1.3.3 — Steady Mercury (hotfix: bots always get a usable provider)

• A bot never fails on a provider that cannot answer. A new bot (from Telegram, the TUI or the web) runs on the default LLM; if the configured default has no key or its key is rejected (401), Mercury uses the first usable provider instead, and a provider that rejects its key is remembered and skipped — for bots, the main agent's fallback chain and the default — until the key is changed. A bot turn that hit a bad key now retries on another provider instead of dead-lettering.
• mercury doctor flags keys that cannot be right (e.g. an OpenAI key that starts with 2sk- instead of sk-) before anything is tried.