog / configuration profile) — the URI path names the CSP area",
+        "Reassign those profiles from device groups to user groups so they apply during/after AccountSetup instead of DeviceSetup",
+        "Alternatively, exclude the Autopilot device group from the profile and deliver the setting post-enrollment"
+      ]
+    },
+    {
+      "title": "Or accept the reboot and set expectations",
+      "steps": [
+        "If the policy must be device-assigned (e.g. a security baseline), keep it and document the expected mid-ESP restart",
+        "Communicate to users that a restart and second sign-in during provisioning is expected for these deployments"
+      ]
+    }
+  ],
+  "relatedDocs": [
+    {
+      "title": "Patch My PC: Avoid the second sign-in screen after Autopilot",
+      "url": "https://patchmypc.com/blog/autopilot-unexpected-reboot-autopilot-second-login-screen/"
+    },
+    {
+      "title": "Microsoft Learn: Enrollment Status Page tracking",
+      "url": "https://learn.microsoft.com/en-us/autopilot/enrollment-status"
+    }
+  ],
+  "markSessionAsFailedDefault": false,
+  "tags": ["esp", "reboot", "coalescing", "second-sign-in", "policy-attribution", "user-experience"]
+}
@@ -1785,6 +1785,105 @@
        "enrollment"
      ]
    },
+    {
+      "ruleId": "ANALYZE-ESP-005",
+      "title": "MDM Policy Forced a Mid-ESP Reboot (Second Sign-In)",
+      "description": "Attributes an observed enrollment reboot to device-assigned MDM policies that Windows flagged as reboot-required. Fires ONLY when both facts are present in the session: at least one actually-observed reboot (system_reboot_detected) AND reboot-required policy flags (mdm_policy_reboot_required). Policy flags alone — e.g. from a user-policy sync during AccountSetup — force no reboot and stay advisory-silent.",
+      "severity": "warning",
+      "category": "esp",
+      "version": "1.1.0",
+      "author": "Autopilot Monitor",
+      "enabled": true,
+      "trigger": "single",
+      "baseConfidence": 70,
+      "conditions": [
+        {
+          "signal": "reboot_forcing_policy_uri",
+          "source": "event_data",
+          "eventType": "mdm_policy_reboot_required",
+          "dataField": "firstRebootUri",
+          "operator": "exists",
+          "required": true
+        },
+        {
+          "signal": "reboot_observed",
+          "source": "event_count",
+          "eventType": "system_reboot_detected",
+          "operator": "count_gte",
+          "value": "1",
+          "required": true
+        },
+        {
+          "signal": "multiple_reboot_uris",
+          "source": "event_data",
+          "eventType": "mdm_policy_reboot_required",
+          "dataField": "uriCount",
+          "operator": "gte",
+          "value": "2",
+          "required": false
+        },
+        {
+          "signal": "omadm_reboot_flag_set",
+          "source": "event_data",
+          "eventType": "mdm_policy_reboot_required",
+          "dataField": "omadmRebootRequiredFlag",
+          "operator": "equals",
+          "value": "true",
+          "required": false
+        }
+      ],
+      "confidenceFactors": [
+        {
+          "signal": "multiple_reboot_uris",
+          "condition": "exists",
+          "weight": 10
+        },
+        {
+          "signal": "omadm_reboot_flag_set",
+          "condition": "exists",
+          "weight": 15
+        }
+      ],
+      "confidenceThreshold": 70,
+      "explanation": "This session **rebooted during enrollment**, and Windows flagged one or more device-assigned MDM policies as **reboot-required** — the classic cause of the coalesced mid-ESP restart and the unexpected **second sign-in screen** before AccountSetup.\n\nFirst reboot-forcing policy URI: `{{firstRebootUri}}`\n\nThe complete URI list is in the `mdm_policy_reboot_required` timeline event (`rebootUris`). Policies applied DURING ESP DeviceSetup are coalesced into one forced restart at the end of DeviceSetup; the same flags raised later (e.g. user-policy sync in AccountSetup) have no immediate effect — this advisory only fires when a reboot was actually observed.\n\nThis is expected OS behavior, not a failure — but it degrades the enrollment experience, confuses users, and is invisible in the Intune console.",
+      "remediation": [
+        {
+          "title": "Reassign the reboot-forcing policies to user groups",
+          "steps": [
+            "Open the `mdm_policy_reboot_required` timeline event and note the CSP URIs in `rebootUris` (e.g. `./Device/Vendor/MSFT/...`)",
+            "Map each URI to its Intune profile (Settings Catalog / configuration profile) — the URI path names the CSP area",
+            "Reassign those profiles from device groups to user groups so they apply during/after AccountSetup instead of DeviceSetup",
+            "Alternatively, exclude the Autopilot device group from the profile and deliver the setting post-enrollment"
+          ]
+        },
+        {
+          "title": "Or accept the reboot and set expectations",
+          "steps": [
+            "If the policy must be device-assigned (e.g. a security baseline), keep it and document the expected mid-ESP restart",
+            "Communicate to users that a restart and second sign-in during provisioning is expected for these deployments"
+          ]
+        }
+      ],
+      "relatedDocs": [
+        {
+          "title": "Patch My PC: Avoid the second sign-in screen after Autopilot",
+          "url": "https://patchmypc.com/blog/autopilot-unexpected-reboot-autopilot-second-login-screen/"
+        },
+        {
+          "title": "Microsoft Learn: Enrollment Status Page tracking",
+          "url": "https://learn.microsoft.com/en-us/autopilot/enrollment-status"
+        }
+      ],
+      "markSessionAsFailedDefault": false,
+      "tags": [
+        "esp",
+        "reboot",
+        "coalescing",
+        "second-sign-in",
+        "policy-attribution",
+        "user-experience"
+      ]
+    },
    {
      "ruleId": "ANALYZE-ID-001",
      "title": "Expected Machine Certificate Not Found",
@@ -0,0 +1,336 @@
+#nullable enable
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using AutopilotMonitor.Agent.V2.Core.Logging;
+using AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals;
+using AutopilotMonitor.Agent.V2.Core.Orchestration;
+using AutopilotMonitor.Agent.V2.Core.Tests.Harness;
+using AutopilotMonitor.Agent.V2.Core.Tests.Orchestration;
+using AutopilotMonitor.DecisionCore.Engine;
+using AutopilotMonitor.DecisionCore.Signals;
+using AutopilotMonitor.Shared;
+using Xunit;
+
+namespace AutopilotMonitor.Agent.V2.Core.Tests.Monitoring.SystemSignals
+{
+    /// <summary>
+    /// MdmRebootPolicyTracker — aggregates DM-Enterprise EventID 2800 bursts into ONE neutral
+    /// <c>mdm_policy_reboot_required</c> event (session b2e890c1 rework: per-record events were
+    /// spam, and the raw event must not CLAIM a reboot — ANALYZE-ESP-005 does, gated on an
+    /// observed system_reboot_detected). Drives the primitive ProcessEvent seam + explicit
+    /// FlushPending (debounce 0 = manual-flush mode; no timers, no SerialThreading needed).
+    /// The registry probe is always overridden — tests never touch the live registry.
+    /// </summary>
+    public sealed class MdmRebootPolicyTrackerTests : IDisposable
+    {
+        private static readonly DateTime At = new DateTime(2026, 7, 20, 16, 20, 57, DateTimeKind.Utc);
+        private const string UriSvchost = "./Device/Vendor/MSFT/Policy/Config/ServiceControlManager/SvchostProcessMitigation";
+        private const string UriSystemGuard = "./Device/Vendor/MSFT/Policy/Config/DeviceGuard/ConfigureSystemGuardLaunch";
+
+        // Verified real 2800 description shape (session b2e890c1, 2026-07-20).
+        private const string RealDescription =
+            "The following URI has triggered a reboot: (./Device/Vendor/MSFT/Policy/Config/ServiceControlManager/SvchostProcessMitigation).";
+
+        private readonly TempDirectory _tmp = new TempDirectory();
+        private readonly FakeSignalIngressSink _sink;
+        private readonly MdmRebootPolicyTracker _tracker;
+        private long _nextRecordId = 1;
+
+        public MdmRebootPolicyTrackerTests()
+        {
+            _sink = new FakeSignalIngressSink();
+            _tracker = MakeTracker(stateDirectory: null);
+        }
+
+        public void Dispose() => _tmp.Dispose();
+
+        private MdmRebootPolicyTracker MakeTracker(string? stateDirectory)
+        {
+            var post = new InformationalEventPost(_sink, new VirtualClock(At));
+            var logger = new AgentLogger(_tmp.Path, AgentLogLevel.Info);
+            var tracker = new MdmRebootPolicyTracker(
+                sessionId: "sess-mdm",
+                tenantId: "tenant-mdm",
+                post: post,
+                logger: logger,
+                backfillEnabled: false,
+                stateDirectory: stateDirectory,
+                debounceMilliseconds: 0); // manual-flush mode — tests call FlushPending explicitly
+            tracker.RebootRequiredFlagProbe = () => null; // registry untouched by default
+            return tracker;
+        }
+
+        private void Buffer(string? rebootUri, long? recordId = null, bool isBackfill = false, DateTime? timeCreatedUtc = null, string? description = null)
+        {
+            _tracker.ProcessEvent(
+                eventId: MdmRebootPolicyTracker.EventId_PolicyRebootRequired,
+                recordId: recordId ?? _nextRecordId++,
+                timeCreatedUtc: timeCreatedUtc ?? At,
+                rebootUri: rebootUri,
+                formattedDescription: description,
+                isBackfill: isBackfill);
+        }
+
+        private IReadOnlyList<FakeSignalIngressSink.PostedSignal> Emitted() =>
+            _sink.Posted.Where(p =>
+                p.Kind == DecisionSignalKind.InformationalEvent
+                && p.Payload != null
+                && p.Payload.TryGetValue(SignalPayloadKeys.EventType, out var et)
+                && et == Constants.EventTypes.MdmPolicyRebootRequired).ToList();
+
+        private static IReadOnlyDictionary<string, object> Data(FakeSignalIngressSink.PostedSignal s) =>
+            (IReadOnlyDictionary<string, object>)s.TypedPayload!;
+
+        [Fact]
+        public void Burst_FlushesAsOneAggregatedEvent_InfoSeverity_ImmediateUpload()
+        {
+            Buffer(UriSvchost, timeCreatedUtc: At);
+            Buffer(UriSystemGuard, timeCreatedUtc: At.AddMilliseconds(120));
+            _tracker.FlushPending();
+
+            var s = Assert.Single(Emitted());
+            Assert.Equal("Info", s.Payload![SignalPayloadKeys.Severity]);
+            Assert.Equal("true", s.Payload![SignalPayloadKeys.ImmediateUpload]);
+
+            var data = Data(s);
+            Assert.Equal(2, data["uriCount"]);
+            Assert.Equal(2, data["recordCount"]);
+            Assert.Equal(UriSvchost, data["firstRebootUri"]);
+            var uris = Assert.IsType<List<string>>(data["rebootUris"]);
+            Assert.Equal(2, uris.Count);
+            Assert.Contains(UriSvchost, uris);
+            Assert.Contains(UriSystemGuard, uris);
+        }
+
+        [Fact]
+        public void Message_IsNeutralObservation_NoRebootClaim()
+        {
+            // Session b2e890c1: flags raised during AccountSetup have no effect — the raw event
+            // must state the observation only, never a future consequence.
+            Buffer(UriSvchost);
+            _tracker.FlushPending();
+
+            var s = Assert.Single(Emitted());
+            var message = s.Payload![SignalPayloadKeys.Message];
+            Assert.Contains("flagged", message);
+            Assert.DoesNotContain("will restart", message);
+            Assert.DoesNotContain("second sign-in", message);
+        }
+
+        [Fact]
+        public void FlushPending_Empty_EmitsNothing()
+        {
+            _tracker.FlushPending();
+            Assert.Empty(Emitted());
+        }
+
+        [Fact]
+        public void AggregateTimestamp_IsEarliestRecordTime()
+        {
+            var early = At.AddMinutes(-30);
+            Buffer(UriSystemGuard, timeCreatedUtc: At, isBackfill: true);
+            Buffer(UriSvchost, timeCreatedUtc: early, isBackfill: true);
+            _tracker.FlushPending();
+
+            var s = Assert.Single(Emitted());
+            Assert.Equal(early, s.OccurredAtUtc);
+            Assert.Equal(true, Data(s)["backfilled"]);
+            // firstRebootUri follows record-time order, not buffer order.
+            Assert.Equal(UriSvchost, Data(s)["firstRebootUri"]);
+        }
+
+        [Fact]
+        public void Backfilled_False_WhenAnyRecordIsLive()
+        {
+            Buffer(UriSvchost, isBackfill: true);
+            Buffer(UriSystemGuard, isBackfill: false);
+            _tracker.FlushPending();
+
+            Assert.Equal(false, Data(Assert.Single(Emitted()))["backfilled"]);
+        }
+
+        [Fact]
+        public void DuplicateUris_AreDistinctInAggregate()
+        {
+            Buffer(UriSvchost);
+            Buffer(UriSvchost);
+            _tracker.FlushPending();
+
+            var data = Data(Assert.Single(Emitted()));
+            Assert.Equal(1, data["uriCount"]);
+            Assert.Equal(2, data["recordCount"]);
+        }
+
+        [Fact]
+        public void UnparsedRecords_CountedWithSampleDescription_StillEmitted()
+        {
+            Buffer(rebootUri: null, description: "Some unexpected 2800 wording");
+            _tracker.FlushPending();
+
+            var s = Assert.Single(Emitted());
+            var data = Data(s);
+            Assert.False(data.ContainsKey("rebootUris"));
+            Assert.False(data.ContainsKey("firstRebootUri"));
+            Assert.Equal(0, data["uriCount"]);
+            Assert.Equal(1, data["unparsedCount"]);
+            Assert.Equal("Some unexpected 2800 wording", data["sampleDescription"]);
+        }
+
+        [Fact]
+        public void SameRecordId_BufferedTwice_CountsOnce()
+        {
+            Buffer(UriSvchost, recordId: 42);
+            Buffer(UriSvchost, recordId: 42);
+            _tracker.FlushPending();
+
+            Assert.Equal(1, Data(Assert.Single(Emitted()))["recordCount"]);
+        }
+
+        [Fact]
+        public void RecordAfterFlush_GoesIntoNextAggregate()
+        {
+            Buffer(UriSvchost, recordId: 10);
+            _tracker.FlushPending();
+            Buffer(UriSystemGuard, recordId: 11);
+            _tracker.FlushPending();
+
+            Assert.Equal(2, Emitted().Count);
+        }
+
+        [Fact]
+        public void BackfillRecordWithLowerRecordId_AfterLiveRecord_IsStillBuffered()
+        {
+            // Live watcher is armed BEFORE the backfill scan — an older, never-seen backfill
+            // record must not be suppressed by a high-water mark.
+            Buffer(UriSvchost, recordId: 100);
+            Buffer(UriSystemGuard, recordId: 50, isBackfill: true);
+            _tracker.FlushPending();
+
+            Assert.Equal(2, Data(Assert.Single(Emitted()))["recordCount"]);
+        }
+
+        [Fact]
+        public void NegativeRecordId_IsNeverDeduped()
+        {
+            Buffer(UriSvchost, recordId: -1);
+            Buffer(UriSvchost, recordId: -1);
+            _tracker.FlushPending();
+
+            Assert.Equal(2, Data(Assert.Single(Emitted()))["recordCount"]);
+        }
+
+        [Fact]
+        public void Watermark_PersistedAtFlush_SkipsReReadAcrossInstances()
+        {
+            // The coalesced reboot restarts the agent; the post-reboot backfill re-reads the same
+            // records — a FLUSHED record must be skipped by the next instance.
+            var first = MakeTracker(stateDirectory: _tmp.Path);
+            first.ProcessEvent(MdmRebootPolicyTracker.EventId_PolicyRebootRequired, recordId: 500,
+                timeCreatedUtc: At, rebootUri: UriSvchost, formattedDescription: null, isBackfill: false);
+            first.FlushPending();
+
+            var second = MakeTracker(stateDirectory: _tmp.Path);
+            second.LoadWatermark();
+            second.ProcessEvent(MdmRebootPolicyTracker.EventId_PolicyRebootRequired, recordId: 500,
+                timeCreatedUtc: At, rebootUri: UriSvchost, formattedDescription: null, isBackfill: true);
+            second.FlushPending();
+
+            Assert.Single(Emitted());
+        }
+
+        [Fact]
+        public void Watermark_NotPersisted_WhenBufferedButNeverFlushed()
+        {
+            // Process killed by the very reboot the records announce: nothing was flushed, so the
+            // next instance must re-read and emit the records.
+            var first = MakeTracker(stateDirectory: _tmp.Path);
+            first.ProcessEvent(MdmRebootPolicyTracker.EventId_PolicyRebootRequired, recordId: 500,
+                timeCreatedUtc: At, rebootUri: UriSvchost, formattedDescription: null, isBackfill: false);
+            // no FlushPending — simulated reboot kill
+
+            var second = MakeTracker(stateDirectory: _tmp.Path);
+            second.LoadWatermark();
+            second.ProcessEvent(MdmRebootPolicyTracker.EventId_PolicyRebootRequired, recordId: 500,
+                timeCreatedUtc: At, rebootUri: UriSvchost, formattedDescription: null, isBackfill: true);
+            second.FlushPending();
+
+            var s = Assert.Single(Emitted());
+            Assert.Equal(true, Data(s)["backfilled"]);
+        }
+
+        [Fact]
+        public void RebootRequiredFlagProbe_True_AddsField_Null_OmitsIt()
+        {
+            _tracker.RebootRequiredFlagProbe = () => true;
+            Buffer(UriSvchost, recordId: 1);
+            _tracker.FlushPending();
+
+            _tracker.RebootRequiredFlagProbe = () => null;
+            Buffer(UriSystemGuard, recordId: 2);
+            _tracker.FlushPending();
+
+            var emitted = Emitted();
+            Assert.Equal(2, emitted.Count);
+            Assert.Equal(true, Data(emitted[0])["omadmRebootRequiredFlag"]);
+            Assert.False(Data(emitted[1]).ContainsKey("omadmRebootRequiredFlag"));
+        }
+
+        [Fact]
+        public void RebootRequiredFlagProbe_Throwing_IsFailSoft()
+        {
+            _tracker.RebootRequiredFlagProbe = () => throw new InvalidOperationException("boom");
+            Buffer(UriSvchost);
+            _tracker.FlushPending();
+
+            Assert.False(Data(Assert.Single(Emitted())).ContainsKey("omadmRebootRequiredFlag"));
+        }
+
+        [Fact]
+        public void BuildXPath_Targets2800()
+        {
+            Assert.Equal("*[System[(EventID=2800)]]", MdmRebootPolicyTracker.BuildXPath());
+        }
+
+        // ------------------------------------------------------------------ URI extraction
+
+        [Fact]
+        public void ExtractRebootUri_FromVerifiedRealDescription()
+        {
+            // Real 2800 text wraps the URI in parentheses and ends with a period — both must be
+            // excluded from the extracted URI.
+            var uri = MdmRebootPolicyTracker.ExtractRebootUri(null, RealDescription);
+            Assert.Equal(UriSvchost, uri);
+        }
+
+        [Fact]
+        public void ExtractRebootUri_PrefersEventDataValue_OverDescription()
+        {
+            var eventData = new Dictionary<string, string> { ["Data0"] = " " + UriSystemGuard + " " };
+            var uri = MdmRebootPolicyTracker.ExtractRebootUri(eventData, RealDescription);
+            Assert.Equal(UriSystemGuard, uri);
+        }
+
+        [Fact]
+        public void ExtractRebootUri_ReturnsNull_WhenNothingUriLike()
+        {
+            Assert.Null(MdmRebootPolicyTracker.ExtractRebootUri(
+                new Dictionary<string, string> { ["Data0"] = "plain" }, "no uri here"));
+            Assert.Null(MdmRebootPolicyTracker.ExtractRebootUri(null, null));
+        }
+
+        [Fact]
+        public void ParseEventData_CollectsNamedAndPositionalData()
+        {
+            const string xml =
+                "<Event xmlns='http://schemas.microsoft.com/win/2004/08/events/event'>" +
+                "<System><EventID>2800</EventID></System>" +
+                "<EventData><Data Name='Uri'>./Device/Vendor/MSFT/X</Data><Data>positional</Data></EventData>" +
+                "</Event>";
+
+            var parsed = MdmRebootPolicyTracker.ParseEventData(xml);
+            Assert.Equal("./Device/Vendor/MSFT/X", parsed["Uri"]);
+            Assert.Equal("positional", parsed["Data0"]);
+        }
+    }
+}
@@ -0,0 +1,628 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.Eventing.Reader;
+using System.IO;
+using System.Linq;
+using System.Text.RegularExpressions;
+using System.Threading;
+using System.Xml.Linq;
+using AutopilotMonitor.Agent.V2.Core.Logging;
+using AutopilotMonitor.Agent.V2.Core.Orchestration;
+using AutopilotMonitor.Shared;
+using AutopilotMonitor.Shared.Models;
+using Newtonsoft.Json;
+
+namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
+{
+    /// <summary>
+    /// Watches <c>Microsoft-Windows-DeviceManagement-Enterprise-Diagnostics-Provider/Admin</c> for
+    /// EventID 2800 — logged once per MDM policy URI that matches the OS reboot-required catalog —
+    /// and emits ONE aggregated <c>mdm_policy_reboot_required</c> event per burst carrying the URI
+    /// list (<c>rebootUris</c>, <c>uriCount</c>, <c>firstRebootUri</c>).
+    /// <para>
+    /// Verified against session b2e890c1 (2026-07-20): the 2800 description reads
+    /// <c>The following URI has triggered a reboot: (./Device/...).</c> and records arrive in
+    /// sub-second bursts during policy sync — hence the debounce aggregation instead of per-record
+    /// events. CRITICAL semantics: only URIs applied DURING ESP DeviceSetup cause the coalesced
+    /// mid-ESP reboot ("second sign-in", PMPC research); later syncs (AccountSetup and beyond)
+    /// merely flag the requirement with no forced reboot. The event is therefore a NEUTRAL
+    /// observation (Info) — the reboot claim lives in ANALYZE-ESP-005, which requires an
+    /// actually-observed <c>system_reboot_detected</c> before attributing anything.
+    /// </para>
+    /// <para>
+    /// <b>Backfill + watermark.</b> Device policies can apply before the agent starts, and a
+    /// genuine coalesced reboot kills the agent BEFORE the debounced emit — in both cases the
+    /// post-(re)start backfill re-reads the .evtx and emits the aggregate then (historical
+    /// timestamps). The cross-restart RecordId watermark is persisted only at successful flush, so
+    /// a pre-emit death loses nothing and a completed emit is never repeated.
+    /// </para>
+    /// </summary>
+    internal sealed class MdmRebootPolicyTracker : IDisposable
+    {
+        internal const string Channel = "Microsoft-Windows-DeviceManagement-Enterprise-Diagnostics-Provider/Admin";
+        internal const int EventId_PolicyRebootRequired = 2800;
+
+        internal const string WatermarkStateFileName = "mdm-reboot-watermark.json";
+
+        /// <summary>Cap for the emitted <c>rebootUris</c> list — <c>uriCount</c> always carries the uncapped distinct total.</summary>
+        internal const int MaxUrisPerEvent = 20;
+
+        /// <summary>Default quiet-period before a burst of 2800 records is flushed as one event.</summary>
+        internal const int DefaultDebounceMilliseconds = 10000;
+
+        /// <summary>Registry key whose <c>RebootRequired</c> value/subkey flags a pending OMA-DM coalesced reboot.</summary>
+        internal const string OmadmSyncMlKeyPath = @"SOFTWARE\Microsoft\Provisioning\OMADM\SyncML";
+
+        // Permissive OMA-DM URI shape ("./Device/Vendor/MSFT/...", "./User/..."). The verified 2800
+        // text wraps the URI in parentheses — ')' is deliberately outside the class so the match
+        // stops cleanly; trailing sentence punctuation is trimmed after the match.
+        private static readonly Regex UriPattern = new Regex(
+            @"\./[A-Za-z0-9_\-./\[\]{}%~+]+", RegexOptions.Compiled);
+
+        private readonly AgentLogger _logger;
+        private readonly string _sessionId;
+        private readonly string _tenantId;
+        private readonly InformationalEventPost _post;
+        private readonly bool _backfillEnabled;
+        private readonly int _backfillLookbackMinutes;
+        private readonly string _stateDirectory;
+        private readonly int _debounceMilliseconds;
+
+        private EventLogWatcher _watcher;
+        private Timer _debounceTimer;
+
+        private sealed class PendingRecord
+        {
+            public long RecordId;
+            public DateTime TimeUtc;
+            public string Uri;          // null when extraction failed
+            public string Description;  // may be null
+            public bool IsBackfill;
+        }
+
+        // Pending burst buffer + dedup state, all guarded by _stateLock. Same claim contract as
+        // WindowsUpdateTracker (immutable cross-restart boundary + intra-run HashSet), with ONE
+        // deliberate difference: the watermark is persisted at FLUSH time, not at claim time —
+        // records buffered but never flushed (process killed by the very reboot they announce)
+        // must be re-read and emitted by the post-restart backfill.
+        private readonly List<PendingRecord> _pending = new List<PendingRecord>();
+        private long _restartWatermark = -1;
+        private readonly HashSet<long> _seenThisRun = new HashSet<long>();
+        private long _maxPersistedRecordId = -1;
+        private readonly object _stateLock = new object();
+
+        /// <summary>
+        /// Fail-soft corroboration probe for the OMA-DM RebootRequired flag — null = unknown
+        /// (key absent or unreadable). Settable test seam; the default reads the live registry.
+        /// </summary>
+        internal Func<bool?> RebootRequiredFlagProbe { get; set; } = ReadOmadmRebootRequiredFlag;
+
+        public MdmRebootPolicyTracker(
+            string sessionId,
+            string tenantId,
+            InformationalEventPost post,
+            AgentLogger logger,
+            bool backfillEnabled = true,
+            int backfillLookbackMinutes = 60,
+            string stateDirectory = null,
+            int debounceMilliseconds = DefaultDebounceMilliseconds)
+        {
+            _sessionId = sessionId ?? throw new ArgumentNullException(nameof(sessionId));
+            _tenantId = tenantId ?? throw new ArgumentNullException(nameof(tenantId));
+            _post = post ?? throw new ArgumentNullException(nameof(post));
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+            _backfillEnabled = backfillEnabled;
+            _backfillLookbackMinutes = backfillLookbackMinutes;
+            _stateDirectory = stateDirectory != null ? Environment.ExpandEnvironmentVariables(stateDirectory) : null;
+            _debounceMilliseconds = debounceMilliseconds;
+        }
+
+        public void Start()
+        {
+            LoadWatermark();
+            StartWatcher();
+
+            if (_backfillEnabled && _backfillLookbackMinutes > 0)
+            {
+                BackfillRecentEvents();
+                // The backfill batch is complete — flush immediately instead of waiting out the
+                // debounce (live records that raced in are simply included).
+                FlushPending();
+            }
+            else
+            {
+                _logger.Info("MdmRebootPolicy backfill disabled by config");
+            }
+        }
+
+        public void Stop()
+        {
+            // Flush any un-emitted burst before tearing down (normal agent shutdown path).
+            try { FlushPending(); }
+            catch (Exception ex) { _logger.Warning($"MdmRebootPolicy flush on stop failed: {ex.Message}"); }
+
+            var timer = Interlocked.Exchange(ref _debounceTimer, null);
+            if (timer != null)
+            {
+                try { timer.Dispose(); } catch { }
+            }
+
+            if (_watcher == null) return;
+            try
+            {
+                _watcher.Enabled = false;
+                _watcher.Dispose();
+                _logger.Info("MdmRebootPolicy watcher stopped");
+            }
+            catch (Exception ex)
+            {
+                _logger.Error("Error stopping MdmRebootPolicy watcher", ex);
+            }
+            finally
+            {
+                _watcher = null;
+            }
+        }
+
+        public void Dispose() => Stop();
+
+        // -----------------------------------------------------------------------
+        // Watcher lifecycle
+        // -----------------------------------------------------------------------
+
+        private void StartWatcher()
+        {
+            try
+            {
+                var query = new EventLogQuery(Channel, PathType.LogName, BuildXPath());
+                _watcher = new EventLogWatcher(query);
+                _watcher.EventRecordWritten += OnEventRecordWritten;
+                _watcher.Enabled = true;
+                _logger.Info($"MdmRebootPolicy watcher started: {Channel} (EventID {EventId_PolicyRebootRequired})");
+            }
+            catch (EventLogNotFoundException)
+            {
+                _logger.Warning($"MdmRebootPolicy event log not found: {Channel} (normal on non-MDM-enrolled test environments)");
+            }
+            catch (UnauthorizedAccessException ex)
+            {
+                _logger.Warning($"MdmRebootPolicy watcher access denied for {Channel}: {ex.Message}");
+            }
+            catch (Exception ex)
+            {
+                _logger.Error($"Failed to start MdmRebootPolicy watcher for {Channel}", ex);
+                // MON-D1: surface a dead watcher as one-shot telemetry, not just a local log line.
+                CollectorDegradationReporter.Report(_post, _sessionId, _tenantId,
+                    collectorName: "MdmRebootPolicyTracker", reason: $"watcher_arm_failed:{Channel}", ex: ex);
+            }
+        }
+
+        /// <summary>Targeted-EventID XPath filter. Exposed as internal for tests.</summary>
+        internal static string BuildXPath() =>
+            $"*[System[(EventID={EventId_PolicyRebootRequired})]]";
+
+        // -----------------------------------------------------------------------
+        // Event processing — buffer + debounce
+        // -----------------------------------------------------------------------
+
+        private void OnEventRecordWritten(object sender, EventRecordWrittenEventArgs e)
+        {
+            if (e.EventRecord == null) return;
+            try
+            {
+                ProcessRecord(e.EventRecord, isBackfill: false);
+            }
+            catch (Exception ex)
+            {
+                _logger.Error("Error processing MdmRebootPolicy event", ex);
+            }
+        }
+
+        private void ProcessRecord(EventRecord record, bool isBackfill)
+        {
+            var recordId = record.RecordId ?? -1;
+
+            // Cheap dedup gate BEFORE the expensive XML/FormatDescription work.
+            if (IsAlreadyProcessed(recordId))
+                return;
+
+            string xml = null;
+            try { xml = record.ToXml(); }
+            catch { /* fall back to description-only parse below */ }
+
+            string description = null;
+            try { description = record.FormatDescription(); }
+            catch { /* some events lack formatting resources */ }
+
+            var rebootUri = ExtractRebootUri(ParseEventData(xml), description);
+
+            ProcessEvent(
+                eventId: record.Id,
+                recordId: recordId,
+                timeCreatedUtc: record.TimeCreated?.ToUniversalTime(),
+                rebootUri: rebootUri,
+                formattedDescription: description,
+                isBackfill: isBackfill);
+        }
+
+        /// <summary>
+        /// Buffers one 2800 record into the pending burst (primitive-input test seam, mirroring the
+        /// WindowsUpdateTracker pattern). The aggregated event is emitted by <see cref="FlushPending"/>
+        /// — after the debounce quiet-period, at backfill completion, or at <see cref="Stop"/>.
+        /// </summary>
+        internal void ProcessEvent(
+            int eventId,
+            long recordId,
+            DateTime? timeCreatedUtc,
+            string rebootUri,
+            string formattedDescription,
+            bool isBackfill)
+        {
+            lock (_stateLock)
+            {
+                if (recordId >= 0)
+                {
+                    // Already emitted in a prior run, or already buffered/emitted this run.
+                    if (recordId <= _restartWatermark || !_seenThisRun.Add(recordId))
+                        return;
+                }
+
+                _pending.Add(new PendingRecord
+                {
+                    RecordId = recordId,
+                    TimeUtc = timeCreatedUtc ?? DateTime.UtcNow,
+                    Uri = string.IsNullOrEmpty(rebootUri) ? null : rebootUri,
+                    Description = formattedDescription,
+                    IsBackfill = isBackfill,
+                });
+            }
+
+            ArmDebounce();
+        }
+
+        private void ArmDebounce()
+        {
+            if (_debounceMilliseconds <= 0) return; // manual-flush mode (tests; backfill/Stop flush explicitly)
+
+            var timer = _debounceTimer;
+            if (timer == null)
+            {
+                var created = new Timer(_ =>
+                {
+                    try { FlushPending(); }
+                    catch (Exception ex) { _logger.Warning($"MdmRebootPolicy debounce flush failed: {ex.Message}"); }
+                }, null, Timeout.Infinite, Timeout.Infinite);
+
+                timer = Interlocked.CompareExchange(ref _debounceTimer, created, null) ?? created;
+                if (!ReferenceEquals(timer, created))
+                {
+                    try { created.Dispose(); } catch { }
+                }
+            }
+
+            try { timer.Change(_debounceMilliseconds, Timeout.Infinite); }
+            catch (ObjectDisposedException) { /* raced Stop() — Stop's flush covers the buffer */ }
+        }
+
+        /// <summary>
+        /// Emits the pending burst as ONE aggregated <c>mdm_policy_reboot_required</c> event and
+        /// persists the watermark. No-op when nothing is pending. Internal for tests.
+        /// </summary>
+        internal void FlushPending()
+        {
+            List<PendingRecord> batch;
+            long watermarkToPersist = -1;
+
+            lock (_stateLock)
+            {
+                if (_pending.Count == 0) return;
+                batch = new List<PendingRecord>(_pending);
+                _pending.Clear();
+
+                foreach (var r in batch)
+                {
+                    if (r.RecordId > _maxPersistedRecordId)
+                        _maxPersistedRecordId = r.RecordId;
+                }
+                watermarkToPersist = _maxPersistedRecordId;
+            }
+
+            if (watermarkToPersist >= 0) PersistWatermark(watermarkToPersist);
+
+            batch.Sort((a, b) => a.TimeUtc.CompareTo(b.TimeUtc));
+
+            var distinctUris = batch
+                .Where(r => r.Uri != null)
+                .Select(r => r.Uri)
+                .Distinct(StringComparer.OrdinalIgnoreCase)
+                .ToList();
+            var firstUri = batch.FirstOrDefault(r => r.Uri != null)?.Uri;
+            var unparsedCount = batch.Count(r => r.Uri == null);
+            var allBackfill = batch.All(r => r.IsBackfill);
+            var earliest = batch[0].TimeUtc;
+
+            var data = new Dictionary<string, object>
+            {
+                { "windowsEventId", EventId_PolicyRebootRequired },
+                { "eventLogChannel", Channel },
+                { "recordCount", batch.Count },
+                { "uriCount", distinctUris.Count },
+                { "backfilled", allBackfill },
+            };
+            if (distinctUris.Count > 0)
+            {
+                data["rebootUris"] = distinctUris
+                    .OrderBy(u => u, StringComparer.OrdinalIgnoreCase)
+                    .Take(MaxUrisPerEvent)
+                    .ToList();
+                data["firstRebootUri"] = firstUri;
+            }
+            if (unparsedCount > 0)
+            {
+                data["unparsedCount"] = unparsedCount;
+                var sample = batch.FirstOrDefault(r => r.Uri == null && !string.IsNullOrEmpty(r.Description))?.Description;
+                if (sample != null)
+                    data["sampleDescription"] = sample.Length > 500 ? sample.Substring(0, 500) + "…" : sample;
+            }
+
+            var flag = SafeProbeRebootRequiredFlag();
+            if (flag.HasValue) data["omadmRebootRequiredFlag"] = flag.Value;
+
+            string message;
+            if (distinctUris.Count == 1)
+                message = $"Windows flagged an MDM policy URI as reboot-required: {firstUri}";
+            else if (distinctUris.Count > 1)
+                message = $"Windows flagged {distinctUris.Count} MDM policy URIs as reboot-required: {firstUri} (+{distinctUris.Count - 1} more)";
+            else
+                message = $"Windows flagged {batch.Count} MDM policy record(s) as reboot-required (URI not parsed — see sampleDescription)";
+
+            _post.Emit(new EnrollmentEvent
+            {
+                SessionId = _sessionId,
+                TenantId = _tenantId,
+                // Earliest record time, not UtcNow: backfilled (and post-reboot re-read) bursts
+                // must land on the timeline at when the policies were actually flagged.
+                Timestamp = earliest,
+                EventType = Constants.EventTypes.MdmPolicyRebootRequired,
+                // Neutral observation — reboot-required flags outside ESP DeviceSetup have no
+                // immediate effect. The reboot CLAIM is ANALYZE-ESP-005's job, gated on an
+                // actually-observed system_reboot_detected.
+                Severity = EventSeverity.Info,
+                Source = "MdmRebootPolicyWatcher",
+                Phase = EnrollmentPhase.Unknown,
+                Message = message,
+                Data = data,
+                // Cheap (one event per burst) and still time-critical: a burst DURING DeviceSetup
+                // precedes a coalesced reboot that kills the agent.
+                ImmediateUpload = true,
+            });
+
+            _logger.Info($"MdmRebootPolicy: flushed {batch.Count} record(s) as one event " +
+                $"(uris={distinctUris.Count}, unparsed={unparsedCount}, backfilled={allBackfill})");
+        }
+
+        /// <summary>
+        /// Extracts the reboot-forcing OMA-DM URI. Preference order: (1) a structured EventData
+        /// value that starts with <c>./</c>, (2) a permissive regex over the formatted description
+        /// (verified shape: <c>The following URI has triggered a reboot: (./Device/...).</c>).
+        /// Returns null when nothing URI-like is found — the record still counts into the
+        /// aggregate (<c>unparsedCount</c> + <c>sampleDescription</c>).
+        /// </summary>
+        internal static string ExtractRebootUri(Dictionary<string, string> eventData, string description)
+        {
+            if (eventData != null)
+            {
+                foreach (var value in eventData.Values)
+                {
+                    var trimmed = value?.Trim();
+                    if (!string.IsNullOrEmpty(trimmed) && trimmed.StartsWith("./", StringComparison.Ordinal))
+                        return trimmed;
+                }
+            }
+
+            if (!string.IsNullOrEmpty(description))
+            {
+                var match = UriPattern.Match(description);
+                if (match.Success)
+                {
+                    // The permissive pattern can swallow sentence punctuation trailing the URI.
+                    // OMA-DM URI segments never end in punctuation — trim it.
+                    var candidate = match.Value.TrimEnd('.', ',', ';', ':', '\'', '"', ')');
+                    if (candidate.Length > 2) return candidate;
+                }
+            }
+
+            return null;
+        }
+
+        /// <summary>
+        /// Extracts <c>&lt;Data Name="..."&gt;value&lt;/Data&gt;</c> pairs from an event's rendered
+        /// XML, keyed case-insensitively. Also collects UNNAMED Data elements under positional keys
+        /// (<c>Data0</c>, <c>Data1</c>, …) — DM-Enterprise events frequently carry positional-only
+        /// payloads. Namespace-agnostic; returns an empty map on null/malformed XML — never throws.
+        /// </summary>
+        internal static Dictionary<string, string> ParseEventData(string xml)
+        {
+            var result = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+            if (string.IsNullOrEmpty(xml)) return result;
+
+            try
+            {
+                var doc = XDocument.Parse(xml);
+                var positionalIndex = 0;
+                foreach (var el in doc.Descendants().Where(e => e.Name.LocalName == "Data"))
+                {
+                    var nameAttr = el.Attribute("Name");
+                    var key = nameAttr != null && !string.IsNullOrEmpty(nameAttr.Value)
+                        ? nameAttr.Value
+                        : "Data" + positionalIndex++;
+                    if (!result.ContainsKey(key))
+                        result[key] = el.Value;
+                }
+            }
+            catch
+            {
+                // Malformed / unexpected XML — best effort, return what we have.
+            }
+
+            return result;
+        }
+
+        // -----------------------------------------------------------------------
+        // OMA-DM RebootRequired flag probe (fail-soft corroboration)
+        // -----------------------------------------------------------------------
+
+        private bool? SafeProbeRebootRequiredFlag()
+        {
+            try
+            {
+                return RebootRequiredFlagProbe?.Invoke();
+            }
+            catch
+            {
+                return null; // corroboration only — never let the probe break the emit
+            }
+        }
+
+        /// <summary>
+        /// Reads the pending-reboot flag under <see cref="OmadmSyncMlKeyPath"/>. Both a value and a
+        /// subkey named <c>RebootRequired</c> count as "pending". Fail-soft: null = unknown
+        /// (key absent / unreadable), matching the EspSkipConfigurationProbe convention.
+        /// </summary>
+        internal static bool? ReadOmadmRebootRequiredFlag()
+        {
+            try
+            {
+                using (var key = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(OmadmSyncMlKeyPath))
+                {
+                    if (key == null) return null;
+                    if (key.GetValue("RebootRequired") != null) return true;
+                    using (var sub = key.OpenSubKey("RebootRequired"))
+                    {
+                        return sub != null ? (bool?)true : false;
+                    }
+                }
+            }
+            catch
+            {
+                return null;
+            }
+        }
+
+        // -----------------------------------------------------------------------
+        // Backfill
+        // -----------------------------------------------------------------------
+
+        private void BackfillRecentEvents()
+        {
+            try
+            {
+                var lookbackMs = (long)_backfillLookbackMinutes * 60 * 1000;
+                var xpath = $"*[System[(EventID={EventId_PolicyRebootRequired}) and TimeCreated[timediff(@SystemTime) <= {lookbackMs}]]]";
+
+                _logger.Info($"MdmRebootPolicy backfill: scanning {Channel} " +
+                    $"(lookback={_backfillLookbackMinutes}min, restartWatermark={_restartWatermark})");
+
+                var query = new EventLogQuery(Channel, PathType.LogName, xpath);
+
+                int processed = 0;
+                using (var reader = new EventLogReader(query))
+                {
+                    EventRecord record;
+                    while ((record = reader.ReadEvent()) != null)
+                    {
+                        using (record)
+                        {
+                            ProcessRecord(record, isBackfill: true);
+                            processed++;
+                        }
+                    }
+                }
+
+                if (processed == 0)
+                    _logger.Debug($"MdmRebootPolicy backfill: no EventID {EventId_PolicyRebootRequired} records in last {_backfillLookbackMinutes} minutes");
+                else
+                    _logger.Info($"MdmRebootPolicy backfill: scanned {processed} record(s)");
+            }
+            catch (EventLogNotFoundException)
+            {
+                _logger.Warning($"MdmRebootPolicy event log not found during backfill: {Channel} (normal on non-MDM-enrolled test environments)");
+            }
+            catch (UnauthorizedAccessException ex)
+            {
+                _logger.Warning($"MdmRebootPolicy backfill access denied: {ex.Message}");
+            }
+            catch (Exception ex)
+            {
+                _logger.Warning($"MdmRebootPolicy backfill failed: {ex.Message}");
+            }
+        }
+
+        // -----------------------------------------------------------------------
+        // Watermark dedup (cross-restart) — persisted at flush, not at claim
+        // -----------------------------------------------------------------------
+
+        private bool IsAlreadyProcessed(long recordId)
+        {
+            if (recordId < 0) return false; // no RecordId → cannot dedup, let it through
+            lock (_stateLock)
+            {
+                return recordId <= _restartWatermark || _seenThisRun.Contains(recordId);
+            }
+        }
+
+        internal void LoadWatermark()
+        {
+            if (string.IsNullOrEmpty(_stateDirectory)) return;
+
+            var filePath = Path.Combine(_stateDirectory, WatermarkStateFileName);
+            if (!File.Exists(filePath)) return;
+
+            try
+            {
+                var json = File.ReadAllText(filePath);
+                var state = JsonConvert.DeserializeObject<WatermarkState>(json);
+                if (state != null)
+                {
+                    lock (_stateLock)
+                    {
+                        _restartWatermark = state.LastRecordId;
+                        _maxPersistedRecordId = state.LastRecordId;
+                    }
+                    _logger.Info($"MdmRebootPolicy watermark loaded: lastRecordId={state.LastRecordId} (persisted {state.PersistedUtc:O})");
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.Warning($"Failed to load MdmRebootPolicy watermark: {ex.Message}");
+            }
+        }
+
+        private void PersistWatermark(long recordId)
+        {
+            if (string.IsNullOrEmpty(_stateDirectory)) return;
+
+            try
+            {
+                Directory.CreateDirectory(_stateDirectory);
+                var filePath = Path.Combine(_stateDirectory, WatermarkStateFileName);
+                var state = new WatermarkState { LastRecordId = recordId, PersistedUtc = DateTime.UtcNow };
+                var json = JsonConvert.SerializeObject(state, Formatting.Indented);
+                var tempPath = filePath + ".tmp";
+                File.WriteAllText(tempPath, json);
+                File.Copy(tempPath, filePath, overwrite: true);
+                try { File.Delete(tempPath); } catch { }
+            }
+            catch (Exception ex)
+            {
+                _logger.Warning($"Failed to persist MdmRebootPolicy watermark: {ex.Message}");
+            }
+        }
+
+        internal sealed class WatermarkState
+        {
+            public long LastRecordId { get; set; }
+            public DateTime PersistedUtc { get; set; }
+        }
+    }
+}
@@ -17,6 +17,12 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals
    ///             CommercialOOBE_ESPProgress_WhiteGlove_Success — WhiteGlove complete
    ///             CommercialOOBE_ESPProgress_Failure/_Timeout/_Abort/WhiteGlove_Failed — ESP failure
    ///
+    /// NOTE (session b2e890c1, 2026-07-20): a bare "RebootCoalescing" substring match on 62407 was
+    /// tried and REMOVED — the token appears in the ROUTINE SubcategoryProcessing_Started marker
+    /// ("Starting subcategory DeviceSetup.RebootCoalescing...") on every enrollment, so it proves
+    /// nothing about an actual coalesced reboot. Policy-reboot attribution lives entirely in
+    /// MdmRebootPolicyTracker (EventID 2800) + the ANALYZE-ESP-005 rule gated on an observed reboot.
+    ///
    /// Raises <see cref="FinalizingSetupPhaseTriggered"/>, <see cref="WhiteGloveCompleted"/>,
    /// and <see cref="EspFailureDetected"/>. Cross-notifies the <see cref="HelloTracker"/>
    /// on Hello wizard start and ESP exit so Hello timers can react.
@@ -335,6 +335,23 @@ namespace AutopilotMonitor.Agent.V2.Core.Orchestration
                    osBuildChangedProvider: () => osBuildChangeHost.BuildChanged));
            }

+            // MDM reboot-policy watcher — subscribes to DeviceManagement-Enterprise-Diagnostics-
+            // Provider/Admin EventID 2800 and attributes the "unexpected reboot + second sign-in"
+            // pattern to the device-assigned policy URIs that forced the coalesced reboot.
+            // Agent-native collector (NOT an IAgentAnalyzer); the config flag is an internal
+            // steering lever only.
+            if (collectors.MdmRebootPolicyWatcherEnabled)
+            {
+                hosts.Add(new MdmRebootPolicyWatcherHost(
+                    sessionId: sessionId,
+                    tenantId: tenantId,
+                    logger: logger,
+                    ingress: ingress,
+                    clock: clock,
+                    backfillLookbackMinutes: collectors.MdmRebootPolicyBackfillLookbackMinutes,
+                    stateDirectory: _stateDirectory));
+            }
+
            // ----- Peripheral hosts (event-only; driven by remote-config toggles) --------------

            // V1 parity (PeriodicCollectorManager) — combine Performance + AgentSelfMetrics under
@@ -0,0 +1,68 @@
+#nullable enable
+using System;
+using System.Threading;
+using AutopilotMonitor.Agent.V2.Core.Logging;
+using AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.SystemSignals;
+using AutopilotMonitor.DecisionCore.Engine;
+using AutopilotMonitor.DecisionCore.Signals;
+
+namespace AutopilotMonitor.Agent.V2.Core.Orchestration
+{
+    /// <summary>
+    /// Standalone host for the <see cref="MdmRebootPolicyTracker"/> — watches
+    /// <c>Microsoft-Windows-DeviceManagement-Enterprise-Diagnostics-Provider/Admin</c> (EventID
+    /// 2800) for MDM policies that force a coalesced reboot during ESP DeviceSetup and forwards
+    /// them via the shared single-rail ingress. Mirrors <see cref="WindowsUpdateWatcherHost"/>:
+    /// builds its own <see cref="InformationalEventPost"/> and delegates Start/Stop to the tracker.
+    /// </summary>
+    internal sealed class MdmRebootPolicyWatcherHost : ICollectorHost
+    {
+        public string Name => "MdmRebootPolicyTracker";
+
+        private readonly MdmRebootPolicyTracker _tracker;
+        private readonly AgentLogger _logger;
+        private int _disposed;
+
+        public MdmRebootPolicyWatcherHost(
+            string sessionId,
+            string tenantId,
+            AgentLogger logger,
+            ISignalIngressSink ingress,
+            IClock clock,
+            int backfillLookbackMinutes,
+            string stateDirectory)
+        {
+            if (ingress == null) throw new ArgumentNullException(nameof(ingress));
+            if (clock == null) throw new ArgumentNullException(nameof(clock));
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+
+            var post = new InformationalEventPost(ingress, clock, logger);
+            _tracker = new MdmRebootPolicyTracker(
+                sessionId: sessionId,
+                tenantId: tenantId,
+                post: post,
+                logger: logger,
+                backfillEnabled: backfillLookbackMinutes > 0,
+                backfillLookbackMinutes: backfillLookbackMinutes,
+                stateDirectory: stateDirectory);
+        }
+
+        public void Start()
+        {
+            _tracker.Start();
+            _logger.Info("MdmRebootPolicyWatcherHost: started.");
+        }
+
+        public void Stop()
+        {
+            try { _tracker.Stop(); }
+            catch (Exception ex) { _logger.Warning($"MdmRebootPolicyWatcherHost: stop failed: {ex.Message}"); }
+        }
+
+        public void Dispose()
+        {
+            if (Interlocked.Exchange(ref _disposed, 1) == 1) return;
+            Stop();
+        }
+    }
+}
@@ -270,7 +270,7 @@ namespace AutopilotMonitor.Functions.Functions.Config
            var response = req.CreateResponse(HttpStatusCode.OK);
            await response.WriteAsJsonAsync(new AgentConfigResponse
            {
-                ConfigVersion = 34, // Gather rule phase scoping (ActivePhases/ActiveFromPhase) + EmitMode on_change anti-spam
+                ConfigVersion = 35, // MDM reboot-policy watcher (mdm_policy_reboot_required / esp_reboot_coalescing)
                UploadIntervalSeconds = 10,
                SelfDestructOnComplete = tenantConfig.SelfDestructOnComplete ?? true,
                KeepLogFile = tenantConfig.KeepLogFile ?? false,
@@ -24,6 +24,7 @@ export const EVENT_TYPES_CATALOG = {
    'esp_failure_settle_started',
    'esp_failure_settle_recovered',
    'esp_exiting',
+    'mdm_policy_reboot_required',
    'esp_config_detected',
    'completion_check',
    'completion_waiting',
@@ -405,6 +405,18 @@ namespace AutopilotMonitor.Shared
            public const string OsBuildChanged             = "os_build_changed";               // OS build (CurrentBuild.UBR) differs across an agent restart — an update was installed during enrollment
            public const string WindowsUpdateChannelCensus = "windows_update_channel_census";  // One-shot EventID histogram of WU Client + UpdateOrchestrator channels when os_build_changed but zero targeted WU events captured

+            // MDM reboot-required policy flags (MdmRebootPolicyTracker; PMPC "unexpected reboot /
+            // second sign-in" research). DM-Enterprise EventID 2800 fires once per policy URI that
+            // matches the OS reboot-required catalog ("The following URI has triggered a reboot:
+            // (./Device/...)."; verified session b2e890c1). Only URIs applied DURING ESP DeviceSetup
+            // cause the coalesced mid-ESP reboot — later syncs (AccountSetup+) merely flag, no forced
+            // reboot. The tracker therefore emits ONE aggregated Info event per burst with the URI
+            // list; the reboot CLAIM lives in ANALYZE-ESP-005, gated on an actually-observed
+            // system_reboot_detected. Deliberately DISTINCT from system_reboot_detected: the backend
+            // RebootCount matches that string exactly (EventIngestProcessor.Classification + terminal
+            // recount) — this attribution event must never inflate the reboot count.
+            public const string MdmPolicyRebootRequired    = "mdm_policy_reboot_required";     // Aggregated per burst — Data.rebootUris[] + uriCount + firstRebootUri
+
            // TEMPORARY: shadow SM rollout verification — remove when CompletionStateMachine is promoted to primary
            public const string ShadowDiscrepancy         = "shadow_discrepancy";

@@ -482,6 +482,28 @@ namespace AutopilotMonitor.Shared.Models
        /// </summary>
        public bool WindowsUpdateChannelCensusEnabled { get; set; } = true;

+        // -----------------------------------------------------------------------
+        // MDM reboot-policy watcher (DeviceManagement-Enterprise-Diagnostics-Provider/Admin)
+        // -----------------------------------------------------------------------
+
+        /// <summary>
+        /// Master switch for the MDM reboot-policy watcher. When enabled the agent subscribes to
+        /// <c>Microsoft-Windows-DeviceManagement-Enterprise-Diagnostics-Provider/Admin</c> EventID
+        /// 2800 and emits one <c>mdm_policy_reboot_required</c> event per device-assigned policy
+        /// URI that forces a coalesced reboot during ESP DeviceSetup (the "unexpected reboot +
+        /// second sign-in" pattern). Internal steering lever only — not surfaced in any admin UI;
+        /// disable by pushing config server-side. Default: true.
+        /// </summary>
+        public bool MdmRebootPolicyWatcherEnabled { get; set; } = true;
+
+        /// <summary>
+        /// Lookback window in minutes for the MDM reboot-policy backfill scan on startup. Device
+        /// policies can apply before the agent starts, and after the coalesced reboot the restarted
+        /// agent must re-scan past the reboot gap (the cross-restart watermark keeps re-reads from
+        /// re-emitting). 0 = backfill disabled. Default: 60 minutes.
+        /// </summary>
+        public int MdmRebootPolicyBackfillLookbackMinutes { get; set; } = 60;
+
        /// <summary>
        /// Creates default collector configuration
        /// </summary>