fix(loop): make Docker sandbox opt-in and preserve progress file

- Add --sandbox flag to loop command (default: use plain claude -p)
- Append to progress.txt instead of overwriting between runs
- Display execution mode (Docker sandbox vs Claude CLI) in output

.changeset/loop-sandbox-optional.md

@@ -0,0 +1,10 @@
+---
+"@tm/core": patch
+"@tm/cli": patch
+---
+
+Make Docker sandbox mode opt-in for loop command
+
+- Add `--sandbox` flag to `task-master loop` (default: use plain `claude -p`)
+- Preserve progress.txt between runs (append instead of overwrite)
+- Display execution mode in loop startup output

apps/cli/src/commands/loop.command.ts

@@ -22,6 +22,7 @@ export interface LoopCommandOptions {
 	progressFile?: string;
 	tag?: string;
 	project?: string;
+	sandbox?: boolean;
 }
 
 export class LoopCommand extends Command {
@@ -47,6 +48,7 @@ export class LoopCommand extends Command {
 				'--project <path>',
 				'Project root directory (auto-detected if not provided)'
 			)
+			.option('--sandbox', 'Run Claude in Docker sandbox mode')
 			.action((options: LoopCommandOptions) => this.execute(options));
 	}
 
@@ -80,11 +82,17 @@ export class LoopCommand extends Command {
 				storageType: this.tmCore.tasks.getStorageType()
 			});
 
-			this.handleSandboxAuth();
+			// Only check sandbox auth when --sandbox flag is used
+			if (options.sandbox) {
+				this.handleSandboxAuth();
+			}
 
 			console.log(chalk.cyan('Starting Task Master Loop...'));
 			console.log(chalk.dim(`Preset: ${prompt}`));
 			console.log(chalk.dim(`Max iterations: ${iterations}`));
+			console.log(
+				chalk.dim(`Mode: ${options.sandbox ? 'Docker sandbox' : 'Claude CLI'}`)
+			);
 
 			// Show next task only for default preset (other presets don't use Task Master tasks)
 			if (prompt === 'default') {
@@ -105,7 +113,8 @@ export class LoopCommand extends Command {
 				iterations,
 				prompt,
 				progressFile,
-				tag: options.tag
+				tag: options.tag,
+				sandbox: options.sandbox
 			};
 
 			const result = await this.tmCore.loop.run(config);

package-lock.json

@@ -67,6 +67,7 @@
 				"ollama-ai-provider-v2": "^1.3.1",
 				"open": "^10.2.0",
 				"ora": "^8.2.0",
+				"proper-lockfile": "^4.1.2",
 				"simple-git": "^3.28.0",
 				"steno": "^4.0.2",
 				"terminal-link": "^5.0.0",

package.json

@@ -117,7 +117,8 @@
 		"turndown": "^7.2.2",
 		"undici": "^7.16.0",
 		"uuid": "^11.1.0",
-		"zod": "^4.1.12"
+		"zod": "^4.1.12",
+		"proper-lockfile": "^4.1.2"
 	},
 	"optionalDependencies": {
 		"@anthropic-ai/claude-code": "^2.0.59",

packages/tm-core/src/modules/loop/loop-domain.ts

@@ -188,7 +188,8 @@ export class LoopDomain {
 				partial.progressFile ??
 				path.join(this.projectRoot, '.taskmaster', 'progress.txt'),
 			sleepSeconds: partial.sleepSeconds ?? 5,
-			tag: partial.tag
+			tag: partial.tag,
+			sandbox: partial.sandbox ?? false
 		};
 	}
 }

packages/tm-core/src/modules/loop/services/loop.service.ts

@@ -3,7 +3,7 @@
  */
 
 import { spawnSync } from 'node:child_process';
-import { appendFile, mkdir, readFile, writeFile } from 'node:fs/promises';
+import { appendFile, mkdir, readFile } from 'node:fs/promises';
 import path from 'node:path';
 import { PRESETS, isPreset as checkIsPreset } from '../presets/index.js';
 import type {
@@ -80,7 +80,11 @@ export class LoopService {
 			console.log(`━━━ Iteration ${i} of ${config.iterations} ━━━`);
 
 			const prompt = await this.buildPrompt(config, i);
-			const iteration = this.executeIteration(prompt, i);
+			const iteration = this.executeIteration(
+				prompt,
+				i,
+				config.sandbox ?? false
+			);
 			iterations.push(iteration);
 
 			// Check for early exit conditions
@@ -135,9 +139,11 @@ export class LoopService {
 	private async initProgressFile(config: LoopConfig): Promise<void> {
 		await mkdir(path.dirname(config.progressFile), { recursive: true });
 		const tagLine = config.tag ? `# Tag: ${config.tag}\n` : '';
-		await writeFile(
+		// Append to existing progress file instead of overwriting
+		await appendFile(
 			config.progressFile,
-			`# Task Master Loop Progress
+			`
+# Task Master Loop Progress
 # Started: ${new Date().toISOString()}
 # Preset: ${config.prompt}
 # Max Iterations: ${config.iterations}
@@ -217,20 +223,23 @@ Loop iteration ${iteration} of ${config.iterations}${tagInfo}`;
 
 	private executeIteration(
 		prompt: string,
-		iterationNum: number
+		iterationNum: number,
+		sandbox: boolean
 	): LoopIteration {
 		const startTime = Date.now();
 
-		const result = spawnSync(
+		// Use docker sandbox or plain claude based on config
-			'docker',
+		const command = sandbox ? 'docker' : 'claude';
-			['sandbox', 'run', 'claude', '-p', prompt],
+		const args = sandbox
-			{
+			? ['sandbox', 'run', 'claude', '-p', prompt]
-				cwd: this.projectRoot,
+			: ['-p', prompt, '--allowedTools', 'Edit,Write,Bash,Read,Glob,Grep'];
-				encoding: 'utf-8',
+
-				maxBuffer: 50 * 1024 * 1024, // 50MB buffer
+		const result = spawnSync(command, args, {
-				stdio: ['inherit', 'pipe', 'pipe']
+			cwd: this.projectRoot,
-			}
+			encoding: 'utf-8',
-		);
+			maxBuffer: 50 * 1024 * 1024, // 50MB buffer
+			stdio: ['inherit', 'pipe', 'pipe']
+		});
 
 		const output = (result.stdout || '') + (result.stderr || '');
 

packages/tm-core/src/modules/loop/types.ts

@@ -26,6 +26,8 @@ export interface LoopConfig {
 	sleepSeconds: number;
 	/** Tag context to operate on (optional) */
 	tag?: string;
+	/** Run Claude in Docker sandbox mode (default: false) */
+	sandbox?: boolean;
 }
 
 /**