This PR adds AbortSignal support to isomorphic-git, allowing users to cancel long-running operations using the standard AbortController API.

Motivation

Currently there's no way to cancel Git operations in isomorphic-git. This is particularly problematic for:

• Large repository clones that take a long time
• Network operations that hang or are slow
• Web applications that need cancel buttons for better UX

The signal property was already reserved in GitHttpRequest typedef for this purpose.

Changes

New functionality

• Added optional signal parameter to git.clone(), git.fetch(), and git.push()
• Created AbortError class for consistent error handling
• Signal is passed through the entire operation chain from API to HTTP requests

Implementation

• src/errors/AbortError.js - New error class following project patterns
• src/utils/abortSignal.js - Utility functions for signal handling
• Updated API functions (clone.js, fetch.js, push.js) to accept signal parameter
• Updated command layer to propagate signal through operations
• Updated HTTP clients to support native AbortSignal
• Added proper TypeScript definitions

Usage

const controller = new AbortController()

// Cancel after 10 seconds
setTimeout(() => controller.abort(), 10000)

try {
  await git.clone({
    fs,
    http,
    dir: '/repo',
    url: 'https://github.com/user/repo.git',
    signal: controller.signal
  })
} catch (err) {
  if (err instanceof git.Errors.AbortError) {
    console.log('Operation was cancelled')
  }
}

Or with a cancel button:

const controller = new AbortController()
document.getElementById('cancel').onclick = () => controller.abort()

await git.fetch({ fs, http, gitdir, signal: controller.signal })

Testing

Added tests to verify:

• Immediate abort (signal already aborted)
• Normal operation with non-aborted signal
• Proper error types and messages

Tests added to __tests__/test-clone.js, __tests__/test-fetch.js, and __tests__/test-push.js.

Compatibility

This is a non-breaking change. The signal parameter is optional and all existing code continues to work unchanged. AbortController is supported in all target browsers and Node.js 14+.

Checklist

• Added parameter to API functions and commands
• Documented parameter in JSDoc comments with examples
• Added test cases for abort scenarios
• Maintained backward compatibility