Phototriac for low voltage AC motor control without external triac
Thought experiment
Some small water pumps use a lot of current then with motion they cutout and return with a spring like an oscillating solenoid and use AC with a diode to pump at the line frequency on a half cycle. The contacts have hysteresis so you have a relaxation oscillator that is very noisy unless submerged. So if it is a small aquatic pump measure the DC resistance in both polarities and confirm my hunch.
The Tiny uC might be able to drive the emitter with 10mA at 2.1V from 3.3V dropping 400mV @ 10mA from Figure 22-21 in the atTiny85P spec meaning it has a “typical” Ron of 40 Ohms at Vdd=3V so consider that as a max for 3.3V. Thus a 2.9Vout to 2.1Vf = 800mV/10mA means you need a 80 ohm series instead of 680.
From fig 3 of the Triac spec, it has an output resistance slope of a nominal value = 3.125 Ohms plus 2 diode drops. So once you fix the trigger current, now you have the pulse current to worry about burning up the Triac from I^2*DCR resistance of the pump coil.  This current reduces with velocity of BEMF but with a 250mW power limit in open air @ 25’C, you may be out of luck. 5W average could be as much as 20W peak for 25% df (guesstimate).

this is all based on Ohm’s Law and linear behaviors in conduction mode. and the nonlinear current of aquatic pumps like all solenoids and motors alike with V/DCR surge currents.