The channel-override baseline from #131295 skipped the session /model tier and
normalized the expected model with the agent's current provider. Both disagree with
how the agent was built, which turned three cases main handled into wrong verdicts:
- a recorded Nous switch off a session /model choice was evicted (the baseline was
the channel model, so the (alias, backing) record never matched);
- a session-primary fallback that landed on the channel's model was kept;
- an OpenRouter primary that fell back to native Anthropic was kept, because the
channel slug normalized under the fallback provider equals the fallback model.
Resolve the baseline in the same order as _resolve_session_agent_runtime (session
/model, channel_overrides, global) and normalize it for the agent's primary provider,
the same route the welcome-host pin already uses. A session override whose provider
was unavailable this turn ran on the default route (the resolver drops it for that
turn and retries next turn), so it is the baseline only when its provider is the
agent's primary provider.
A model-name comparison cannot see a fallback that serves the configured model on
another endpoint; with a channel model that differs from the global one, #131295
turned that case from evicted into kept. A turn whose agent has
_provider_fallback_active (set only by _try_activate_fallback, cleared by
restore_primary_runtime) now evicts before any name comparison.
The baseline lives in GatewayAgentCacheMixin._fallback_baseline_model beside
_is_intentional_model_switch, which keeps gateway/run_turn.py under its code-health
line cap (the channel lookup from #131295 had grown it past main).
Session tier taken from #132238; both regressions diagnosed in review by @andrexibiza.
Co-authored-by: salch-cred <141555468+salch-cred@users.noreply.github.com>
Co-authored-by: andrexibiza <84248988+andrexibiza@users.noreply.github.com>
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