The session-stable system prompt embeds Model:/Provider: identity lines,
but mid-turn failover (try_activate_fallback) swaps the runtime without
touching them, so a fallback model misreports itself as the primary when
asked "what model are you?".
rewrite_prompt_model_identity() rewrites the last occurrence of each line
on _cached_system_prompt when a fallback activates (and back on restore,
byte-identical so the primary's prefix cache still hits). The rewrite is
never persisted to the session DB. _sync_failover_system_message() patches
the in-flight api_messages[0] at all 8 failover sites so the current turn
ships the corrected identity. Cache-safe: the fallback's prefix cache is
cold on a model switch anyway.
Co-authored-by: Hermes Agent <noreply@nousresearch.com>
