When a sub-agent (Task tool) completes, the progress result now includes a resolvedModel field reporting the actual model the spawn resolved to, which may differ from the requested model.
Evidence
New field added to agent result object (search for "resolvedModel" near "totalDurationMs" in agent completion code), also in the string diff as "Model the spawn resolved (may differ from the requested one)")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.