build_model_state dropped every inventory row whose slug name matched a
named `providers:` entry and relabelled the current provider `custom:<key>`
unconditionally. When a `providers:` key shadows a canonical provider name
(providers.openrouter: -> proxy with a models: list), a session genuinely
running on openrouter.ai lost all canonical rows and its current id became
custom:openrouter:..., which resolves to the proxy base_url — picking the
"current" row silently re-routed the session to a different endpoint.
Only rows flagged is_user_defined are replaced by the named catalogs now,
and the current provider is promoted to custom:<key> only when the session
base_url matches that entry's api_url or no canonical row for the raw key
exists (the reported relay/MixedCase class keeps its custom:<key> id).
Review finding: named entry shadowing a canonical provider dropped canonical rows and re-routed the current session to the proxy.
No runtime consumer read the proxy (terminal_tool/environments call is_interrupted()/set_interrupt()
directly); its only users were tests patching tools.interrupt._interrupt_event, which had no effect on
the code under test. tools/terminal_tool.py's own re-export of the name is owned by another worker.
