Excellent advice and explanation. It is rightly on top.
The only thing I would take issue with is the first paragraph where you try to calm down the OP:
> Okay, first things first - take a breath. This is not that big a deal. If you're at a company that's big enough to have a PIP process, then there are two possibilities: (1) it's well-established enough to know that junior engineers aren't productive for about a year after hiring, or (2) it's completely incompetent. If it's (1), even if you actually are way below average, you still have some runway left. If it's (2), they almost certainly have enough of a reputation that you can "fail" at your current job without it really harming your long-term career path.
This way things are at least in US, is next to impossible to harm your long-term career path by failing at one job. One needs to be at least prosecuted to harm their long-term career.
OP, if tomorrow you'll get fired on the spot, in a year time frame your most-likely will find yourself better of than you are now (and, frankly, likely to be better off if you stay at your present company).
The only thing I would take issue with is the first paragraph where you try to calm down the OP:
> Okay, first things first - take a breath. This is not that big a deal. If you're at a company that's big enough to have a PIP process, then there are two possibilities: (1) it's well-established enough to know that junior engineers aren't productive for about a year after hiring, or (2) it's completely incompetent. If it's (1), even if you actually are way below average, you still have some runway left. If it's (2), they almost certainly have enough of a reputation that you can "fail" at your current job without it really harming your long-term career path.
This way things are at least in US, is next to impossible to harm your long-term career path by failing at one job. One needs to be at least prosecuted to harm their long-term career.
OP, if tomorrow you'll get fired on the spot, in a year time frame your most-likely will find yourself better of than you are now (and, frankly, likely to be better off if you stay at your present company).