Pot kept in a hot trunk can be pretty much ruined. Don't know the critical temp or time, but it's likely not binary. A little bit hot is prolly a little bit bad.
There are 3 main things that will degrade the quality of your herb.
1. Light exposure
2. heat exposure
3. Air exposure
if you can remove these 3 factors you can expect your bud to be smokeable for a year at the very least from inside of a jar, this is also why smaller jars are better than large jars so you dont have to constantly open 1 stash to the air every time you want some out of it
call those your bedtime bowls and find yourself a jar that you can keep inside for the next pick-up
It's not that the heat has "spoiled" your weed, but there are definitely chemical conversions happening if you keep your stash locked up in a hot car all day (or all week, or all month.)