Yep, your right, can't be used by the on board volt-reg. And, yep, oscillation is the issue.
On the other hand, while the trace resistance has to be controlled tightly to keep the Vcore in spec, they aren't concerned with the tempco (results in mV changes).
At ~0.004/K the temperature coefficient of resistance is way too high to for the power traces to be used as a current sense resistor. My error budget for current was 1%, a 2.5°C (averaged through the trace, weighted by current) deviation would blow that before I even got to the instruments.
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