Performance: Implement parallel assignment fetching in AppScript classroom snapshot exporter

Problem

The AppScript classroom snapshot exporter is running slowly due to sequential assignment fetching with rate limiting delays.

Current Performance Issues

• Assignment fetching uses sequential processing (one-by-one with delays)
• Each assignment takes ~1-2 seconds to fetch
• Rate limiting delays compound the total export time
• Only submission collection has parallel processing, not assignment fetching

Impact

• Slow exports for teachers with classrooms containing many assignments
• Poor user experience during data export
• Timeouts possible for very large classrooms

Proposed Solution

1. Create Parallel Assignment Fetching

// New function in DataCollectors.js
collectAssignmentsParallel: function(courseId, config = {}) {
  // Use UrlFetchApp.fetchAll() for batched parallel requests
  // Process assignments in batches of 5-10 to avoid rate limiting
  // Implement adaptive rate limiting between batches
}

2. Update Export Logic

// In ClassroomSnapshotExporter.js
enrichClassroomWithData: function(classroom, config, teacherEmail) {
  // Detect classrooms with many assignments (>10)
  // Switch to parallel processing when beneficial
  // Fall back to sequential for smaller classrooms
}

3. Performance Optimization

• Current: ~1-2 seconds per assignment (sequential)
• Target: ~5-10 assignments in parallel batches
• Expected: 5-10x faster for classrooms with many assignments

Files to Modify

1. appscript/development/classroom-snapshot-exporter/DataCollectors.js

• Add collectAssignmentsParallel() function
• Implement batched parallel requests using UrlFetchApp.fetchAll()

1. appscript/development/classroom-snapshot-exporter/ClassroomSnapshotExporter.js

• Update enrichClassroomWithData() to use parallel assignment fetching
• Add logic to detect when parallel processing is beneficial

Technical Requirements

• Maintain API rate limit compliance
• Preserve existing error handling and retry logic
• Keep adaptive rate limiting between batches
• Ensure backward compatibility with current export format

Success Criteria

• [ ] Parallel assignment fetching implemented
• [ ] Export time reduced by 5-10x for classrooms with >10 assignments
• [ ] No increase in API rate limit violations
• [ ] Existing functionality preserved
• [ ] Updated AppScript deployed to production

Priority

Medium - Performance enhancement that significantly improves user experience for teachers with large classrooms.

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Labels: performance, enhancement, appscript, google-classroom-api

Related to teacherEmail implementation work in recent commits.