The channel cache holds a groupID -> platform map with a 10 minute TTL, and
only channel Create/Update/Delete call invalidateCache(). Changing a group's
platform through the admin API therefore leaves the cache pointing at the old
platform for up to 10 minutes.
Channel pricing, model mapping and the model whitelist are all matched per
platform, so during that window the lookups silently miss: pricing falls back
to the global LiteLLM price list, renames stop applying and the whitelist
stops restricting. Nothing is logged.
Inject a narrow ChannelCacheInvalidator into the admin service (same shape as
the existing APIKeyAuthCacheInvalidator) and call it from UpdateGroup only when
the platform actually changed. The dependency is optional -- when it is nil the
cache simply rebuilds on TTL expiry, as before.
