Retry YouTube uploads on transient 5xx errors #4

Problem

shortube/upload.py makes a single attempt to upload. A transient YouTube API 5xx (or rate-limit 429) aborts the whole pipeline with an UploadError even though the upload would succeed a moment later.

Task

Add a bounded retry with exponential backoff around the upload request (e.g. 3 attempts, 2s/4s backoff), only for transient statuses (429, 5xx). Keep permanent errors (403, 401, quota) failing immediately.

Acceptance criteria

• Unit tests simulate transient-then-success and permanent-failure (mock the youtube.videos().insert() call)
• Existing tests in tests/test_upload.py still pass
• Errors are logged per attempt

Files

• shortube/upload.py
• tests/test_upload.py