Fix VK API error code 10 with retry logic and exponential backoff

[konard]

🎯 Summary

This PR fixes issue #15 by implementing automatic retry logic with exponential backoff to handle VK API error code 10 ("Internal server error: Unknown error, try later").

📋 Issue Reference

Fixes #15

🔍 Problem Analysis

The VK API occasionally returns error code 10, which is an internal server error. According to VK API error schema, this error is defined as:

• Error Code: 10
• Name: "api_error_server"
• Description: "Internal server error"
• Global: true (can occur across all API methods)

This is a transient server-side error that requires retrying the request.

✨ Implementation Details

Changes to execute.sh:

1. Retry Logic: Added automatic retry mechanism with up to 3 attempts
2. Exponential Backoff: Implements progressive delays (2s → 4s → 8s) between retries
3. Enhanced Error Detection: Uses jq to properly extract error_code field from JSON responses
4. Informative Feedback: Logs retry attempts to stderr for better debugging
5. Backward Compatibility: Preserves existing token refresh functionality for authentication errors

Key Features:

• ✅ Handles error code 10 specifically with retry logic
• ✅ Exponential backoff to avoid overwhelming the server
• ✅ Maximum of 3 retry attempts before failing
• ✅ Clear error messages for debugging
• ✅ Maintains all existing error handling (token expiration, IP changes, etc.)
• ✅ Returns appropriate exit codes for success/failure

🧪 Testing

The solution has been validated for:

• ✅ Bash syntax checking (no errors)
• ✅ Preserves existing functionality for token-related errors
• ✅ Proper JSON parsing with jq
• ✅ Correct retry and backoff timing logic

📚 References

• VK API Error Schema: https://github.com/VKCOM/vk-api-schema/blob/master/errors.json
• Related discussions on error code 10 handling in various VK API SDKs

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