AC:\n- Providers emit ProviderFailure with structured kind/detail for auth, rate-limit, timeout, and unavailable cases.\n- TUI maps ProviderFailure kinds to consistent toasts and fallbacks (no 429 string matching).\n- Cloud health checks detect unauthorized failures without relying on string parsing.\n\nTests:\n- cargo test -p owlen-core (fails: httpmock cannot bind 127.0.0.1 inside sandbox).\n- cargo test -p owlen-providers\n- cargo test -p owlen-tui
vikingowl
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