feat(agent,web,shared): phase_exit gather trigger — one-shot collection at a phase's end

Follow-up to gather-rule phase scoping. One-shot collection at a phase START
already existed (phase_change dedups per (rule, phase)) and at enrollment END
(on_event + enrollment_complete); the END of a specific phase had no trigger.

New trigger value "phase_exit": fires once when TriggerPhase is LEFT (empty =
every phase transition). Together with phase_change it forms the two one-shot
bookends of a phase.

Agent (GatherRuleExecutor.OnPhaseChanged):
- Exit rules are evaluated BEFORE _currentPhase advances, so both the
  TriggerPhase match and the phase-scope gate see the phase being LEFT. A rule
  scoped to DeviceSetup therefore fires on its own exit even though the phase
  being entered is out of scope.
- A transition into Failed fires the exit rules of the failing phase — the
  snapshot at a failure boundary is the point of the trigger.
- Exit of Unknown never fires; a repeated identical phase signal is not a
  transition.
- Dedup key "exit:{ruleId}|{phase}" shares _phaseRulesExecuted with the
  phase_change keys but stays in a disjoint key space, so an enter-rule and an
  exit-rule on the same phase cannot consume each other's slot.

Portal: trigger labels are now "Phase Start" / "Phase End"; the canonical phase
dropdown and the create/save payloads cover both via PHASE_TRIGGERS; the card
renders "entering X" / "leaving X".

No ConfigVersion bump: no new field is transported. Old agents do not know the
value and simply never fire the rule (silent no-op).

Tests: GatherRuleExecutorPhaseExitTests (11) — enter-vs-exit, no refire on
re-entry, empty-triggerPhase, exit-of-Unknown, same-phase-signal, into-Failed,
Complete, scope-against-left-phase, out-of-scope slot preservation, key-space
disjointness, on_change interplay. Build 0 Errors; V2.Core.Tests 1884/1884;
Functions.Tests 3099/3099; vitest 557/557; tsc silent.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/index.md

@@ -22,7 +22,7 @@ https://docs.autopilotmonitor.com (separate repository).
 
 # Rules
 
-* [Gather Rule Phase Scoping & Emit-on-Change](rules/gather-rule-phase-scoping.md) - Restricting gather rules to enrollment phases (activePhases / activeFromPhase sticky latch) and emitMode "on_change" result-dedup — the anti-spam pair for interval rules.
+* [Gather Rule Phase Scoping, One-Shot Triggers & Emit-on-Change](rules/gather-rule-phase-scoping.md) - Restricting gather rules to enrollment phases (activePhases / activeFromPhase sticky latch), one-shot collection at a phase's start/end (phase_change / phase_exit), and emitMode "on_change" result-dedup.
 
 # Backend
 

docs/log.md

@@ -2,6 +2,7 @@
 
 ## 2026-07-20
 
+* **Update**: Extended `rules/gather-rule-phase-scoping.md` with the `phase_exit` trigger — the closing bookend to `phase_change`, for one-shot collection when a phase is LEFT (e.g. "state at the end of Account Setup"). Documents the evaluation-before-phase-advance rule (triggerPhase match and scope gate see the phase being left), firing into `Failed`, the disjoint `exit:` dedup key space, and why no ConfigVersion bump is needed (no new field — old agents simply never fire the rule).
 * **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.
 

docs/rules/gather-rule-phase-scoping.md

@@ -1,7 +1,7 @@
 ---
 type: Concept
-title: Gather Rule Phase Scoping & Emit-on-Change
-description: How gather rules are restricted to enrollment phases (activePhases / activeFromPhase) and how emitMode "on_change" suppresses repeated identical results — the anti-spam pair for interval rules.
+title: Gather Rule Phase Scoping, One-Shot Triggers & Emit-on-Change
+description: How gather rules are restricted to enrollment phases (activePhases / activeFromPhase), collect once at a phase boundary (phase_change / phase_exit), and how emitMode "on_change" suppresses repeated identical results.
 resource: /src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Telemetry/Gather/GatherRuleExecutor.cs
 tags:
   - agent
@@ -35,6 +35,35 @@ Backend validation (`GatherRulesFunction.ValidateScopeAndEmitMode`) rejects `Unk
 numeric tokens, unknown emit modes, and both scope fields set at once (400). The agent
 defensively prefers `activePhases` if both arrive anyway.
 
+# One-shot collection at phase boundaries
+
+Scoping answers "while *may* this rule run". The trigger answers "when does it fire". For
+one-shot collection the two phase triggers are the bookends of a phase:
+
+| Trigger | Fires |
+|---|---|
+| `phase_change` | Once when `triggerPhase` is **entered** (dedup key `{ruleId}\|{phase}`). |
+| `phase_exit` | Once when `triggerPhase` is **left** (dedup key `exit:{ruleId}\|{phase}`). |
+
+Empty `triggerPhase` means every transition. Both keys live in the same
+`_phaseRulesExecuted` set; the `exit:` prefix keeps the two key spaces disjoint, so an
+enter-rule and an exit-rule on the same phase never cannibalise each other's slot.
+
+`phase_exit` semantics that are easy to get wrong:
+
+* It is evaluated **before** `_currentPhase` advances, so both the `triggerPhase` match and
+  the phase-scope gate see the phase being **left**. A rule scoped to `DeviceSetup` therefore
+  still fires on its own exit, even though the phase being entered is outside that scope.
+* A transition into `Failed` **does** fire the exit rules of the failing phase — capturing
+  state at the failure boundary is the point.
+* Exit of `Unknown` never fires (nothing was entered yet), and a repeated identical phase
+  signal is not a transition.
+* An exit rule on `Complete` only fires if something transitions *away* from Complete. For
+  "at the end of enrollment", use `phase_change` on `Complete` or `on_event` with
+  `enrollment_complete`.
+* Old agents do not know the trigger value and simply never fire the rule (silent no-op) —
+  which is why `phase_exit` needs no ConfigVersion bump: no new field is transported.
+
 # Scope semantics (agent, `GatherRuleExecutor`)
 
 * Scope applies to **all trigger types**:

rules/schema/gather-rule.schema.json

@@ -80,8 +80,8 @@
         },
         "trigger": {
           "type": "string",
-          "description": "When to collect data.",
-          "enum": ["startup", "phase_change", "interval", "on_event"]
+          "description": "When to collect data. \"phase_change\" fires once when triggerPhase is entered, \"phase_exit\" once when it is left.",
+          "enum": ["startup", "phase_change", "phase_exit", "interval", "on_event"]
         },
         "intervalSeconds": {
           "type": "integer",
@@ -90,7 +90,7 @@
         },
         "triggerPhase": {
           "type": "string",
-          "description": "Phase to trigger on (only used when trigger = \"phase_change\")."
+          "description": "Phase to trigger on (used when trigger = \"phase_change\" or \"phase_exit\"). Empty = every phase transition."
         },
         "triggerEventType": {
           "type": "string",

src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Gather/GatherRuleExecutorPhaseExitTests.cs

@@ -0,0 +1,246 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Threading;
+using AutopilotMonitor.Agent.V2.Core.Logging;
+using AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Gather;
+using AutopilotMonitor.Agent.V2.Core.Tests.Harness;
+using AutopilotMonitor.Shared.Models;
+using Xunit;
+
+namespace AutopilotMonitor.Agent.V2.Core.Tests.Monitoring.Gather
+{
+    /// <summary>
+    /// The <c>phase_exit</c> trigger: a one-shot collection when a phase is LEFT — the closing
+    /// bookend to <c>phase_change</c> (which fires on ENTER). The distinguishing invariant is that
+    /// both the TriggerPhase match and the phase-scope gate must evaluate against the phase being
+    /// left, i.e. before the executor's current-phase state moves forward.
+    /// Rules use the absent-registry-path pattern so no real system state is touched.
+    /// </summary>
+    [Collection("SerialThreading")] // rules execute on the shared ThreadPool
+    public sealed class GatherRuleExecutorPhaseExitTests : IDisposable
+    {
+        private readonly TempDirectory _tmp = new TempDirectory();
+        private readonly List<EnrollmentEvent> _events = new List<EnrollmentEvent>();
+        private readonly object _eventsGate = new object();
+        private readonly GatherRuleExecutor _executor;
+
+        private const string AbsentPath =
+            "HKLM\\SOFTWARE\\AutopilotMonitorTests\\DefinitelyAbsent_9c4d2a7f-0000-0000-0000-000000000000";
+
+        public GatherRuleExecutorPhaseExitTests()
+        {
+            var logger = new AgentLogger(_tmp.Path, AgentLogLevel.Info);
+            _executor = new GatherRuleExecutor(
+                "sess", "tenant",
+                evt => { lock (_eventsGate) _events.Add(evt); },
+                logger)
+            {
+                UnrestrictedMode = true
+            };
+        }
+
+        public void Dispose()
+        {
+            _executor.Dispose();
+            _tmp.Dispose();
+        }
+
+        private int EventCount { get { lock (_eventsGate) return _events.Count; } }
+
+        private bool WaitForEventCount(int count, int timeoutMs = 10000)
+        {
+            var sw = Stopwatch.StartNew();
+            while (sw.ElapsedMilliseconds < timeoutMs)
+            {
+                if (EventCount >= count) return true;
+                Thread.Sleep(25);
+            }
+            return EventCount >= count;
+        }
+
+        private static GatherRule ExitRule(
+            string id, string triggerPhase, List<string> activePhases = null, string fromPhase = null)
+            => new GatherRule
+            {
+                RuleId = id,
+                Title = id,
+                CollectorType = "registry",
+                Target = AbsentPath,
+                Trigger = "phase_exit",
+                TriggerPhase = triggerPhase,
+                OutputEventType = "gather_test",
+                Enabled = true,
+                ActivePhases = activePhases,
+                ActiveFromPhase = fromPhase,
+            };
+
+        [Fact]
+        public void FiresOnceWhenTheNamedPhaseIsLeft_NotWhenItIsEntered()
+        {
+            _executor.UpdateRules(new List<GatherRule> { ExitRule("GATHER-PX-001", "AccountSetup") });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.DeviceSetup);
+            Thread.Sleep(300);
+            Assert.Equal(0, EventCount);
+
+            // Entering AccountSetup must NOT fire an exit rule.
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup);
+            Thread.Sleep(300);
+            Assert.Equal(0, EventCount);
+
+            // Leaving it does.
+            _executor.OnPhaseChanged(EnrollmentPhase.AppsUser);
+            Assert.True(WaitForEventCount(1));
+        }
+
+        [Fact]
+        public void DoesNotRefireWhenThePhaseIsLeftTwice()
+        {
+            _executor.UpdateRules(new List<GatherRule> { ExitRule("GATHER-PX-002", "AccountSetup") });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup);
+            _executor.OnPhaseChanged(EnrollmentPhase.AppsUser);
+            Assert.True(WaitForEventCount(1));
+
+            // A phase can be re-entered (ESP re-reporting); the one-shot slot stays consumed.
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup);
+            _executor.OnPhaseChanged(EnrollmentPhase.AppsUser);
+            Thread.Sleep(400);
+            Assert.Equal(1, EventCount);
+        }
+
+        [Fact]
+        public void EmptyTriggerPhase_FiresOnEveryExit()
+        {
+            _executor.UpdateRules(new List<GatherRule> { ExitRule("GATHER-PX-003", "") });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.DeviceSetup); // exit of Unknown — must NOT fire
+            Thread.Sleep(300);
+            Assert.Equal(0, EventCount);
+
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup); // exit of DeviceSetup
+            Assert.True(WaitForEventCount(1));
+
+            _executor.OnPhaseChanged(EnrollmentPhase.AppsUser);     // exit of AccountSetup
+            Assert.True(WaitForEventCount(2));
+        }
+
+        [Fact]
+        public void NeverFiresOnExitOfUnknown()
+        {
+            // Before the first phase signal there is no phase to leave.
+            _executor.UpdateRules(new List<GatherRule> { ExitRule("GATHER-PX-004", "") });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.Start);
+            Thread.Sleep(300);
+            Assert.Equal(0, EventCount);
+        }
+
+        [Fact]
+        public void RepeatedSamePhaseSignal_IsNotAnExit()
+        {
+            _executor.UpdateRules(new List<GatherRule> { ExitRule("GATHER-PX-005", "") });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup);
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup); // same phase — no transition
+            Thread.Sleep(300);
+            Assert.Equal(0, EventCount);
+        }
+
+        [Fact]
+        public void FiresOnTransitionIntoFailed_CapturingStateAtTheFailurePoint()
+        {
+            _executor.UpdateRules(new List<GatherRule> { ExitRule("GATHER-PX-006", "AccountSetup") });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup);
+            _executor.OnPhaseChanged(EnrollmentPhase.Failed);
+
+            Assert.True(WaitForEventCount(1), "leaving a phase into Failed must still snapshot it");
+        }
+
+        [Fact]
+        public void FiresOnExitOfCompleteOnly_WhenCompleteIsActuallyLeft()
+        {
+            // "End of enrollment" is better served by phase_change on Complete / on_event; an exit
+            // rule on Complete only fires if a later transition happens at all.
+            _executor.UpdateRules(new List<GatherRule> { ExitRule("GATHER-PX-007", "Complete") });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.FinalizingSetup);
+            _executor.OnPhaseChanged(EnrollmentPhase.Complete);
+            Thread.Sleep(300);
+            Assert.Equal(0, EventCount);
+        }
+
+        [Fact]
+        public void ScopeGate_EvaluatesAgainstThePhaseBeingLeft()
+        {
+            // Scope = only during DeviceSetup. Leaving DeviceSetup must fire (the rule is still in
+            // scope at that instant) even though the NEW phase is outside the scope.
+            _executor.UpdateRules(new List<GatherRule>
+            {
+                ExitRule("GATHER-PX-010", "DeviceSetup", activePhases: new List<string> { "DeviceSetup" })
+            });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.DeviceSetup);
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup);
+
+            Assert.True(WaitForEventCount(1),
+                "the scope gate must see the phase being left, not the one being entered");
+        }
+
+        [Fact]
+        public void OutOfScopeExit_DoesNotFire_AndDoesNotConsumeTheOneShotSlot()
+        {
+            // Scope = only during AccountSetup; the rule exits DeviceSetup while out of scope.
+            var rule = ExitRule("GATHER-PX-011", "", activePhases: new List<string> { "AccountSetup" });
+            _executor.UpdateRules(new List<GatherRule> { rule });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.DeviceSetup);
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup); // exit of DeviceSetup: out of scope
+            Thread.Sleep(300);
+            Assert.Equal(0, EventCount);
+
+            _executor.OnPhaseChanged(EnrollmentPhase.AppsUser);     // exit of AccountSetup: in scope
+            Assert.True(WaitForEventCount(1));
+        }
+
+        [Fact]
+        public void ExitAndChangeRulesForTheSamePhase_BothFireIndependently()
+        {
+            // The dedup key spaces must not collide: same ruleId shape, same phase, different trigger.
+            var enter = new GatherRule
+            {
+                RuleId = "GATHER-PX-020",
+                Title = "enter",
+                CollectorType = "registry",
+                Target = AbsentPath,
+                Trigger = "phase_change",
+                TriggerPhase = "AccountSetup",
+                OutputEventType = "gather_test",
+                Enabled = true,
+            };
+            var exit = ExitRule("GATHER-PX-021", "AccountSetup");
+            _executor.UpdateRules(new List<GatherRule> { enter, exit });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup);
+            Assert.True(WaitForEventCount(1)); // enter fired
+
+            _executor.OnPhaseChanged(EnrollmentPhase.AppsUser);
+            Assert.True(WaitForEventCount(2)); // exit fired
+        }
+
+        [Fact]
+        public void ExitRuleWithEmitOnChange_StillEmitsItsFirstResult()
+        {
+            var rule = ExitRule("GATHER-PX-030", "AccountSetup");
+            rule.EmitMode = "on_change";
+            _executor.UpdateRules(new List<GatherRule> { rule });
+
+            _executor.OnPhaseChanged(EnrollmentPhase.AccountSetup);
+            _executor.OnPhaseChanged(EnrollmentPhase.AppsUser);
+
+            Assert.True(WaitForEventCount(1));
+        }
+    }
+}

src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Telemetry/Gather/GatherRuleExecutor.cs

@@ -176,12 +176,59 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Telemetry.Gather
 
         /// <summary>
         /// Called when a phase change event occurs - executes rules triggered by phase changes
+        /// (<c>phase_change</c> on entering the new phase, <c>phase_exit</c> on leaving the old one).
         /// </summary>
         public void OnPhaseChanged(EnrollmentPhase newPhase)
         {
             var phaseName = newPhase.ToString();
 
-            // Update the phase + from-phase latches FIRST so deferred startup activation and
+            // phase_exit runs FIRST and against the phase being LEFT: both the TriggerPhase match
+            // and the scope gate must see the old phase, so this block has to complete before
+            // _currentPhase moves below. A transition INTO Failed still fires the exit rules of the
+            // phase that failed — that snapshot is the whole point at a failure boundary.
+            List<GatherRule> exitRules = null;
+            lock (_scopeLock)
+            {
+                var previousPhase = _currentPhase;
+                if (previousPhase != EnrollmentPhase.Unknown && previousPhase != newPhase)
+                {
+                    var previousPhaseName = previousPhase.ToString();
+                    exitRules = new List<GatherRule>();
+
+                    foreach (var rule in _activeRules)
+                    {
+                        if (rule.Trigger != "phase_exit") continue;
+                        if (!string.IsNullOrEmpty(rule.TriggerPhase)
+                            && !string.Equals(rule.TriggerPhase, previousPhaseName, StringComparison.OrdinalIgnoreCase))
+                            continue;
+
+                        // Scope gate before the dedup add — an out-of-scope pass must not consume
+                        // the once-per-(rule, phase) slot. IsRuleInScopeLocked still sees the old phase.
+                        if (!IsRuleInScopeLocked(rule)) continue;
+
+                        // "exit:" prefix keeps this key space disjoint from the phase_change keys.
+                        if (!_phaseRulesExecuted.Add($"exit:{rule.RuleId}|{previousPhaseName}"))
+                        {
+                            _logger.Debug($"Phase-exit rule {rule.RuleId} already executed for exit of {previousPhaseName}, skipping");
+                            continue;
+                        }
+
+                        _logger.Info($"Phase exit triggered rule {rule.RuleId} (left phase: {previousPhaseName}, now: {phaseName})");
+                        exitRules.Add(rule);
+                    }
+                }
+            }
+
+            if (exitRules != null)
+            {
+                foreach (var rule in exitRules)
+                {
+                    var exitRule = rule;
+                    ThreadPool.QueueUserWorkItem(_ => ExecuteRule(exitRule));
+                }
+            }
+
+            // Update the phase + from-phase latches so deferred startup activation and
             // the phase_change rules below all evaluate against the NEW phase.
             List<GatherRule> deferredStartup;
             lock (_scopeLock)

src/Shared/AutopilotMonitor.Shared/Models/Rules/GatherRule.cs

@@ -107,7 +107,11 @@ namespace AutopilotMonitor.Shared.Models
         // ===== WHEN TO COLLECT =====
 
         /// <summary>
-        /// Trigger type: "startup", "phase_change", "interval", "on_event"
+        /// Trigger type: "startup", "phase_change", "phase_exit", "interval", "on_event".
+        /// <para>
+        /// "phase_change" fires once when the phase in <see cref="TriggerPhase"/> is ENTERED,
+        /// "phase_exit" once when it is LEFT — the two one-shot bookends of a phase.
+        /// </para>
         /// </summary>
         public string Trigger { get; set; } = default!;
 
@@ -117,8 +121,9 @@ namespace AutopilotMonitor.Shared.Models
         public int? IntervalSeconds { get; set; }
 
         /// <summary>
-        /// Phase to trigger on (only used when Trigger = "phase_change")
-        /// e.g., "Identity", "MdmEnrollment", "AppInstallation"
+        /// Phase to trigger on (used when Trigger = "phase_change" or "phase_exit").
+        /// Canonical tokens are the <see cref="EnrollmentPhase"/> enum names, e.g.
+        /// "DeviceSetup", "AccountSetup", "Complete". Empty = every phase transition.
         /// </summary>
         public string TriggerPhase { get; set; } = default!;
 

src/Web/autopilot-monitor-web/app/gather-rules/components/GatherRuleCard.tsx

@@ -293,7 +293,16 @@ export function GatherRuleCard({
                 )}
                 {rule.trigger === "phase_change" && rule.triggerPhase && (
                   <span className="text-gray-500">
-                    on phase: <code className="px-1 bg-gray-200 rounded text-xs">{rule.triggerPhase}</code>
+                    entering <code className="px-1 bg-gray-200 rounded text-xs">{formatGatherPhase(rule.triggerPhase)}</code>
+                  </span>
+                )}
+                {rule.trigger === "phase_exit" && (
+                  <span className="text-gray-500">
+                    {rule.triggerPhase ? (
+                      <>leaving <code className="px-1 bg-gray-200 rounded text-xs">{formatGatherPhase(rule.triggerPhase)}</code></>
+                    ) : (
+                      "on every phase exit"
+                    )}
                   </span>
                 )}
                 {rule.trigger === "on_event" && rule.triggerEventType && (

src/Web/autopilot-monitor-web/app/gather-rules/components/GatherRuleFormFields.tsx

@@ -11,6 +11,7 @@ import {
   TARGET_PLACEHOLDERS,
   TARGET_HINTS,
   GATHER_PHASES,
+  PHASE_TRIGGERS,
   EMIT_MODES,
   formatTrigger,
 } from "../types";
@@ -425,7 +426,7 @@ export function GatherRuleFormFields({ form, setForm, showRuleId, unrestrictedMo
         </div>
       )}
 
-      {form.trigger === "phase_change" && (
+      {PHASE_TRIGGERS.includes(form.trigger) && (
         <div>
           <label className="block text-sm font-medium text-gray-700 mb-1">Trigger Phase</label>
           <select
@@ -433,7 +434,7 @@ export function GatherRuleFormFields({ form, setForm, showRuleId, unrestrictedMo
             onChange={(e) => setForm({ ...form, triggerPhase: e.target.value })}
             className="w-full px-4 py-2 border border-gray-300 rounded-lg text-sm text-gray-900 bg-white focus:outline-none focus:ring-2 focus:ring-indigo-500 focus:border-indigo-500 transition-colors"
           >
-            <option value="">Any phase change</option>
+            <option value="">Any phase</option>
             {form.triggerPhase && !GATHER_PHASES.some((p) => p.value === form.triggerPhase) && (
               <option value={form.triggerPhase}>{form.triggerPhase} (legacy value)</option>
             )}
@@ -441,7 +442,11 @@ export function GatherRuleFormFields({ form, setForm, showRuleId, unrestrictedMo
               <option key={p.value} value={p.value}>{p.label}</option>
             ))}
           </select>
-          <p className="text-xs text-gray-400 mt-1">Run this rule when the enrollment reaches this phase. &quot;Any phase change&quot; fires once per phase transition.</p>
+          <p className="text-xs text-gray-400 mt-1">
+            {form.trigger === "phase_exit"
+              ? "Collect once when the enrollment LEAVES this phase — a snapshot of its end state. \"Any phase\" fires on every phase transition. Also fires when the phase is left because enrollment failed."
+              : "Collect once when the enrollment REACHES this phase. \"Any phase\" fires on every phase transition."}
+          </p>
         </div>
       )}
 

src/Web/autopilot-monitor-web/app/gather-rules/page.tsx

@@ -16,7 +16,7 @@ import { FormJsonToggle, JsonModeToggleButtons } from "@/components/rules/FormJs
 import { useAuthenticatedFetch, useNotificationMessages, useGlobalAdminScope } from "@/hooks";
 import { GlobalAdminBanner, globalAdminSubtitle } from "@/components/GlobalAdminBanner";
 import { TenantScopeSelector } from "@/components/TenantScopeSelector";
-import { GatherRule, NewRuleForm, EMPTY_FORM, CATEGORY_COLORS, withDerivedScopeMode } from "./types";
+import { GatherRule, NewRuleForm, EMPTY_FORM, CATEGORY_COLORS, PHASE_TRIGGERS, withDerivedScopeMode } from "./types";
 import { GatherRuleFormFields } from "./components/GatherRuleFormFields";
 import { GatherRuleCard } from "./components/GatherRuleCard";
 
@@ -209,7 +209,7 @@ export default function GatherRulesPage() {
       parameters: buildParameters(form),
       trigger: form.trigger,
       intervalSeconds: form.trigger === "interval" ? form.intervalSeconds : null,
-      triggerPhase: form.trigger === "phase_change" ? form.triggerPhase : null,
+      triggerPhase: PHASE_TRIGGERS.includes(form.trigger) ? form.triggerPhase : null,
       triggerEventType: form.trigger === "on_event" ? form.triggerEventType : null,
       activePhases: form.scopeMode === "during" && form.activePhases.length > 0 ? form.activePhases : null,
       activeFromPhase: form.scopeMode === "from" && form.activeFromPhase ? form.activeFromPhase : null,
@@ -296,7 +296,7 @@ export default function GatherRulesPage() {
       parameters: buildParameters(form),
       trigger: form.trigger,
       intervalSeconds: form.trigger === "interval" ? form.intervalSeconds : null,
-      triggerPhase: form.trigger === "phase_change" ? form.triggerPhase : null,
+      triggerPhase: PHASE_TRIGGERS.includes(form.trigger) ? form.triggerPhase : null,
       triggerEventType: form.trigger === "on_event" ? form.triggerEventType : null,
       activePhases: form.scopeMode === "during" && form.activePhases.length > 0 ? form.activePhases : null,
       activeFromPhase: form.scopeMode === "from" && form.activeFromPhase ? form.activeFromPhase : null,

src/Web/autopilot-monitor-web/app/gather-rules/types.ts

@@ -61,7 +61,10 @@ export interface NewRuleForm {
 
 export const CATEGORIES = ["network", "identity", "apps", "device", "esp", "enrollment"] as const;
 export const COLLECTOR_TYPES = ["registry", "eventlog", "wmi", "file", "command_allowlisted", "logparser", "json", "xml"] as const;
-export const TRIGGERS = ["startup", "phase_change", "interval", "on_event"] as const;
+export const TRIGGERS = ["startup", "phase_change", "phase_exit", "interval", "on_event"] as const;
+
+/** Triggers that collect at a phase boundary and therefore use the triggerPhase field. */
+export const PHASE_TRIGGERS: ReadonlyArray<string> = ["phase_change", "phase_exit"];
 export const SEVERITIES = ["info", "warning", "error", "critical"] as const;
 
 // Canonical phase-scope tokens: the backend EnrollmentPhase enum NAMES from Start(0) through
@@ -168,7 +171,8 @@ export const EMPTY_FORM: NewRuleForm = {
 
 export function formatTrigger(trigger: string) {
   switch (trigger) {
-    case "phase_change": return "Phase Change";
+    case "phase_change": return "Phase Start";
+    case "phase_exit": return "Phase End";
     case "on_event": return "On Event";
     default: return trigger.charAt(0).toUpperCase() + trigger.slice(1);
   }