In the rule “Running”, replace this bullet:

If the Grue’s Location is in the same row or column as any other Runners (excluding those in the same Cell as it), change the Grue’s Heading to face a secretly random such Runner.

with this bullet:

If the Grue’s Location is in the same row or column as any other Runners (excluding those in the same Cell as it), select all of the Headings where the Grue would be facing such Runners, and where the orthogonally adjacent Cell to the Grue in the direction of each Heading does not contain “Firewall”, and change the Grue’s Heading to a randomly chosen Heading from this selection. If there are no such selections possible, instead select all of the Headings where the orthogonally adjacent Cell to the Grue in the direction of each Heading does not contain “Firewall”, and change the Grue’s Heading to a randomly chosen Heading from this selection if possible.