Not so fast. Compile up the install and run it:
Error 2708: No entries found in the file table.
Say what? Must have been a file system glitch. Open up the MSI with Orca and check the file table; well, yes, it has lots of entries, no trouble there. What's going on here?
Buried deep in the search results for the error code I found this page. The comment from Jane D pointed out that she'd seen this error while having problems with the Duplicate File table rather than the File table - and that jogged my memory. In a separate component I had a CopyFile element that was pointing to my file, and it still had the old file ID reference, now orphaned. Update the reference, recompile, and bingo. Working install.
I see this as a bug in the WiX linker: why did it build the MSI with this unresolved reference? I'll have to post something to the mailing list at some point.