feat(prompts): add editable system/planning/agent prompt files

Introduces ~/.todo-app/prompts/{system,planning,agent}.md as the canonical
location for prompt content. The settings modal exposes "Open in editor"
shortcuts for each, and TaskRunner merges system.md (always) and agent.md
(for "agent"-tagged tasks) into the effective system prompt alongside the
existing global/list/task layers.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Data/PromptFiles.cs

@@ -0,0 +1,58 @@
+namespace ClaudeDo.Data;
+
+public enum PromptKind { System, Planning, Agent }
+
+public static class PromptFiles
+{
+    public static string Root => Path.Combine(Paths.AppDataRoot(), "prompts");
+
+    public static string PathFor(PromptKind kind) => kind switch
+    {
+        PromptKind.System => Path.Combine(Root, "system.md"),
+        PromptKind.Planning => Path.Combine(Root, "planning.md"),
+        PromptKind.Agent => Path.Combine(Root, "agent.md"),
+        _ => throw new ArgumentOutOfRangeException(nameof(kind))
+    };
+
+    public static void EnsureExists(PromptKind kind)
+    {
+        Directory.CreateDirectory(Root);
+        var path = PathFor(kind);
+        if (File.Exists(path)) return;
+        File.WriteAllText(path, DefaultFor(kind));
+    }
+
+    public static string? ReadOrNull(PromptKind kind)
+    {
+        var path = PathFor(kind);
+        if (!File.Exists(path)) return null;
+        var content = File.ReadAllText(path).Trim();
+        return string.IsNullOrEmpty(content) ? null : content;
+    }
+
+    private static string DefaultFor(PromptKind kind) => kind switch
+    {
+        PromptKind.System =>
+            "# System Prompt\n\n" +
+            "Baseline instructions appended to every task run.\n" +
+            "Edit this file to inject project-wide rules (style, conventions, hard constraints).\n",
+        PromptKind.Planning =>
+            "You are a planning assistant for ClaudeDo.\n" +
+            "Your role is to help break down a task into smaller, actionable subtasks.\n" +
+            "Your final goal WILL ALWAYS be the creation of Subtasks.\n\n" +
+            "ALWAYS invoke the `superpowers:brainstorming` skill via the Skill tool at the\n" +
+            "start of every planning session, and follow its process end-to-end. It guides\n" +
+            "you through clarifying questions, approach exploration, and design approval\n" +
+            "BEFORE any subtasks are created. Do not create child tasks until the user has\n" +
+            "approved a design.\n\n" +
+            "NEVER change files yourself.\n\n" +
+            "ALWAYS use the available MCP tools (mcp__claudedo__*) to create child tasks once\n" +
+            "the design is approved. When you are done planning, finalize the session.\n\n" +
+            "Be concise and focused. Each subtask should be independently executable.\n",
+        PromptKind.Agent =>
+            "# Agent Prompt\n\n" +
+            "Appended to the system prompt for tasks tagged \"agent\" (auto-queued runs).\n" +
+            "Use this for autonomous-execution rules that don't apply to manual runs.\n",
+        _ => ""
+    };
+}

src/ClaudeDo.Ui/ViewModels/Modals/SettingsModalViewModel.cs

@@ -38,6 +38,10 @@ public sealed partial class SettingsModalViewModel : ViewModelBase
     public string LogsFolderPath { get; } = Path.Combine(Paths.AppDataRoot(), "logs");
     public string WorkerConfigPath { get; } = Path.Combine(Paths.AppDataRoot(), "worker.config.json");
 
+    public string SystemPromptPath { get; } = PromptFiles.PathFor(PromptKind.System);
+    public string PlanningPromptPath { get; } = PromptFiles.PathFor(PromptKind.Planning);
+    public string AgentPromptPath { get; } = PromptFiles.PathFor(PromptKind.Agent);
+
     public Action? CloseAction { get; set; }
 
     public SettingsModalViewModel(WorkerClient worker)
@@ -199,4 +203,20 @@ public sealed partial class SettingsModalViewModel : ViewModelBase
         }
         catch { /* ignore */ }
     }
+
+    [RelayCommand]
+    private void OpenPrompt(string? kindName)
+    {
+        if (!Enum.TryParse<PromptKind>(kindName, ignoreCase: true, out var kind)) return;
+        try
+        {
+            PromptFiles.EnsureExists(kind);
+            var path = PromptFiles.PathFor(kind);
+            Process.Start(new ProcessStartInfo(path) { UseShellExecute = true });
+        }
+        catch (Exception ex)
+        {
+            StatusMessage = $"Open failed: {ex.Message}";
+        }
+    }
 }

src/ClaudeDo.Ui/Views/Modals/SettingsModalView.axaml

@@ -201,6 +201,38 @@
             </Border>
           </StackPanel>
 
+          <!-- PROMPTS -->
+          <StackPanel Spacing="0">
+            <TextBlock Classes="section-label" Text="PROMPTS"/>
+            <Border Classes="section">
+              <Grid RowDefinitions="Auto,Auto,Auto" ColumnDefinitions="90,*,Auto" RowSpacing="8">
+                <TextBlock Grid.Row="0" Grid.Column="0" Classes="field-label" Text="System"
+                           VerticalAlignment="Center"/>
+                <TextBlock Grid.Row="0" Grid.Column="1" Classes="path-mono"
+                           Text="{Binding SystemPromptPath}" VerticalAlignment="Center"/>
+                <Button Grid.Row="0" Grid.Column="2" Content="Open in editor"
+                        Command="{Binding OpenPromptCommand}"
+                        CommandParameter="System"/>
+
+                <TextBlock Grid.Row="1" Grid.Column="0" Classes="field-label" Text="Planning"
+                           VerticalAlignment="Center"/>
+                <TextBlock Grid.Row="1" Grid.Column="1" Classes="path-mono"
+                           Text="{Binding PlanningPromptPath}" VerticalAlignment="Center"/>
+                <Button Grid.Row="1" Grid.Column="2" Content="Open in editor"
+                        Command="{Binding OpenPromptCommand}"
+                        CommandParameter="Planning"/>
+
+                <TextBlock Grid.Row="2" Grid.Column="0" Classes="field-label" Text="Agent"
+                           VerticalAlignment="Center"/>
+                <TextBlock Grid.Row="2" Grid.Column="1" Classes="path-mono"
+                           Text="{Binding AgentPromptPath}" VerticalAlignment="Center"/>
+                <Button Grid.Row="2" Grid.Column="2" Content="Open in editor"
+                        Command="{Binding OpenPromptCommand}"
+                        CommandParameter="Agent"/>
+              </Grid>
+            </Border>
+          </StackPanel>
+
           <!-- ABOUT -->
           <StackPanel Spacing="0">
             <TextBlock Classes="section-label" Text="ABOUT"/>

src/ClaudeDo.Worker/Runner/TaskRunner.cs

@@ -404,14 +404,22 @@ public sealed class TaskRunner
         TaskEntity task, ListConfigEntity? listConfig, string? resumeSessionId, CancellationToken ct)
     {
         AppSettingsEntity global;
+        bool isAgentTask;
         using (var ctx = _dbFactory.CreateDbContext())
         {
             var settingsRepo = new AppSettingsRepository(ctx);
             global = await settingsRepo.GetAsync(ct);
+
+            var taskRepo = new TaskRepository(ctx);
+            var tags = await taskRepo.GetEffectiveTagsAsync(task.Id, ct);
+            isAgentTask = tags.Any(t => string.Equals(t.Name, "agent", StringComparison.OrdinalIgnoreCase));
         }
 
+        var systemFile = PromptFiles.ReadOrNull(PromptKind.System);
+        var agentFile = isAgentTask ? PromptFiles.ReadOrNull(PromptKind.Agent) : null;
+
         var instructions = MergeInstructions(
-            global.DefaultClaudeInstructions, listConfig?.SystemPrompt, task.SystemPrompt);
+            systemFile, global.DefaultClaudeInstructions, listConfig?.SystemPrompt, task.SystemPrompt, agentFile);
 
         return new ClaudeRunConfig(
             Model: task.Model ?? listConfig?.Model ?? global.DefaultModel,
@@ -422,12 +430,11 @@ public sealed class TaskRunner
             PermissionMode: global.DefaultPermissionMode);
     }
 
-    public static string MergeInstructions(string? global, string? list, string? task)
+    public static string MergeInstructions(params string?[] parts)
     {
-        var parts = new List<string>(3);
-        if (!string.IsNullOrWhiteSpace(global)) parts.Add(global.Trim());
-        if (!string.IsNullOrWhiteSpace(list)) parts.Add(list.Trim());
-        if (!string.IsNullOrWhiteSpace(task)) parts.Add(task.Trim());
-        return string.Join("\n\n", parts);
+        var trimmed = parts
+            .Where(p => !string.IsNullOrWhiteSpace(p))
+            .Select(p => p!.Trim());
+        return string.Join("\n\n", trimmed);
     }
 }