This is worth keeping an eye on given Dart's history. On August 15, after a preseason loss to the Vikings, Dart was reportedly "puzzled" by his concussion test results and "irritated" about being sent to the blue medical tent again (from the John Harbaugh page and Giants team page). That's notable because he already dealt with concussion issues during his 2025 rookie season (from the Jaylen Dart page).
Harbaugh's response when asked about it wasn't reassuring from a protection standpoint — he essentially said "We need to block better" (from the John Harbaugh page). That puts the onus on the O-line rather than the scheme, which is a bit of a yellow flag given the Giants are already trying to cut Dart's designed runs by ~50% to protect him in Nagy's RPO-heavy offense (from the Jaxson Dart page).
If you roster Dart, the concern is cumulative: a second QB with a concussion history in a scheme that still asks him to run (even if reduced). The coaching staff is aware and has brought in Brian Callahan and Greg Roman to help him play smarter, but this preseason scare doesn't help the durability narrative.