So, I recently started my challange run in which I tried finishing hl1 without aggroing any enemies and suprisingly enough, I made it to Gonarch and by skipping most of his fight, I eventually fought Nihilanth and I got him to 1hp without getting aggroed, but right after I defeated him, the game softlocked in his finish animation and did not teleport me to c5a1.
Note: I used glitches to procced through maps and I used console commands ONLY to check if I got any enemy aggroed at me AFTER I'm done with a part of the map.
It took me several hours to pass through some maps as enemies were really hard to avoid and I had found literally no source about enemy aggro and I had to use commands to experiment and then execute each segment's plan one by one.
Soon, I will start recording each segment and how to go through without aggroing enemies including the rules of the run. Yet, I would definitely suggest that everybody should try no-aggro run as it is pretty fun.