chore(worker): external MCP tools return explicit results instead of empty responses

set_task_config/set_list_config now echo which fields were set vs cleared, get_list_config/get_task_config return an explicit found=false instead of null, and delete_list/run_task_now/reset_failed_task/remove_task_attachment return a confirmation record — matching the found/ok convention already used by batch_get_tasks and get_task_log.

tests/ClaudeDo.Worker.Tests/External/ConfigMcpToolsTests.cs

@@ -37,14 +37,31 @@ public sealed class ConfigMcpToolsTests : IDisposable
     {
         var listId = await SeedListAsync();
 
-        await _sut.SetListConfig(listId, "sonnet", "be terse", null, 42, CancellationToken.None);
+        var setResult = await _sut.SetListConfig(listId, "sonnet", "be terse", null, 42, CancellationToken.None);
+        Assert.True(setResult.Ok);
+        Assert.Equal(listId, setResult.ListId);
+        Assert.NotNull(setResult.Config);
+        Assert.Equal("sonnet", setResult.Config!.Model);
+
         var cfg = await _sut.GetListConfig(listId, CancellationToken.None);
 
-        Assert.NotNull(cfg);
-        Assert.Equal("sonnet", cfg!.Model);
-        Assert.Equal("be terse", cfg.SystemPrompt);
-        Assert.Null(cfg.AgentPath);
-        Assert.Equal(42, cfg.MaxTurns);
+        Assert.True(cfg.Found);
+        Assert.NotNull(cfg.Config);
+        Assert.Equal("sonnet", cfg.Config!.Model);
+        Assert.Equal("be terse", cfg.Config.SystemPrompt);
+        Assert.Null(cfg.Config.AgentPath);
+        Assert.Equal(42, cfg.Config.MaxTurns);
+    }
+
+    [Fact]
+    public async Task GetListConfig_NoConfigSet_ReturnsNotFound()
+    {
+        var listId = await SeedListAsync();
+
+        var cfg = await _sut.GetListConfig(listId, CancellationToken.None);
+
+        Assert.False(cfg.Found);
+        Assert.Null(cfg.Config);
     }
 
     [Fact]
@@ -53,9 +70,12 @@ public sealed class ConfigMcpToolsTests : IDisposable
         var listId = await SeedListAsync();
         await _sut.SetListConfig(listId, "sonnet", null, null, null, CancellationToken.None);
 
-        await _sut.SetListConfig(listId, null, null, null, null, CancellationToken.None);
+        var clearResult = await _sut.SetListConfig(listId, null, null, null, null, CancellationToken.None);
 
-        Assert.Null(await _sut.GetListConfig(listId, CancellationToken.None));
+        Assert.True(clearResult.Ok);
+        Assert.Null(clearResult.Config);
+        var cfg = await _sut.GetListConfig(listId, CancellationToken.None);
+        Assert.False(cfg.Found);
     }
 
     [Fact]
@@ -73,10 +93,65 @@ public sealed class ConfigMcpToolsTests : IDisposable
         };
         await _tasks.AddAsync(task);
 
-        await _sut.SetTaskConfig(task.Id, "opus", null, null, 15, CancellationToken.None);
+        var result = await _sut.SetTaskConfig(task.Id, "opus", null, null, 15, CancellationToken.None);
+
+        Assert.True(result.Ok);
+        Assert.Equal(task.Id, result.TaskId);
+        Assert.Equal("opus", result.Config!.Model);
+        Assert.Equal(15, result.Config.MaxTurns);
 
         var loaded = await _tasks.GetByIdAsync(task.Id);
         Assert.Equal("opus", loaded!.Model);
         Assert.Equal(15, loaded.MaxTurns);
     }
+
+    [Fact]
+    public async Task SetTaskConfig_NullField_ClearsThatOverride()
+    {
+        var listId = await SeedListAsync();
+        var task = new TaskEntity
+        {
+            Id = Guid.NewGuid().ToString(),
+            ListId = listId,
+            Title = "t",
+            Status = ClaudeDo.Data.Models.TaskStatus.Idle,
+            CreatedAt = DateTime.UtcNow,
+            CommitType = "chore",
+        };
+        await _tasks.AddAsync(task);
+        await _sut.SetTaskConfig(task.Id, "opus", "be terse", "agent.md", 15, CancellationToken.None);
+
+        var result = await _sut.SetTaskConfig(task.Id, "opus", null, "agent.md", null, CancellationToken.None);
+
+        Assert.True(result.Ok);
+        Assert.Equal("opus", result.Config!.Model);
+        Assert.Null(result.Config.SystemPrompt);
+        Assert.Equal("agent.md", result.Config.AgentPath);
+        Assert.Null(result.Config.MaxTurns);
+
+        var loaded = await _tasks.GetByIdAsync(task.Id);
+        Assert.Null(loaded!.SystemPrompt);
+        Assert.Null(loaded.MaxTurns);
+    }
+
+    [Fact]
+    public async Task GetTaskConfig_NoOverrideSet_ReturnsNotFound()
+    {
+        var listId = await SeedListAsync();
+        var task = new TaskEntity
+        {
+            Id = Guid.NewGuid().ToString(),
+            ListId = listId,
+            Title = "t",
+            Status = ClaudeDo.Data.Models.TaskStatus.Idle,
+            CreatedAt = DateTime.UtcNow,
+            CommitType = "chore",
+        };
+        await _tasks.AddAsync(task);
+
+        var cfg = await _sut.GetTaskConfig(task.Id, CancellationToken.None);
+
+        Assert.False(cfg.Found);
+        Assert.Null(cfg.Config);
+    }
 }