Cloudflare Sandbox

Cloudflare Sandboxes SDK

Status: Production Ready (Open Beta) Last Updated: 2025-10-29 Dependencies: cloudflare-worker-base, cloudflare-durable-objects (recommended for understanding) Latest Versions: @cloudflare/sandbox@0.4.12, Docker image: cloudflare/sandbox:0.4.12

Quick Start (15 Minutes)

1. Install SDK and Setup Wrangler

npm install @cloudflare/sandbox@latest

wrangler.jsonc:

{
  "name": "my-sandbox-worker",
  "main": "src/index.ts",
  "compatibility_flags": ["nodejs_compat"],
  "containers": [{
    "class_name": "Sandbox",
    "image": "cloudflare/sandbox:0.4.12",
    "instance_type": "lite"
  }],
  "durable_objects": {
    "bindings": [{
      "class_name": "Sandbox",
      "name": "Sandbox"
    }]
  },
  "migrations": [{
    "tag": "v1",
    "new_sqlite_classes": ["Sandbox"]
  }]
}

Why this matters:

• nodejs_compat enables Node.js APIs required by SDK
• containers defines the Ubuntu container image
• durable_objects binding enables persistent routing
• migrations registers the Sandbox class

2. Create Your First Sandbox Worker

import { getSandbox, type Sandbox } from '@cloudflare/sandbox';
export { Sandbox } from '@cloudflare/sandbox';

type Env = {
  Sandbox: DurableObjectNamespace<Sandbox>;
};

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    // Get sandbox instance (creates if doesn't exist)
    const sandbox = getSandbox(env.Sandbox, 'my-first-sandbox');

    // Execute Python code
    const result = await sandbox.exec('python3 -c "print(2 + 2)"');

    return Response.json({
      output: result.stdout,
      success: result.success,
      exitCode: result.exitCode
    });
  }
};

CRITICAL:

• MUST export { Sandbox } from @cloudflare/sandbox in your Worker
• Sandbox ID determines routing (same ID = same container)
• First request creates container (~2-3 min cold start)
• Subsequent requests are fast (<1s)

3. Deploy and Test

npm run deploy
curl https://your-worker.workers.dev

Expected output:

{
  "output": "4\n",
  "success": true,
  "exitCode": 0
}

Architecture (Understanding the 3-Layer Model)

How Sandboxes Work

┌─────────────────────────────────────────┐
│  Your Worker (Layer 1)                  │
│  - Handles HTTP requests                │
│  - Calls getSandbox()                   │
│  - Uses sandbox.exec(), writeFile(), etc│
└──────────────┬──────────────────────────┘
               │ RPC via Durable Object
┌──────────────▼──────────────────────────┐
│  Durable Object (Layer 2)               │
│  - Routes by sandbox ID                 │
│  - Maintains persistent identity        │
│  - Geographic stickiness                │
└──────────────┬──────────────────────────┘
               │ Container API
┌──────────────▼──────────────────────────┐
│  Ubuntu Container (Layer 3)             │
│  - Full Linux environment               │
│  - Python 3.11, Node 20, Git, etc.      │
│  - Filesystem: /workspace, /tmp, /home  │
│  - Process isolation (VM-based)         │
└─────────────────────────────────────────┘

Key Insight: Workers handle API logic (fast), Durable Objects route requests (persistent identity), Containers execute code (full capabilities).

Critical Container Lifecycle (Most Important Section!)

Container States

┌─────────┐  First request  ┌────────┐  ~10 min idle  ┌──────┐
│ Not     │ ───────────────>│ Active │ ─────────────> │ Idle │
│ Created │                 │        │                │      │
└─────────┘                 └───┬────┘                └──┬───┘
                                │ ^                      │
                                │ │ New request          │
                                │ └──────────────────────┘
                                │                         │
                                ▼                         ▼
                            Files persist          ALL FILES DELETED
                            Processes run          ALL PROCESSES KILLED
                            State maintained       ALL STATE RESET

The #1 Gotcha: Ephemeral by Default

While Container is Active (~10 min after last request):

• ✅ Files in /workspace, /tmp, /home persist
• ✅ Background processes keep running
• ✅ Shell environment variables remain
• ✅ Session working directories preserved

When Container Goes Idle (after inactivity):

• ❌ ALL files deleted (entire filesystem reset)
• ❌ ALL processes terminated
• ❌ ALL shell state lost
• ⚠️ Next request creates fresh container from scratch

This is NOT like a traditional server. Sandboxes are ephemeral by design.

Handling Persistence

For Important Data: Use external storage

// Save to R2 before container goes idle
await sandbox.writeFile('/workspace/data.txt', content);
const fileData = await sandbox.readFile('/workspace/data.txt');
await env.R2.put('backup/data.txt', fileData);

// Restore on next request
const restored = await env.R2.get('backup/data.txt');
if (restored) {
  await sandbox.writeFile('/workspace/data.txt', await restored.text());
}

For Build Artifacts: Accept ephemerality or use caching

// Check if setup needed (handles cold starts)
const exists = await sandbox.readdir('/workspace/project').catch(() => null);
if (!exists) {
  await sandbox.gitCheckout(repoUrl, '/workspace/project');
  await sandbox.exec('npm install', { cwd: '/workspace/project' });
}
// Now safe to run build
await sandbox.exec('npm run build', { cwd: '/workspace/project' });

Session Management (Game-Changer for Chat Agents)

What Are Sessions?

Sessions are bash shell contexts within one sandbox. Think terminal tabs.

Key Properties:

• Each session has separate working directory
• Sessions share same filesystem
• Working directory persists across commands in same session
• Perfect for multi-step workflows

Pattern: Chat-Based Coding Agent

type ConversationState = {
  sandboxId: string;
  sessionId: string;
};

// First message: Create sandbox and session
const sandboxId = `user-${userId}`;
const sandbox = getSandbox(env.Sandbox, sandboxId);
const sessionId = await sandbox.createSession();

// Store in conversation state (database, KV, etc.)
await env.KV.put(`conversation:${conversationId}`, JSON.stringify({
  sandboxId,
  sessionId
}));

// Later messages: Reuse same session
const state = await env.KV.get(`conversation:${conversationId}`);
const { sandboxId, sessionId } = JSON.parse(state);
const sandbox = getSandbox(env.Sandbox, sandboxId);

// Commands run in same context
await sandbox.exec('cd /workspace/project', { session: sessionId });
await sandbox.exec('ls -la', { session: sessionId }); // Still in /workspace/project
await sandbox.exec('git status', { session: sessionId }); // Still in /workspace/project

Without Sessions (Common Mistake)

// ❌ WRONG: Each command runs in separate session
await sandbox.exec('cd /workspace/project');
await sandbox.exec('ls'); // NOT in /workspace/project (different session)

Pattern: Parallel Execution

const session1 = await sandbox.createSession();
const session2 = await sandbox.createSession();

// Run different tasks simultaneously
await Promise.all([
  sandbox.exec('python train_model.py', { session: session1 }),
  sandbox.exec('node generate_reports.js', { session: session2 })
]);

Sandbox Naming Strategies

Per-User Sandboxes (Persistent Workspace)

const sandbox = getSandbox(env.Sandbox, `user-${userId}`);

Pros: User's work persists while actively using (10 min idle time) Cons: Geographic lock-in (first request determines location) Use Cases: Interactive notebooks, IDEs, persistent workspaces

Per-Session Sandboxes (Fresh Each Time)

const sandboxId = `session-${Date.now()}-${crypto.randomUUID()}`;
const sandbox = getSandbox(env.Sandbox, sandboxId);
// Always destroy after use
await sandbox.destroy();

Pros: Clean environment, no state pollution Cons: No persistence between requests Use Cases: One-shot code execution, CI/CD, testing

Per-Task Sandboxes (Idempotent & Traceable)

const sandbox = getSandbox(env.Sandbox, `build-${repoName}-${commitSha}`);

Pros: Reproducible, debuggable, cacheable Cons: Need explicit cleanup strategy Use Cases: Build systems, data pipelines, automated workflows

Core API Reference

Getting a Sandbox

import { getSandbox } from '@cloudflare/sandbox';

const sandbox = getSandbox(env.Sandbox, 'unique-sandbox-id');
// Creates new sandbox if doesn't exist, or gets existing one

Executing Commands

// Basic execution
const result = await sandbox.exec('python3 script.py');
console.log(result.stdout);   // Standard output
console.log(result.stderr);   // Standard error
console.log(result.exitCode); // Exit code (0 = success)
console.log(result.success);  // Boolean (exitCode === 0)

// With options
const result = await sandbox.exec('npm install', {
  cwd: '/workspace/project',        // Working directory
  timeout: 120000,                   // Timeout in ms (default: 30s)
  session: sessionId,                // Session ID
  env: { NODE_ENV: 'production' }   // Environment variables
});

// Always check exit codes!
if (!result.success) {
  throw new Error(`Command failed: ${result.stderr}`);
}

File Operations

// Write file
await sandbox.writeFile('/workspace/data.txt', 'content');

// Read file
const content = await sandbox.readFile('/workspace/data.txt');

// Create directory
await sandbox.mkdir('/workspace/project', { recursive: true });

// List directory
const files = await sandbox.readdir('/workspace');
console.log(files); // ['data.txt', 'project']

// Delete file/directory
await sandbox.rm('/workspace/data.txt');
await sandbox.rm('/workspace/project', { recursive: true });

Git Operations

// Clone repository (optimized, faster than exec('git clone'))
await sandbox.gitCheckout(
  'https://github.com/user/repo',
  '/workspace/repo'
);

// Now use standard git commands
await sandbox.exec('git status', { cwd: '/workspace/repo' });
await sandbox.exec('git diff', { cwd: '/workspace/repo' });

Code Interpreter (Jupyter-like)

// Create Python context
const ctx = await sandbox.createCodeContext({ language: 'python' });

// Execute code - last expression auto-returned
const result = await sandbox.runCode(`
import pandas as pd
df = pd.DataFrame({'a': [1, 2, 3], 'b': [4, 5, 6]})
df['a'].sum()  # This value is automatically returned
`, { context: ctx });

console.log(result.results[0].text); // "6"
console.log(result.logs); // Output from print() statements
console.log(result.error); // Any errors

Background Processes

// Start long-running process
const proc = await sandbox.spawn('python server.py');
console.log(proc.pid);

// Check if still running
const running = await sandbox.isProcessRunning(proc.pid);

// Kill process
await sandbox.killProcess(proc.pid);

Cleanup

// Destroy sandbox permanently
await sandbox.destroy();
// All files deleted, container removed, cannot be recovered

Critical Rules

Always Do

✅ Check exit codes - if (!result.success) { handle error } ✅ Use sessions for multi-step workflows - Preserve working directory ✅ Handle cold starts - Check if files exist before assuming they're there ✅ Set timeouts - Prevent hanging on long operations ✅ Destroy ephemeral sandboxes - Cleanup temp/session-based sandboxes ✅ Use external storage for persistence - R2/KV/D1 for important data ✅ Validate user input - Sanitize before exec() to prevent command injection ✅ Export Sandbox class - export { Sandbox } from '@cloudflare/sandbox'

Never Do

❌ Assume files persist after idle - Container resets after ~10 min ❌ Ignore exit codes - Always check result.success or result.exitCode ❌ Chain commands without sessions - cd /dir then ls won't work ❌ Execute unsanitized user input - Use code interpreter or validate thoroughly ❌ Forget nodejs_compat flag - Required in wrangler.jsonc ❌ Skip migrations - Durable Objects need migration entries ❌ Use .workers.dev for preview URLs - Need custom domain ❌ Create unlimited sandboxes - Destroy ephemeral ones to avoid leaks

Known Issues Prevention

This skill prevents 10 documented issues:

Issue #1: Missing nodejs_compat Flag

Error: ReferenceError: fetch is not defined or Buffer is not defined Source: https://developers.cloudflare.com/sandbox/get-started/ Why It Happens: SDK requires Node.js APIs not available in standard Workers Prevention: Add "compatibility_flags": ["nodejs_compat"] to wrangler.jsonc

Issue #2: Missing Migrations

Error: Error: Class 'Sandbox' not found Source: https://developers.cloudflare.com/durable-objects/ Why It Happens: Durable Objects must be registered via migrations Prevention: Include migrations array in wrangler.jsonc

Issue #3: Assuming File Persistence

Error: Files disappear after inactivity Source: https://developers.cloudflare.com/sandbox/concepts/sandboxes/ Why It Happens: Containers go idle after ~10 min, all state reset Prevention: Use external storage (R2/KV) or check existence on each request

Issue #4: Session Directory Confusion

Error: Commands execute in wrong directory Source: https://developers.cloudflare.com/sandbox/concepts/sessions/ Why It Happens: Each exec() uses new session unless explicitly specified Prevention: Create session with createSession(), pass to all related commands

Issue #5: Ignoring Exit Codes

Error: Assuming command succeeded when it failed Source: Shell best practices Why It Happens: Not checking result.success or result.exitCode Prevention: Always check: if (!result.success) throw new Error(result.stderr)

Issue #6: Not Handling Cold Starts

Error: Commands fail because dependencies aren't installed Source: https://developers.cloudflare.com/sandbox/concepts/sandboxes/ Why It Happens: Container resets after idle period Prevention: Check if setup needed before running commands

Issue #7: Docker Not Running (Local Dev)

Error: Failed to build container during local development Source: https://developers.cloudflare.com/sandbox/get-started/ Why It Happens: Local dev requires Docker daemon Prevention: Ensure Docker Desktop is running before npm run dev

Issue #8: Version Mismatch (Package vs Docker Image)

Error: API methods not available or behaving unexpectedly Source: GitHub issues Why It Happens: npm package version doesn't match Docker image version Prevention: Keep @cloudflare/sandbox package and cloudflare/sandbox image in sync

Issue #9: Not Cleaning Up Ephemeral Sandboxes

Error: Resource exhaustion, unexpected costs Source: Resource management best practices Why It Happens: Creating sandboxes without destroying them Prevention: await sandbox.destroy() in finally block for temp sandboxes

Issue #10: Command Injection Vulnerability

Error: Security breach from unsanitized user input Source: Security best practices Why It Happens: Passing user input directly to exec() Prevention: Use code interpreter API or validate/sanitize input thoroughly

Configuration Files Reference

wrangler.jsonc (Full Example)

{
  "name": "my-sandbox-app",
  "main": "src/index.ts",
  "compatibility_date": "2025-10-29",
  "compatibility_flags": ["nodejs_compat"],

  "containers": [{
    "class_name": "Sandbox",
    "image": "cloudflare/sandbox:0.4.12",
    "instance_type": "lite"
  }],

  "durable_objects": {
    "bindings": [{
      "class_name": "Sandbox",
      "name": "Sandbox"
    }]
  },

  "migrations": [{
    "tag": "v1",
    "new_sqlite_classes": ["Sandbox"]
  }],

  "env": {
    "ANTHROPIC_API_KEY": {
      "description": "Optional: For AI features"
    }
  },

  "observability": {
    "enabled": true
  }
}

Why these settings:

• nodejs_compat: Required for SDK to work
• containers.image: Specific version ensures consistency
• instance_type: "lite": Smallest instance, upgrade to "large" for more resources
• migrations: Registers Sandbox Durable Object class
• observability: Enable logging for debugging

Dockerfile (Optional - For Local Dev)

Only needed if extending base image:

FROM cloudflare/sandbox:0.4.12

# Install additional tools
RUN apt-get update && apt-get install -y \
    ffmpeg \
    imagemagick \
    && rm -rf /var/lib/apt/lists/*

# Expose port for preview URLs (local dev only)
EXPOSE 8080

Common Patterns

Pattern 1: One-Shot Code Execution

export default {
  async fetch(request: Request, env: Env) {
    const { code, language } = await request.json();

    // Create ephemeral sandbox
    const sandboxId = `exec-${Date.now()}-${crypto.randomUUID()}`;
    const sandbox = getSandbox(env.Sandbox, sandboxId);

    try {
      // Create code context
      const ctx = await sandbox.createCodeContext({ language });

      // Execute code safely
      const result = await sandbox.runCode(code, {
        context: ctx,
        timeout: 10000
      });

      return Response.json({
        result: result.results?.[0]?.text,
        logs: result.logs,
        error: result.error
      });
    } finally {
      // Always cleanup
      await sandbox.destroy();
    }
  }
};

When to use: API endpoints for code execution, code playgrounds, learning platforms

Pattern 2: Persistent User Workspace

export default {
  async fetch(request: Request, env: Env) {
    const userId = request.headers.get('X-User-ID');
    const { command, sessionId: existingSession } = await request.json();

    // User-specific sandbox (persists while active)
    const sandbox = getSandbox(env.Sandbox, `user-${userId}`);

    // Get or create session
    let sessionId = existingSession;
    if (!sessionId) {
      sessionId = await sandbox.createSession();
    }

    // Execute command in persistent context
    const result = await sandbox.exec(command, {
      session: sessionId,
      timeout: 30000
    });

    return Response.json({
      sessionId, // Return for next request
      output: result.stdout,
      error: result.stderr,
      success: result.success
    });
  }
};

When to use: Interactive coding environments, notebooks, IDEs, development workspaces

Pattern 3: CI/CD Build Pipeline

async function runBuild(repoUrl: string, commit: string, env: Env) {
  const sandboxId = `build-${repoUrl.split('/').pop()}-${commit}`;
  const sandbox = getSandbox(env.Sandbox, sandboxId);

  try {
    // Clone repository
    await sandbox.gitCheckout(repoUrl, '/workspace/repo');

    // Checkout specific commit
    await sandbox.exec(`git checkout ${commit}`, {
      cwd: '/workspace/repo'
    });

    // Install dependencies
    const install = await sandbox.exec('npm install', {
      cwd: '/workspace/repo',
      timeout: 180000 // 3 minutes
    });

    if (!install.success) {
      throw new Error(`Install failed: ${install.stderr}`);
    }

    // Run build
    const build = await sandbox.exec('npm run build', {
      cwd: '/workspace/repo',
      timeout: 300000 // 5 minutes
    });

    if (!build.success) {
      throw new Error(`Build failed: ${build.stderr}`);
    }

    // Save artifacts to R2
    const dist = await sandbox.exec('tar -czf dist.tar.gz dist', {
      cwd: '/workspace/repo'
    });
    const artifact = await sandbox.readFile('/workspace/repo/dist.tar.gz');
    await env.R2.put(`builds/${commit}.tar.gz`, artifact);

    return { success: true, artifactKey: `builds/${commit}.tar.gz` };
  } finally {
    // Optional: Keep sandbox for debugging or destroy
    // await sandbox.destroy();
  }
}

When to use: Build systems, testing pipelines, deployment automation

Pattern 4: AI Agent with Claude Code

async function runClaudeCodeOnRepo(
  repoUrl: string,
  task: string,
  env: Env
): Promise<{ diff: string; logs: string }> {
  const sandboxId = `claude-${Date.now()}`;
  const sandbox = getSandbox(env.Sandbox, sandboxId);

  try {
    // Clone repository
    await sandbox.gitCheckout(repoUrl, '/workspace/repo');

    // Run Claude Code CLI with secure environment injection
    // ⚠️ SECURITY: Use env option instead of shell export to prevent key exposure in logs
    const result = await sandbox.exec(
      `claude -p "${task}" --permission-mode acceptEdits`,
      {
        cwd: '/workspace/repo',
        timeout: 300000, // 5 minutes
        env: {
          ANTHROPIC_API_KEY: env.ANTHROPIC_API_KEY
        }
      }
    );

    // Get diff of changes
    const diff = await sandbox.exec('git diff', {
      cwd: '/workspace/repo'
    });

    return {
      diff: diff.stdout,
      logs: result.stdout
    };
  } finally {
    await sandbox.destroy();
  }
}

When to use: Automated code refactoring, code generation, AI-powered development

Using Bundled Resources

Scripts (scripts/)

• setup-sandbox-binding.sh - Interactive wrangler.jsonc configuration
• test-sandbox.ts - Validation script to test sandbox setup

Example Usage:

# Setup wrangler config
./scripts/setup-sandbox-binding.sh

# Test sandbox
npx tsx scripts/test-sandbox.ts

References (references/)

• references/persistence-guide.md - Deep dive on container lifecycle and persistence
• references/session-management.md - Advanced session patterns and best practices
• references/common-errors.md - Complete list of errors with solutions
• references/naming-strategies.md - Choosing sandbox IDs for different use cases

When Claude should load these:

• Load persistence-guide.md when debugging state issues or cold starts
• Load session-management.md when building multi-step workflows or chat agents
• Load common-errors.md when encountering specific errors
• Load naming-strategies.md when designing sandbox architecture

Advanced Topics

Geographic Distribution

First request to a sandbox ID determines its geographic location (via Durable Objects).

For Global Apps:

// Option 1: Multiple sandboxes per user (better latency)
const region = request.cf?.colo || 'default';
const sandbox = getSandbox(env.Sandbox, `user-${userId}-${region}`);

// Option 2: Single sandbox (simpler, higher latency for distant users)
const sandbox = getSandbox(env.Sandbox, `user-${userId}`);

Error Handling Strategy

async function safeSandboxExec(
  sandbox: Sandbox,
  cmd: string,
  options?: any
) {
  try {
    const result = await sandbox.exec(cmd, {
      ...options,
      timeout: options?.timeout || 30000
    });

    if (!result.success) {
      console.error(`Command failed: ${cmd}`, {
        exitCode: result.exitCode,
        stderr: result.stderr
      });

      return {
        success: false,
        error: result.stderr,
        exitCode: result.exitCode
      };
    }

    return {
      success: true,
      output: result.stdout,
      exitCode: 0
    };
  } catch (error) {
    console.error(`Sandbox error:`, error);
    return {
      success: false,
      error: error.message,
      exitCode: -1
    };
  }
}

Security Hardening

// Input validation
function sanitizeCommand(input: string): string {
  const dangerous = ['rm -rf', '$(', '`', '&&', '||', ';', '|'];
  for (const pattern of dangerous) {
    if (input.includes(pattern)) {
      throw new Error(`Dangerous pattern detected: ${pattern}`);
    }
  }
  return input;
}

// Use code interpreter instead of direct exec for untrusted code
async function executeUntrustedCode(code: string, sandbox: Sandbox) {
  const ctx = await sandbox.createCodeContext({ language: 'python' });
  return await sandbox.runCode(code, { context: ctx, timeout: 10000 });
}

Dependencies

Required:

• @cloudflare/sandbox@0.4.12 - Sandbox SDK
• wrangler@latest - Deployment CLI
• Docker Desktop - Local development only

Optional:

• @anthropic-ai/sdk - For AI features
• @cloudflare/workers-types - TypeScript types

Official Documentation

• Cloudflare Sandboxes: https://developers.cloudflare.com/sandbox/
• Architecture Guide: https://developers.cloudflare.com/sandbox/concepts/architecture/
• API Reference: https://developers.cloudflare.com/sandbox/api-reference/
• Durable Objects: https://developers.cloudflare.com/durable-objects/
• GitHub SDK: https://github.com/cloudflare/sandbox-sdk

Package Versions (Verified 2025-10-29)

{
  "dependencies": {
    "@cloudflare/sandbox": "^0.4.12"
  },
  "devDependencies": {
    "wrangler": "^3.80.0",
    "@cloudflare/workers-types": "^4.20241106.0"
  }
}

Docker Image: cloudflare/sandbox:0.4.12

Production Example

This skill is based on official Cloudflare tutorials:

• Claude Code Integration: https://developers.cloudflare.com/sandbox/tutorials/claude-code/
• AI Code Executor: https://developers.cloudflare.com/sandbox/tutorials/ai-code-executor/
• Build Time: ~15 min (setup) + ~5 min (first deploy)
• Errors: 0 (all 10 known issues prevented)
• Validation: ✅ Tested with Python, Node.js, Git, background processes, sessions

Troubleshooting

Problem: "Class 'Sandbox' not found"

Solution: Add migrations to wrangler.jsonc and ensure export { Sandbox } in Worker

Problem: Files disappear after some time

Solution: Container goes idle after ~10 min. Use R2/KV for persistence or rebuild environment

Problem: Commands execute in wrong directory

Solution: Create session with createSession(), pass sessionId to all related commands

Problem: Docker error during local dev

Solution: Ensure Docker Desktop is running before npm run dev

Problem: "fetch is not defined"

Solution: Add "compatibility_flags": ["nodejs_compat"] to wrangler.jsonc

Complete Setup Checklist

• npm install @cloudflare/sandbox@latest
• Add nodejs_compat to compatibility_flags
• Add containers configuration with correct image version
• Add Durable Objects binding
• Add migrations for Sandbox class
• Export Sandbox class in Worker: export { Sandbox } from '@cloudflare/sandbox'
• Docker Desktop running (local dev only)
• Test with simple exec command
• Verify exit codes are being checked
• Implement cleanup for ephemeral sandboxes
• Test cold start behavior

Questions? Issues?

1. Check references/common-errors.md for specific error solutions
2. Verify all steps in wrangler.jsonc configuration
3. Check official docs: https://developers.cloudflare.com/sandbox/
4. Ensure Docker is running for local development
5. Confirm package version matches Docker image version