The heaters are fed from the ecu individually and return through a common wire that runs through the CTS. (as well as the cam sensor and mass air sensor).
The cam sensor is on/off, so as long as it sees a signal, no issue.
The MAF is variable and cross references with the throttle position, and again no code so is apparently within limits.
The CTS doesn't trigger an error within the ecu, ie it is within reason. If the car had been driven upto temp within the preceding few hours, then the coolant could easily have been at 42°. No mention of this, but Migalot did say that it wasn't from overnight stone cold. And unless the temp is verified by a secondary check such as the gauge, and or hands on, there's a fair chance the ecu sensor is reading correctly. (from experience, when these fail, they tend to go full Siberia mode and read - 40°, which increases the injector times enough to flood a remotely warm engine in a UK winter).
Cold start enrichment will happen as a result of intake air temp/external temp and possibly coolant temp, and at idle will be active for several minutes unless the throttle is pressed. Don't forget, it's sole purpose is to get the cats upto temp.
The O2 sensors contain two circuits... Heater and sensor.
The sensor side is reporting normally, ie no fault.
The heater side is reporting a fault on one consistent sensor. Replacing this three times has not changed the fault at all.
Ergo, the fault is in the wiring.