This PR addresses critical memory management issues that were causing "JavaScript heap out of memory" errors during browser test execution, particularly when loading file content via the /api/file endpoint.

Root Causes Identified

The memory issues were caused by several factors:

1. Synchronous file loading: The /api/file endpoint used fs.readFileSync() which loads entire files into memory synchronously
2. Unbounded memory accumulation: Worker processes accumulated errors and test results without limits
3. Inefficient object serialization: Large objects and arrays could cause memory spikes during WebSocket serialization

Changes Made

File API Memory Safety

• Replaced synchronous fs.readFileSync() with streaming fs.createReadStream()
• Added 10MB file size limit to prevent memory overload
• Implemented proper error handling and HTTP status codes
• Files are now streamed directly to the response without loading into memory

Worker Process Memory Management

• Added MAX_ERRORS (1000) and MAX_FINISHED_TESTS (500) limits to prevent unbounded array growth
• Implemented automatic cleanup using Array.shift() to remove oldest entries
• Added cleanupWorkerMemory() function for post-test cleanup

Enhanced Object Serialization

• Improved safe-serialize utility with memory-conscious limits:
  • Array truncation at 1000 items with truncation message
  • Object property limit of 100 per object
  • Stack trace truncation to 2000 characters
  • Better handling of Functions, Buffers, and complex objects
• Maintains all existing circular reference protection

Before/After Comparison

Before:

// File API - loads entire file into memory
res.send(fs.readFileSync(req.file));

// Worker arrays grow indefinitely 
errors.push(err);
finishedTests.push(test);

After:

// File API - streams with size limits
const stats = await fs.promises.stat(req.file);
if (stats.size > MAX_FILE_SIZE) return res.status(413)...
fs.createReadStream(req.file).pipe(res);

// Worker arrays with bounds
if (errors.length > MAX_ERRORS) errors.shift();
if (finishedTests.length > MAX_FINISHED_TESTS) finishedTests.shift();

Testing

• 25+ new tests covering memory management scenarios
• All existing 140+ tests continue to pass
• Stress testing with large data structures (2000+ item arrays, 150+ property objects)
• Verified backward compatibility for all APIs
• Manual testing confirms streaming functionality works correctly

The implementation resolves the heap overflow errors while maintaining full backward compatibility and adding robust memory safeguards throughout the codebase.

Fixes #568.

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