diff --git a/src/ClaudeDo.Data/PromptFiles.cs b/src/ClaudeDo.Data/PromptFiles.cs
index d2551f76..b1a9cc60 100644
--- a/src/ClaudeDo.Data/PromptFiles.cs
+++ b/src/ClaudeDo.Data/PromptFiles.cs
@@ -236,7 +236,7 @@ public static class PromptFiles
         Work the five phases in order. Do not start a phase before the previous one is finished.
 
         ## Phase 0 — Read everything
-        Call batch_get_tasks with every id from the brief and read each task's title, description, status and parent/child links. Do not act on any single task before you have read them all — Phase 1 needs the whole set in view.
+        The brief is the primary source: it already lists every task's title, id, status and full description. Read it in full before acting. Only call batch_get_tasks if you need something the brief does not carry for a specific task, e.g. parent/child links. Do not act on any single task before you have read them all — Phase 1 needs the whole set in view.
 
         ## Phase 1 — Dedupe
         Compare the tasks pairwise for overlap: same goal stated twice, one task fully contained in another, two tasks that would edit the same thing for the same reason.
diff --git a/src/ClaudeDo.Worker/Runner/InteractiveLaunchSpecService.cs b/src/ClaudeDo.Worker/Runner/InteractiveLaunchSpecService.cs
index 2bfde47b..a0648a24 100644
--- a/src/ClaudeDo.Worker/Runner/InteractiveLaunchSpecService.cs
+++ b/src/ClaudeDo.Worker/Runner/InteractiveLaunchSpecService.cs
@@ -206,7 +206,7 @@ public sealed class InteractiveLaunchSpecService : IInteractiveLaunchSpecService
         {
             var task = await taskRepo.GetByIdAsync(id, ct)
                 ?? throw new KeyNotFoundException($"Task not found: {id}");
-            briefLines.Add($"- [{task.Status}] {task.Title} (id: {task.Id})");
+            briefLines.Add(RenderBriefEntry(task));
         }
 
         var sessionDir = Path.Combine(Paths.AppDataRoot(), "merge-helper-sessions", Guid.NewGuid().ToString());
@@ -253,6 +253,39 @@ public sealed class InteractiveLaunchSpecService : IInteractiveLaunchSpecService
         return new LaunchSpec(repoDir, resolvedClaude, args, env);
     }
 
+    // Renders one task as a brief list item. A description can itself be arbitrary Markdown
+    // (headings, lists, fenced code) — those must not merge into the brief's own task list, so
+    // the description is placed in a fenced code block indented to the list item's continuation
+    // column (2 spaces, matching "- "). That keeps CommonMark parsing the fence as part of THIS
+    // bullet rather than breaking the list, while the code fence itself stops any inner heading
+    // or list syntax from being interpreted. The fence length is extended past the longest run of
+    // backticks already present in the description so an embedded ``` block can't prematurely
+    // close it.
+    private static string RenderBriefEntry(TaskEntity task)
+    {
+        var header = $"- [{task.Status}] {task.Title} (id: {task.Id})";
+        var description = task.Description?.Trim();
+        if (string.IsNullOrEmpty(description)) return header;
+
+        var fence = new string('`', Math.Max(3, LongestBacktickRun(description) + 1));
+        var lines = new List<string>(4) { header, $"  {fence}" };
+        lines.AddRange(description.Replace("\r\n", "\n").Split('\n').Select(line => $"  {line}"));
+        lines.Add($"  {fence}");
+        return string.Join("\n", lines);
+    }
+
+    private static int LongestBacktickRun(string text)
+    {
+        var max = 0;
+        var current = 0;
+        foreach (var ch in text)
+        {
+            current = ch == '`' ? current + 1 : 0;
+            if (current > max) max = current;
+        }
+        return max;
+    }
+
     // Creates the ClaudeDo task that hosts a list-handler run (Mission Control's "Let Claude
     // handle it") and stamps the list repo's current HEAD as the review range's base commit.
     // The handler never gets its own worktree -- it commits straight to the list's working
diff --git a/tests/ClaudeDo.Data.Tests/PromptFilesTests.cs b/tests/ClaudeDo.Data.Tests/PromptFilesTests.cs
index 9f989c5b..dca6c205 100644
--- a/tests/ClaudeDo.Data.Tests/PromptFilesTests.cs
+++ b/tests/ClaudeDo.Data.Tests/PromptFilesTests.cs
@@ -87,6 +87,15 @@ public class PromptFilesTests
         Assert.DoesNotContain("whenever you are unsure", d);
     }
 
+    [Fact]
+    public void DefaultFor_merge_helper_phase0_treats_brief_as_primary_source()
+    {
+        var d = PromptFiles.DefaultFor(PromptKind.MergeHelper);
+        Assert.Contains("primary source", d, StringComparison.OrdinalIgnoreCase);
+        Assert.Contains("batch_get_tasks", d);
+        Assert.Contains("Do not act on any single task before you have read", d);
+    }
+
     [Fact]
     public void DefaultFor_merge_helper_initial_has_repo_token()
     {
diff --git a/tests/ClaudeDo.Worker.Tests/Runner/InteractiveLaunchSpecServiceTests.cs b/tests/ClaudeDo.Worker.Tests/Runner/InteractiveLaunchSpecServiceTests.cs
index fa71b9d6..f375c21e 100644
--- a/tests/ClaudeDo.Worker.Tests/Runner/InteractiveLaunchSpecServiceTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Runner/InteractiveLaunchSpecServiceTests.cs
@@ -88,13 +88,13 @@ public sealed class InteractiveLaunchSpecServiceTests : IDisposable
         return listId;
     }
 
-    private async Task SeedTaskAsync(string taskId, string listId, TaskStatus status, string? sessionSkillsJson = null, string title = "T")
+    private async Task SeedTaskAsync(string taskId, string listId, TaskStatus status, string? sessionSkillsJson = null, string title = "T", string? description = null)
     {
         using var ctx = _db.CreateContext();
         await new TaskRepository(ctx).AddAsync(new TaskEntity
         {
             Id = taskId, ListId = listId, Title = title, Status = status,
-            CreatedAt = DateTime.UtcNow, SessionSkills = sessionSkillsJson,
+            CreatedAt = DateTime.UtcNow, SessionSkills = sessionSkillsJson, Description = description,
         });
         _seededTaskIds.Add(taskId); // a fresh-task ConPTY spec may write a real brief.md under
                                      // ~/.todo-app/task-sessions/<taskId> -- clean it up on dispose
@@ -562,6 +562,82 @@ public sealed class InteractiveLaunchSpecServiceTests : IDisposable
         Assert.Contains(t2, brief);
     }
 
+    [Fact]
+    public async Task BuildForMergeHelperAsync_BriefIncludesTaskDescription()
+    {
+        var repo = Path.Combine(_tempDir, "repoDesc");
+        Directory.CreateDirectory(repo);
+
+        var listId = await SeedListAsync(workingDir: repo, name: "Alpha");
+        var t1 = Guid.NewGuid().ToString();
+        await SeedTaskAsync(t1, listId, TaskStatus.Idle, title: "First task",
+            description: "Do the thing carefully and report back.");
+
+        var svc = BuildService();
+        var spec = await svc.BuildForMergeHelperAsync(new[] { t1 }, listId, CancellationToken.None);
+        var sessionDir = TrackSessionDir(spec);
+
+        var brief = File.ReadAllText(Path.Combine(sessionDir, "brief.md"));
+        Assert.Contains("Do the thing carefully and report back.", brief);
+    }
+
+    [Fact]
+    public async Task BuildForMergeHelperAsync_TaskWithoutDescription_RendersCleanly()
+    {
+        var repo = Path.Combine(_tempDir, "repoNoDesc");
+        Directory.CreateDirectory(repo);
+
+        var listId = await SeedListAsync(workingDir: repo, name: "Alpha");
+        var t1 = Guid.NewGuid().ToString();
+        await SeedTaskAsync(t1, listId, TaskStatus.Idle, title: "No description task", description: null);
+
+        var svc = BuildService();
+        var spec = await svc.BuildForMergeHelperAsync(new[] { t1 }, listId, CancellationToken.None);
+        var sessionDir = TrackSessionDir(spec);
+
+        var brief = File.ReadAllText(Path.Combine(sessionDir, "brief.md"));
+        var line = brief.Split('\n').Single(l => l.Contains("No description task"));
+        Assert.Equal($"- [Idle] No description task (id: {t1})", line.TrimEnd('\r'));
+    }
+
+    [Fact]
+    public async Task BuildForMergeHelperAsync_BriefDescriptionWithCodeFenceAndHeadingsKeepsTaskListRecognizable()
+    {
+        var repo = Path.Combine(_tempDir, "repoMd");
+        Directory.CreateDirectory(repo);
+
+        var listId = await SeedListAsync(workingDir: repo, name: "Alpha");
+        var t1 = Guid.NewGuid().ToString();
+        var t2 = Guid.NewGuid().ToString();
+        var trickyDescription = """
+            # Heading inside description
+
+            - a nested list item
+            - another one
+
+            ```csharp
+            var x = "fenced code block";
+            ```
+            """;
+        await SeedTaskAsync(t1, listId, TaskStatus.Idle, title: "First task", description: trickyDescription);
+        await SeedTaskAsync(t2, listId, TaskStatus.WaitingForReview, title: "Second task", description: "plain description");
+
+        var svc = BuildService();
+        var spec = await svc.BuildForMergeHelperAsync(new[] { t1, t2 }, listId, CancellationToken.None);
+        var sessionDir = TrackSessionDir(spec);
+
+        var brief = File.ReadAllText(Path.Combine(sessionDir, "brief.md"));
+        var lines = brief.Replace("\r\n", "\n").Split('\n');
+
+        // The two task bullets must still be recognizable top-level list items, unbroken
+        // by the embedded heading/list/code-fence in the first task's description.
+        Assert.Contains(lines, l => l == $"- [Idle] First task (id: {t1})");
+        Assert.Contains(lines, l => l == $"- [WaitingForReview] Second task (id: {t2})");
+        Assert.Contains("Heading inside description", brief);
+        Assert.Contains("fenced code block", brief);
+        Assert.Contains("var x = \"fenced code block\";", brief);
+    }
+
     // ── CreateMergeHelperTaskAsync ──
 
     [Fact]