PoolDoc, thanks for the tip -- after three days the Cl snapped back and the water's crystal clear again.

New numbers:

Free Cl = 5.8
Combined Cl = 0.2
Total Cl (OTO) = 3.0
pH = 7.4
Alkalinity = 120
Cya = 70 +
NaCl = 3000

(The pH dropped to 7.0 when I added cyanuric acid and I bumped it back up with borax)

I'll keep adding bleach for a week like you suggested so I don't have a recurrence (just added an extra pint this morning because I expect a heavy swimmer load for the 4th).