Problem

When calling getDirectoryHandle() with {create: true} in parallel for the same folder, the Node.js to FSA adapter was throwing an EEXIST error:

await Promise.all([
  dir.getDirectoryHandle('test', {create: true}),
  dir.getDirectoryHandle('test', {create: true}),
])
// Error: EEXIST: file already exists, mkdir '/test'

This occurred because both parallel calls would:

1. Check if the directory exists (stat returns ENOENT)
2. Attempt to create the directory (mkdir)
3. The second mkdir fails with EEXIST

Solution

Modified NodeFileSystemDirectoryHandle.getDirectoryHandle() to handle the EEXIST error gracefully. When mkdir throws EEXIST during directory creation:

1. Verify the path is actually a directory using stat
2. If it's a directory, return a handle to it (no error)
3. If it's a file, throw TypeMismatchError as before

This aligns with the File System Access API specification where creating a directory that already exists should succeed when using the create option.

Changes

• src/node-to-fsa/NodeFileSystemDirectoryHandle.ts: Added try-catch around mkdir to handle EEXIST error
• src/node-to-fsa/tests/NodeFileSystemDirectoryHandle.test.ts: Added test case for parallel folder creation

Testing

• ✅ New test validates parallel folder creation works correctly
• ✅ All existing tests pass (83 tests in NodeFileSystemDirectoryHandle, 130 in node-to-fsa module)
• ✅ Type checking, linting, and formatting pass
• ✅ Backward compatibility maintained - existing behavior unchanged for all other scenarios

Closes #97ba9c15-6996-496b-a9a0-a4699dbcd7ac

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