The upload card printed the SDK's toString — 'MatrixError: [413] nope
(http://<hs>/_matrix/media/v3/upload?filename=…)'. describeUploadError() maps
the common cases to one sentence: 413/M_TOO_LARGE → 'This file is larger than
the server allows (limit N)' using m.upload.size when known, 429 → 'Slow down —
try again in a moment.', 401/403 → 'The server refused this upload: <server
text>', 5xx/transport after the retry loop → 'Couldn't reach the server. Check
your connection and retry.', other 4xx → the server's own sentence, URL
stripped. Both card renderers use it; the raw error is still console.warn-ed
by uploadContent for debugging. Unit-tested; verified headless with routed
413/403/503 responses.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA
