Dear Miss Snark,
If an agent requests a full after reading a partial (say chapters 1-2), then do I have to resend the partial or assume that the agent has held on to the pages and just requires the remainder of the manuscript (i.e. everything but chapters 1-2)?
If the agent hasn't specified, ask him/her. There's no industry standard on this. I ask for the entire thing all over again, but I also ask for it electronically, not on pages. I do this because as I've read the partial I've noted all the typos and told you about them, and expect them to be fixed not just in the partial but in the full. This is one of the things that tells me a lot about what an author is like to work with.
For example if I've pointed out the misuse of "lay" (and that's the #1 error on otherwise well honed mss) on page 3, I expect you to search out all uses of "lay" in your ms and FIX THEM before I see a full.
Don't worry about asking question at this point. If an agent is interested in your work, your questions aren't in the "don't bug me about your query" category. I'm interested in working with you, you're interested in working with me, we're getting to know each other.