For me, climax of session is eruption of precum.

I don't feel anything when I get pre-cum. Unless I'm watching out for it, the only sign is some wetness. I do like seeing it in a session, having a little string of pre hanging down is a vaguely sexy affirmation of what's going on inside.

Unless it's not pre-cum you're experiencing at all. There is another clear slippy liquid called seminal vesicle fluid. Which you can identify by the stickiness as it dries (from the fructose) relative to pre-cum. Or it could be a mix of the two.
I think the seminal vesicles have to discharge via the prostate, so maybe you're experiencing some buildup of pressure in that area, and then there's some kind of release... possibly helped by contractions?
I'd say it's possible that your p-waves and dry-o's are causing the seminal vesicles to fill.

I don't see that stuff often, but one time during a long abstinence streak, I was playing with my dick probably a little too much, and suddenly had an unbelievable amount of clear seminal vesicle fluid flow out. There was no orgasm or ejaculation contractions with it, just a steady flow of this stuff. I didn't even feel it coming. It was one of the weirdest things. Though I could imagine if this had happened during an aneros session, it might have felt really great.

Yes. To all that. Thanks @Clenchy

Honestly I hardly ever leak precum so I wouldn't know.  Every once in a while if I get extremely hard (with at least some clothing on) and I'm not doing anything about it for a long time, I'll find I've leaked a bit in my boxers.  I wouldn't say that there's ever been too much pleasure attached to this, though.