AM - I decided that I would prefer not to have the "discomfort" that I noticed in the top of the left foot advance/progress any worse - and honestly it is barely noticeable - but I have been down this road before with stress fractures; so I walked 2 miles with Finn this morning instead of running and then did some rowing and yoga thereafter. Will likely do some elliptical machine work at lunchtime.
Looked back at a similar issue I had in February/March 2018. Took about 10 days of cross-training to drop out of any mention in the day logs. My memory is that this is probably less severe than that, so I will plan to cross train for a few days or a week and gradually reintroduce some running as tolerated.
PM - 8 miles on the elliptical at an HR rate equivalent to a solid running effort (without the pounding). I don't particularly like ellipticals or cross training, but as I listened to the "Running to the Edge" book and the discussion about Meb - they mentioned that he would use elliptical machines and ellipti-go bikes as cross training to moderate the workload/pounding that running was putting on his aging body. It inspired me to keep at it.