feat(worker): create ephemeral worktree and write .mcp.json in StartAsync

Rewrites StartAsync to provision a git worktree before transitioning the
task to Planning state, writes .mcp.json and .claude/settings.local.json
into the worktree, and fixes ResumeAsync to supply the updated
PlanningSessionResumeContext fields (Token, WorktreePath).

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

src/ClaudeDo.Worker/Planning/PlanningSessionManager.cs

@@ -73,6 +73,46 @@ public sealed class PlanningSessionManager
         if (task.Status != TaskStatus.Manual)
             throw new InvalidOperationException($"Task is in status {task.Status}; only Manual can start planning.");
 
+        var list = await lists.GetByIdAsync(task.ListId, ct)
+            ?? throw new InvalidOperationException($"List {task.ListId} not found.");
+        var listWorkingDir = list.WorkingDir
+            ?? throw new InvalidOperationException($"List {task.ListId} has no working directory configured.");
+
+        if (!await _git.IsGitRepoAsync(listWorkingDir, ct))
+            throw new InvalidOperationException($"Working directory is not a git repository: {listWorkingDir}");
+
+        var appSettings = await settings.GetAsync(ct);
+        var worktreePath = WorktreePathFor(taskId, appSettings.WorktreeStrategy, appSettings.CentralWorktreeRoot, listWorkingDir);
+        var branchName = BranchNameFor(taskId);
+        var baseCommit = await _git.RevParseHeadAsync(listWorkingDir, ct);
+
+        Directory.CreateDirectory(Path.GetDirectoryName(worktreePath)!);
+        try
+        {
+            await _git.WorktreeAddAsync(listWorkingDir, branchName, worktreePath, baseCommit, ct);
+        }
+        catch (InvalidOperationException ex) when (ex.Message.Contains("already exists", StringComparison.OrdinalIgnoreCase))
+        {
+            // Self-heal: remove phantom worktrees, prune, delete branch, retry once.
+            var stalePaths = await _git.ListWorktreePathsForBranchAsync(listWorkingDir, branchName, ct);
+            foreach (var stale in stalePaths)
+            {
+                try { await _git.WorktreeRemoveAsync(listWorkingDir, stale, force: true, ct); } catch { }
+            }
+            try { await _git.WorktreePruneAsync(listWorkingDir, ct); } catch { }
+            try { await _git.BranchDeleteAsync(listWorkingDir, branchName, force: true, ct); } catch { }
+            await _git.WorktreeAddAsync(listWorkingDir, branchName, worktreePath, baseCommit, ct);
+        }
+
+        // Write .mcp.json and .claude/settings.local.json into the worktree.
+        var mcpPath = Path.Combine(worktreePath, ".mcp.json");
+        await File.WriteAllTextAsync(mcpPath, BuildMcpConfigJson(), ct);
+
+        var claudeDir = Path.Combine(worktreePath, ".claude");
+        Directory.CreateDirectory(claudeDir);
+        await File.WriteAllTextAsync(Path.Combine(claudeDir, "settings.local.json"), SettingsLocalJson, ct);
+
+        // Session dir + token + prompt files.
         var token = GenerateToken();
         var started = await tasks.SetPlanningStartedAsync(taskId, token, ct)
             ?? throw new InvalidOperationException("Failed to transition task to Planning.");
@@ -82,17 +122,20 @@ public sealed class PlanningSessionManager
 
         var files = new PlanningSessionFiles(
             sessionDir,
-            Path.Combine(sessionDir, "mcp.json"),
             Path.Combine(sessionDir, "system-prompt.md"),
             Path.Combine(sessionDir, "initial-prompt.txt"));
 
-        await File.WriteAllTextAsync(files.McpConfigPath, BuildMcpConfigJson(), ct);
+        await WriteTokenFileAsync(TokenFilePathFor(sessionDir), token, ct);
         await File.WriteAllTextAsync(files.SystemPromptPath, BuildSystemPrompt(), ct);
         await File.WriteAllTextAsync(files.InitialPromptPath, BuildInitialPrompt(task), ct);
 
-        var list = await lists.GetByIdAsync(task.ListId, ct)
+        return new PlanningSessionStartContext(
-            ?? throw new InvalidOperationException($"List {task.ListId} not found.");
+            ParentTaskId: taskId,
-        return new PlanningSessionStartContext(taskId, list.WorkingDir ?? throw new InvalidOperationException($"List {task.ListId} has no working directory configured."), files);
+            WorkingDir: worktreePath,
+            Token: token,
+            WorktreePath: worktreePath,
+            BranchName: branchName,
+            Files: files);
     }
 
     public async Task<int> FinalizeAsync(string taskId, bool queueAgentTasks, CancellationToken ct)
@@ -139,13 +182,19 @@ public sealed class PlanningSessionManager
             throw new InvalidOperationException("No Claude session ID captured yet; cannot resume.");
 
         var sessionDir = Path.Combine(_rootDirectory, taskId);
-        var mcpConfigPath = Path.Combine(sessionDir, "mcp.json");
+        if (!Directory.Exists(sessionDir))
-        if (!File.Exists(mcpConfigPath))
             throw new InvalidOperationException($"Session directory missing: {sessionDir}");
 
         var list = await lists.GetByIdAsync(task.ListId, ct)
             ?? throw new InvalidOperationException($"List {task.ListId} not found.");
-        return new PlanningSessionResumeContext(taskId, list.WorkingDir ?? throw new InvalidOperationException($"List {task.ListId} has no working directory configured."), task.PlanningSessionId, mcpConfigPath);
+        var listWorkingDir = list.WorkingDir
+            ?? throw new InvalidOperationException($"List {task.ListId} has no working directory configured.");
+
+        var appSettings = await settings.GetAsync(ct);
+        var worktreePath = WorktreePathFor(taskId, appSettings.WorktreeStrategy, appSettings.CentralWorktreeRoot, listWorkingDir);
+        var token = task.PlanningSessionToken ?? string.Empty;
+
+        return new PlanningSessionResumeContext(taskId, listWorkingDir, task.PlanningSessionId, token, worktreePath);
     }
 
     private static string GenerateToken()