feat: Failure reporting and dead letter queue

[Snider]

Summary

Track all failures and provide options for handling them.

Use Case

After a large collection, need to know what failed and why, and optionally retry just the failures.

Dead Letter Queue

Failed items go to a queue for later processing:

.borg-failures/
├── 2024-01-15T10-30-00/
│   ├── failures.json
│   └── retry.sh

Failure Report

{
  "collection": "github:repos:org",
  "started": "2024-01-15T10:30:00Z",
  "completed": "2024-01-15T11:45:00Z",
  "stats": {
    "total": 150,
    "success": 145,
    "failed": 5
  },
  "failures": [
    {
      "url": "https://github.com/org/deleted-repo",
      "error": "404 Not Found",
      "attempts": 3,
      "retryable": false
    },
    {
      "url": "https://github.com/org/large-repo",
      "error": "timeout after 300s",
      "attempts": 3,
      "retryable": true
    }
  ]
}

Commands

# Retry failures from a run
borg retry .borg-failures/2024-01-15T10-30-00/

# Show failure summary
borg failures show .borg-failures/2024-01-15T10-30-00/

# Retry only specific errors
borg retry .borg-failures/... --only-retryable

# Clear old failures
borg failures clear --older-than 7d

Options

Flag	Description
--on-failure continue	Log and continue (default)
--on-failure stop	Stop on first failure
--on-failure prompt	Ask user what to do
--failures-dir	Custom failures directory

Acceptance Criteria

• Track all failures with context
• Generate retry scripts
• Retry command for failures
• Failure categorization (retryable vs permanent)
• Failure summary command

[google-labs-jules]

Jules is on it. When finished, you will see another comment and be able to review a PR.

[google-labs-jules]

Ready for a review! A PR has been created.

[google-labs-jules]

I apologize, but I encountered an unexpected error and wasn't able to complete the task.