fix(ui): suppress auto-open conflict resolver during MCP-driven merges

review_task/continue_merge on a planning parent always leaves conflicts in
the tree, and the UI auto-opened the resolver on every PlanningMergeConflict
broadcast regardless of who started the merge -- so a running Claude session
resolving a unit-merge conflict could race a human editing the same shared
checkout in a resolver window neither of them asked for.

PlanningMergeOrchestrator.StartAsync now takes an externallyDriven flag (set
by ExternalMcpService's MCP-driven review_task path, left false for the UI's
ApproveReview) that rides along on the PlanningMergeConflict broadcast. The
UI only auto-opens the resolver when it's false; otherwise it shows a
persistent banner with a manual "Open resolver" button, cleared on
PlanningMergeAborted/PlanningCompleted. A new GetActiveExternalConflictsAsync
query (checked against GitService.IsMidMergeAsync rather than the in-memory
flag alone) lets the UI resync the banner on reconnect instead of trusting a
one-shot broadcast that isn't replayed after a restart.

The childless single-task conflict path was checked and needed no change --
it only broadcasts the generic TaskUpdated, never PlanningMergeConflict.

tests/ClaudeDo.Ui.Tests/IslandsShellViewModelExternalMergeTests.cs

@@ -0,0 +1,101 @@
+using System;
+using System.Threading.Tasks;
+using ClaudeDo.Ui.ViewModels;
+using Xunit;
+
+namespace ClaudeDo.Ui.Tests;
+
+// Covers the MCP-driven-merge popup fix: a unit-merge conflict started by an MCP session
+// (review_task/continue_merge) must not auto-open the in-app resolver — two parties editing the
+// same shared checkout at once is how the original bug manifested. The UI-driven path (a human
+// clicking Approve) keeps opening the resolver as before.
+public class IslandsShellViewModelExternalMergeTests
+{
+    [Fact]
+    public void ExternallyDriven_ShowsBanner()
+    {
+        var vm = new IslandsShellViewModel();
+
+        vm.OnPlanningMergeConflict("plan1", "sub1", new[] { "file.txt" }, externallyDriven: true);
+
+        Assert.True(vm.IsExternalMergeBannerVisible);
+    }
+
+    [Fact]
+    public void UiDriven_DoesNotShowExternalBanner()
+    {
+        var vm = new IslandsShellViewModel();
+
+        vm.OnPlanningMergeConflict("plan1", "sub1", new[] { "file.txt" }, externallyDriven: false);
+
+        Assert.False(vm.IsExternalMergeBannerVisible);
+    }
+
+    [Fact]
+    public void Aborted_ClearsBanner()
+    {
+        var vm = new IslandsShellViewModel();
+        vm.OnPlanningMergeConflict("plan1", "sub1", Array.Empty<string>(), externallyDriven: true);
+        Assert.True(vm.IsExternalMergeBannerVisible);
+
+        vm.OnPlanningMergeAborted("plan1");
+
+        Assert.False(vm.IsExternalMergeBannerVisible);
+    }
+
+    [Fact]
+    public void Completed_ClearsBanner()
+    {
+        var vm = new IslandsShellViewModel();
+        vm.OnPlanningMergeConflict("plan1", "sub1", Array.Empty<string>(), externallyDriven: true);
+
+        vm.OnPlanningMergeCompleted("plan1");
+
+        Assert.False(vm.IsExternalMergeBannerVisible);
+    }
+
+    [Fact]
+    public void UnrelatedPlanningTaskEnding_LeavesBannerVisible()
+    {
+        var vm = new IslandsShellViewModel();
+        vm.OnPlanningMergeConflict("plan1", "sub1", Array.Empty<string>(), externallyDriven: true);
+
+        vm.OnPlanningMergeCompleted("some-other-plan");
+
+        Assert.True(vm.IsExternalMergeBannerVisible);
+    }
+
+    [Fact]
+    public void LaterConflictOnSamePlanningTask_UpdatesInPlaceWithoutDuplicating()
+    {
+        var vm = new IslandsShellViewModel();
+        vm.OnPlanningMergeConflict("plan1", "subA", Array.Empty<string>(), externallyDriven: true);
+        vm.OnPlanningMergeConflict("plan1", "subB", Array.Empty<string>(), externallyDriven: true);
+        Assert.True(vm.IsExternalMergeBannerVisible);
+
+        // A single terminal event for that planning task clears it entirely — proves the second
+        // conflict updated the same entry rather than piling up a second one.
+        vm.OnPlanningMergeCompleted("plan1");
+
+        Assert.False(vm.IsExternalMergeBannerVisible);
+    }
+
+    [Fact]
+    public async Task OpenExternalMergeConflictCommand_NoPendingConflict_DoesNotThrow()
+    {
+        var vm = new IslandsShellViewModel();
+
+        await vm.OpenExternalMergeConflictCommand.ExecuteAsync(null);
+    }
+
+    [Fact]
+    public async Task OpenExternalMergeConflictCommand_NoDialogsWired_DoesNotThrow()
+    {
+        var vm = new IslandsShellViewModel();
+        vm.OnPlanningMergeConflict("plan1", "sub1", Array.Empty<string>(), externallyDriven: true);
+
+        // Dialogs/ConflictResolverFactory aren't wired in the test-only ctor — a deliberate
+        // click must degrade gracefully rather than throw, same as the existing UI-driven path.
+        await vm.OpenExternalMergeConflictCommand.ExecuteAsync(null);
+    }
+}

tests/ClaudeDo.Ui.Tests/StubWorkerClient.cs

@@ -33,7 +33,7 @@ public abstract class StubWorkerClient : IWorkerClient
     public event Action<string, bool, string?>? RefineFinishedEvent;
     public event Action<string, string>? PlanningMergeStartedEvent;
     public event Action<string, string>? PlanningSubtaskMergedEvent;
-    public event Action<string, string, IReadOnlyList<string>>? PlanningMergeConflictEvent;
+    public event Action<string, string, IReadOnlyList<string>, bool>? PlanningMergeConflictEvent;
     public event Action<string>? PlanningMergeAbortedEvent;
     public event Action<string>? PlanningCompletedEvent;
     public event Action<PrimeFiredEvent>? PrimeFired;
@@ -53,6 +53,10 @@ public abstract class StubWorkerClient : IWorkerClient
     public void RaiseTaskQuestionAsked(string taskId, string questionId, string question) => TaskQuestionAskedEvent?.Invoke(taskId, questionId, question);
     public void RaiseTaskQuestionResolved(string taskId, string questionId) => TaskQuestionResolvedEvent?.Invoke(taskId, questionId);
     public void RaiseHandoffRequested(string taskId, IReadOnlyList<string> survivingTaskIds) => HandoffRequestedEvent?.Invoke(taskId, survivingTaskIds);
+    public void RaisePlanningMergeConflict(string planningTaskId, string subtaskId, IReadOnlyList<string> files, bool externallyDriven)
+        => PlanningMergeConflictEvent?.Invoke(planningTaskId, subtaskId, files, externallyDriven);
+    public void RaisePlanningMergeAborted(string planningTaskId) => PlanningMergeAbortedEvent?.Invoke(planningTaskId);
+    public void RaisePlanningCompleted(string planningTaskId) => PlanningCompletedEvent?.Invoke(planningTaskId);
 
     public void RaisePrepStarted() => PrepStartedEvent?.Invoke();
     public void RaisePrepLine(string line) => PrepLineEvent?.Invoke(line);
@@ -129,6 +133,8 @@ public abstract class StubWorkerClient : IWorkerClient
         => Task.FromResult<CombinedDiffResultDto?>(null);
     public virtual Task ContinuePlanningMergeAsync(string planningTaskId) => Task.CompletedTask;
     public virtual Task AbortPlanningMergeAsync(string planningTaskId) => Task.CompletedTask;
+    public virtual Task<IReadOnlyList<PlanningMergeConflictStateDto>> GetActiveExternalPlanningMergeConflictsAsync()
+        => Task.FromResult<IReadOnlyList<PlanningMergeConflictStateDto>>(Array.Empty<PlanningMergeConflictStateDto>());
     public virtual Task QueuePlanningSubtasksAsync(string parentTaskId, CancellationToken ct = default) => Task.CompletedTask;
     public virtual Task<string?> GetWeekReportAsync(DateOnly start, DateOnly end) => Task.FromResult<string?>(null);
     public virtual Task<string> GenerateWeekReportAsync(DateOnly start, DateOnly end) => Task.FromResult("");