Does antimagic field actually prevent the casting of a spell from within the field? That is, does the spell automatically fail, and is wasted?

No. An antimagic field suppresses magic used within, brought into, or cast into it's area but is not dispelled (see the second paragraph of the spell description).

Hope that helps somewhat...

ncG1vNJzZmivp6x7prrWqKmlnF6kv6h706GpnpmUqHyiutOipJqfmZh6tLTEpaNmoV2gu7DDjKJkpKafrHtyf49vbGg%3D