Extension-provided models (e.g. claude-code/*) were unavailable during
findInitialModel() because pendingProviderRegistrations had not been
flushed yet, causing the fallback chain to select Google Gemini even
when the user explicitly configured claude-code as their default.
Three compounding issues fixed:
(A) Flush pendingProviderRegistrations in createAgentSession() before
findInitialModel() runs, so extension models are in the registry
when initial model selection happens.
(B) Re-apply the validated model to the session after
validateConfiguredModel() in both print and interactive CLI paths.
Previously, validation updated settingsManager but never called
session.setModel(), leaving the session on the wrong model.
(C) Update defaultModelPerProvider.anthropic from "claude-opus-4-6[1m]"
to "claude-opus-4-6" — the [1m] variant was removed from the model
registry when the base model was upgraded to 1M context, causing the
Anthropic fallback to silently fail and skip to Google.
Closes#3534
9fe13da3f2