diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Ime/ImeLogTrackerOverwriteRewindTests.WriterBoundary.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Ime/ImeLogTrackerOverwriteRewindTests.WriterBoundary.cs
new file mode 100644
index 00000000..a815f120
--- /dev/null
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Ime/ImeLogTrackerOverwriteRewindTests.WriterBoundary.cs
@@ -0,0 +1,361 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime;
+using Xunit;
+
+namespace AutopilotMonitor.Agent.V2.Core.Tests.Monitoring.Ime
+{
+    /// <summary>
+    /// Session 756970cf: IME launched a Win32 detection executor and a platform-script executor 15 ms apart, and both
+    /// opened AgentExecutor.log at the same end-of-file offset. The platform executor's shorter start block overwrote
+    /// the detection executor's, whose identity line the tracker never saw; the detection's end block (exit 1 and its
+    /// stdout), written at its own position behind its own start block, then sat behind the PLATFORM start block, and
+    /// "the nearest preceding marker owns the line" handed another script's output and exit code to the platform
+    /// script. These tests pin the writer boundary: an entry that is not exactly one CMTrace record is where one
+    /// writer's bytes end and another's begin, and nothing behind it belongs to the invocation in front of it.
+    /// </summary>
+    public sealed partial class ImeLogTrackerOverwriteRewindTests
+    {
+        private const string RaceUserId = "00000000-0000-0000-0000-000000000000";
+        private const string RacePlatformId = "1d6f0a52-3c4e-4b7a-9e21-5f8c7d2b9a10";
+        private const string RaceDetectionAppId = "8b2e4c71-6a9d-4f03-b5e8-2c7a1d9f4e36";
+        private const string RaceFillerAppId = "5e1c2b7d-0a4f-4c8e-9d36-7b2f1e8a4c50";
+        private const string ImeDir = @"C:\Program Files (x86)\Microsoft Intune Management Extension";
+        private const string DetectionStdout = "VERBOSE: === Sample Suite Detection Started ===\r\nWARNING: === DETECTION FAILED: Sample Suite is not installed ===";
+        private const string PlatformStdout = "=== bootstrap loader started ===\r\nInstaller finished (exit code 0).";
+
+        private static string EntryAt(string time, string message)
+            => $"<![LOG[{message}]LOG]!><time=\"{time}\" date=\"9-10-2026\" component=\"AgentExecutor\" context=\"\" type=\"1\" thread=\"1\" file=\"\">\r\n";
+
+        /// <summary>The four lines every AgentExecutor invocation starts with — identical length for every executor.</summary>
+        private static string ExecutorBanner(string time)
+            => EntryAt(time, "ExecutorLog AgentExecutor gets invoked")
+            + EntryAt(time, "Creating command line parser, name delimiter is - and value separator is  .")
+            + EntryAt(time, "Getting Ordered Parameters")
+            + EntryAt(time, "Parsing Ordered Parameters.");
+
+        private static string ExecutorLaunch(string time, string scriptPath, string pid)
+            => EntryAt(time, "Prepare to run Powershell Script ..")
+            + EntryAt(time, $"cmd line for running powershell is -NoProfile -executionPolicy bypass -file  \"{scriptPath}\" ")
+            + EntryAt(time, "runAs32BitOn64 = False, so Disable Wow64FsRedirection")
+            + EntryAt(time, @"PowerShell path is C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe")
+            + EntryAt(time, $"[Executor] created powershell with process id {pid}");
+
+        private static string PlatformStartBlock(string time, string policyId, string pid)
+        {
+            var path = $@"{ImeDir}\Policies\Scripts\{RaceUserId}_{policyId}.ps1";
+            var results = $@"{ImeDir}\Policies\Results\{RaceUserId}_{policyId}";
+            return ExecutorBanner(time)
+                + EntryAt(time, $"Adding argument powershell with value {path} to the named argument list.")
+                + EntryAt(time, "Powershell option gets invoked")
+                + EntryAt(time, path)
+                + EntryAt(time, results + ".output")
+                + EntryAt(time, results + ".error")
+                + EntryAt(time, results + ".timeout")
+                + ExecutorLaunch(time, path, pid);
+        }
+
+        private static string DetectionStartBlock(string time, string appId, string pid)
+        {
+            var path = $@"{ImeDir}\Content\DetectionScripts\{appId}_2.ps1";
+            return ExecutorBanner(time)
+                + EntryAt(time, $"Adding argument powershellDetection with value {path} to the named argument list.")
+                + EntryAt(time, "PowershellDetection option gets invoked")
+                + EntryAt(time, path)
+                + EntryAt(time, path + "quotedResultFilePath.txt")
+                + EntryAt(time, path + "quotedErrorFilePath.txt")
+                + EntryAt(time, path + "quotedTimeoutFilePath.txt")
+                + EntryAt(time, path + "quotedExitCodeFilePath.txt")
+                + ExecutorLaunch(time, path, pid);
+        }
+
+        private static string ExecutorEndBlock(string time, int exitCode, string stdout)
+            => EntryAt(time, $"Powershell exit code is {exitCode}")
+            + EntryAt(time, $"length of out={stdout.Length}")
+            + EntryAt(time, "length of error=0")
+            + EntryAt(time, "error from script =")
+            + EntryAt(time, exitCode == 0 ? "Powershell script is successfully executed." : "Powershell script is failed to execute")
+            + EntryAt(time, $"write output done. output = {stdout}, error = ")
+            + EntryAt(time, "Revert Wow64FsRedirection")
+            + EntryAt(time, "Agent executor completed.");
+
+        private static string PlatformResultLine(string policyId)
+            => $"[PowerShell] User Id = {RaceUserId}, Policy id = {policyId}, policy result = Success";
+
+        /// <summary>The file offsets at which the entries of an ASCII <paramref name="block"/> start when it is written at <paramref name="at"/>.</summary>
+        private static HashSet<long> EntryStarts(string block, long at)
+        {
+            Assert.True(block.All(c => c < 128), "offset arithmetic assumes ASCII test content");
+            var starts = new HashSet<long>();
+            for (var i = block.IndexOf("<![LOG[", StringComparison.Ordinal); i >= 0; i = block.IndexOf("<![LOG[", i + 1, StringComparison.Ordinal))
+                starts.Add(at + i);
+            return starts;
+        }
+
+        [Fact]
+        public async Task Executor_that_opened_at_the_same_offset_never_lends_its_end_block_to_the_platform_script()
+        {
+            using var h = new Harness("AgentExecutor.log", ScriptPatterns());
+
+            // An earlier, finished detection run: the race starts mid-file like in the field log.
+            h.Append(DetectionStartBlock("12:00:00.0000000", RaceFillerAppId, "1548") + ExecutorEndBlock("12:00:00.5000000", 0, "detected"));
+            await h.Pass();
+            var x = h.Length;
+
+            // Detection executor C and platform executor D open the file at the same end x. C writes first; the tracker
+            // reads C's banner, then D writes its own start block over C's.
+            var cStart = DetectionStartBlock("12:00:01.0000000", RaceDetectionAppId, "6416");
+            var dStart = PlatformStartBlock("12:00:01.2000000", RacePlatformId, "2524");
+            var cHead = cStart.Substring(0, cStart.IndexOf("<![LOG[Getting Ordered Parameters", StringComparison.Ordinal));
+            h.Append(cHead);
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+            h.Append(cStart.Substring(cHead.Length));
+            h.Overwrite(x, dStart);
+
+            // The field geometry: D's start block is shorter and ends inside one of C's lines, so the tail of that line
+            // sits between D's start block and C's remaining bytes.
+            Assert.True(dStart.Length < cStart.Length);
+            Assert.DoesNotContain(x + dStart.Length, EntryStarts(cStart, x));
+            h.Now = h.Now.AddMilliseconds(150);
+            await h.Pass();
+            Assert.True(h.Health.OverwriteRewinds >= 1);
+
+            // C ends: its end block lands at its own position, right behind its own (overwritten) start block.
+            Assert.Equal(x + cStart.Length, h.Length);
+            var cEnd = ExecutorEndBlock("12:00:07.0000000", 1, DetectionStdout);
+            h.Append(cEnd);
+            h.Now = h.Now.AddSeconds(6);
+            await h.Pass();
+
+            // IME's result for D reaches the tracker before D's own end block: the completion must wait for it.
+            h.Tracker.ProcessLogMessageForTest(PlatformResultLine(RacePlatformId), sourceFileName: "IntuneManagementExtension.log");
+            Assert.Empty(h.Completed);
+
+            // D ends: its end block lands at ITS position, over the fragment and C's bytes; C's last line survives.
+            var dEnd = ExecutorEndBlock("12:00:09.5000000", 0, PlatformStdout);
+            Assert.True(dEnd.Length < cStart.Length - dStart.Length + cEnd.Length);
+            h.Overwrite(x + dStart.Length, dEnd);
+            h.Now = h.Now.AddMilliseconds(130);
+            await h.Pass();
+            h.Tracker.FlushPendingPlatformScriptResults(h.Now);
+
+            var script = Assert.Single(h.Completed);
+            Assert.Equal(RacePlatformId, script.PolicyId);
+            Assert.Equal("Success", script.Result);
+            Assert.Equal(0, script.ExitCode);
+            Assert.Equal(PlatformStdout.Replace("\r\n", "\n"), script.Stdout);
+            Assert.DoesNotContain(h.Completed, s => (s.Stdout ?? string.Empty).Contains("Detection"));
+        }
+
+        /// <summary>
+        /// The mirror image: a foreign executor whose stream position lies inside the platform start block (it opened
+        /// at the same end with a shorter start block) writes its end block there. Its first line merges with the head of
+        /// a platform line — cut inside the message or inside the trailer, which the parser would otherwise read up to
+        /// the foreign trailer — and its output line follows without any marker in between.
+        /// </summary>
+        [Theory]
+        [InlineData(15)]
+        [InlineData(-30)]
+        public async Task Foreign_end_block_merged_into_the_platform_start_block_never_reaches_the_platform_script(int cut)
+        {
+            using var h = new Harness("AgentExecutor.log", ScriptPatterns());
+            h.Append(DetectionStartBlock("12:00:00.0000000", RaceFillerAppId, "1548") + ExecutorEndBlock("12:00:00.5000000", 0, "detected"));
+            await h.Pass();
+            var x = h.Length;
+
+            var dStart = PlatformStartBlock("12:00:01.0000000", RacePlatformId, "2524");
+            h.Append(dStart);
+            await h.Pass();
+
+            // The foreign end block starts inside the line after D's argument line.
+            var lineAfterArgument = x + dStart.IndexOf("<![LOG[Powershell option gets invoked", StringComparison.Ordinal);
+            var lineLength = EntryAt("12:00:01.0000000", "Powershell option gets invoked").Length;
+            var at = lineAfterArgument + (cut > 0 ? cut : lineLength + cut);
+            var foreignEnd = ExecutorEndBlock("12:00:03.0000000", 1, "foreign output");
+            Assert.True(at + foreignEnd.Length < x + dStart.Length, "the foreign block must end inside D's start block");
+            h.Overwrite(at, foreignEnd);
+            h.Tracker.RequestOverwriteCheckForTest();
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+
+            h.Tracker.ProcessLogMessageForTest(PlatformResultLine(RacePlatformId), sourceFileName: "IntuneManagementExtension.log");
+            h.Now = h.Now.Add(ImeLogTracker.PlatformScriptEndBlockGrace);
+            h.Tracker.FlushPendingPlatformScriptResults(h.Now);
+
+            // No owner is provable behind the cut: the completion goes out without end-block data, never with the foreign one.
+            var script = Assert.Single(h.Completed);
+            Assert.Equal("Success", script.Result);
+            Assert.Null(script.ExitCode);
+            Assert.Null(script.Stdout);
+        }
+
+        [Fact]
+        public async Task Entry_read_unchanged_after_a_rewind_keeps_its_platform_marker()
+        {
+            const string platformId = "2b7d9e41-8c3a-4f60-a5d2-9e1b7c4f3a08";
+            using var h = new Harness("AgentExecutor.log", ScriptPatterns());
+
+            // Detection W waits for its script; detection X runs completely behind it; platform F starts behind X.
+            var wStart = DetectionStartBlock("12:00:00.0000000", RaceFillerAppId, "1111");
+            var xRun = DetectionStartBlock("12:00:00.2000000", RaceDetectionAppId, "2222") + ExecutorEndBlock("12:00:00.4000000", 0, "x detected");
+            h.Append(wStart + xRun + PlatformStartBlock("12:00:01.0000000", platformId, "3333"));
+            await h.Pass();
+
+            // W ends at its own position, over the head of X's run; F's start block keeps its bytes and offset.
+            var wEnd = ExecutorEndBlock("12:00:02.0000000", 0, "w detected");
+            Assert.True(wEnd.Length < xRun.Length);
+            h.Overwrite(wStart.Length, wEnd);
+            h.Tracker.RequestOverwriteCheckForTest();
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+            Assert.Equal(1, h.Health.OverwriteRewinds);
+
+            // F's end block lands behind its start block: still F's, because F's marker survived with its bytes.
+            h.Append(ExecutorEndBlock("12:00:05.0000000", 7, "Hello from F"));
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+            h.Tracker.ProcessLogMessageForTest(PlatformResultLine(platformId), sourceFileName: "IntuneManagementExtension.log");
+
+            var script = Assert.Single(h.Completed);
+            Assert.Equal(platformId, script.PolicyId);
+            Assert.Equal(7, script.ExitCode);
+            Assert.Equal("Hello from F", script.Stdout);
+        }
+
+        [Fact]
+        public async Task Writer_boundary_read_unchanged_after_a_rewind_still_closes_the_platform_invocation()
+        {
+            using var h = new Harness("AgentExecutor.log", ScriptPatterns());
+
+            // Detection Q waits for its script while detection R runs completely behind it.
+            var qStart = DetectionStartBlock("12:00:00.0000000", RaceFillerAppId, "1111");
+            var rRun = DetectionStartBlock("12:00:00.2000000", "6c3f8a20-1d5e-4b97-8f4a-0e2d6b9c7a13", "2222") + ExecutorEndBlock("12:00:00.4000000", 0, "r detected");
+            h.Append(qStart + rRun);
+            await h.Pass();
+            var x = h.Length;
+
+            // The race of the field case behind them: the boundary closes D.
+            var cStart = DetectionStartBlock("12:00:01.0000000", RaceDetectionAppId, "6416");
+            var dStart = PlatformStartBlock("12:00:01.2000000", RacePlatformId, "2524");
+            h.Append(cStart);
+            h.Overwrite(x, dStart);
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+
+            // Q ends at its own position, over R's run: the rewind starts in front of the race, whose bytes read unchanged.
+            var qEnd = ExecutorEndBlock("12:00:02.0000000", 0, "q detected");
+            Assert.True(qEnd.Length < rRun.Length);
+            h.Overwrite(qStart.Length, qEnd);
+            h.Tracker.RequestOverwriteCheckForTest();
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+
+            // C's end block behind the boundary stays unowned; D's own end block completes D.
+            var cEnd = ExecutorEndBlock("12:00:07.0000000", 1, DetectionStdout);
+            h.Append(cEnd);
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+            h.Tracker.ProcessLogMessageForTest(PlatformResultLine(RacePlatformId), sourceFileName: "IntuneManagementExtension.log");
+            Assert.Empty(h.Completed);
+
+            h.Overwrite(x + dStart.Length, ExecutorEndBlock("12:00:09.5000000", 0, PlatformStdout));
+            h.Now = h.Now.AddMilliseconds(130);
+            await h.Pass();
+            h.Tracker.FlushPendingPlatformScriptResults(h.Now);
+
+            var script = Assert.Single(h.Completed);
+            Assert.Equal(0, script.ExitCode);
+            Assert.Equal(PlatformStdout.Replace("\r\n", "\n"), script.Stdout);
+        }
+
+        [Fact]
+        public async Task Raw_text_in_the_executor_log_is_never_matched_and_closes_the_platform_invocation()
+        {
+            using var h = new Harness("AgentExecutor.log", ScriptPatterns());
+            h.Append(PlatformStartBlock("12:00:00.0000000", RacePlatformId, "2524"));
+            await h.Pass();
+
+            // The tail of a cut line that happens to read like an exit line, then a foreign end block.
+            h.Append("Powershell exit code is 5\r\n" + ExecutorEndBlock("12:00:02.0000000", 6, "foreign output"));
+            // A fragment right at the bookmark stops the first pass for a check; the second one reads it.
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+
+            h.Tracker.ProcessLogMessageForTest(PlatformResultLine(RacePlatformId), sourceFileName: "IntuneManagementExtension.log");
+            h.Now = h.Now.Add(ImeLogTracker.PlatformScriptEndBlockGrace);
+            h.Tracker.FlushPendingPlatformScriptResults(h.Now);
+
+            var script = Assert.Single(h.Completed);
+            Assert.Null(script.ExitCode);
+            Assert.Null(script.Stdout);
+        }
+
+        [Fact]
+        public async Task Fragment_in_the_ime_log_does_not_close_the_platform_run_context()
+        {
+            using var h = new Harness("IntuneManagementExtension.log", ScriptPatterns());
+            // In the IME log the service writes the platform marker and the context line itself; the fragment in
+            // between is the tail of an executor's telemetry line and separates nothing.
+            h.Append(Entry(@"Script file C:\Program Files (x86)\Microsoft Intune Management Extension\Policies\Scripts\" + RaceUserId + "_" + RacePlatformId + ".ps1 is generated.", "17")
+                + "ing mananger...]LOG]!><time=\"12:00:00.0000000\" date=\"9-10-2026\" component=\"AgentExecutor\" context=\"\" type=\"1\" thread=\"1\" file=\"\">\r\n"
+                + Entry("Launch powershell executor in user session", "17"));
+            await h.Pass();
+
+            h.Tracker.ProcessLogMessageForTest(PlatformResultLine(RacePlatformId));
+            h.Now = h.Now.Add(ImeLogTracker.PlatformScriptEndBlockGrace);
+            h.Tracker.FlushPendingPlatformScriptResults(h.Now);
+
+            var script = Assert.Single(h.Completed);
+            Assert.Equal("User", script.RunContext);
+        }
+
+        [Fact]
+        public async Task Cut_multi_line_output_adds_one_boundary_not_one_per_line()
+        {
+            using var h = new Harness("AgentExecutor.log", ScriptPatterns());
+            h.Append(PlatformStartBlock("12:00:00.0000000", RacePlatformId, "2524"));
+            await h.Pass();
+            var markersBefore = h.Tracker.InvocationMarkerCountForTest("AgentExecutor.log");
+
+            var lines = string.Concat(Enumerable.Range(1, 600).Select(i => $"orphaned output line {i}\r\n"));
+            h.Append(lines);
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+            h.Now = h.Now.AddMilliseconds(100);
+            await h.Pass();
+
+            Assert.Equal(markersBefore + 1, h.Tracker.InvocationMarkerCountForTest("AgentExecutor.log"));
+        }
+
+        [Theory]
+        [InlineData("<![LOG[Powershell exit code is 0]LOG]!><time=\"12:00:00.0000000\" date=\"9-10-2026\" component=\"AgentExecutor\" context=\"\" type=\"1\" thread=\"1\" file=\"\">", true)]
+        [InlineData("<![LOG[write output done. output = line one\nline two, error = ]LOG]!><time=\"12:00:00.0000000\" date=\"9-10-2026\" component=\"AgentExecutor\" context=\"\" type=\"1\" thread=\"1\" file=\"\">", true)]
+        [InlineData("\uFEFF<![LOG[ExecutorLog AgentExecutor gets invoked]LOG]!><time=\"12:00:00.0000000\" date=\"9-10-2026\" component=\"AgentExecutor\" context=\"\" type=\"1\" thread=\"1\" file=\"\">", true)]
+        [InlineData("t code is 3]LOG]!><time=\"12:00:00.0000000\" date=\"9-10-2026\" component=\"AgentExecutor\" context=\"\" type=\"1\" thread=\"1\" file=\"\">", false)]
+        [InlineData("", false)]
+        [InlineData("<![LOG[Powe<![LOG[Powershell exit code is 1]LOG]!><time=\"12:00:00.0000000\" date=\"9-10-2026\" component=\"AgentExecutor\" context=\"\" type=\"1\" thread=\"1\" file=\"\">", false)]
+        [InlineData("<![LOG[Powershell option gets invoked]LOG]!><time=\"12:00:00.0000000\" da<![LOG[Powershell exit code is 1]LOG]!><time=\"12:00:01.0000000\" date=\"9-10-2026\" component=\"AgentExecutor\" context=\"\" type=\"1\" thread=\"1\" file=\"\">", false)]
+        [InlineData("<![LOG[write output done. output = line one\nline<![LOG[Agent executor completed.]LOG]!><time=\"12:00:00.0000000\" date=\"9-10-2026\" component=\"AgentExecutor\" context=\"\" type=\"1\" thread=\"1\" file=\"\">", false)]
+        public void Single_cmtrace_record_is_told_apart_from_the_cut_of_two_writers(string text, bool expected)
+        {
+            Assert.Equal(expected, ImeLogTracker.IsSingleCmTraceRecord(text));
+        }
+
+        [Theory]
+        [InlineData("AgentExecutor.log", true)]
+        [InlineData("AgentExecutor-20261003-233348.log", true)]
+        [InlineData("IntuneManagementExtension.log", false)]
+        [InlineData("IntuneManagementExtension-20261003-233348.log", false)]
+        [InlineData("HealthScripts.log", false)]
+        [InlineData("AppWorkload.log", false)]
+        public void Writer_boundaries_apply_to_the_executor_log_live_and_rotated(string fileName, bool expected)
+        {
+            Assert.Equal(expected, ImeLogTracker.IsWriterBoundaryLogFile(fileName));
+        }
+    }
+}
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Ime/ImeLogTrackerOverwriteRewindTests.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Ime/ImeLogTrackerOverwriteRewindTests.cs
index 2e431067..585eb830 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Ime/ImeLogTrackerOverwriteRewindTests.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core.Tests/Monitoring/Ime/ImeLogTrackerOverwriteRewindTests.cs
@@ -25,7 +25,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Tests.Monitoring.Ime
     /// contract: unchanged bytes never rewind, changed bytes are processed exactly once, and the
     /// executor lines a rewind uncovers belong to the invocation that owns their file position.
     /// </summary>
-    public sealed class ImeLogTrackerOverwriteRewindTests
+    public sealed partial class ImeLogTrackerOverwriteRewindTests
     {
         private static readonly DateTime T0 = new DateTime(2026, 9, 10, 19, 30, 0, DateTimeKind.Utc);
 
@@ -42,7 +42,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Tests.Monitoring.Ime
         private static readonly string[] ScriptPatternIds =
         {
             "PS-AGENT-INVOCATION", "PS-AGENT-ARG", "PS-AGENT-SCRIPT-START", "PS-AGENT-EXITCODE",
-            "PS-AGENT-OUTPUT", "PS-AGENT-COMPLETED", "PS-SCRIPT-GENERATED", "PS-SCRIPT-CONTEXT", "PS-SCRIPT-RESULT",
+            "PS-AGENT-OUTPUT", "PS-AGENT-ERROR", "PS-AGENT-COMPLETED", "PS-SCRIPT-GENERATED", "PS-SCRIPT-CONTEXT", "PS-SCRIPT-RESULT",
         };
 
         /// <summary>The shipped pattern JSON — the same source combine.js embeds — so the contract is the real one.</summary>
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.Handlers.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.Handlers.cs
index 351b70b9..29fdb0ff 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.Handlers.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.Handlers.cs
@@ -439,6 +439,8 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
                 ApplyExitCode(script, exitCode, LastMatchedLogTimestamp ?? UtcNowProvider(), CaptureLastMatchedProvenance());
             else if (ownerPolicyId != null)
                 _logger.Debug($"ImeLogTracker: exit code {exitCode} belongs to platform script {ownerPolicyId}, whose completion was already emitted — dropped");
+            else
+                LogLineBehindWriterBoundary($"exit code {exitCode}");
             // An exit code means the executor just wrote its end block and IME is about to
             // write the result — both land at a stale stream position when another process
             // appended meanwhile. Check the ledgers on the next pass.
@@ -465,7 +467,11 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
         {
             var outputType = parameters != null && parameters.TryGetValue("outputType", out var ot) ? ot : null;
             var script = GetCurrentScriptForLineUpdate(parameters);
-            if (script == null) return;
+            if (script == null)
+            {
+                LogLineBehindWriterBoundary($"script output ({outputType ?? "combined"})");
+                return;
+            }
 
             // PS-AGENT-OUTPUT captures both stdout and stderr in one pattern
             var output = match.Groups["output"]?.Value;
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.LogProcessing.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.LogProcessing.cs
index ce7fe183..5740d40c 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.LogProcessing.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.LogProcessing.cs
@@ -123,16 +123,18 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
             var ledger = IsMultiWriterLogFile(fileName) ? GetLedger(fileName) : null;
 
             // Set by a rewind: entries that still read unchanged behind the old bookmark are
-            // skipped, and nothing below the old bookmark is fresh or a calibration anchor.
-            HashSet<LedgerEntry> rewoundEntries = null;
+            // skipped (their invocation markers are given back), and nothing below the old
+            // bookmark is fresh or a calibration anchor.
+            RewindState rewind = null;
             long oldBookmark = -1;
+            var writerBoundaries = IsWriterBoundaryLogFile(fileName);
 
             if (ledger != null)
             {
                 var rewindTo = await PrepareLedgerAsync(filePath, fileName, ledger, startPos, passNowUtc, token);
                 if (rewindTo >= 0)
                 {
-                    rewoundEntries = ApplyRewind(filePath, fileName, ledger, rewindTo, startPos);
+                    rewind = ApplyRewind(filePath, fileName, ledger, rewindTo, startPos);
                     oldBookmark = startPos;
                     startPos = rewindTo;
                 }
@@ -164,7 +166,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
             {
                 // Guard zone: the file grew and is open anyway — re-check the entries just behind
                 // the bookmark, where a stale writer's block lands when it is short.
-                if (ledger != null && rewoundEntries == null && ledger.Entries.Count > 0)
+                if (ledger != null && rewind == null && ledger.Entries.Count > 0)
                 {
                     var guardFrom = ledger.OffsetOfEntryAtOrAfter(startPos - OverwriteGuardBytes);
                     if (guardFrom >= 0 && guardFrom < startPos)
@@ -178,7 +180,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
                             _verifiedBytes += startPos - ledger.StartOffset;
                             _verifyPasses++;
                             if (earliest >= 0) divergence = earliest;
-                            rewoundEntries = ApplyRewind(filePath, fileName, ledger, divergence, startPos);
+                            rewind = ApplyRewind(filePath, fileName, ledger, divergence, startPos);
                             oldBookmark = startPos;
                             startPos = divergence;
                         }
@@ -259,7 +261,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
                         // A fragment right at the bookmark of a multi-writer file (the previous
                         // entry ended exactly here, this one does not open an entry) is the tail of
                         // a block a stale writer laid over already-read bytes: verify before reading on.
-                        if (ledger != null && rewoundEntries == null && entry.Offset == ledger.EndOffset
+                        if (ledger != null && rewind == null && entry.Offset == ledger.EndOffset
                             && ledger.LastFragmentOffset != entry.Offset && !entry.Text.StartsWith("<![LOG["))
                         {
                             ledger.VerifyRequested = true;
@@ -270,8 +272,20 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
                     }
 
                     if (ledger != null) ledger.Record(entry);
-                    if (rewoundEntries != null && rewoundEntries.Contains(new LedgerEntry { Offset = entry.Offset, Hash = entry.Hash }))
-                        continue; // unchanged behind the old bookmark — processed before the rewind
+                    var unchanged = rewind != null && rewind.IsUnchanged(entry);
+                    if (unchanged) RestoreInvocationMarkers(rewind, entry.Offset);
+
+                    // Writer boundary (see ImeLogTracker.Overwrite.cs): an AgentExecutor.log entry that is
+                    // not exactly one CMTrace record ends the bytes of the executor in front of it. Never
+                    // matched — its text is the cut of two writers. Evaluated for unchanged entries too:
+                    // what owns the position in front of them may have changed with the rewind.
+                    if (writerBoundaries && !IsSingleCmTraceRecord(entry.Text))
+                    {
+                        CloseAtWriterBoundary(fileName, entry.Offset, entry.Text);
+                        continue;
+                    }
+
+                    if (unchanged) continue; // unchanged behind the old bookmark — processed before the rewind
 
                     _currentPassLinesAreFresh = passLinesAreFresh && entry.Offset >= oldBookmark;
 
diff --git a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.Overwrite.cs b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.Overwrite.cs
index ae053c76..f6ce8166 100644
--- a/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.Overwrite.cs
+++ b/src/Agent/AutopilotMonitor.Agent.V2.Core/Monitoring/Enrollment/Ime/ImeLogTracker.Overwrite.cs
@@ -293,13 +293,40 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
             }
         }
 
-        /// <summary>Moves the bookmark back to the first changed entry; returns the entries to skip if they still read unchanged behind it.</summary>
-        private HashSet<LedgerEntry> ApplyRewind(string filePath, string fileName, FileLedger ledger, long rewindTo, long bookmark)
+        /// <summary>
+        /// What one rewind pass carries: the entries to skip if they still read unchanged behind the rewind point, and
+        /// the invocation markers set aside there until their entries prove unchanged. Pass-local by design — whatever
+        /// is not given back dies with the pass on every exit path.
+        /// </summary>
+        private sealed class RewindState
+        {
+            public RewindState(string fileName, HashSet<LedgerEntry> unchanged, List<InvocationMarker> markers, InvocationMarker lastPlatformMarker)
+            {
+                FileName = fileName;
+                Unchanged = unchanged;
+                Markers = markers;
+                LastPlatformMarker = lastPlatformMarker;
+            }
+
+            public string FileName { get; }
+            public HashSet<LedgerEntry> Unchanged { get; }
+            /// <summary>Set aside at the rewind, ascending by offset.</summary>
+            public List<InvocationMarker> Markers { get; }
+            /// <summary>The tracker-wide last platform marker, when it was among the set-aside ones.</summary>
+            public InvocationMarker LastPlatformMarker { get; }
+            public int Next { get; set; }
+
+            public bool IsUnchanged(AssembledEntry entry) => Unchanged.Contains(new LedgerEntry { Offset = entry.Offset, Hash = entry.Hash });
+        }
+
+        /// <summary>Moves the bookmark back to the first changed entry; returns what the re-read needs to skip and to give back.</summary>
+        private RewindState ApplyRewind(string filePath, string fileName, FileLedger ledger, long rewindTo, long bookmark)
         {
             var removed = ledger.TruncateFrom(rewindTo);
             _positionTracker.SetPosition(filePath, rewindTo);
             _heldTails.Remove(filePath);
-            InvalidateInvocationMarkersFrom(fileName, rewindTo);
+            var lastPlatformMarker = _lastPlatformMarker;
+            var markers = TakeInvocationMarkersFrom(fileName, rewindTo, out var tookLastPlatformMarker);
             _overwriteRewinds++;
             _overwriteBytesReprocessed += bookmark - rewindTo;
 
@@ -314,7 +341,7 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
             {
                 _logger.Debug(message);
             }
-            return removed;
+            return new RewindState(fileName, removed, markers, tookLastPlatformMarker ? lastPlatformMarker : null);
         }
 
         private long RetentionFloor(string fileName, long bookmark)
@@ -331,20 +358,35 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
         // -----------------------------------------------------------------------
         //
         // AgentExecutor.log carries "Powershell exit code is N" / "write output done" without a
-        // policy id. Their owner is decided by FILE POSITION, not by the order lines were read:
-        // an executor writes its end block at its own stream position, i.e. directly after its
-        // own start block in the final bytes, so the nearest preceding invocation marker names
-        // it — and stays right after a rewind re-reads that region. A marker is a platform start
-        // (policy id), some other invocation (detection, remediation, requirement: null) or a
-        // close ("gets invoked" banner, "Agent executor completed").
+        // policy id. Their owner is decided by FILE POSITION: the nearest preceding marker — a
+        // platform start (policy id), some other invocation (detection, remediation, requirement:
+        // null), a close ("gets invoked" banner, "Agent executor completed") or a writer boundary.
+        //
+        // Every executor writes its lines contiguously from its own stream position, so its end
+        // block follows its own start block — but that start block may be gone. Two executors that
+        // open the file at the same end write their start blocks over each other, and the end block
+        // of the one that lost then sits behind the OTHER executor's start block (session 756970cf:
+        // a detection script's exit code and output on a platform script). Where one writer's bytes
+        // meet another's, the cut leaves an entry that is not exactly one CMTrace record — a
+        // fragment, a merged line or an empty line — unless the line boundaries of both writers
+        // coincide byte-exactly. That writer boundary closes the platform invocation in front of it.
+        // AgentExecutor.log only: in the IME log the service writes the markers and the lines they
+        // own itself, and its fragments are executor telemetry lines.
+        //
+        // A marker lives exactly as long as the bytes of its entry: a rewind sets the markers from
+        // the rewind point on aside, and an entry that reads unchanged gets its markers back.
 
         private sealed class InvocationMarker
         {
             public long Offset;
             public string PolicyId;
             public bool IsClose;
+            /// <summary>Set on a writer boundary: the platform invocation it closed.</summary>
+            public string ClosedPolicyId;
         }
 
+        private const string ExecutorLogFileName = "AgentExecutor.log";
+
         private readonly Dictionary<string, List<InvocationMarker>> _invocationMarkers =
             new Dictionary<string, List<InvocationMarker>>(StringComparer.OrdinalIgnoreCase);
         private InvocationMarker _lastPlatformMarker;
@@ -354,22 +396,59 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
         private readonly HashSet<string> _platformMarkerFiles = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
         private long _testEntryOrdinal;
 
-        private void RecordInvocationMarker(string policyId, bool isClose)
+        /// <summary>
+        /// The executor log, live or rotated (<c>AgentExecutor-yyyyMMdd-HHmmss.log</c>): its invocations are one process
+        /// each, so a writer boundary ends an invocation — in the final bytes of a rotation as much as in the live file.
+        /// </summary>
+        internal static bool IsWriterBoundaryLogFile(string fileName)
+            => string.Equals(fileName, ExecutorLogFileName, StringComparison.OrdinalIgnoreCase)
+            || (fileName != null
+                && fileName.StartsWith("AgentExecutor-", StringComparison.OrdinalIgnoreCase)
+                && fileName.EndsWith(".log", StringComparison.OrdinalIgnoreCase));
+
+        /// <summary>
+        /// True when the entry is exactly one CMTrace record: it opens with <c>&lt;![LOG[</c> (culture-sensitive like
+        /// <c>CmTraceLogParser.TryParseLine</c>, so a BOM is ignorable) and holds no second one — the parser takes the
+        /// message up to the LAST trailer, so a line cut anywhere, its trailer included, would swallow the record
+        /// written over it. An empty entry is the terminator of a cut line. A script whose own output contains the
+        /// open tag loses that output line: the bytes cannot tell it from a merged line.
+        /// </summary>
+        internal static bool IsSingleCmTraceRecord(string text)
+        {
+            if (string.IsNullOrEmpty(text) || !text.StartsWith(LogOpenTag)) return false;
+            var first = text.IndexOf(LogOpenTag, StringComparison.Ordinal);
+            return first >= 0 && text.IndexOf(LogOpenTag, first + LogOpenTag.Length, StringComparison.Ordinal) < 0;
+        }
+
+        private List<InvocationMarker> GetOrCreateMarkerList(string file)
         {
-            if (_currentEntryOffset < 0) return;
-            var file = _currentSourceFileName ?? TestSourceFileName;
             List<InvocationMarker> list;
             if (!_invocationMarkers.TryGetValue(file, out list))
             {
                 list = new List<InvocationMarker>();
                 _invocationMarkers[file] = list;
             }
+            return list;
+        }
+
+        private static void AppendInvocationMarker(List<InvocationMarker> list, InvocationMarker marker)
+        {
+            if (list.Count >= MaxInvocationMarkersPerFile) list.RemoveAt(0);
+            list.Add(marker);
+        }
+
+        private void RecordInvocationMarker(string policyId, bool isClose)
+        {
+            if (_currentEntryOffset < 0) return;
+            var file = _currentSourceFileName ?? TestSourceFileName;
+            var list = GetOrCreateMarkerList(file);
 
             if (list.Count > 0 && list[list.Count - 1].Offset == _currentEntryOffset)
             {
                 // Two patterns on one line: the platform start outranks the generic argument line.
+                // A writer boundary is never upgraded.
                 var last = list[list.Count - 1];
-                if (!isClose && policyId != null)
+                if (!isClose && policyId != null && last.ClosedPolicyId == null)
                 {
                     last.PolicyId = policyId;
                     last.IsClose = false;
@@ -379,9 +458,8 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
                 return;
             }
 
-            if (list.Count >= MaxInvocationMarkersPerFile) list.RemoveAt(0);
             var marker = new InvocationMarker { Offset = _currentEntryOffset, PolicyId = policyId, IsClose = isClose };
-            list.Add(marker);
+            AppendInvocationMarker(list, marker);
             if (!isClose && policyId != null)
             {
                 _lastPlatformMarker = marker;
@@ -390,21 +468,34 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
         }
 
         /// <summary>
-        /// The pending platform script that owns the entry being processed, or null.
-        /// <paramref name="ownerPolicyId"/> names the owning platform script even when its slot is
-        /// gone (completion already emitted); null when no platform invocation owns the entry.
+        /// An entry of <paramref name="fileName"/> at <paramref name="offset"/> that is not exactly one CMTrace record:
+        /// the bytes behind it were written by another process than the bytes in front of it. Closes the platform
+        /// invocation that owns the position; records nothing when none is open there (a cut multi-line output yields
+        /// one fragment per line). Idempotent at the same offset.
         /// </summary>
-        private ScriptExecutionState ResolvePlatformScriptForCurrentEntry(out string ownerPolicyId)
+        private void CloseAtWriterBoundary(string fileName, long offset, string text)
+        {
+            var owner = FindOwningMarker(fileName, offset);
+            if (owner == null || owner.IsClose || owner.PolicyId == null) return;
+
+            var list = GetOrCreateMarkerList(fileName);
+            if (list.Count > 0 && list[list.Count - 1].Offset >= offset) return;
+            AppendInvocationMarker(list, new InvocationMarker { Offset = offset, IsClose = true, ClosedPolicyId = owner.PolicyId });
+
+            var kind = string.IsNullOrEmpty(text) ? "empty line" : text.StartsWith(LogOpenTag) ? "merged line" : "fragment";
+            _logger.Debug($"ImeLogTracker: writer boundary in {fileName} at offset {offset} ({kind}, {text?.Length ?? 0} chars) closes platform script {owner.PolicyId} (opened at {owner.Offset}) — the bytes behind it belong to another executor");
+        }
+
+        /// <summary>The marker that owns <paramref name="offset"/> in <paramref name="file"/>, or null.</summary>
+        private InvocationMarker FindOwningMarker(string file, long offset)
         {
-            ownerPolicyId = null;
-            var file = _currentSourceFileName ?? TestSourceFileName;
             InvocationMarker marker = null;
             List<InvocationMarker> list = null;
-            if (_currentEntryOffset >= 0 && _invocationMarkers.TryGetValue(file, out list))
+            if (offset >= 0 && _invocationMarkers.TryGetValue(file, out list))
             {
                 for (var i = list.Count - 1; i >= 0; i--)
                 {
-                    if (list[i].Offset <= _currentEntryOffset)
+                    if (list[i].Offset <= offset)
                     {
                         marker = list[i];
                         break;
@@ -420,6 +511,18 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
             // (session 24dc69d1: the health-script worker's exit line pre-filled a platform slot's
             // exit code, its launch line the slot's context).
             if (marker == null && (list == null || list.Count == 0) && _platformMarkerFiles.Contains(file)) marker = _lastPlatformMarker;
+            return marker;
+        }
+
+        /// <summary>
+        /// The pending platform script that owns the entry being processed, or null.
+        /// <paramref name="ownerPolicyId"/> names the owning platform script even when its slot is
+        /// gone (completion already emitted); null when no platform invocation owns the entry.
+        /// </summary>
+        private ScriptExecutionState ResolvePlatformScriptForCurrentEntry(out string ownerPolicyId)
+        {
+            ownerPolicyId = null;
+            var marker = FindOwningMarker(_currentSourceFileName ?? TestSourceFileName, _currentEntryOffset);
             if (marker == null || marker.IsClose || marker.PolicyId == null) return null;
 
             ownerPolicyId = marker.PolicyId;
@@ -427,17 +530,32 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
             return _pendingPlatformScripts.TryGetValue(marker.PolicyId, out state) ? state : null;
         }
 
-        private void InvalidateInvocationMarkersFrom(string fileName, long offset)
+        /// <summary>Debug trace for an executor line that a writer boundary kept away from a platform script.</summary>
+        private void LogLineBehindWriterBoundary(string what)
         {
+            var marker = FindOwningMarker(_currentSourceFileName ?? TestSourceFileName, _currentEntryOffset);
+            if (marker?.ClosedPolicyId == null) return;
+            _logger.Debug($"ImeLogTracker: {what} at offset {_currentEntryOffset} lies behind the writer boundary at {marker.Offset} that closed platform script {marker.ClosedPolicyId} — another executor's end block, not attributed");
+        }
+
+        /// <summary>Removes the markers from <paramref name="offset"/> on and returns them in offset order.</summary>
+        private List<InvocationMarker> TakeInvocationMarkersFrom(string fileName, long offset, out bool tookLastPlatformMarker)
+        {
+            tookLastPlatformMarker = false;
+            var taken = new List<InvocationMarker>();
             List<InvocationMarker> list;
-            if (!_invocationMarkers.TryGetValue(fileName, out list) || list.Count == 0) return;
-            var removedLast = false;
-            for (var i = list.Count - 1; i >= 0 && list[i].Offset >= offset; i--)
+            if (!_invocationMarkers.TryGetValue(fileName, out list) || list.Count == 0) return taken;
+
+            var from = list.Count;
+            while (from > 0 && list[from - 1].Offset >= offset) from--;
+            for (var i = from; i < list.Count; i++)
             {
-                if (ReferenceEquals(list[i], _lastPlatformMarker)) removedLast = true;
-                list.RemoveAt(i);
+                if (ReferenceEquals(list[i], _lastPlatformMarker)) tookLastPlatformMarker = true;
+                taken.Add(list[i]);
             }
-            if (removedLast)
+            list.RemoveRange(from, list.Count - from);
+
+            if (tookLastPlatformMarker)
             {
                 _lastPlatformMarker = null;
                 for (var i = list.Count - 1; i >= 0; i--)
@@ -449,6 +567,28 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
                     }
                 }
             }
+            return taken;
+        }
+
+        private void InvalidateInvocationMarkersFrom(string fileName, long offset) => TakeInvocationMarkersFrom(fileName, offset, out _);
+
+        /// <summary>
+        /// An entry that reads unchanged after a rewind keeps its markers: gives back the set-aside markers at exactly
+        /// <paramref name="entryOffset"/>. Set-aside markers in front of it belonged to entries that changed and stay
+        /// gone with their bytes.
+        /// </summary>
+        private void RestoreInvocationMarkers(RewindState rewind, long entryOffset)
+        {
+            var markers = rewind.Markers;
+            while (rewind.Next < markers.Count && markers[rewind.Next].Offset < entryOffset) rewind.Next++;
+            while (rewind.Next < markers.Count && markers[rewind.Next].Offset == entryOffset)
+            {
+                var marker = markers[rewind.Next++];
+                var list = GetOrCreateMarkerList(rewind.FileName);
+                if (list.Count > 0 && list[list.Count - 1].Offset >= marker.Offset) continue;
+                AppendInvocationMarker(list, marker);
+                if (ReferenceEquals(marker, rewind.LastPlatformMarker)) _lastPlatformMarker = marker;
+            }
         }
 
         private long OldestPendingScriptMarkerOffset(string fileName)
@@ -474,6 +614,9 @@ namespace AutopilotMonitor.Agent.V2.Core.Monitoring.Enrollment.Ime
         /// <summary>What a rollover of the file does to its invocation markers.</summary>
         internal void ClearInvocationMarkersForTest(string fileName) => InvalidateInvocationMarkersFrom(fileName, 0);
 
+        internal int InvocationMarkerCountForTest(string fileName)
+            => _invocationMarkers.TryGetValue(fileName, out var list) ? list.Count : 0;
+
         internal int LedgerEntryCountForTest(string fileName)
         {
             FileLedger ledger;