find_custom_provider_identity_by_model (runtime_provider.py:895,908) and
acp_adapter/server.py:149 still used the old f"custom:{_normalize_custom_provider_name(...)}"
pattern while the rest of the codebase migrated to custom_provider_slug.
For keyed providers whose display name differs from their config key, the
model-based reverse lookup would return custom:<display-name> instead of
the stable custom:<provider_key> identity every other code path returns.
Co-authored-by: Gille <4317663+helix4u@users.noreply.github.com>
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