feat(worker): build merge-helper interactive launch spec

src/ClaudeDo.Worker/Runner/InteractiveLaunchSpecService.cs

@@ -157,6 +157,101 @@ public sealed class InteractiveLaunchSpecService : IInteractiveLaunchSpecService
         return Task.FromResult(new LaunchSpec(directory, resolvedClaude, Array.Empty<string>(), env));
     }
 
+    // Tools the merge helper may use without prompting: the claudedo MCP surface (run, poll,
+    // diff, review/merge, continue/abort merge), read/search, Edit + Bash for hand-resolving
+    // conflict markers the MCP tools left behind, and web/skill lookups.
+    private const string MergeHelperAllowedTools =
+        "mcp__claudedo__*,Read,Grep,Glob,Edit,Bash,WebFetch,WebSearch,Skill";
+
+    public async Task<LaunchSpec> BuildForMergeHelperAsync(IReadOnlyList<string> taskIds, string? listId, CancellationToken ct)
+    {
+        if (taskIds.Count == 0)
+            throw new InvalidOperationException("No tasks selected for the merge helper.");
+
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+        var taskRepo = new TaskRepository(ctx);
+        var listRepo = new ListRepository(ctx);
+
+        var listsById = new Dictionary<string, ListEntity?>();
+        var briefLines = new List<string>();
+        var repoDirs = new List<string>(); // distinct, existing, in first-seen order
+
+        foreach (var id in taskIds)
+        {
+            var task = await taskRepo.GetByIdAsync(id, ct)
+                ?? throw new KeyNotFoundException($"Task not found: {id}");
+            if (!listsById.TryGetValue(task.ListId, out var list))
+                listsById[task.ListId] = list = await listRepo.GetByIdAsync(task.ListId, ct);
+
+            var workingDir = list?.WorkingDir;
+            if (!string.IsNullOrEmpty(workingDir) && Directory.Exists(workingDir) && !repoDirs.Contains(workingDir))
+                repoDirs.Add(workingDir);
+
+            briefLines.Add(
+                $"- [{task.Status}] {task.Title} (id: {task.Id}, list: {list?.Name ?? "—"}, " +
+                $"repo: {(string.IsNullOrEmpty(workingDir) ? "—" : workingDir)})");
+        }
+
+        if (repoDirs.Count == 0)
+            throw new InvalidOperationException("none of the selected tasks are in a working directory");
+
+        string scopeLabel;
+        string cwd;
+        if (listId is not null)
+        {
+            var scopeList = await listRepo.GetByIdAsync(listId, ct)
+                ?? throw new KeyNotFoundException($"List not found: {listId}");
+            scopeLabel = $"List: {scopeList.Name}";
+            cwd = scopeList.WorkingDir is { Length: > 0 } wd && Directory.Exists(wd) ? wd : repoDirs[0];
+        }
+        else
+        {
+            scopeLabel = "All lists";
+            cwd = repoDirs[0];
+        }
+
+        var sessionDir = Path.Combine(Paths.AppDataRoot(), "merge-helper-sessions", Guid.NewGuid().ToString());
+        Directory.CreateDirectory(sessionDir);
+
+        var systemPromptPath = Path.Combine(sessionDir, "system-prompt.md");
+        await File.WriteAllTextAsync(systemPromptPath, PromptFiles.ReadOrDefault(PromptKind.MergeHelper), ct);
+
+        var briefPath = Path.Combine(sessionDir, "brief.md");
+        await File.WriteAllTextAsync(briefPath, PromptFiles.Render(PromptKind.MergeHelperInitial,
+            new Dictionary<string, string>
+            {
+                ["scope"] = scopeLabel,
+                ["tasks"] = string.Join("\n", briefLines),
+            }), ct);
+
+        var resolvedClaude = WindowsTerminalLauncher.Resolve(_claudePath)
+            ?? throw new InvalidOperationException($"claude executable not found: {_claudePath}");
+
+        // Mirrors WindowsTerminalLauncher.BuildPlanningStartArgs ordering: variadic flags
+        // (--allowedTools, --add-dir) first, then a single-value flag, then the single-line
+        // positional kickoff LAST — a multi-line positional prompt truncates at the first
+        // newline, so the full multi-line brief travels via the file exposed through --add-dir.
+        var args = new List<string>
+        {
+            "--permission-mode", "default",
+            "--allowedTools", MergeHelperAllowedTools,
+            "--add-dir", sessionDir,
+        };
+        args.AddRange(repoDirs);
+        args.Add("--append-system-prompt-file");
+        args.Add(systemPromptPath);
+        args.Add(
+            $"Read the file {briefPath} first. It lists the tasks you must merge and their status. " +
+            "After reading it, begin the merge-helper session as your instructions describe.");
+
+        var env = new Dictionary<string, string>
+        {
+            ["MCP_TOOL_TIMEOUT"] = "200000",
+        };
+
+        return new LaunchSpec(cwd, resolvedClaude, args, env);
+    }
+
     // The positional prompt claude opens the interactive session on. Empty (no positional arg)
     // if the task has neither a title nor a description.
     private static IReadOnlyList<string> BuildFreshPromptArgs(TaskEntity task)

src/ClaudeDo.Worker/Runner/Interfaces/IInteractiveLaunchSpecService.cs

@@ -26,4 +26,12 @@ public interface IInteractiveLaunchSpecService
     /// no task, no worktree, no session-skills seeding. Throws InvalidOperationException if the
     /// directory doesn't exist.</summary>
     Task<LaunchSpec> BuildForDirectoryAsync(string directory, CancellationToken ct);
+
+    /// <summary>Builds a LaunchSpec for an embedded ConPTY "merge helper" session that drives the
+    /// given tasks to a merged/Done state via the mcp__claudedo__* tools. Writes a per-session
+    /// system prompt + task brief under ~/.todo-app/merge-helper-sessions/&lt;guid&gt; and exposes
+    /// that dir plus every distinct existing repo dir via --add-dir. listId scopes the brief label
+    /// and the cwd to that list; null means all lists (cwd = first existing repo dir). Throws
+    /// InvalidOperationException if taskIds is empty or no task has an existing working directory.</summary>
+    Task<LaunchSpec> BuildForMergeHelperAsync(IReadOnlyList<string> taskIds, string? listId, CancellationToken ct);
 }