Did my mechanic killl my engine?
 

04 mt. bnr coils, new fuel pump, plugs, cas, aftermarket fuel injectors.
I rebuilt the engine. After rebuild had difficulty starting it. Push starting worked. after idling for 5 minutes, the cat glows red.
At this point, took it to my mechanic to have him look at it. Told him to take a look and either let me know if it's a major repair or/and if there's any engine damage and if so I'll unload the car, otherwise I'll have him fix it.
He looked at it, said he could handle it, said engine compression is in the upper 90 psi range. That was a month ago.
Since then, he said 2 of the injector wires were swapped. He fixed that and it starts right up. That's the good--the only good.
The bad is, after 5 minutes, the cat still glows red. He replaced the cat, cas, plugs, coils, wires, pretty much everything related to ignition. Rather than diagnose or/and first handle the cause of the issue(the excess fuel ruining the cat), he's just been replacing everything ignition related.
A couple of days ago, I got a call from him saying that the engine compression is 70 psi on both rotors, he can't do anything else with the car and (the best part) I owe him $2000. I asked him how could it be 70 psi now since he said it was in the 90's when he first started working on the car. He says that he may have 'read it wrong'.
This is not the best news to hear when you are on vacation hoping that your car will be ready for you when you get back.
I'm wondering 1. if possibly he ran it alot with the clogged cat and somehow ruined the compression on the engine. 2. what could be causing all the excess fuel to be dumped into the engine over a short period of time that could ruin another cat.

I would say it's possible he made it worse.
If he installed a cheap cat before properly resolving any misfire or fuel dumping issues, he could have easily melted that cat.
I would suggest you ask for the old cat, and have him disconnect the 'new' cat for your inspection before payment.
Save anything written or texts for negotiating the bill, a small claims court threat may be useful, but if he's unethical, he knows that's probably hard to prove and ineffective.
Good luck.

Any idea what could cause all of that excess fuel to be dumped into the exhaust in a short period of time?

Did you test the coils?
Even though you have the BHR kit and they're very dependable, some of the coils do occasionally fail.

I 've used a cheap Walker cat for a couple of weeks at a time prior to inspection with no issues.
But, except for when I first got my 8 and didn't know better, I've maintained my engine regularly and have replaced a complete set of coils, plugs, & wires 3 times in 5 years & 50k miles.

The mechanic pulled my bhr coils and put in new coils/wires and spark plugs and it's doing the same thing that it was doing prior with the bhr coils. According to the mechanic, it runs ok until it warms up, then starts dumping fuel.

Did he say what coils he used?
Did he have, or did you give him the OEM mounting bracket to use?

He used the cheapo autozone type oem coils.
He used the stock mounting bracket I think.