@wchargin, I think we’re implicitly modeling very different scopes for the Discord plugin. The way I am thinking about it, only messages that receive :sourcecred: 
reactions become nodes in the graph.
This means that Cred intersects with Discord only deliberately / intentionally rather than passively / implicitly. Discord would still be a different kind of space from Discourse–“Cred off by default” vs “Cred on by default”–but it would still be possible to flow cred based on the interactions.
In my mind, this is both an epistemically better model (some Discord interactions are valuable and do merit cred) and it feels more compassionate to SourceCred’s users. Saying “we aren’t going to allow anyone to value your contribution unless you go through the extra effort of writing a Discourse post” feels heavy-handed to me, and will bias cred flows towards people who are willing to both jump through hoops, and self promote.
In the past, some community members have expressed that they’re less comfortable posting on Discourse than on Discord; is it appropriate for people who mostly participate on Discord to not have any first-class way to get cred?
Also, to use a recent concrete example, you posted a helpful and informative message to the Discord earlier this week:
Floats are handled slightly differently in Python from JavaScript. Both attempt to conform to IEEE 754, but JavaScript has some edge cases. For instance, the spec says that
pow(1.0, NaN)should be1.0, but JavaScript implements it asNaN.You’re probably not going to hit these edge cases, but it is important to understand some of the intricacies of 754-compliant floating point arithmetic. Operations on floats do not have the properties that you expect: most famously, they’re not associative (
1.0 + 1e-16 + 1e-16is1.0, but1.0 + (1e-16 + 1e-16)is slightly greater than1.0). So most of the trouble, I expect, is going to come from places where the Python and JS implementations are “clearly mathematically equivalent” with real numbers but not with floats. (For instance, summing a list of floats in forward order vs. in reverse order.)
It would be silly for me to write a Discourse post saying “thank you @wchargin for explaining some details about floating point arithmetic”. Both because the friction of doing would be a meaningful overhead, and because it would create a very low-signal notification. (SourceCred’s discourse audience doesn’t come to this site to read about floating point arithmetic; we shouldn’t build a system where regular community kudos crowd out deep discussion.)
While we’re still on the mint-on-reaction paradigm (cf Mint on Likes), I imagine that the Discord reaction would have materially lower weight than the Discourse 
reaction – maybe 1/3 to 1/5th as much cred – so there would still be an incentive to record significant contributions onto the Discourse.