The fallback helpers (llm_call_with_fallback, llm_call_async_with_fallback,
stream_llm_with_fallback) build their candidate list as the primary target
followed by the configured fallbacks. Callers prepend the session's live
(url, model) to default_model_fallbacks, so if the user also lists their current
model among the fallbacks — a common misconfiguration — the chain re-attempts
the very route that just failed: a wasted round-trip (and, for the streaming
path, a spurious 'fallback' notice for a switch that didn't actually happen).
Add a small _dedupe_candidates() helper that filters malformed entries and drops
a later repeat of an already-seen (url, model), preserving order (first wins,
keeping its headers). Apply it in all three fallback chains.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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