When `fetch_nous_models()` fails silently during setup, the model
selection falls through to the OpenRouter static list. Users then pick
models in OpenRouter format (e.g. `anthropic/claude-opus-4.6`) which
the Nous inference API rejects with a 400 "missing model" error.
Add an explicit `elif selected_provider == "nous"` branch that prompts
for manual model entry instead of falling through to the generic
OpenRouter fallback.
The transcript extraction used len(history) to find new messages, but
history includes session_meta entries that are stripped before passing
to the agent. This mismatch caused 1 message to be lost from the
transcript on every turn after the first, because the slice offset
was too high. Use the filtered history length (history_offset) returned
by _run_agent instead.
Also changed the else branch from returning all agent_messages to
returning an empty list, so compressed/shorter agent output does not
duplicate the entire history into the transcript.
PercyDikec