diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Architecture/TelemetryEventEmitterCallersBaselineTests.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Architecture/TelemetryEventEmitterCallersBaselineTests.cs
new file mode 100644
index 00000000..7e57796d
--- /dev/null
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Architecture/TelemetryEventEmitterCallersBaselineTests.cs
@@ -0,0 +1,132 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using AutopilotMonitor.Agent.V2.Core.Orchestration;
+using AutopilotMonitor.Agent.V2.Core.Telemetry.Events;
+using Xunit;
+
+namespace AutopilotMonitor.Agent.V2.Core.Tests.Architecture
+{
+    /// <summary>
+    /// Single-rail refactor plan §4.4 / §8 — baseline inventory of every type in
+    /// <c>AutopilotMonitor.Agent.V2.Core</c> that can reach
+    /// <see cref="TelemetryEventEmitter"/>. The test is a living document: as the migration PRs
+    /// (#1 through #9) remove bypass paths one by one, the baseline shrinks. PR #10 tightens
+    /// the expected set to only the two permitted callers — <see cref="EventTimelineEmitter"/>
+    /// (Rail A) and <see cref="BackPressureEventObserver"/> (documented meta exception).
+    /// <para>
+    /// <b>Scope</b>: this test inspects the V2.Core assembly only. Program.cs lives in the
+    /// V2 executable assembly and reaches the emitter via
+    /// <see cref="EnrollmentOrchestrator.EventEmitter"/>; internalizing that property in PR #10
+    /// removes the reach automatically. Until then Program.cs is tracked via the plan's §2
+    /// inventory (B2–B6), not this test.
+    /// </para>
+    /// <para>
+    /// <b>Detection strategy</b>: reflection over fields, constructor parameters, method
+    /// parameters, and property return types. IL-level call-site detection is deliberately
+    /// avoided — structural dependencies are sufficient to guarantee a type has any way to
+    /// reach the emitter, and the reflection approach is cheap and dependency-free.
+    /// </para>
+    /// </summary>
+    public sealed class TelemetryEventEmitterCallersBaselineTests
+    {
+        private static readonly Type EmitterType = typeof(TelemetryEventEmitter);
+
+        /// <summary>
+        /// Types permitted to reach <see cref="TelemetryEventEmitter"/> at the end of the
+        /// single-rail refactor (PR #10 enforcement gate). Kept separate from the transitional
+        /// baseline so that a single-line diff in PR #10 switches enforcement on:
+        /// <c>Assert.Equal(PermittedCallers, ActualCallers)</c>.
+        /// </summary>
+        private static readonly HashSet<string> PermittedCallersAfterPr10 = new HashSet<string>(StringComparer.Ordinal)
+        {
+            "AutopilotMonitor.Agent.V2.Core.Telemetry.Events.EventTimelineEmitter",
+            "AutopilotMonitor.Agent.V2.Core.Telemetry.Events.BackPressureEventObserver",
+        };
+
+        /// <summary>
+        /// Current transitional baseline (PR #0). Every additional entry is a documented
+        /// bypass that a later PR will remove. Adding a new bypass requires updating this list
+        /// explicitly — the review signal is loud because tests fail.
+        /// </summary>
+        private static readonly HashSet<string> ExpectedCurrentBaseline = new HashSet<string>(StringComparer.Ordinal)
+        {
+            // Rail A — engine effect path. Permitted after PR #10.
+            "AutopilotMonitor.Agent.V2.Core.Telemetry.Events.EventTimelineEmitter",
+            // Meta exception — cannot route through the ingress without a cycle. Permitted after PR #10.
+            "AutopilotMonitor.Agent.V2.Core.Telemetry.Events.BackPressureEventObserver",
+            // Owns the field and exposes it via the public EventEmitter property (BuildTelemetryEventSink
+            // factory + Program.cs direct calls). Removed / internalized in PR #10.
+            "AutopilotMonitor.Agent.V2.Core.Orchestration.EnrollmentOrchestrator",
+            // Static RunAsync takes the emitter as a parameter to emit geo / timezone / ntp events.
+            // Migrated to ISignalIngressSink in PR #2.
+            "AutopilotMonitor.Agent.V2.Core.Runtime.StartupEnvironmentProbes",
+        };
+
+        [Fact]
+        public void V2Core_types_with_structural_dependency_on_TelemetryEventEmitter_match_current_baseline()
+        {
+            var actual = FindStructuralDependents(EmitterType.Assembly);
+
+            Assert.Equal(ExpectedCurrentBaseline.OrderBy(x => x), actual.OrderBy(x => x));
+        }
+
+        [Fact]
+        public void Current_baseline_is_a_superset_of_the_PR10_permitted_callers()
+        {
+            // Sanity guard: every permitted-after-PR10 caller must be present today, otherwise
+            // we've accidentally removed Rail A or the meta exception.
+            foreach (var permitted in PermittedCallersAfterPr10)
+            {
+                Assert.Contains(permitted, ExpectedCurrentBaseline);
+            }
+        }
+
+        private static ISet<string> FindStructuralDependents(Assembly assembly)
+        {
+            const BindingFlags AllMembers =
+                BindingFlags.Public | BindingFlags.NonPublic |
+                BindingFlags.Instance | BindingFlags.Static |
+                BindingFlags.DeclaredOnly;
+
+            var dependents = new HashSet<string>(StringComparer.Ordinal);
+
+            foreach (var type in assembly.GetTypes())
+            {
+                if (type == EmitterType) continue;
+                if (type.FullName == null) continue;
+                // Compiler-generated display classes / iterators show up with '<' in the name; skip.
+                if (type.FullName.Contains("<")) continue;
+
+                if (HasFieldOfType(type, EmitterType, AllMembers)
+                    || HasPropertyOfType(type, EmitterType, AllMembers)
+                    || HasMethodOrCtorParameterOfType(type, EmitterType, AllMembers))
+                {
+                    dependents.Add(type.FullName);
+                }
+            }
+
+            return dependents;
+        }
+
+        private static bool HasFieldOfType(Type type, Type target, BindingFlags flags) =>
+            type.GetFields(flags).Any(f => f.FieldType == target);
+
+        private static bool HasPropertyOfType(Type type, Type target, BindingFlags flags) =>
+            type.GetProperties(flags).Any(p => p.PropertyType == target);
+
+        private static bool HasMethodOrCtorParameterOfType(Type type, Type target, BindingFlags flags)
+        {
+            foreach (var method in type.GetMethods(flags))
+            {
+                if (method.GetParameters().Any(p => p.ParameterType == target)) return true;
+            }
+            foreach (var ctor in type.GetConstructors(flags))
+            {
+                if (ctor.GetParameters().Any(p => p.ParameterType == target)) return true;
+            }
+            return false;
+        }
+    }
+}