Thanks for all the comments, guys.
@joaz: I guess the question about tenuki at

is whether my

is sente or not. Tenuki away from a sente sequence strikes me as unduly aggressive. Maybe he can make some probes, but I think black needs to come back to fix those cutting points pretty soon. Right?
on the sequence in the upper left: black needs various ladders for most reasonable variations, the most important of which he didn't have, and others of which he would need to ignore important ladder-breakers.
on the lower left: well, it seems that I don't know anything about defending ogeima's. D4, D5, and for that matter E4 I rejected as being too close to the lonesome enemy stones. But I guess I should have thought of it more as a forcing move than an invasion.
@mitsun: I'm surprised that you don't like

(the k17 extension). There are eight spaces between B and W on the top, and 4 spaces between B and W on the left. Further, it seemed to me that if B got k17, his position would become rather deep and it would be impossible, for example, to profitably invade the upper right corner. In fact, in reviewing I wondered whether maybe

(c9) was a mistake, since I was never able to figure out any way to threaten B with it... When you say c9 is more interesting and has more territory at stake than k17, do you mean purely in terms of the relative safety of the lower left and the center left, or is there more to it than that?
@aurik: agreed, :w124: was bone-headed.
@loons: thanks for all the detail! very helpful.