So, based on the hints you folks gave about photodiode and such, I double-checked the schematic from the board traces and fixed mistakes, as well as changed the laser diode and phototransistor.
I found that the 3-pin laser diode was not one with a N/C pin (by measuring with the diode-test function of my multimeter), and most of the datasheets I found showed the laser diode combined with photodiode in same package. But this module also has an external device that is glued above the LD with a partial mirrored glass at 45deg. This has a black and a red wire, which now makes more sense with a photodiode vs a phototransistor (I assumed those terms were interchangeable.)
I guess the external PD in parallel with the internal PD increases the sensitivity of the arrangement?
I see that the PDs drive Q3 to draw current away from Q2, so that more light results in less LD current.
Yes, the visible-light LED lights up during operation. I suppose it could be an emission indicator, but it feels like that would be a wasted penny or two on these cheap giveaway devices. Would a LED be lower cost than a zener diode?
Another question: What would R1/C2 be doing? Would I likely be correct to think that the R4/R5 group would be the setpoint for the power regulation, and that increasing the resistance to greater than 12kohm would increase the output power? Or would lowering R3 be most likely the regulation setpoint? I tend to think R4/R5 because having 2 series resistors looks like a development iteration of this design would have a fixed and variable resistance there, and they dialed in the final product specs, and replaced the variable with a fixed.