matrix-js-sdk rejects an upload whose XHR ends with status 0 (offline,
connection reset, DNS) with DOMException('AbortError') to mimic fetch,
the same name mx.cancelUpload() produces. isRetryableUploadError bailed
on any AbortError, so the one failure class the retry loop was built
for was never retried. Decide by our own cancel AbortSignal instead.
Verified with Playwright routing the upload endpoint: 502 → network drop
→ ok now completes in 3 attempts (1 s, 2 s back-off) and the image sends;
413 still fails fast after 1 attempt; persistent 503 gives up after 4.
Unit tests in utils/uploadRetry.test.ts.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA
