Model downloads that fail (e.g., when Ollama is too old for a model)
were silently retrying 40 times with no UI feedback. Now errors are
broadcast via SSE and shown in the Active Model Downloads section.
Version mismatch errors use UnrecoverableError to fail immediately
instead of retrying. Stale failed jobs are cleared on retry so users
aren't permanently blocked.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>